• On a Mission to web 2.0

    The last iteration of missionengineering.com has served us well for some time, but let’s be fair it was starting to look a little long in the tooth.

     
    Most web transactions are now done on the go using mobile devices. Photo, audio, and video are now built into the fabric of the web just like they were supposed to be, now that many of us have the technology and bandwidth to make it happen.

    So now we’ve moved on with the new missionengineering.com. We’ve updated the look with the latest responsive capabilities, so you’ll get an optimized view for the device you are connecting with. We’ve moved the complete site, rather than just the store over to encrypted connections using http over SSL, so we can provide you with a safe experience while you are with us. The store has received a complete make over, with better photos, easier to read information, and a streamlined check out process.

    There are several new tools to make finding what you need faster, easier, and more fun. Quickview brings up a temporary side bar that let’s you quickly check out an item, and easily add or remove items in your cart, while you are browsing. Geolocation will give you a shipping cost estimate right away without having to enter all your address info. If you make regular visits to the Mission store, you now have the option to securely save your credit card info as well as your account information to make your purchases faster and easier.

    Over the next few weeks we’ll be adding a new support section with electronic user guides, tutorial videos, regularly updated FAQ’s and more tools to get you going quickly with your Mission products.

    We’ve also taken the opportunity to merge missionengineering with some of our other projects. Technical and business blog effectsblog.com is now here in the same place, and we have adopted a similar look and feel with our sister site stagecraftgear.com that handles our custom speaker cabinet business. We’ll be seeing more integration both in terms of web and products with Stagecraft over the next few weeks, so keep an eye out for more announcements.

    If you had an account on the old missionengineering, first rest assured that all data is secure and all orders are proceeding as normal. There will be no change in processing orders and everyone will receive notifications of shipments just as before. Over the next few days registered users with accounts on missionengineering.com will be receiving an email with the opportunity to enable their account on the new site. If you don’t have an account yet, then you can open one right now.

    Create an account here.
    Signup for effectsblog here.

  • Fake it ’til you make it

    There’s little the guitar gear forum community enjoys more than a good scandal. Top of the list for Pedalgate performances is the case of the altered identity: Unmasking a popular pedal, rated for its boutique tones, as a repainted Far Eastern bargain box available on Ebay for half the price, is guaranteed to turn the internet apoplectic. When it emerges that each butter smooth overdrive with haunting mids is not carefully built from hand-picked parts over many days by a white haired guru with smoldering iron, but in fact, assembled in runs of a thousand in about 45 seconds from jelly bean parts on a pick and place machine in Shenzhen, the race to post the pithy comments begins. The angry, the indignant, the pseudo-scientific, and a curiously large number of lawyers, all compete for space, and much more than their 2 cents. It can be pretty funny and enlightening to read, until it gets threatening, which amazingly sometimes it does. If you’ve never read one of these it’s worth searching a few out.

    Each case has its own merits (and demerits) of course, and there may be some real issues. For example, Country of Origin labels are often carefully regulated by international governments. In the United States, the FTC controls what can be sold with ‘Made in the USA’ labels, and the rules are complex and not at all obvious. Many quite large companies have fallen foul of this legislation and penalties can be very serious. If you are planning on selling products marked as made in the USA, I strongly recommend employing the services of (real) legal counsel, and a trade compliance specialist. Hint: just actually making it in the USA, doesn’t count.

    The general gist of things though, is that taking someone elses product, sticking a new label on it, and selling it on as your own at a higher price must be immoral, illegal, or in some way or other wrong, surely? Except often it isn’t. I’ll bet almost none of the consumer electronics around your house were manufactured by the company whose name is on them. Your computer, phone, TV, refrigerator, microwave, power tools, yes, maybe your amplifier, effects, and even your guitar could have been manufactured by a completely different company. Don’t believe me? I have a sandwich grill on my kitchen counter called the George Foreman. It even has his signature right on the top. Now, he may have knocked out Joe Frazier, but I’m pretty sure no one here believes that the former heavyweight champion of the world is banging away in a shed behind his house knocking out griddle plates. The name on the front doesn’t necessarily tell you who made it.

    If you design a product and take it to a specialist manufacturer to build it for you, this is called contract manufacturing, and it’s common with projects of all types and sizes. Take electronics for example. Many modern components, especially digital ones, are surface mount and extremely small. They are purpose designed to be installed by machines. Hand soldering surface mount parts is difficult, slow, and unreliable. The machinery and facilities to do it correctly cost tens of millions of dollars, but a CM can assemble your boards for a few bucks and make a perfect job every time. It’s the economy of scale. Hand soldering PCB’s doesn’t scale, so you send them out to a CM. Maybe you also use another CM with specialist milling machines for drilling enclosures, and one with coating facilities for painting. You get a high quality, consistent product at a reasonable price. Why would anyone complain about that?

    Ok, so having a contract manufacturer build your product is one thing, it’s still your design and your work: You designed the circuit, laid out the PCB, did the 3D enclosure design, and created all the artwork and output files. The CM is just providing the machinery to make it. What you absolutely cannot do is take someone else’s finished product, paint over their name with yours, and sell it on as your own at a higher price, right? Wrong. Many manufacturers not only don’t care that you take their product and stick your own label on it, they have whole divisions whose sole job is to help you do it. it’s a hundreds of billions, probably trillions of dollars worldwide industry. It’s what Chinese manufacturing was built on. Welcome to the world of the OEM.

    OEM is an acronym for Original Equipment Manufacturer. You may also hear it called private label, or white-box. There’s also ODM, or Original Design Manufacturer, which is sometimes used interchangeably but is slightly different. If you’ve ever looked at something such as a coffee machine, electric drill, or microwave and thought it looked exactly the same as another brand, there’s a good chance it was. OEM’s can grow their business and spread their R&D costs by selling the same product over again to different companies. Sometimes well-known brands have OEM divisions. My home wireless router has an ATT logo on it, but it has a Cisco part #. I have no idea who’s factory it was actually manufactured in. On the other side of the coin are companies with no real brand of their own who mostly only build products for others to put their names on. Ever heard of Westec or Quanta? Probably not, but I bet they made some of your electronics.

    So what does this have to do with effects pedals? I probably get 10 emails a week from overseas companies, some I have heard of, most I have not, offering pedals, amps, guitars, cables, all manner of musical hardware. There’s one or two new ones every week. They have full ranges of pedals, amps of all shapes and sizes. Here’s an extract from a typical email I received a week or so ago:

     

    We are the best manufactory of guitar effect pedals in china.

    43 kinds of Tones be provided here.

    Distortion, Overdrive, Chorus, Heavy Metal, Fuzz, Flanger, Phaser, ECHO/Delay, Booster ETC.

    Accept OEM & ODM.

     

    You can’t make this stuff up. Their price list has a full range of analog and digital pedals including digital delays, loopers, reverb and five different distortions, and that’s just their mini line. They also have tuners, flight cases, pedal boards. Prices go from $12 – $26. I can get a mixed case of 50 units for around $500 and they’ll send me free samples for testing. There’s no brand name on them, I can put on whatever I want. According to the literature they also have a ‘shinning surface’, ‘patend design’ and are fire-proof! Yowza! What am I waiting for? I’m setting myself up in the pedal biz right away.

  • Fail Better

    Guitar signal noisy, intermittent, or just plain dead? Unable to make it through a rehearsal without something fizzing, popping, or blowing up? Sooner or later something is going to fail, and every rig needs some regular maintenance to keep it running at it’s best. If you are not in a platinum selling band with your own guitar tech, then you are going to have to do it yourself. Here are the top fails, and how to fix them.

    Begin at the beginning

    The most effective way to diagnose signal problems is usually to start at the signal source and follow it through to the end. For electric guitars, our practical signal source is the guitar pickups, and the end is the speakers. Connect the guitar to the amp by itself with a known good cable. Tap on the pole pieces of the pickups to make sure they are working. Wiggle the cable jack around to make sure there is not an intermittent issue with the jack on the guitar itself. Turn the volume and tone pots around a few times and listen for noises. If all is good, then connect the guitar back to the rig and follow the signal through one step at a time until you are able to isolate which device, cable, or interface is causing the problem.

    Cables Cable Cables

    I’m sure you have heard the humorous phrase used by realtors describing the major factors influencing property prices as being ‘location, location, location’. The equivalent for guitar rig failures is ‘Cables, cables, cables’. Other things can go wrong, but it’s astounding how many apparent gear failures are just down to a bad cable. Following a logical cable testing process will usually find the cause of a problem in short order.

    To identify cable problems, test one cable at a time with a known good guitar and amp. Examine the exterior of the cable for any obvious signs of physical damage such as cuts or deformities. Damage due to excessive pulling, shutting in doors, or chewing on from household pets or drummers can usually be uncovered from a visual examination.

    Wiggling the cable around at both ends can help point to an intermittent connection. A common failure point for cables is where the conductor is terminated on the connector. If the plug is not the over-molded type, you should be able to remove the cover and perform a visual exam, checking for broken solder or screw joints. Use a cable tester or multi-meter to check for shorts or disconnects. To test a ¼” guitar cable with a multi-meter, set the meter to the continuity setting and touch the two probes together. Most meters will give an audible beep to indicate continuity. The resistance display should read something close to 0 ohms. Now touch one probe to the tip (pointy end) of one jack plug, and the second probe to the tip of the other. The meter should beep, and the resistance should read close to 0 ohms. If there is no beep, and a high resistance reading, then the conductor is likely broken or damaged at some point. Now check the sleeve connection the same way, there should be continuity between the sleeves at both ends. Now measure between the tip and the sleeve. These should not be connected and there should be no continuity between these. If the meter beeps when the probes are between tip and sleeve, you have a short circuit which will need to be repaired or the cable replaced.

    TRS and XLR cables have 3 conductors rather than two, but the checking procedure is mostly the same: Making sure that you have continuity between the matching pins at each end of the cable, and no shorts between different pins.

    Cable testers designed for the pro-audio market can save a lot of time. Available from many audio and music stores, these small metal boxes can often test around 10 different cable types providing audible and visual indications of cable status. They usually cost less than a single average quality guitar cable and are a worthwhile addition to any musician’s toolkit. Google ‘Pro Audio Cable Tester’ for more info.

    Most plugs have the conductors soldered to the terminals, but some use screw terminals, and others still often called ‘solderless’ may be an interference fit. Broken solder joints can usually be re-soldered if you have the right tools. Screw and interference terminals can be screwed back into place. If there is a break at an unknown point inside the cable itself, then it’s usually best just to replace it.

    Power to the People

    Power issues are right behind cables as a major cause of rig failures. For battery powered devices, make sure to try a fresh battery. If there is any doubt, check the battery in another device to be sure it is good. Even if you are using external power, it’s worth trying a battery if the device supports it as it can help isolate if the issue is coming from the device itself, or the external power supply.

    When using external power, make sure that the supply you are using is correct. Just because the plug fits, doesn’t mean it’s the the right power source. Check to see that the polarity is correct. Although a center pin negative barrel connector is common for effects pedals, it’s unusual in general, and most other consumer devices that use a similar connector are center pin positive. Well engineered devices will have polarity reversal protection which will minimize the chance of damage if you use a reversed DC power supply, but not all do. Using a reversed polarity power supply on a device without protection will usually cause serious damage, requiring the unit to be repaired.

    Check that the voltage of the power supply is correct. 9VDC is common for effects pedals, but some require other voltages such as 12V 18V or even 24V. Over voltage is more likely to cause damage than under voltage, so if you are not sure for any reason, start with a lower voltage.

    The most common power connector for effects pedals and similar devices is a 2.1mm barrel connector, but there are other diameter connectors that are almost the same that don’t quite fit. The plug may go into the jack but not make a good connection resulting in no power or intermittent issues. Check the manual for the device to make sure you have the right size power plug.

    Some devices don’t play nicely with others when the power supply grounds are common. A good quality pedal board power supply will normally have some or all isolated grounds. If your device is not behaving as expected, or is particularly noisy, try using a power output from your pedal board power supply with an isolated ground, or use a separate power supply.

    KISS

    Let’s be honest here; finding a fault in your analog/digital, piezo/magnetic, wet-dry, stereo, MIDI switched, 19” rack mounted, power conditioned, wireless stadium monster is going to be a major pain unless you break it down into smaller elements. So Keep It Simple, and work on one section at a time.

    Start with a known good guitar and a cable that you have triple checked to be working correctly. Connect to one channel on one amp and test it. Does it work OK? Good. Now add ONE THING at a time until you find the device or cable that is causing the problem.

    Interaction

    Remember that sometimes an issue may not be the result of a failure, but could just be some type of mismatch, for example some fuzz pedals will not operate correctly after a buffer, and wah pedals can often sound odd after distortion pedals. There is nothing wrong with these devices, it’s just the way the were designed to work. If adding a device to a signal chain causes a problem, the device itself may not be at fault, it could be how and where it is connected.

    In this case, try using the device on it’s own with just a guitar and amp. Does it work ok now? Check the user manual for any information on different settings or use cases, and try repositioning the pedal order. If you have a lot of pedal interaction issues, using a switching unit such as the RJM Mastermind PBC can help. This lets you organize pedals into individual loops and then connect them as and when needed using programmable switches.

  • Fix your tone with a dead battery

    Have you ever heard the story about how renowned tone magician Eric Johnson, keeps around a box of partially discharged 9 volt batteries, and can tell the state of charge from the sound of his fuzz pedal?

    There are plenty of people who are convinced their gear sounds better with different levels of battery charge. Some pedal board power supplies even come with controls that allow you to adjust the voltage range so you can simulate a low battery. But does this really work, and if so, how? Let’s find out.

     

    Many effects pedals, in particular digital effects, include voltage regulators for many parts of the circuit. Digital devices such as micro-controllers, digital signal processors, and others rarely operate on 9v, and are very sensitive to the voltage variations. 5v or 3.3v are typical supply voltages for micros, so DC-DC converters are utilized to ensure they receive a stable voltage, regardless of fluctuations in the supply. If the supply drops too low for them to function, they simply shut down. If the main audio elements of the circuit in your effects pedal are powered by a regulated voltage, then using a partially discharged battery is going to have no effect other than to reduce the run time of the device.

    Some analog devices can also be sensitive to voltage changes, and the designer may choose to regulate their power supply. The case here is much the same as for digital pedals; if the voltage is regulated, then using a half dead battery or reduced voltage power supply is going to have no perceivable effect on the audio. This said, there are some devices where varying the supply voltage might have an effect on the audio. Let’s take a look at those and see how it might work.

    As a battery discharges, it’s output voltage gradually reduces. Check out these previous articles for more information on how this process works. If the powered device is unregulated, it will be running with the reduced voltage. This particularly impacts amplifiers such as the op-amp, diode, and transistor based circuits in effects such as boost, overdrive, and fuzz pedals. These pedals are basically amplifiers, and the load on the output, is being controlled by the power supply. The signal from the guitar pickups is modulating the power supply to provide the varying output current, but the eventual output power depends on the gain of the amplifier and the limits of the input power supply.

    As an example, lets take an amplifier with a gain of 2 and a 3V power supply. If we provide a 1V input signal, the amplifier will try to increase this at the output to 2V. The output is 2V and our power supply can deliver 3V, so all should be well. Now let’s increase our input signal voltage to 2V. Again we’ll multiply our input signal by our gain which is now 2 x 2, or an output voltage of 4V. Now the amplifier is trying to increase the output voltage to 4V, but the input power supply is only 3V. In this scenario the amp will begin clipping. So, in these types of circuits, reducing the input voltage can make the effect clip earlier. It’s worth trying your boost or overdrive pedal to see if a lower input voltage has this effect.

    Distortion and fuzz pedals are more likely to be always clipping to some extent, so reducing the voltage will have a different effect. On the traditional transistor based fuzz pedal, changing the battery voltage causes a response very similar to that of the volume control. Reducing the battery voltage, reduces the signal level at the output. In combination with the existing controls and a tube amp on the edge of breakup, it gives you an extra knob to twiddle, although does not provide a dramatic change in behavior.

    Testing with a Fuzz Face shows a proportional reduction in output level as the voltage is reduced. The effect continues to operate down to about 5V at which point the signal from a single coil passive pickup begins dropping out.

    Inside the Dunlop Eric Johnson Fuzz Face. It’s a simple circuit utilizing a pair of BC 183 NPN transistors. Here the battery input is connected up to an external variable power supply for testing.
    Inside the Dunlop Eric Johnson Fuzz Face. It’s a simple circuit utilizing a pair of BC 183 NPN transistors. Here the battery input is connected up to an external variable power supply for testing.

     

    A variable power supply allows precise control over the input voltage to the Fuzz Face, simulating a discharging battery. As the input voltage reduces, the signal level at the output reduces. Here we are setup for 9V. The signal begins to drop out at about 5V.
    A variable power supply allows precise control over the input voltage to the Fuzz Face, simulating a discharging battery. As the input voltage reduces, the signal level at the output reduces. Here we are setup for 9V. The signal begins to drop out at about 5V.

     

    Here’s a nice clean 1KHz test signal with the Fuzz Face bypassed.
    Here’s a nice clean 1KHz test signal with the Fuzz Face bypassed.
    Here’s the output from the Fuzz Face at 9V with the volume and fuzz controls turned up around full.
    Here’s the output from the Fuzz Face at 9V with the volume and fuzz controls turned up around full.
    Here’s the output from the Fuzz Face with the input power reduced down to 6V. The output level has reduced by about 50mV.
    Here’s the output from the Fuzz Face with the input power reduced down to 6V. The output level has reduced by about 50mV.

    The story of the discharged battery improving tone, does have elements of truth, but it helps to understand a bit more about how it works to see what benefits may be had. In some effects pedals, this will have no impact at all since the effect regulates its voltage. In others there is some change to the behavior either in output level, headroom, or both. Try it out with some of your pedals and see if it works for you.

    A version of this article first appeared in Gearphoria.

  • batteries

    More Batteries Included

    In the last post  we reviewed the pros and cons of various disposable battery technologies for effects pedals. This time around we are going to study rechargeables as an alternative.

     

    The Contenders

    Theoretically, rechargeable versions of the alkaline batteries we discussed last time would be a good choice for effects pedals. The chemistry is the same, but the battery is constructed so as not to explode when being recharged! Rechargeable alkalines are inexpensive to make, and only require a simple charger. They are non-toxic, and have a low self-discharge: left unused they have a shelf life up to 10 years. Unfortunately, few companies seem to make them these days and I couldn’t find a 9V at all. Newer technologies seem to have pushed them aside.

    One limitation to rechargeable alkalines is the high internal resistance which means they are not suitable for high current devices. Although this doesn’t matter for many effects pedals, technology had to evolve support the high drain digital products we use today. New rechargeable chemistries had to be developed, and one of the first was Nickel Cadmium (NiCd).

    The common chemistry used in the early days had drawbacks. Recharging a single battery a hundred or even a thousand times over before disposal should be much more environmentally friendly, especially if you have access to domestic power from renewable sources such as solar. Unfortunately the Cadmium used in NiCd rechargables is highly toxic, and requires special processing for disposal, undoing much of the environmental benefit of recharging. The use of Cadmium is now significantly restricted in the European Union under the RoHS and REACH programs, making these pretty much unusable in Europe.

    Early NiCd cells suffered from an issue where a particular sequence of charge discharge events could cause the battery to apparently lose capacity.  The story goes that this behavior was first observed on a satellite in space, but there was also a much more down to earth use case. Imagine you regularly drain a battery to a particular level, say 50% such as when using a laptop in a normal workday. In the evening you plug in the charger and leave it to charge slowly overnight. You do this for a week or so, then one day, you go on a long trip, you try to use all the batteries capacity: Although apparently fully charged, it dies at 50%, as if it ‘remembered’ it’s usual workday. For this reason it became known as the ‘memory effect’.

    In reality what was happening was the cadmium-hydroxide crystals in the cells were growing as much as 100 times, increasing the internal resistance and causing voltage depression. The capacity was actually still there, but could no longer supply the voltage necessary to drive the device. The issue can be countered by exercising (discharge /charge) and reconditioning (slow discharge to below cut off voltage). Recent design NiCd’s have significantly reduced this behavior.

    Nickel Metal Hydride (NiMH) is a good choice for effects pedals. They can last up to a thousand cycles with reasonable performance. They are prone to self-discharge which means they will lose some of their charge just sitting unused. However, advances have been made recently that improve this and good quality ‘low self-discharge’ 9V batteries with capacities of around 250mAh are available for under $10 each. A charger can be had for around $20.

    The new kid on the block for 9v rechargeable batteries is Lithium-Ion, using the same chemistry as the batteries in smart gadgets like phones and computers, but in a 9V format. The specifications look attractive: The batteries are really light, have capacities up to 600mAh, and a 4 pack with charger can be had for less than $30. There is not much choice though. The two big name battery manufacturers do not offer Li-Ion rechargeables, and there is little technical information on the brands that are available. It’s early days for these. It will be interesting to see how they work out.

    Pros and Cons

    Alkaline
    Low cost
    Very low self discharge
    Non-toxic

    Unavailable in 9V
    High internal resistance

    NiCd
    High discharge rate
    Good over charge discharge tolerance
    Long cycle life

    Heavy
    Toxic
    Low energy density

    NiMH
    Non-toxic
    Good energy density
    Wide availability

    High self discharge
    Low over charge discharge tolerance

    Li-Ion
    Very light
    Non-toxic
    Very high energy density

    Limited choice
    Low over charge discharge tolerance
    Unproven in 9V form

     Conclusions

    Charging a rechargeable costs pennies, and with hundreds of recharges over several years, the extra initial cost is soon recovered. When they reach the end of their useful lives, disposing of one rechargeable vs. one hundred alkalines is always going to be better for the environment. Music equipment such as effects pedals, wireless microphones, headphones, and portable recorders make great candidates for rechargeable batteries.

    Apart from a few niche applications such as RC car racing, NiCd is on its way out. The low energy capacity and toxic contents are 20th Century battery technology.

    NiMH is going to get the Best Buy rating here. NiMH has a reasonable energy density, and should be able to provide about 20 hours use per charge for a typical middle of the road analog effects pedal.  Most of the common battery types, including 9V are available, from a wide range of different manufacturers, including the major brands. A top of the line 9V NiMH will cost about $10, with cheap ones for around $3. I’d steer clear of the real low end ones. There’s plenty to choose from reputable manufacturers for just a little more. Get a decent quality ‘smart’ charger rather than a ‘value’ or ‘dumb’ charger. The smart charger will reduce the likelihood of over overcharging or shorting. If you don’t use the batteries regularly, take them out every few months and give them a full charge.

    Li-Ion gets the Most Promising Newcomer award. The chemistry is well proven in numerous electronic gadgets, computers, power tools, medical and industrial applications, even cars and airplanes, but is somewhat new to the 9V. The choice is pretty limited, but the light weight, and high energy density make them appealing. After researching this article, I bought a few and I’ll be using them here around the lab. I’ll report back on how they do.

  • Batteries Included

    I’m not sure of the reason the de-facto standard for effects pedal power became the 9V battery. Many low current pedals such as buffers, boosts, and distortions could easily be designed to run equally well on the more common AA battery type if we so desired.

     

    I’ll hazard a guess that history has a lot to do with it. If I recall correctly, the Boss, Electro-Harmonix, and other pedals of the day I used in the 80’s, pretty much all used the 9V battery. I imagine this same history has a lot to do with why we are also stuck with the evil center pin negative DC power connector on most pedals. I’m sure Roland must have had a good reason for using this back in the day on the iconic Boss effects, but really, from a product design standpoint it’s a pain in the rear.

    This is a multi-part article. Here we are going to look into disposable battery choices, and do some fun calculations to find out exactly how long is this battery going to last in my shiny new Professor Nutboffin’s Windy Cutlass? In part two, we’ll review rechargeable batteries and later we’ll uncover if using part discharged batteries really will make my fuzz sound like Eric Johnson.

    Let’s get started. We are going to try to figure out the best choice of battery for effects pedals and how long they will last in each of our devices. To do this we are going need a few bits of information. Roughly in order of significance, these are:

    1. Battery chemistry
    2. Device current draw
    3. Device cut off voltage

    Battery chemistry defines the chemical make up of the battery. The most common chemistries for consumer primary cells are Zinc-Carbon (or Carbon-Zinc or just Zinc it’s the same thing), Alkaline, and Lithium. Let’s get a bit of terminology out of the way first. A primary cell is a single use or disposable battery. These are designed to be used once and then disposed of, preferably recycled. A secondary cell is a rechargeable battery, and we’ll get to those in a future article. Checkout Workbench Confidential in Gearphoria if you would like to read it now.

    The naming of the chemistry is all rather confusing. Zinc-Carbon cells do contain carbon, but it’s the reaction between zinc and manganese dioxide that forms the basis of the battery. We really should call them Zinc-Manganese batteries, but nobody ever does. Alkaline batteries also use Zinc and Manganese so they could be called the same thing. However, we call them Alkaline because they use a base electrolyte rather than the acid electrolyte used in Zinc batteries. Lithium batteries use a Lithium anode but are not the same as Lithium-Ion, which are secondary batteries. Got it yet? No? Let’s go through them one by one.

    Zinc-Carbon batteries are the cheap ones you can buy in boxes of 50 for $19.99 on Ebay. They are often called Heavy Duty, or Super Heavy Duty, neither of which means anything. They have a lower capacity than alkaline batteries resulting a shorter usable life. The body of the battery is made of zinc and forms the anode. The acid electrolyte eats into the zinc over a fairly short time giving these types of batteries a much shorter shelf life, and they are more prone to leaking. This type of battery is OK for something like, say a TV remote, but best avoided for effects pedals. You can use them in a pinch, but don’t leave them in the pedal unused for long periods.

    Alkaline batteries are the most commonly used in effects pedals. These are the Duracell and Energizer batteries that most of us use day to day. Lithium batteries are relatively new and quite expensive. We’ll do some calculations later and see if they make sense to use in effects pedals.

    Current draw is a nominal figure that defines how much current will flow through the device during operation. Depending on the pedal design, this can change during use, but most pedal manufacturers will publish a figure for current draw, and we can use this to calculate our battery life.

    If the pedal uses DC-DC converters, which digital devices usually do, it will have a Cutoff Voltage. This is the point at which the voltage from the battery gets low enough that the pedal stops working. These pedals will work the same all the way down to the cut off voltage, and then just stop. Other types of design may not have a hard cutoff voltage as such, they can continue working but the performance will change. We’ll get to that later. It’s unusual to see a cutoff voltage published in the specs. Fortunately there are some common industry practices around this, so we can get an estimate for our calculations.

    Head over to your favorite search engine and search for a datasheet on your battery. Reputable manufacturers will publish these. If you can’t find your exact make, an equivalent will do. I use the Duracell 6LR61. Find the specs on your pedal from the User Guide or manufacturers web site and look for the current draw. For ease of demonstration I picked a few from the Roland Boss product line, and looked up the current draw on the spec sheets.

    DS-1 Distortion – 4mA

    OD-3 Overdrive – 9mA

    DD-7 Digital Delay – 55mA

    There’s no exact cutoff voltage listed for these so we’ll have to estimate. It’s common industry practice for 9v battery operated products to work at least down to about 7v, so we’ll use that for our calculations. On the 6LR61 datasheet we are going to look for the constant current discharge graphs. Let’s start with the OD-3, which has a draw of 9mA. The red line on the graph is close at 10mA so we’ll use that. Draw a line across from the 7v cutoff voltage until it intersects the 10mA line. Then draw a line down to read off the service hours.

     

    Battery Service Hours Graph OD-3
    Battery Service Hours Graph

    From this we can see the approximate life of a 9v Alkaline battery in the OD-3 Overdrive is about 50 hours. Pretty neat. Let’s try some more. The DD-7 has a higher current draw of 55mA. We’ll need to go to the second chart from the datasheet for that. The closest line is 50mA, so again we’ll start at 7v cutoff, draw across to the 50mA graph and then read off the service hours.

     

    Battery service hours graph - DD7
    Battery service hours graph – DD7

    From this we can estimate about 7 hours life from the same battery in our DD-7.

    What if there is no chart for the current draw of our device? Well we can approximate it by drawing our own line. The DS-1 has a pretty low current draw for an effects pedal at 4mA. Lets draw our own estimated graph based on the information we have.

     

    Battery service hours graph - Estimated
    Battery service hours graph – Estimated

    Here we can see a rough estimate of the battery life in the DS-1 would be about 200 hours.

    Modern programmable digital pedals and multi-effects with DSP’s, micro-controllers and digital displays consume quite a bit more power. A Strymon Timeline for example has a recommended minimum power supply current rating of 300mA, which would give us a battery life of less than 30 minutes. That explains why these types of pedals don’t run on primary batteries!

    A few Lithium Alkaline batteries are available billed as offering twice the capacity. Let’s take a quick look and see if they would be a good choice for effects pedals.

     

    Picture4

    This is a chart comparing the life of 9v Lithium battery vs Zinc-Carbon and Alkaline equivalents at 50mA continuous discharge. If you recall, we used 50mA as our number for the Boss DD-7, so lets do a quick comparison. The graph for the alkaline battery is probably an average, rather than the specific chart we looked at for the 6LR61 so the numbers are a little different, but they are in the same ball-park.

    This chart it is showing a service life of around 6 hours for 50mA at 6.6v cut out voltage. We got around 7 hours at 7v on the specific battery model, so it’s close enough.

    The Lithium battery is showing around 15 hours vs 6 hours for the alkaline. That’s 2.5 times the service life, which sounds pretty good. So we should start using Lithium batteries in all our effects pedals and get double or more the life, right? Well here’s the problem: Battery Junction has 9v Duralocks (essentially the 6LR61 in our tests) at $1.15, whereas the lowest cost Lithium 9v are $6. So in our DD-7 we’d get 2.5 times the life for 5.75 times the cost.

    There maybe corner cases where a Lithium battery makes sense. If you needed to run our example DD-7 on battery for a day at a festival with minimal opportunity to change batteries and it was worth the cost to avoid the possibility of failure? Maybe. You can also see that the discharge curve is much flatter which means if you have a pedal with a very high cutoff voltage, above 7v for example, the Lithium might make sense, but such products are unusual.

    So there we have it, the old favorite alkaline 9v remains the best choice in most cases. The range of service life is quite interesting. Just with the three pedals in our example we have almost 30 times difference in battery life. If you need to run your effects on batteries, it’s definitely worth making the calculations to figure out how long you should expect in each device.

    Note that we have a margin of error in our examples. If you need to be more precise, factors such as operating temperature and the batteries internal resistance need to be taken into account. Devices with voltage regulators will draw more current as the voltage in the battery decreases and this will also impact the figures. A manufacturers current draw figure is a nominal value that should be used as a guideline. Even so, these details are only going to make a few percentage points difference. Unless you are designing a pedal for sale and are concerned with optimizing it for energy efficiency, using the techniques here should be quite adequate for most.

    This article first appeared in Gearphoria.

     

     

     

  • Regulatory

    What’s the big deal with Certification?

    Have you ever looked at the underside of a pedal or the rear of a guitar amplifier and wondered about all those little symbols such as FCC, CE, CSA, TUV or UL? Why is it that we typically see those on products from the big players, but not on the boutique devices? What  does ‘This equipment has been tested and found to comply with the FCC Part 15 limits for a class B digital device’ mean exactly? In this weeks’ episode of ‘What’s The Big Deal’, we ask ‘What’s the big deal with …….. Certification?’

     

    The short explanation is that these are marks indicating that the products comply with various safety and performance standards around the world. The standards vary quite significantly between different nations, which is why we often see many different marks on one product. If the manufacturer is expecting so sell their product around the world, they will often indicate compliance with multiple standards with labels on the device. The European Community has a set of harmonized standards for different types of devices. The CE mark that you see on many products indicates the manufacturer is confirming that their product complies with these standards.

    An interesting thing about the United States is that the majority of the standards bodies are independent groups. There are often few laws requiring compliance to these standards to be able to sell a product. So this largely answers our question about why we typically don’t see these marks on things such as boutique effects pedals: There is no law that says they have to comply. And complying is a significant undertaking. The standards are often complex and difficult to follow. Testing requires hugely expensive specialty facilities with vast arrays of costly equipment and expert test engineers.

    If certification is not compulsory, it begs the question why do the  manufacturers even bother? This usually comes down to a couple of things. In some countries, certain levels of compliance are compulsory, so a manufacturer will at least need to test to those if they expect to sell into those regions. Some standards bodies will recognize tests of other groups, so if you have to do compliance for one location, then some others may come almost for free. Some distributors or resellers may require compliance in order to resell a product, so that might have an influence. Lastly it just makes sense for larger manufacturers to develop and test to standards. It can help with design decisions and quality control, minimize support and legal issues, and most importantly, give the company and their customers reassurance that the product they have made is safe and functions reliably.

    If you are manufacturing a digital device though, one set of rules in the US that you WILL have to comply with is the FCC Part 15. This recognizes that certain digital devices emit radio signals, even though this is not part of their intended operation. We refer to these devices as ‘unintentional radiators’. The radio frequencies that these devices emit have the potential to cause interference with intentional radiators, and its part of the FCC’s job makes sure that your whizz bang digital delay does not trash your neighbors WiFi or cause an international aviation incident over your back yard.

    Recently I was involved in testing some Mission products for FCC compliance so I thought I would share some of the photos from the day.

    Early in April 2015, myself and Missions CTO and designer of the Mission Gemini amplifier, took some Gemini units down to EMT Labs in Mountain View, CA.

    Here’s a Gemini 1 inside the anechoic chamber. The amp is a 50 pound two feet high 1×12 combo. It looks tiny in the photo, which gives you some idea of the size of the chamber. The device under test sits on a metal turntable and is rotated through 360 degrees during the test so they can measure the emissions all the way around. The scary looking red thing is the receiving antenna. This is motorized and raised several meters in height, during the test, again to measure the emissions at different points.

    Anechoic Chamber

    Outside the chamber, here are the results being shown on a monitor. The goal is to stay below the red line, so far we are looking good as you can see.

    IMG_2420

    Here’s one of the many racks full of test equipment. A decent spectrum analyzer alone can cost $20K. EMT has many millions of dollars worth of measurement gear.

    IMG_2421

    This is a state of the art 360 degree anechoic chamber used for testing devices such as wireless routers and smart phones. The engineer told us it can take weeks or even months to complete testing on some smart phones.

    IMG_2422

    Here’s some power emissions testing being done in a room completely lined with metal.

    IMG_2424

    The door of the chamber is several inches thick with thousands of copper fingers around the frame. It’s lined with hundreds of little space shuttle like tiles for absorbing reflections.

    IMG_2426 IMG_2425

    We had a very informative and productive day at the lab. Thanks to everyone at EMT Labs for helping us out and completing our testing within a day. I’m happy to say we passed all our FCC emissions tests.

    A version of this article was first published in Gearphoria. You can read the latest articles in Workbench Confidential at Gearphoria.com

  • TRS Cables

    What is a TRS Cable?

    Pro-Audio devices sometimes call for TRS cables. What are these, and why do they frequently cause confusion? Let’s find out.

     

    The letters TRS stand for Tip, Ring, and Sleeve, and refer to the parts of the jack plug that the different conductors are connected to. A TRS cable has three conductors vs the two on a standard guitar cable. A guitar cable is a TS, or Tip Sleeve cable.

    TS and TRS Jack Plugs

    The jack plug at the top is a TS jack. The pointed metal bit at the end, is logically enough, the tip, and the long metal shaft is the sleeve. The black band between them is an insulator preventing the two parts of the jack from shorting together. Notice we said ‘band’ and not ‘ring’. It’s easy to look at a TS jack and assume the black insulation ring is the ‘R’ in TRS but it’s not. The TRS jack is at the bottom. It has a metal ring in the middle which is the third conductor. The three conductors are separated by two black insulation bands.

    There are other types, most commonly a TRRS which has two rings, and four conductors in total. TRRS jacks are often used for stereo headsets with microphones where four conductors are needed for ground, left channel, right channel, and mic.

    TRRS Jack Plug

    A TS cable is fine for carrying a mono instrument signal such as from a guitar pickup to amp. The tip carries the signal and the sleeve is the return path and also usually the ground. Sometimes an additional conductor is needed such as for carrying a stereo signal, a balanced signal, or when connecting a voltage divider such as in an expression pedal. When a device requires a TRS cable, it’s because the application needs a third wire, and it will normally not work correctly if you try to use a TS cable in it’s place.

    When we refer to a TRS cable, it normally means that there is a TRS jack at both ends. However, there is also another variant often called a TRS Insert cable or TRS Y cable.

     

    TRS Insert Cable

    The insert cable has a TRS jack plug on one end and two TS jack plugs on the other. They are called insert cables because they are often used in recording studios to connect outboard equipment to insert points on a mixer. They can also be used to connect stereo signals between equipment where device A uses separate jacks for left and right channels, and device B uses a combined TRS jack.

    Like regular TS cables, TRS cables come with different jack plug sizes. The most common in pro-audio is the 1/4″ jack. The outside diameter at the sleeve is 1/4″. These are sometimes also called phone jacks, since they originated in the 19th Century for use in the first manual telephone switchboards. Wikipedia suggests that the 1/4″ jack may well be the oldest type of electrical connector still in widespread use: Having begun it’s life in 1878, the venerable 1/4″ jack is now 137 years old.

    The smaller jacks commonly used are 3.5mm for computers and 2.5mm for handheld devices. Since much of the world had switched to the metric system by the time these smaller jacks were created, we now have to deal with the mixed units of measurement of the 1/4″ phone jack from the 1800’s and the modern metric computer audio plug.

    A 1/4″ jack is 6.35mm
    A 3.5mm jack is approx 1/8″
    A 2.5mm jack is approx 3/32″

  • Practical Electronics

    Building pedals for fun and profit

     

    When I was a kid learning about engineering and electronics, the magazines that we read in the pre-internet days were full of articles, projects, and kits promising hours of enjoyment and even the proposition of making money from our favorite pastime.

     

    Electronics kit building kind of fell out of favor during the computer age as the home based technology enthusiasts moved to assembling PC’s, and software development. But home brew electronics has enjoyed a resurgence in recent years in what is now called the maker community. Internet electronics stores such as Adafruit and Element 14 are enabling 21st century geeks to build anything from simple circuits to complex embedded computing projects. These sites provide documentation, tutorials, video channels, and of course, a store, where you can purchase the tools and components required to internet enable your toaster, or feed your cat from the couch.

    Guitar effects pedals are a great way to get started with electronics. The simplest ones only require some basic skills to assemble. The few parts can be easily obtained, and the minimum of tools required can be purchased quite cheaply. Better still is the gratification from plugging it in for the first time and being able to incorporate a pedal that you made yourself into your music. With the skills you acquire, you can graduate from simple to more complex projects; maybe build an entire pedal board of your own effects. Your friends might ask you to build pedals for them too. What you learn can also be put to use with commercial pedals, as you will better understand how they work, and will be able to repair and hot rod old pedals. If you are interested in working at a repair shop, as a guitar tech, or for an electronics company in the future, your portfolio of home built pedals will be a great advertisement for your skills.

    The entry point for guitar pedal self-assembly is the effects pedal kit. A lot of the work such as designing and manufacturing the circuit board, drilling the enclosure, and selecting suitable parts has already been done for you. With a little care and careful following of the instructions, there’s no reason not to have a first time success with a pedal kit.

     

    Pedal Kit
    For: Beginner to intermediate
    Requirements: Soldering iron, solder, pliers, cutters, small screwdrivers
    Key Benefit: High chance of first time success
    Resources: buildyourownclone, Mammoth Electronics, modkitsdiy

     

    Get started

    Choose a pedal kit or two from one of the kit suppliers. If you are new to this, start with one of the simpler kits such as a boost pedal. You can move on to more complex circuits such as delays and reverbs later. You can order multiple kits at once if you want, but learn your skills on the easy ones first. Good kits come with comprehensive documentation. They normally list the tools that you will need, so read the docs online first and make sure you have the tools available. If not, order them at the same time as your kits so you’ll have everything ready. It’s very irritating when you are keen to get started on a pedal project and are missing that one small tool or part.

    If you are new to electronics, the essential tool you most likely need to buy is a decent temperature controlled soldering station. A basic one such as a Weller WLC100 can be had for less than $40 and will do the job just fine. Really nice ones with digital temperature readouts from Weller or Hakko are $100-$150 and as much as you will ever need for a home pedal shop. The soldering pencils have interchangeable tips, so you can keep a selection of different sizes. The one that normally comes with a new station will be suitable for most through-hole pedal kits.

    Make sure you have a sharp pair of wire cutters and a pair of those pointy nose pliers for bending and cutting component leads. Don’t forget solder too. There are a whole bunch of solder specifications covering materials, size, process etc. You’ll need rosin core solder. It comes in different thicknesses. 0.031” diameter is a common size, and will work for most pedal projects. Solder is normally sold in reels by weight. A 1/4lb reel will be enough to last a good few pedal projects. Lastly, get lead free, no clean solder. Although not strictly necessary for personal projects, lead-free solder is common now and safer. No clean, means that you can leave the flux residue behind without having to clean it off, and it won’t damage your board.

    If you have little or no experience in electronic assembly, there are some great free video tutorials on the web. In particular check out Adafruit learn, and search Collins Lab on Youtube. These include fun and informative tutorials on components and soldering. Watch these before you attack your first board with a hot iron.

    Now you should have all you need to assemble your first effects pedal. Make sure you have a clean, well-ventilated area to work. Wash your hands before you start. If you like, wear some conductive nitrile gloves. Avoid handling components any more than necessary. Contaminants on the components and PCB will make them harder to solder and can cause reliability problems. Certain IC’s can be damaged by static electricity from handling. Solder is hot and creates dangerous fumes so be careful. Follow the instructions carefully, in particular making sure you insert components in the correct places and the correct way around. Many components look alike and some are polarity sensitive, so take your time to get it right. Solder one pin of a component and then double-check it before soldering the rest. It’s much easier to move or remove a component with only one lead soldered to the board.

    The tip of a soldering iron is very hot, around 700F, and can damage the board, component packages, and wire insulation in a fraction of a second, not to mention your own skin, so be careful the tip does not touch anything as you move it in and out of the soldering area. Put the pencil back in its holder when not soldering. Don’t leave a hot iron laying on a bench or table.

    Once everything is assembled, check through the instructions one last time for any additional notes on connections, power etc (don’t waste all your hard work by blowing up the board with the wrong power supply). Then plug in your pedal and give it a try. There’s a good chance it will work first time. If not, go through the instructions again step by step and look to see where the problem might be. Missed, incorrect, or reversed components are the most common causes and can be diagnosed just by checking each step carefully.

    After your experience with a kit or two, you may want to make a few changes.

     

    Project Board
    For: Intermediate to advanced
    Requirements: As above plus digital multi-meter, digital calipers, drill and drill bits, hook-up wire, wire strippers
    Key Benefit: Customize with your own parts
    Resources: AMZ, Smallbear, Pedalpartsplus

     

    Get started

    Sooner or later you may want to experiment further: What happens if I use a different opamp here, or change a capacitor value there? Specifying your own components is the next step. Two of the specialty jobs in building a typical effects pedal are the design of the circuit itself, and the production of the printed circuit board (PCB) on which to install the components. The next logical step from a kit is to order a pre-built PCB and then customize the component and enclosure choices yourself. AMZ effects, is the go-to place for a huge variety of pre-designed PCB’s. The cost is quite low and the projects include clear documentation providing guidance on different options and components.

    You’ll need to get yourself setup with an account on some of the web stores selling components such as effects pedal specialty stores listed above, and some general component stores such as Mouser and Digikey. AMZ provides a list of the components required for each project. Make sure you check carefully the component requirements such as type of capacitors. Many components may have suitable electrical values but different physical layouts, so use the datasheets for your chosen component. Measure the spaces and holes on your PCB to make sure the components will fit. Remember that you’ll also need an enclosure in which to install the finished circuit and don’t forget things such as knobs, battery holders etc.

    If you think you might build more than one of a pedal, it’s helpful to keep a list of your preferred parts and their specifications in a spreadsheet. In manufacturing this is called a BOM (Bill of Materials). Some online stores will let you import a BOM direct into their web store and will build a purchase order for you based on the information. It’s a big time saver each time you need to order parts, and lets you compare different vendors stocks easily.

    Design Your Own
    For: Advanced
    Requirements: PCB Design Software
    Key Benefit: Complete control
    Resources: Eagle, Circuit Maker, KiCad

     

    Get started

    Designing your own pedal from scratch requires some experience in electrical engineering, but it’s not especially hard or expensive these days to learn from online resources and pickup the tools for low cost or even free.

    You’ll need schematic and PCB design software and there are plenty to choose from.

    Cadsoft Eagle is a very popular tool with pedal builders. A basic version can be had for free. There are limitations on board size and number of layers in the free version, but these won’t come in to play for the majority of basic analog effects pedals.  Element14  includes a host of documents and tutorials.  If you get into complex designs or full professional use later,  full versions of Eagle, at time of writing cost $575, and $1640.

    Altium is known for it’s high end PCB development application called Altium Designer which starts at around $7000 and there’s a yearly subscription fee too. Gulp! Altium Designer is used by many industry professionals for product development. Altium just recently released Circuit Maker, which has many of the features of Designer and is, Gasp!…. Completely free!  The trade off at this point seems to be that it’s designed around a community and apart from a couple of private slots, you have to share your work, so it’s not very useful for completely proprietary projects.

    If you want free and private, other than the basic version of Eagle, there is KiCad, which is an open source tool developed by GIPSA Lab, which is a research institute out of Grenoble in France. Like Eagle, there are Windows, Mac, and Linux versions, whereas Circuit Maker is Windows only. There are also tools now being offered for free by some of the big component dealers such as Mouser.

    I’ve used Eagle for a long time, but I just recently started using Circuit Maker, and I like it so far. I’ll probably end up using both since I do most of my work on a Mac, and Eagle still works fine on that. I had to set up a dedicated Windows machine for Circuit Maker. Circuit Maker has a 3D view of the finished PCB which is a very helpful tool if you are dealing with odd board sizes and very constrained layouts.

    Free to use schematics to get started can be had from the web but remember, if you are going to use someone else’s work, either completely or as a starting point for your own design, check first to see what copyright and any other terms are associated with it. If it’s not clear, ask first. There are plenty of open source designs available to use, but schematics, like other written works are covered by copyright law so check you have permission before using them.

    Once you have a board design complete, you can send it out for manufacture. Years ago this used to be the major challenge for the home or small builder, but these days a large number of board manufacturers have a web presence and will quickly fabricate single, or low volume boards for fairly modest cost. Eagle (or whichever CAD software you are using) outputs a set of files called gerber files. These files can be emailed or uploaded over the web to the board manufacturer who will plug these into their manufacturing tools and then send the finished boards to you in the mail.

    A version of this article was first published in Gearphoria. You can read the latest articles in Workbench Confidential at Gearphoria.com

     

  • More Pedal Power

    This is a follow on from a previous Pedal Power post on power supplies for effects pedals. In this article we are going to take a look at how to match power supply features with your pedals, and choose the right supply to meet your requirements.

     

    1. Input Power

    First, you are going to need to check that the input power requirements of the power supply are compatible with the locations where you will be using it, i.e. Can you plug it into the wall in the country where you live?

    Power from a  wall socket is almost always AC (alternating current). The power is delivered at different voltages and with different connectors (plugs) around the world. Wikipedias Mains electricity by country maintains a useful table with voltages and plug types by country.

    Check the specifications of your intended power supply to make sure it can support the voltages where you intend to use it. In the United States we use 120VAC wall power. Most devices rated at 120V will normally work with a range of voltages around that number, say 100V – 130V, but check the specs to be sure. Most European countries supply something between 220VAC and 240VAC. Again a power supply rated at 220V will normally support this range.

    A power supply that is switchable or automatically supports both 120V and 220V ranges is very useful if you tour or travel around the world with your rig. Otherwise you will have to use a separate transformer. You will also need the country specific power cables, or suitable adapters. The Pedaltrain Powertrain 1250 is switch selectable between 120V and 240V and comes with a set of power cables for worldwide use.

    Powertrain 1250 with selectable voltage switch
    Powertrain 1250 with selectable voltage switch

     

    2. DC Output jacks

    The majority of effects pedals use a 2.1mm co-axial, aka ‘barrel’, connector for their DC power input connection. This is often referred to by musicians as a ‘Boss type’ connector due to it’s use on the popular Roland Boss range of effects pedals.

    The outside diameter of the jack plug is 5.5mm and the inside diameter is 2.1mm. Unfortunately there is another connector sometimes used for pedals where the inside diameter is 2.5mm. It’s  hard to tell these apart just by looking as the difference is less than half a millimeter, but you’ll need the correct cable or an adapter if your pedal uses a 2.5mm connector. The 2.5mm connector is often used by devices that use AC rather than DC such as some MIDI controllers and multi-effects devices, but there’s no standard that says it has to be that way. There are a few pedals that require DC inputs and use a 2.5mm connector, so read the manual or check with the manufacturer if you are not sure.

    2-1mm
    2.1mm barrel connector

     

    Make sure the power supply has enough outputs for all your pedals, and a few spare for future upgrades. For very large rigs you may need more than one power supply. If you need to use multiple power supplies, look for a units with a through power connector that lets you connect two together. The power supply may have several different DC voltage outputs which we cover in item 5.

    3. DC Polarity

    Most effects pedals use a ‘center pin negative’ DC polarity where the pin in the center is the negative conductor, and the outside of the jack is the positive. On rare occasions you may come across a center pin positive pedal. To power these pedals from a power supply you need two things. Firstly you need to use a reverse polarity DC power cable such as this from Voodoo Lab. Secondly you need to make sure that you only connect the reverse polarity cable to an isolated output on the power supply so that it does not cause a problem with the other center pin negative pedals connected to the same source. We cover isolated outputs in the first Pedal Power article.

    4. AC Output Jacks

    Some devices such as multi-effects and MIDI controllers may require a AC output. Power supplies such as the MXR MC403 feature 2.5mm 9VAC as well as DC outputs.

    MC403PowerSystem
    MXR Power Supply with 9VAC outputs in red.

     

    5. Output voltage

    The vast majority of small effects pedals require a 9VDC supply. This is due to a history of effects pedals being designed to run on a 9V battery. The 9VDC from an external power supply simply replaces the 9V battery without any extra circuitry required in the pedal. Some pedals though, may require a different DC voltage: pedals requiring 12V, 15V, 18V and even 48V can be found.

    Some pedals can be run on a range of inputs, in particular op-amp driven pedals will often support 9-18V, with the higher voltage providing more headroom. Check the voltage requirements of all your pedals, it’s normally listed in the user manual, and make sure the power supply has outputs for each of them. You may have to run unusual pedals from their own separate wall power supply.

    6. Output current

    Pedal power supplies commonly use current draw as a method for rating. A power supply will be rated for a maximum current, either per output, or per group of similar outputs. For example, the Powertrain 1250 has 3 isolated 9V outputs rated at 210mA each, and 4 linked 9V outputs rated at 500mA in total. Check the current draw of each of your pedals, it’s normally in the user guide or can be obtained by contacting the manufacturer. Simply add up the current draw for each pedal that you will connect to an output, and make sure it does not exceed the rating.

    Let’s use the 4 x 9V outputs on the Powertrain as an example. The total rating across all of these outputs is 500mA. If I connect 4 x 9V pedals that have current draws of 25mA, 50mA, 100mA and 200mA, the total current draw is 25+50+100+200=375mA. Since we don’t always know if the specifications are maximum, nominal, or typical, it’s best to leave some headroom, 10% seems reasonable. 10% of 500mA=50mA. Add that to our 375mA total draw = 425mA. This is less than the 500mA maximum, so this configuration is acceptable.

    Current draw will be higher if you increase the voltage on pedals that support it. For example, the Mission VM-PRO will run on any DC voltage from 9V-18V. It’s nominal current draw is 3mA at 9V but it’s 4mA at 18V. Check the documentation or with the manufacturer to get this information if possible, or just make sure you have left enough headroom for the increased current if you are using higher voltages.

    7. Additional Information

    It is not recommended to exceed a power supplies rating or to continuously run a power supply at or very near to it’s maximum rating. It won’t be working at it’s best efficiency, and a lot of energy will be lost to heat. You may feel the power supply get quite hot if this happens, and it may even start to hum if you exceed the rated current. Some power supplies have over-current protection such as a fuse or similar safety device that will blow if the current is exceeded and have to be replaced or reset. Continuously running a supply near it’s maximum rating may also shorten it’s life.

    Power supplies generate electro-magnetic interference (EMI) that can cause unwanted noise in the audio signal, especially in high gain applications  where the signal is amplified many times over. A good quality power supply will be properly designed and tested to minimize this, but it will still occur. Keep the power supply away from sensitive devices such as wah pedals. Test out the position of the power supply on your board, particularly if mounting it directly under pedals, and experiment with different positions to minimize noise.

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