Tech

Technical blog posts

  • 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.

  • Blueboard Expression Pedal

    Here’s a quick guide to configuring the iRig Blueboard wireless MIDI controller with a Mission SP-1 switching expression pedal.

     

    We had a request recently via the Mission Customer Service queue about using the iRig Blueboard with a Mission SP-1. The Blueboard is a handy little battery operated MIDI controller that can send  MIDI Program Change and Continuous Controller messages via Bluetooth wireless to a desktop computer, smartphone or tablet. I actually use one of these myself at home where I run Scuffham S-Gear on my Apple iMac connected via USB to a Mission Gemini 1 full range amplified cabinet and use the Blueboard to change S-Gear presets.

    The Blueboard has two expression pedal inputs and the customer wanted to know if they could connect the a Mission SP-1 switching expression pedal to these. The SP-1 is an expression pedal that has a switch integrated into it. When used with a compatible MIDI controller, the switch can be used to send MIDI messages to turn effects on and off. Typical uses would be to turn an expression pedal controlled effect such as wah or whammy on and off, or to use the expression pedal as a volume and have the switch turn on a boost or distortion effect.

    It turns out the Blueboard works great with the SP-1. I tested this with the Blueboard iPhone app, but have no reason to believe software on other systems should not work just the same. Since the Blueboard is only intended to have continuous controllers connected to the pedal inputs, there is a little workaround that has to be done on the calibration,  after which it should work just fine.

    Connect the pedal out on the SP-1 to the first input on the Blueboard with a TRS cable and run the Blueboard pedal calibration utility. Then connect the pedal out on the SP-1 to the second pedal input on the Blueboard and run the calibration utility again. After calibration is complete, you can connect both the pedal and the switch outputs on the SP-1 with two TRS cables to the two pedal inputs on the Blueboard and both continuous and switch functions will work. For applications where a switch is not required, the Mission EP-1 is an appropriate alternative.

    Since the Blueboard only has 4 switches to start with, having an extra one is pretty handy, and being mounted on the expression pedal, it’s perfect for turning your wah on.

  • Multi Tap Tempo Hack

    Someone asked me recently if the Mission Expressionator could be used as a multi-tap tempo controller, so I created this little hack to do it. It will work with any Expressionator, so read on to see how you can try this for yourself.

     

    Many modern digital effects pedals and multi-effects units include a tap tempo capability. By tapping on a button you can adjust the timing of parameters such as delay repeats to match the tempo of the music. If you are using multiple separate effects pedals, the ability to tap a single button to adjust the tempo of all the devices simultaneously is a useful feature. There’s a more complex way to do this if the pedals are MIDI capable. If not, or you just need something simple, you can make a tap tempo switch to work with an Expressionator.

    The Mission Expressionator is a device that lets you connect a single expression pedal to multiple expression controlled devices. In this hack we are going to replace the expression pedal with a switch. You’ll need the correct type of tap tempo switch. It works with a normally open momentary switch, but it needs to be wired TRS. The Strymon Tap Favorite would probably work. You can get one from the Strymon Store for $49. A mono TS only tap tempo won’t work for this, it needs to be TRS, so if you don’t have one of these, you’ll need to get one, or you can make your own. You’ll need:

    1 x TRS (stereo) 1/4″ Jack such as a Switchcraft 112BX
    1 x Momentary SPST switch such as Smallbear 0602A
    1 x 1K Ohm 1/4W through hole resistor
    An enclosure such as a Hammond 1590LB
    Some hook up wire

    You can get all the parts from many electronics parts suppliers.  Smallbear Electronics keeps them in stock.

    Basically you are going to connect the two terminals of the switch to the tip and sleeve of the jack, and then bridge the tip and ring of the jack with the 1K Ohm resistor.

    Connect the switch using a 1/4″ TRS (stereo) cable to the pedal input on Expressionator. Connect one or more outputs from Expressionator to the external tap tempo input on your pedals. For my test I used a Timeline and a Mobius from Strymon. Check your pedal user manual to for the connections and see if it needs to be configured for tap tempo. In the case of the Strymon pedals, I connected outputs A and B from Expressionator to the EXP inputs on the Timeline and Mobius using TRS cables . I set them both for external tap tempo as follows: GLOBAL – EXP MD – TAP.

    Set the Expressionator outputs to raw taper and enable all the channels that you want to send tap tempo to. Tap the switch at least two times. The bar graph LEDs on Expressionator will all toggle on and off with the taps, and your pedals should sync to the tempo. In the case of the Mobius and Timeline, their own tempo LED’s also flash appropriately, and the tempo and can be shown on their LCD displays in BPM or mS.

    In my testing, the Mobius and Timeline normally showed within 3 or 4 BPM of each other on their displays, which should be perfectly good enough for most applications. If you really do need more precise synchronization, then you’ll need to use a more complex MIDI based solution if your pedals support it.

    Note:

    The Expressionator tap tempo hack uses an analog tap tempo signal. Each receiving device will have it’s own internal clock reference and likely do some filtering and switch debouncing in software. This may result in the tempos being very slightly out of sync between multiple units and the clocks may drift over time. It probably won’t be noticeable for most applications, but If you really need a greater level of synchronization, then some pedals with MIDI inputs can be set to derive their timing from a single master MIDI clock. If your pedal has MIDI capability check the User Guide to see if this option is available, then choose a single device to generate the master MIDI clock.

     

     

     

  • Circuit Simulation

    Circuit Simulation for Mac

    I recently discovered iCircuit, a neat little circuit simulator app that works on Mac as well as mobile devices. It’s perfect for simple effects pedal designs.

     

    A common way to prototype simple electronic circuits such as used in guitar effects pedals is to use a breadboard and real components. This is great for audio projects because you get real results that you can actually hear right away.

     

    breadboard

     

    Breadboarding, however, it has it’s challenges:

    The top four breadboarders headaches:

    1 – You have to buy all the parts.
    2 – Anything complicated quickly turns into a rats nest.
    3 – Routing sensitive signal lines is a nightmare.
    4 – It’s hard to get high pin density SMD micro controllers onto a breadboard.

    Now admittedly the last two may not be an issue for basic effects pedals, but we are seeing more and more complex micro controllers and CPU’s becoming available to the maker community, and it’s only a matter of time before home-brew digital guitar effects come more commonplace.

    An alternative to breadboarding is to use a computer based circuit simulation application. The ones most commonly used in professional electronics are based on SPICE. Many companies that develop integrated circuits create their own SPICE based tools, and Linear Devices makes theirs, LTSPICE available for free which is pretty cool.

    The problem for Mac users is that although there is a free LTSPICE version for OS X, the user interface is pretty clunky. It lacks a tool bar for the schematic editor which makes editing layouts directly pretty cumbersome and you have to import schematics in from something else which is a whole other business. The Windows interface is much nicer.

    So this lead me to search for a simulator for OS X and hence to iCircuit. It’s a neat little app that’s great for students and hobbyists and supports both analog and digital circuits with inbuilt oscilloscope and meter simulations. There are a couple of headline features:

    1. OS X, and IOS versions for Mac, iPhone and iPad
    2. Real time simulation

    The OS X version works fine and has a nice Mac like user interface. I didn’t try the iOS version yet but the screenshots look very nice.

    The realtime simulation is quite fun. Most simulators provide simulation results in the form of a series of reports, but iCircuit simulations run as you work, so you can quickly see how changes to components impact your project, and you can monitor signals with the scope and meters as you go.

    The library of components in iCircuit is pretty limited, so it’s not going to replace a SPICE type tool for professional simulation, but for learning and testing simple circuits it’s pretty useful and way more fun.

    There are links to download iCircuit from the developers website. At time of writing, there are versions for OS X, Windows, iOS, and Android at between $4.99 and $9.99 depending on platform.

  • tachometer

    Give Me A Boost

    Boost pedals are a paradox, at once the simplest of devices, most with just a single knob, they can also be a challenge to integrate to achieve the desired effect.

    Much more than say a delay, chorus, or even many distortions, the heart of a good boost lies not in the boost pedal itself, but in the complex interactions between all the parts of the signal chain from the pickups to the speaker driver. This is why the same boost pedal may provide a nice lead volume increase in one rig, creamy overdrive in another, yet make mine sound like I’m using a smoke alarm as an amp. Let’s take a look and see why this should be.

    A boost pedal is really just an amplifier with a single volume control, and an on/off switch. The job of an amplifier is to take a low power signal and increase it’s power level. In the case of our boost pedal, it takes the low level output from a guitar pick up and increases it, before passing on to the next part of the signal chain. The number of times the amplifier can increase the output power over the input power is referred to as the gain. A gain of two means the amp should output twice the input signal, and so on.

    Boost pedals normally list the amount of boost in dB, so how does that relate to amplifier gain? Let’s take a common boost pedal value of 15dB. To convert that to gain in voltage we use the formula

    Vr= antilog(db/20)

    Where Vr is the voltage ratio and db is the increase in dB.

    Converting +15dB gain to voltage gives us 5.623413, or about a 5.5 times increase if we round it. So with our boost pedal, a 1V input signal would be increased up to about 5.5V.

    When we put this into our signal chain there are a couple of things going on. First we are going to increase the input signal level into the next device. If our next device is sensitive to input level, say a fuzz for example, then we are going to get a change in behavior. Our fuzz is now getting 5.5V on the input instead of 1V. It’s like playing five times harder into the fuzz, so your boosted signal is going to be fuzzier. If we change things around though, and put the boost after the fuzz, then the fuzz is back to getting 1V on the input so the boost is just making it louder. If you place the boost in front of a pedal that’s not that sensitive to input level, such as a digital delay for example, then again the boost is mainly just going to make it louder. Of course, the signal from your guitar is not a steady 1V, it’s varying all the time, but the rule still applies.

    The same effect applies to using a boost with a tube amp. Placed in front of an amp that’s just short of break-up, the boost can be used to take the amp over the edge and start clipping, increasing the distortion from the amp. When used with an amp that has a lot of clean headroom though, the increase in voltage may not be enough to cause clipping, and the signal will just get louder.

    So this is the first thing to be aware of with a boost. The results will depend very much on where the pedal is placed in the signal chain, and how the other pedals and amp react to the increased signal voltage.

    The second factor to be aware of is what is often called ‘clean boost.’ To understand this we have to go back to looking at the boost as an amplifier. To amplify the signal the amplifier is taking two inputs and creating a single output from them. The two inputs are:

    1: The input signal from the guitar pickups

    2: The power supply (wall power, battery etc)

    The important thing to note here is that the load on the output is being controlled by the power supply and not the guitar pickups. The signal from the guitar pickups is modulating the power supply to provide the varying output voltage, but the eventual output power depends on the gain of the amplifier and the limits of the input power supply.

    Let’s recall our example where 15dB of boost increased our 1V signal to 5.5V, but now let’s increase our input signal voltage to 2V. (As we said the actual input signal from the guitar pickups is varying all the time, but we’ll use this as an example). Again we’ll multiply our input signal by our gain, which is now 5.5 x 2V, or an output voltage of 11V. The interesting thing here is that to deliver 11V at the output, the power supply will have to be capable of at least that, or in practice a little more. A 9v battery is not going to be enough, and in this scenario the amp in the boost pedal will begin clipping. It delivers as much of the 11V output as it can and then stops when there is not enough power available at the power supply. It’s called clipping because if you look at the input signal as a sine wave, the output looks like the tops have been clipped off. A clipped signal will sound distorted, so our ‘clean’ boost is only clean within certain parameters.

    The following images illustrate how power supply voltage can affect a boost pedals behavior. All measurements were taken using a Mission Engineering V-BOOST pedal.

    This shows our input signal, a 1V sine wave.
    This shows our input signal, a 1V sine wave.

    This shows our input signal, a stable 1V sine wave with no boost applied.

    Output 15dB
    Output 15dB

    Output 15dB – With approximately 15dB of boost applied, our 1V signal has increased to 5.34V and we still see a clean sine wave.

    Output Clipping
    Output Clipping

    Output Clipping – Increasing the input voltage is too much for the power supply: The signal clips at 6.43V. This is no longer a ‘clean’ boost at this input signal level.

    Output 18v
    Output 18v

    Output 18v – Increasing the input power supply voltage solves the problem. Here the output is up to 7.4V with no clipping.

    Some boost pedals are designed to run with higher output external power supplies to counteract this. If we could run our example boost pedal with an 18VDC supply for example, there would be enough power to provide 11V at the output avoid clipping in our scenario above.

    Check the specs of your boost pedal to see if it tells you what voltages it begins clipping at. See if it can run with an external power supply and if so, up to what voltage. Experiment with putting a boost pedal in different places in your signal chain to see what works best for you, and remember that something that sounds one way in one rig may sound very different in another, that’s the paradox of the boost pedal.

     

    This article was first published in Gearphoria’s Workbench Confidential column. For more, checkout the latest Geaphoria.

  • mixthroughly

    Don’t Goop Me Bro

    Last quarters Gearphoria article is a look into gooping of effects pedals and it’s more legitimate parent, conformal coating. You can read the latest edition of Workbench Confidential at Gearphoria

     

    I don’t read music gear forums much, but recently I did a little weekend surfing and saw fair bit of comment about the ‘gooping’ of components in guitar effects pedals. Indeed there was even an article on the subject in the last issue of Gearphoria. It got me thinking about what this stuff really is, and how it’s used in various electronics.

    The opaque, glue like substance used to cover up the components in certain effects pedals is in most cases almost certainly potting compound. This is commonly used in components with coils such as transformers, to secure parts in place and deal with vibration issues. Guitar players maybe most familiar with potting compound in pickups, which potted partly for protection, and also to reduce the susceptibility to microphonics, where noise and feedback can be caused by the wires in the coil itself minutely vibrating. Certain pickup manufacturers prefer using wax vs. epoxy for this. I’m not a pickup expert, but I believe the lower viscosity liquid wax can penetrate better into the coils of fine wire. It’s also easier to remove if the pickup has to be repaired. For larger coils, epoxy is a more common choice.

    So, are their sound engineering reasons for using this to cover components on a PCB? Some other components can have issues with vibration. Large electrolytic capacitors for example, can vibrate causing mechanical problems such as noise or even a weakening of the solder joints. However, these can normally be dealt with at the specific component level. If you look inside an AC power supply for example (with the power disconnected of course!) you might see a glue-like substance around the base of some of the large caps. Silicone elastomers such as Dow Corning’s Silastic® are commonly used for this. You only need to apply it around the component in question, though, no need to cover the whole PCB.

    Many years ago I was working for a communications electronics company on a network interface PCB for use by the Navy. The system would be installed on warships and be subjected to hostile environments such as sea air, salt-water ingress, and potentially battle conditions. We covered a large section of the board with epoxy. It weighed a ton, and was impossible to repair if anything went wrong, but at the time with the availability of materials and the unusual environment, it made sense.

    Fortunately, these days we have a much better choice for hostile environments with conformal coatings. Conformal coatings are commonly used now on electronics products that will be installed outside. Think traffic signals, or roof mounted solar panels. The coatings are available in several different base materials, and can be sprayed on either by machine or by hand. They can provide IPC level protection at thicknesses of only around 1000th of an inch. They are also flexible for improved reliability, relatively easy to remove to allow repairs, and often transparent for easier quality control and troubleshooting.

    And therein lies the moral of this tale, if you really do want to go to the extent of protecting the PCB on your effects pedal from the hostile environment of beer spillage and maybe worse at the local dive bar, a transparent conformal coating is the way to go. Many board assembly shops will have conformal coating facilities or can send the boards on to a specialty coating service. Coating can be done with a spray head that covers an entire panel, or with a selective coating machine that dispenses the coating to specific areas. For small run, hand assembled products, you can pick up spray cans from a chemical or electronics supplier.

    Selective conformal coating machines are kinda hypnotic to watch. Well I think so anyway. I’m not sure what that says about me …

     

    If, on the other hand, you wish to hide your work from prying eyes, then gooping is just way too old school. The technique du jour is to laser etch chip ID’s from your integrated circuit packages.

     

     

  • level control

    Where To Put My Volume Pedal

    I had a few questions recently about the best place to put a volume pedal on a pedal board. Some people had some non-conventional, or more complex setups. So here are some tips based on real world questions about positioning a volume pedal on your pedalboard.

     

    The most obvious, and probably most common ordering for a volume pedal in the signal chain is simply to put it first: Take the cable from your instrument and connect it directly to the input of the volume pedal. Everything else comes after that. In this scenario, the volume pedal behaves very much like the volume control on your instrument itself. As you reduce the volume, you will be reducing the signal level into the following devices. For guitar players this means  level sensitive inputs such as overdrive pedals, or the front end of a tube amp will respond accordingly, typically cleaning up an overdriven tone as you reduce the volume. This makes placing the volume pedal first great for things such as swells, or blending between a clean and crunchy tones. It also means that following effects such as delays and reverbs tails will still continue even after the volume is reduced to zero.

    One thing to watch with connecting the volume pedal first is to make sure the input impedance is compatible with what you are connecting. In general passive electric guitar pickups will work best with at least 250K Ohm on the input of the volume pedal, around 500K Ohm is better still. Here’s a rule of thumb for nominal impedance matching to a volume pedal:

    Passive electric guitar pickups – 250K – 1M Ohm
    Active electric guitar pickups – 25K – 50K Ohm
    Buffered pedal output – 25K – 50K Ohm
    Amplified (active) piezo electric pickup – 25K – 50K Ohm
    Line out such as electronic keyboard – < 150K Ohm
    Passive piezo electric pickup – 10M Ohm

    One problem here is that if you connect multiple instruments to your pedalboard it’s not always going to be easy to mix and match. A solution is to use an active volume pedal such as the Mission VM-PRO, which is designed to work with multiple different inputs.

    The second common place to put a volume pedal is at the end of a signal chain after all the other effects . In this case it is going to behave more like a master volume control. This is useful if you don’t want to effect the effects drive level or want to be sure that the signal from all effects is cut off.

    Connecting the output of the volume pedal to the main input on a guitar amp is still potentially going to impact the drive level of the front end of your amp though. One way to avoid this and make the volume pedal even more like a master volume control is to put it into an effects loop. In this case, for most effects loops, the volume pedal will be bypassing the pre amp and tone stack so as not to impact the drive level on the front end of the amp. This is a good if you really just want the volume pedal to control volume, and not have any other effect on a guitar tone. Make sure that the amp has a series effects loop, and not a parallel effects loop for this to work.

    When placing the volume pedal after buffered effects pedals, or in an effects loop, you will want to use either an active volume pedal or a low impedance volume pedal, normally around 25K Ohm. Connecting a high Z passive volume pedal such as one in the 250K – 500K Ohm range will not work that well. The impedance mismatch will cause an uneven response.

    One last thing. Some volume pedals provide a secondary or tuner out. On a passive volume pedal this will split the signal reducing the overall impedance and increasing the resistive and capacitative load on the signal from the extra connector, cables and electronics. This will be a particular issue if you use an always on tuner or  one without a true bypass. To resolve this, one way is use a true two channel active volume pedal, where the tuner/secondary out is driven from a completely separate amplifier. If this solution is not available, make sure to use a tuner with a hard wired bypass, and turn it off when not in use.

    Further reading:

    Whirlwind blog article on impedance
    Effectsblog volume pedal Q&A 

  • old workbench

    Workbench Confidential

    Recently I started writing a regular column for Gearphoria magazine called Workbench Confidential, covering subjects related to electronics in the music industry. Gearphoria is a ground breaking quarterly online magazine that’s attracting a lot of Music Industry attention, so I’m excited to be contributing. I’ll be posting past issues of Workbench Confidential here at effectsblog.com, but you’ll need to go to Gearphoria to read the latest issues.

     

    If you build electronics products for a living, often the difference between making a living and not, is the speed and reliability with which you can assemble and test your products. The lower the selling price of your product, the more efficient you need to be at assembling it. If you are the manufacturer of a $50,000 luxury Swiss watch, then a lot of the value of your product is in the days or weeks its takes the expert craftspeople to create it. For a $100 effects pedal, you are going to have to be quicker off the mark if you hope to pay the bills at the end of the month. Even at the snootiest end of the boutique pedal market, you are soon going to be in pretty deep doo-doo if it takes you days to build something that sells for even $500.

    So how do we do it? We use machines, of course. Assembling circuit boards is one of the most time consuming stages of manufacture, and there are several mechanized techniques to accomplish this. The most efficient, and the way most consumer electronic products are assembled today, employs a Surface Mount Device, or SMD production line. The line comprises a number of machines interconnected by a conveyor. The first machine deposits solder paste onto the surface of the PCB through a stencil. Usually several PCBs are bundled together onto a large board called a panel. The panel is sawn apart, or ‘de-panelized’ into individual PCBs later in the process.

    After paste is applied, the panel passes into a pick and place machine that feeds in components from reels similar to a film reel. A robot arm picks up the parts and drops them into place on the panel. Multi-head machines can place hundreds of components per second. After the parts have been placed, the conveyor carries the panel through a heating tunnel that melts or ‘reflows’ the paste, and solders the components to the board. The finished boards come out at the end where they can be cleaned and de-panelized into individual PCBs. Search ‘SMD Production Line’ on You Tube for some videos of the process.

    Part of the San Francisco Bay Area production line where Mission boards are assembled.
    Part of the San Francisco Bay Area production line where Mission boards are assembled.

    The majority of the work is in programming the machines, and loading the reels of components. After that, the machine can be largely left to do its’ thing. The cost per board goes down when we can leverage the upfront programming and loading, and let the machines build more boards.

    Another type of component is called ‘through hole’. These have leads that push through holes in the PCB and are the type that we often see in hand built boutique pedals. Some fans believe that hand soldered vintage style capacitors and resistors impart a special pedal mojo. If anyone can actually hear the difference in a circuit between through hole and SMD passives in a double blind test, I’ll eat my hat. In some circuits especially digital ones, components such as microcontrollers and flash memory may only be available in SMD anyway.

    SMD has mechanical limits though, and larger components such as electrolytic capacitors, coils, connectors and controls may still be through hole. These can be added to SMD boards using a wave or selective solder machine, which uses a wave of molten solder to attach the component legs to the pads on the board. Running single panels through both SMD and through hole processes, costs more than just one process, so you have to plan for this when designing your product for manufacture.

    Due to the high cost of these machines and the infrastructure to run them, many manufacturers send their board assembly out to specialty facilities. The populated PCBs can then be assembled in house into the final product. For final assembly and other work, such as small run and prototyping, there are machines too. Here are a few we use around our shop on a daily basis.

    Automatic Wire Cutter and Stripper.

    PowerStrip9550
    Automatic wire cutter and stripper

     

    Feeds reels of hook up wire in one end, and precisely cut and stripped wires in specific lengths come out the other. The machine processes hundreds of wires per minute. Not only is it a massive time saver, but it also improves product quality and reduces the risk of repetitive strain injury. No one ever uses it without recalling doing this by hand and quietly whispering to themselves: “I so love this machine”.

    CO2 Laser

    zing24-model
    Our CO2 Laser is used for etching and cutting

     

    Cuts plastic components, makes decals and labels, etches logos onto metal enclosures, creates templates, the list goes on. The Laser is THE general purpose small fabricating tool around the shop. Countless times a week a find myself instructing: “Just put in in the laser”.

    Ultrasonic Cleaner

    36C029_AS01
    Ultrasonic cleaner blasts submerged parts with high frequency sound waves

     

    The best way to remove flux and other residue from small run and re-worked PCBs. Drop in the assembly, and watch the magic bubbles. You can also clean your tools with it afterwards.

    Crimping Machine

    UC_200_F_
    Crimp machine precisely terminates cables

     

    Using crimp terminals from a reel attached to the side of the machine, the operator feeds in the stripped cable end from the wire stripping machine and presses a footswitch, the machine takes care of the rest. 3 tons of force is applied making for a precise crimp. Correct wire termination is essential for compliance with safety standards if you are making AC powered products.

     

  • Car Pedals

    Pedal Power

    Switching power supplies? Regulated outputs? Isolated grounds? Arrgh! All I want to do is to power my pedals without sounding like a can of bees or bursting into flames. What do all these terms mean? Do they make any difference for effects pedals? Let’s find out.

     

    The job of the power supply is to convert the voltage from your wall supply, usually around 110V or 220V depending on your geographical location, to something more appropriate for effects pedals, typically somewhere in the range of 9 – 24V. In many cases the power supply will also convert the current from alternating (AC) to direct (DC) in a process called rectification. This is because most, although not all, effects pedals require a DC supply.

    Why don’t we see effects pedals just plug into the wall? Well there are some, but they are quite unusual. The Ross Flanger from the 70’s is one I can think of.

    The first reason is that effects pedals just don’t need high voltages like say a tube amplifier does. Most components in effects pedals are designed to work with quite small voltages. Although you could do the conversion in the pedal itself, the components are large and expensive, and who wants to make their pedals bigger and costlier? OK, don’t answer that.

    Secondly, if you work with mains voltage, you’ll have to bother yourself with all sorts of regulatory issues designed to make sure you don’t give your customers the entirely wrong kind of hair raising experience. So in most cases, it’s just much more efficient for effects pedals to use an external power supply.

    OK, so now we know why we need a power supply, so what about the terminology. Let’s look at some:

    Switching Power Supply.
    A switching, or switched mode, power supply controls the output by rapidly switching between full on and full off states. The ratio of on time to off time regulates the output voltage. A switched mode power supply dissipates very little power as heat, and is consequently much more efficient than a linear power supply that is continuously dissipating power. Switching power supplies are also typically lighter and smaller than equivalent linear power supplies. One trade off is that the repeated switching generates noise that can be a problem in audio applications. A good quality switching power supply will have well designed filtering that will not cause any problems for effect pedal use. However, in very low cost power supplies, this is often where the corners are cut, so it’s probably best to avoid very cheap switch mode power supplies for effects pedals, especially in high gain applications. A good quality one will be fine.

     

    Regulated Power Supply
    An unregulated power supply delivers an output voltage as a direct ratio of input voltage. If the input voltage fluctuates then so can the output. An unregulated power supply is also designed to provide the published voltage with a particular current draw. As the current through the load increases, the voltage decreases, and vice-versa. If you have a decent multi-meter you can check this. Plug in your power supply to the wall and measure the output voltage with nothing other than the meter connected to the output. An unregulated power supply can measure several volts higher than it’s nominal rating with no load. A regulated power supply should read close to exactly its rated output voltage. Does this matter? Maybe. Digital components that need stable power supplies often have their own internal voltage regulators, so it may not matter that much. However, if they don’t then it will. A digital device receiving power outside it’s required range can shutdown in worst cases. Analog pedals often will continue to work with varying voltages, but at the extremes they may start to sound slightly different, particularly where it results in the changing of headroom on opamp derived effects.

    Isolated outputs
    Isolation in power supplies can refer to all sorts of things such as physical isolation, magnetic or electrical isolation between stages, transformers , optocouplers, blah, blah, it really depends on exactly what you are talking about. Power Supply isolation is a whole subject in it’s own right. However, when effects pedal power supply manufacturers refer to isolated outputs, they are almost always referring to the separation of the output grounds. That is to say, each output has it’s own return, and they are not bonded together at any point. The reason for this is to reduce the possibility of ground loops and the hum that can be generated as a result. Hum from ground loops is a common problem for musicians, and it can vary with the conditions in different locations.

    There are lot’s of great pedal board power supplies available, and hopefully these explanations will help you decide which are suitable to you. Of course, the various features come at a price, so you will need to decide if they make sense depending on your use. If you play at home with a small number of DC pedals, and don’t typically have any ground loop hum, then a decent low cost power supply should do the job, and upgrading to a fancy one is not going to make your pedals sound any better.

    If you travel with your rig, a power supply with at least some isolated outputs is usually a good investment. If you have both AC and DC pedals, look for something with AC outputs as well as DC. Support for variable input ranges will be useful of you travel overseas.

    I’m not going to recommend any particular power supply as there are so many great ones to choose from. For what it’s worth, for small to medium pedal boards I use the Pedaltrain Powertrain 1250. For large rigs I use the  MXR CAE MC403 Power System. I’ve had great results with both, but check out what’s available, because now you know what those features they brag about really mean.

     

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