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Intro to Effectsblog

March 16, 2014
  • 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.

     

     

     

  • 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.

  • 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.

  • Volume Pedal Q&A

    Volume pedals may not be as simple as they seem. In this article we cover some of the common questions and answers about using volume pedals with guitars and other instruments.

     

    Q: What is the difference between active and passive volume pedals?

    A: The difference between these two can cause confusion due a difference in whether we really mean active or passive volume pedals or are in fact referring to volume pedals for active or passive pickups. These are not the same thing, so let’s see if we can clear it up starting with active or passive volume pedals.

    Passive volume pedals are basically a potentiometer mechanically turned by a pedal, and work much the same way as the volume knob on a regular magnetic pickup guitar. A quick way to identify a passive volume pedal is it doesn’t normally need power. Passive volume pedals are simple to use and convenient since they don’t need power, but are often sensitive to the types of instruments they are used with, and where they are placed in the signal chain. Passive volume pedals with tuner outputs can be especially problematic as they have to split the signal into two causing loading on the pickups which can result in a loss of high frequency, AKA ‘tone suck’.

    An active volume pedal contains and amplifier circuit that is normally used as a buffer, and sometimes for other features such as boost, tuner isolation, and so on. Active volume pedals require power from an internal battery or an external power supply.  The buffer isolates the input side from the output ensuring that whatever you have after the volume pedal, including effects pedals and long cables, does not cause additional loading and the resulting signal loss.

    Passive pickups are the regular single coil or humbuckers in your typical Strat or Les Paul. They don’t need a power supply of their own, and work happily using only the power generated from the vibrating strings in the magnetic field of the pickup poles. If your electric guitar does not need power or batteries, it has passive pickups.

    Active pickups have, you guessed it, an amplifier. This is normally built into the guitar body or the pickup assembly itself. Active pickups require power from a battery or external power supply. See the next question for information about choosing a volume pedal for active or passive pickups.

    Q: Does it matter what resistance value potentiometer is in my volume pedal?

    A: For passive volume pedals, yes. It’s important to match the input impedance of the volume pedal as closely as possible to what the pickup expects in order to avoid tone loss as a result of an impedance mismatch. If you have passive pickups, a passive volume pedal in the 250K – 500K range will normally be fine. If you have active pickups you’ll need a passive volume pedal in the 25K – 50K range. If you mix these up, you’ll likely suffer some tone loss from the impedance mismatch.

    If you are using an active volume pedal you don’t need to worry about the value of the potentiometer. In this case it is just acting as a controller for the output of the internal amplifier. Both active and passive pickups should work with a well designed active volume pedal.

    Q: What taper should a volume pedal have?

    Volume controls should be logarithmic, sometimes also called ‘audio’ taper, or at least something approximating it. A log control increases the volume more slowly at the beginning of the rotation and more steeply at the end. This is because human loudness perception is also logarithmic. If you were to use a linear control for a volume pedal it would seem like all the volume increase happens when you first move the pedal, and then very little at the end. A logarithmic volume control gives the perception of a smooth, proportional increase in volume.

    Q: Can I use a volume pedal in an effects loop?

    Effects loops generally expect low impedance devices, and often have buffers in them of their own. A passive volume pedal with 25-50K Ohm range should work fine.  It is not generally recommended to use high impedance passive volume pedals in an effects loop. You may find that the taper feels abrupt, more like an on/off switch than and smooth sweep.

    Q: Can I use a volume pedal with other instruments?

    Active volume pedals, can generally be used with many other instruments such as electric bass, keyboards, harmonica mikes etc. Specialty PZ compatible pedals designed to work with passive Piezo electric pickups should be used on acoustic instruments such as guitars, violins, cellos, stand-up bass etc.

    Q: Can I use a volume pedal as an expression pedal?

    You can sometimes use a passive, low impedance volume pedal as an expression pedal by using a TRS stereo insert cable to connect the input and output from the pedal to the expression controlled device. The volume pedal will likely have a log pot and expression devices normally expect a linear input so you may find the response not to be very smooth, unless the device is designed to accommodate a log pot. Some digital devices can be programmed to compensate for a log pot if you use a volume pedal as an expression pedal.

    Q: Will connecting a tuner cause tone suck?

    If you have a passive volume pedal that splits the signal between the instrument and tuner out, you can potentially experience some signal loss. The additional loading of the low impedance tuner device, and that fact that the signal is being split between two different paths can create effectively a low pass filter that removes some of the high frequency component of the signal making it sound less bright. This can be avoided by using a volume pedal with an isolated tuner out, or using a tuner with a hardwire bypass that can be disconnected from the signal chain when not in use.

    Q: My fuzz pedal sounds strange when I use a buffered volume pedal in front of it. What’s wrong?

    Transistor based Fuzz pedals behave strangely after buffers because they depend on the impedance (Z) of  a pickup to limit gain, and since the buffer has a low output Z, the fuzz can sound unusually loud and be non responsive to the volume control. Another effect is that the low input impedance of the fuzz will limit high frequency response when driven by the pickup, but the low Z of the buffer lets more highs through and that can make the fuzz sound harsh. The Mission VM-Pro has a fuzz friendly impedance switch that lets you use it in front of a fuzz. The buffer is always active, and the impedance switch adds a fixed resistance in series with the output to restore the proper fuzz sound and performance.

    References and acknowledgements.

    Keen, R.G. The Secret Life of Pots, for information on pot tapers.
    Thanks to Jack Orman for technical information regarding fuzz pedal impedances.

     

  • freedom of expression

    Understanding Expression Pedals

    Expression pedals are used to control variable parameters on electronic music equipment such as digital amplifiers, rack effects, stomp boxes, MIDI controllers, and keyboards. The pedals do not contribute to the sound themselves, but remotely control aspects of the device they are connected to. It might help to think of an expression pedal as a remote knob that can be controlled with your foot. Exactly what an expression pedal can control, will depend on the features of the device it is connected to.

     

    Most digital amplifiers and multi-effects units support expression pedal control of basic functions such as volume, wah, and whammy which are traditionally controlled from this type of pedal. But often many more functions such as reverb trails, delay feedback, rotary speaker speed, mix, and so forth can also be controlled, giving the musician significant benefit in a live situation. It’s important to remember that expression pedals can only be used with devices that have a dedicated expression pedal input and/or have a MIDI control input.

    Examples of digital amps and multi-effects units with expression pedal control include:

    Line 6 Pod and M Series
    Avid Eleven Rack
    Fractal Audio Axe-Fx

    Increasingly, stomp box manufacturers are also adding expression pedal control to many of their products. Examples include:

    Strymon
    Pigtronix
    Eventide

    How They Work
    Expression Pedals comprise a pedal assembly that sits on the floor or can be mounted to a pedal board, with a rocker that can be moved up and down with the foot. Inside the pedal the rocker attaches to a potentiometer that moves proportionally to the pedal. The potentiometer is connected to an output jack or output cable that attaches to the expression pedal input of the device you are controlling. Unlike an in line volume pedal, there is no ‘input’ on an expression pedal as it does not connect to the instruments signal chain. There is just the single output that connects to the dedicated expression pedal input on the effect device. The device sends out a control voltage on one conductor of the cable which passes through the potentiometer and then is received back by the device on another conductor. As the pedal is moved up and down, the resistance within the potentiometer changes allowing more or less of the input control voltage to be returned. The amount of returned voltage is continually measured by the device allowing it to determine the position of the pedal and hence vary the effect. Expression pedals are typically passive devices that require no power of their own, with the control voltage being generated by the equipment they are connected to.

    Expression pedals and CV pedals are not the same although they are often confused as they perform largely the same function but in a slightly different way. A passive expression pedal does not generate the control voltage itself; it receives it from the connected device, and returns it on a separate conductor along the connecting cable. A CV pedal generates the control voltage itself. A CV pedal requires a battery or external power supply. Some devices can use either, but if a device is not designed to be used with a CV pedal, then it could potentially be damaged by connecting one, so please read the manual before connecting a CV pedal to anything. CV pedals have their origins in analog synthesizers and are commonly, though certainly not exclusively, seen with synths and keyboard related devices. Built in expression pedals that are integrated into certain floor mounted effects units use different proprietary systems.

    Compatibility
    There is no recognized standard for expression pedal inputs. Effects and amp manufacturers use whatever variations are appropriate for their particular application. This can cause problems for the consumer needing to find an expression pedal that will work well with particular devices. The following describes the typical variations.

    1. Potentiometer resistance.
    Many devices require an expression pedal potentiometer resistance of somewhere between 5k Ohm and 50K Ohm. Some equipment is quite forgiving and will work well with anything in this range, others may require a very specific resistance to work properly. Still more equipment needs specific resistances outside this range including 100K, 250K, even 500K. Using a pedal with an incompatible resistance for the device can result in limited range, jumping or notch like response or in some cases, the pedal just won’t function at all.

    2. Potentiometer taper.
    The taper of a potentiometer describes how its electrical resistance changes proportional to its mechanical movement. In a linear potentiometer, the electrical resistance changes at the same rate throughout the mechanical range of the pot. In most cases, although not all, linear taper works best for expression pedals. In a logarithmic taper potentiometer, the resistance changes more slowly as you first move the pot, becoming increasingly faster as you get near the end. Log, or near log pots are commonly used in volume controls but don’t always work well for other effects. This is one of the reasons why trying to repurpose a volume pedal as an expression pedal often produces unsatisfactory results. Some wah pedals use pots approximating a reverse log taper. In most cases this will not work well for an expression pedal either, but there are at least two known cases where this is actually a requirement for an expression pedal.

    3. Wiring.
    Most potentiometers have three connectors; Clockwise, Counter-clockwise, and Wiper. Amazingly, there are multiple different ways these can be wired, all achieving largely the same result, which means yet more variations for expression pedals. The most common expression pedal wiring is to connect the pot to a 1/4″ stereo (TRS) instrument jack as follows:

    CW —— Sleeve
    Wiper — Tip
    CCW —– Ring

    An alternative is with the tip and the ring reversed as follows:

    CW —— Sleeve
    Wiper — Ring
    CCW —– Tip

    Yet a third way is as follows:

    CW —— Sleeve
    Wiper — Tip
    CCW —– Tip

    In this last one, the wiper and CCW are bonded together and connected to the tip and the ring is unused. This requires the use of a mono (TS) cable such as a regular guitar cable, in place of the stereo (TRS) cable used in the other two. These three are the most common that we see in expression pedals, but we keep finding more. Sometimes a dual gang potentiometer is wired in parallel to create a single pot with half the resistance. For example you may see a dual 20K Ohm potentiometer bridged into a single 10K. In this case the pedal will function the same as if it were a native 10K Ohm single pot.

    The most unusual configuration we have seen appears to be the original Univibe speed control pedal which looks like it used a dual gang 100K Ohm log pot with the wipers bridged together and connected to the ground. It would be interesting to find out what the story is behind how that came about. There are some Univibe clones on the market that require a similar type of wiring.

    An expression pedal with wiring polarity that matches the equipment specifications is required. Using a pedal with incompatible wiring can result in limited range, jumping or notch like response, or the pedal just won’t function at all, so make sure you check the requirements of your equipment. It’s often listed in the User Manual.

    Mechanics
    As previously mentioned, most expression pedals are passive devices and employ a mechanical means of converting the linear movement of the rocker to the rotational forces required to turn the potentiometer. Commonly these utilize a rack and gear mechanism or a system that uses a kevlar string or metal band. Most off the shelf potentiometers are designed for panel mounting and to be turned by hand, and this creates a couple of problems for expression pedals. Firstly the physical characteristics are not normally designed for foot operation. The forces involved in a foot pedal are often way beyond the mechanical specifications of a panel mount pot, causing them to break. Secondly, most of the shelf potentiometers with stops will rotate between 270 and 320 degrees. If this is not specifically matched to the movement of the rocker, the pot may not move through it’s full rotation, or may hit the stops. This can cause problems with dead spots and limited range or damage to the pedal. For best performance, it’s important to have a potentiometer that is purpose designed for foot pedal duty and with a rotation angle that matches the movement of the rocker mechanism. Most commercial expression pedals will have this, but if you are attempting to make your own, you will need to keep this in mind.

    Calibration
    Some of the more sophisticated effects and controllers, in particular MIDI devices, incorporate a calibration utility that can mitigate some of the issues with pot rotation. In these devices, there is normally a software option that allows the user to match the device to a specific expression pedal. In most cases this involves moving the pedal between it’s maximum and minimum settings and the device measuring the result. It then sets it’s internal parameters so that it recognizes where the maximum and minimum settings are of that particular pedal. This can often resolve problems of limited range. When using a device with this capability, it’s important to calibrate all expression pedals in accordance with the manufacturers instructions. If the pedal is ever replaced, even with the same model, calibration should be run again.

    Calibration utilities sometimes cause confusion when using MIDI. This confusion is normally due the how the calibration is displayed on the device relative to MIDI values. In MIDI, continuous controller (CC) movement is described using a range 0-127 where 0 is normally minimum or off, and 127 maximum. For example if using a volume CC, 0 would be no volume, 63 would be about half volume, and 127 would be maximum volume. The calibration utility measures the characteristics of a particular pedal and then internally maps them to the correct MIDI values, so that when a pedal is pushed all the way down for example, a MIDI CC value of 127 is sent. The confusion arises because when calibrating, the device is often displaying to the user it’s own measurement scale, and not the MIDI values it is mapping to. For example, if a device displays 0-99 when calibrating a pedal, this does not mean that it will only go to 99 on the MIDI scale. The device is displaying it’s own reference numbers and NOT MIDI VALUES. Internally, the device maps 99 to 127. There is no standard. Different manufacturers use different scales such as 0-10, 0-99, 0-1024. Some manufacturers actually use the MIDI scale 0-127 which reduces the confusion. Either way, when using MIDI, internally all these will all be mapped to the correct MIDI range. Also, users should not be overly concerned about reaching the maximum and minimum calibration values. The purpose of calibration is to map the values of an individual pedal. For example, on a device with a scale 0-99, a pedal may calibrate at 3 and 96. Again, this simply means that on this pedal, 3 will be mapped to MIDI 0, and 96 to MIDI 127. If when calibrating a pedal, the numbers are significantly out of line, such as 59-69, or the numbers don’t change at all, it most likely means something is wrong in the setup such as the pedal is incompatible or is using the wrong cable. Users wishing to validate MIDI CC values can usually connect a computer running MIDI monitoring software such as MIDI-OX to the MIDI channel and monitor the MIDI traffic.

    When using a MIDI configuration, remember that you should use an expression pedal that is compatible with the MIDI device you are connecting it to and not necessarily the MIDI controlled equipment at then end of the chain. For example, if you are using a MIDI floor controller from vendor A, and that is in turn connected to a digital amp from vendor B, and an effects unit from vendor C, the expression pedal would normally be connected to the MIDI controller and you should use a vendor A compatible pedal. The amp and effects unit will be receiving digital MIDI data, not analog expression pedal voltages. Choose an expression pedal that’s compatible with the device that you are plugging it’s cable into.

     

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