Showing posts with label Step by step. Show all posts
Showing posts with label Step by step. Show all posts

Eagle for making guitar pedals PCB: getting started (part 1/3)

Sometimes, especially with complicated builds with a lot of components, or when you have to build several times the same pedal, it is easier to use a printed circuit board (PCB) than veroboard or turrets board. A PCB is easier to assemble, and it prevents from doing many mistakes that can occur when using veroboard: false contacts, misplaced component, complicated wiring involving a lot of wires...etc.

"Eagle" is the name of a beautiful animal, but it also stands for "Easily Applicable Graphical Layout Editor", the name of a famous software that helps you to conceive and make printed circuit boards (PCB). I already used it a lot to make PCBs. For instance, I made a few Klon buffer boards with it. I decided to write a serie of articles explaining how to use it to make PCB for your guitar pedals.

Article parts:
  • Getting started (you are reading this one now)
  • Tracing the circuit (to be published)
  •  Creating the PCB layout (to be published)

Eagle 
Become free to make PCB like you want with Eagle


Why using Eagle?

There are many different different software to create PCBs that are available nowadays: DipTrace, KiCad (open source), Express PCB, Fritzing... Why using Eagle instead of these ones?
Well, there are several reasons.

Eagle is free. If you are using Eagle for your personnal use, it is a freeware. Of course, there are limitations that come with the freeware version, but they are not really a problem when it comes to guitar pedal PCB development: maximum size of 100 x 80 mm (4 x 3.2 inches), which is really big for a guitar pedal PCB, only 2 layers maximum (well, we are not going to use more anyway), and one schematic maximum per project. If you want to sell your projects, you will have to buy it, but for simple projects like guitar pedals, the Lite edition is enough and costs only 69$! If you need to buy it, respect the developpers, do not be ill-eagle (badum tsss) and buy it.

Eagle is well documented. There are a lot of books, websites, videos that are dedicated to Eagle software. If you ever encounter a problem, or if you do not know how to use a precise function, you will always find a solution somewhere. I will write a list of useful websites down this post.

Eagle has the most complete libraries. When creating a PCB, you need to specify what component you are going to use in your circuit. Is it a small 1/8W resistor, a big 1W one?  Is it an electrolytic capacitor or a tantalum one? You can imagine that it is very important to precise it in order to have the good component "shape" on your PCB. In order to do that, you have lists of components that are called "libraries", which contains hundreds of different components! Eagle has a lot of libraries for all kinds of components, and some libraries had been made especially for guitar pedals!

Eagle is easy to use. Most PCB softwares are easy to use, and Eagle is too! The "graphical" word in "EaGle" simply means that you have a wysiwyg interface. The interface is easy to use, and let you directly move the components on the board. Last thing, it works on windows and mac, which is nice if you are using different operating systems.

Convinced? Let's get started!


Installing Eagle

Download Eagle on CadSoft website, and install it as a freeware (except if you are going to sell the PCBs you make with it)


The libraries

When you create a PCB, you need to be very precise about which component you are going to use. Indeed, if you put a wrong reference somewhere, the spaces between the lugs can be too short / too long, the component could be too big to fit the PCB...etc. For instance on this PCB:
Superfuzz PCB circuit board
You can see that every component fits perfectly its location on the PCB. This is because when conceiving the PCB, I used the correct references for each components.

A library is simply a list of components referencing components sizes, values and shapes. Eagle comes with already a lot of libraries pre-installed. Some of them will be really useful (Resistors, Capacitors, Inducors (RLC), transistors, supply...etc), some of them not (Zilog microprocessor devices?).

Some libraries had been created specially for guitar pedal PCB making:
Gauss Markov library: very easy to use library with a lot of useful components.
Madbean pedals library: Brian (owner of madbean pedals) made available libraries for making guitar pedal PCB.
I strongly suggest that you download these libraries. They are easy to use, and contains all the basic tools that you need for making guitar pedal PCBs.

To install a library, unzip the files, and copy the .lbr files in the "Eagle v7.2/lbr" folder. It is in the applications folder on mac, or in the program files folder on windows.

Then, open Eagle. You should have a window like this, which is the control pannel:
eagle control pannel
You can see that there is a "Libraries" folder that can be expended. It contains all the libraries that you have in the "lbr" folder, including the ones you just downloaded and copied.
To tell Eagle which libraries you are going to use, you need to expand the "Libraries" folder, click right on the library you want to use and click on "Use".
Eagle how to use librairies
You can see that you have a quick description of the library on the right. It can help you sometimes to choose whether you want to use a library or not.

Ok so the big question is now... Which libraries should we use? Either you can use every library, but you can easily get lost with the number of different components available, and redundancy of some components. In my experience, I only use a few libraries compared to what Eagle is offering... Guitar pedal making is quite simple electronics, and does not require a lot of differente components.
Here are the libraries that I use when making a PCB:
  • Gauss Markov libraries (all libraries)
  • Madbean libraries (all libraries)
  • belton-engineering.lbr (if you are using tubes)
  • con-jack.lbr (if you want to implement DC jack on your PCB)
  • diode.lbr
  • ic-package.lbr
  • led.lbr (you will only use LED3MM or LED5MM (classic 3 or 5 mm LED) or DUOLED if you want dual colored LED)
  • linear.lbr (IC, OP amps)
  • pot.lbr (potentiometers, nothing else you stoner!)
  • rcl.lbr (dream library with all resistors, capacitors, inductors)
  • regulators.lbr (voltage regulators)
  • supply1.lbr and supply2.lbr (mainly for the ground symbol)
  • switch.lbr
  • transistor-fet.lbr, transistor-neu-to92.lbr, transistor-npn.lbr, transistor-pnp.lbr, transistor-power.lbr, transistor-small-signal.lbr, transistor.lbr (you should have almost every transistor now!)
  • v-reg.lbr (voltage regulators)
OK! That is already a lot of components, and should be largely enough for any guitar pedal circuit! And if a component you absolutely need is missing from these library, do not forget that you can use other libraries, or download libraries online!

Now we are ready to start!
First we have to trace the schematic... in the next blog post!

If you have any question, do not hesitate to post a comment!
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    Relay Bypass: conception and relay bypass code

    You might already have heard about "relay bypass", or even used it without knowing it. It a different true-bypass system than the classical 3PDT switch. Instead of using a mechanical 3PDT switch, a soft switch, a microcontroller and a relay are combined to turn the effect on and off.
    Relay bypass PCB DIY
     So... Why bother? My 3PDT switch is great, don't you think?

    As you may already know, 3PDT switches are the main cause of guitar pedal failure. These switches are not particulary though, and they often break, especially as we smash it continuously with our feet on stage. A classical high quality 3PDT switch is rated for 30,000 activation cycles. With relay bypass, we use a relay that will play the mechanical role of connecting ins and outs. Relays are usually rated between 10 and 100 millions cycles! Thus, this system is much more reliable.

    Moreover, the soft switch that we use to activate the guitar pedals also last longer than a 3PDT, usually around 50,000 cycles! They are also easier to replace, as there are only 2 connections to make with the relay bypass system, and not the full 3PDT wiring.

    This blog post will present you how does it work, and how to make your own relay bypass system using a microcontroller, from the beginning to the end! Long stuff (but good stuff?)!

    How to make patch cables: step by step tutorial

    Patch cables are expensive most of the time; making them yourself can save you a lot of money! Most of the times, high-end boutique patch cables do not have any datasheet or what so ever to really know their characteristics. By making patch cables yourself, you can choose whatever cable and plugs you want. Moreover, you can make it as long (or as short) as you need, and not be embarrassed with a too long cable. Here is a tutorial about how to make guitar patch cables for your pedalboard.

    I would also suggest to make your guitar cables yourself! Here is a step by step tutorial.


    What do you need?

    You will not need a lot of materials to make good patch cables. First, cable of course! I used Sommer Tricone MK2, mainly because it is highly flexible. Capacitance of the cable does not matter because I am using a buffer at the beginning of my chain. To choose the good cable, read my post about guitar cables.

    I used a standard cheap pancake plug that I found on Banzai Music. You can find cheap ones on ebay too. Beware that some of these pancakes are not functional, sometimes the tip and the ground sleeves are connected without any reason (2 upon 26 connectors for my Banzai music ones)... So buy a bit more that you actually need, and check them before soldering!

    Finally, you will need some classical tools: a cutter, pliers, screwdriver, a wire stripper and of course a soldering iron and solder!

    how to make patch cables guitar


    First step: cutting the cable

    Cut the cable at the correct length. To know how much length of cable you need, try to link the two pedals on your pedalboard with the cable. For side by side pedals, a 10 cm (nearly 4 inches) is enough.

    how to make patch cables guitar

    Then, you need to remove the external shielding. To know how much length you need to remove, unscrew the pancake jack plugs, and try to see how much length there is between the lugs of the jack and the part that will hold the cable.

    how to make patch cables guitar

    With a cutter or a razor blade, remove the external shielding. Do not press your blade too hard on the cable, or you will cut the ground wire. Do not hesitate to twist the cable to make it easier. You can see the shielding wire:

    how to make patch cables guitar

    Twist it, you should see the other shielding with the signal wire in the middle of it:

    how to make patch cables guitar

    Use your wire stripper to remove a bit of this shielding. Remove also a bit of the black layer: it is conductive, so you do not want it to make a false contact with the wire conducting the signal. I did not do it here because I am lazy (and have cheked that it was not making any false contact).


    Second step: tinning everything

    Twist the wires, and apply solder on every wire of the cable. Do not put too much solder, just enough to make it shiny. It will make soldering easier.

    how to make patch cables guitar

    Do the same on the lugs of the jack plug. Try to make small shiny solder pads:

    how to make patch cables guitar jack plug



    Last step: soldering, verifying and putting it back together

    Use a third hand to hold the jack plug and solder the signal wire to the top lug, and the ground lug to the bottom one. It is easier if you start by soldering the ground wire. Beware: the jack plug can become very hot, so do not try to hold it with your bare hands before being sure that it is cold enough.

    how to make patch cables guitar jack plug

    Before anything, check that everything is well connected and that there is no false-contact. To do that, use a multimeter in "logic" mode, and verify that there is no connection between the tip and the ground sleeve of the cable ("1": no contact, "-1" or sound: contact). Sometimes, the wires can be too close and make a false contact. If there is a false contact, try to see whether the wires are connected in the jack plug or at the other extremity of the cable (it can happen). If everything is OK, you can close the jack plug with the screws.

    how to make patch cables guitar

    Verify again with the multimeter that everything is OK. Sometimes, the tip lug can touch the top part of the plug and create a false contact. (especially if you put too much solder). Try to bend a bit the lug towards the bottom of the plug if that happen, close it and check it again.

    how to make patch cables guitar

    Redo the same thing on the other side of the jack and boom! You have a perfectly fine and cheap cable!

    how to make patch cables guitar

    Here, you have it! A good patch cable, ready to go on your pedalboard!
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    Any questions? Post a comment!

    How to make guitar cables step by step tutorial

    Making your own cables is really a good idea, mainly because it is easy and will save you a lot of money! High end cables can be very expensive. Moreover, most of the times, there are no datasheets provided for these expensive cables (with at least the capacitance per meter, or the type of cable that is used to make them, because most manufacturers do not make the cable wires themselves). So for me, it would be better to make it yourself so you can control everything,and not pay the extra money of a luxury type of brand.

    To lear more about guitar cables, to know what makes a guitar cable good or bad, read my article: all you ever wanted to know about guitar cables, but were afraid to ask.

    The guitar lead cable is the most important cable of your chain. This is the cable that goes from your guitar to your effects / straight to your amp if you are this kind of guitar player. If your guitar has no buffer in it (or no active pickups), which is highly probable as you are a conservative / vintage lover guitarist like me, the impedance of your signal will be high. You can loose trebles if the capacitance of this cable is too important (see my guitar cables: myths and legends article), before going through a buffer. Thus, if you which to keep it, you should have a short and low capacitance per meter cable.

    If you want to make patch guitar cables, I also wrote a step by step tutorial about how to make patches for your pedal board.



    What do you need?

    For the cable itself, you have different options. The capacitance between the core cable that transmit the signal and the ground wire is the most important value that determine the treble loss. I would suggest to take a look at this table that sums up the capacitance per meter of many brands and types of guitar cables. Another thing to keep in mind is that this cable will go through a lot of gigs, concert, will be plugged / unplugged a lot of times, so it has to be rugged! The best for me is the Sommer LLX which has a super low capacitance per meter value, and is highly resistant. It is really made for guitar lead cable applications. Another option could be the Sommer Spirit XXL or the tricone XXL (they have the same capacitance per meter value, and the XXL stands for the fact that they are rugged). The cable must not be too long, so for me 1.5 to 3 meters is a good length. So to sum up, the cable should be rugged, short and with a low capacitance per meter.

    The connectors have to be also of good quality, because this cable will go through a lot of use. The connectors should be tough. The Amphenol ACP M-GN is a classic plug that will perfectly fit this function. Neutrik NP2C is also a nice option. Remember: you do not need gold plated contacts.
    Then, you will need a soldering iron, solder of course, pliers, a cutter (razor blades can do the trick too) and a wire stripper.

    how to build instrument cable

    You do not need so much stuff in the end. For this example, I used Sommer Tricone MKII XXL and two Amphenol ACP M-GN.

    Step one: removing the shielding

    You can measure approximately how much shielding you need to remove by placing the cable near the opened jack. Just unscrew the jack plug, and try to see how much you need to remove between the lugs of the jack and the ring that will hold the cable:
    Cut instrument cable
    Then, cut the shielding with the cutter / razor blade. Do not press the blade too much in order not to cut the ground wire inside. Be slow, do not hesitate to twist a bit the cable to be able to remove the shielding without cutting the ground cable. You should have something like this:
    Guitar cable shielding

    We can clearly see the ground wire (the silver braid around the cable). Basically, it is a cable inside a cable (cableception!), and the inner cable is made of copper wire, and will transmit the signal.
    Twist the ground wires and place them aside. You have to remove a bit of the shielding surrounding the copper wire.
    How to build guitar cable
    Remove also a bit of the black layer: it is conductive, so you do not want it to make a false contact with the wire conducting the signal. I did not do it here because I am lazy (and have cheked that it was not making any false contact).



    Step two: tinning the wires and plugs

    To make the soldering easier and cleaner, you should tin the wires and the lugs of the plug.
    For that, just apply some solder on the wires (twisted ground and copper wire), and on the lugs of the plug. Beware of not putting too much solder, just a bit to cover it.

    tinning guitar cables
    It will make the soldering much easier.



    Step three: soldering

    Place the cable inside the plug. Do not forget to put the back of the plug on the cable! I did it twice and it is super annoying because you have to unsolder the cable, and remake all the steps above... Avoid that. 
    how to make guitar cable

    Then, just solder every wire where it should go. Try to make a proper solder (shiny, with not too much solder, but enough to maintain the cable in solder). Do not hesitate to heat the jack a bit (beware: the jack can become very very hot, do not burn your fingersby trying to holding it too quickly after soldering).
    Verify that your solder are OK. For that, use a multimeter in "Logic" mod, and verify that the copper wire is indeed connected to the tip of the jack, and that the ground wire is connected to the ground part of the jack. Sometimes it is possible that false contacts happen... Try to avoid that.


    Step four: putting it together

    With pliers, torn the metallic part to prevent the cable from moving. Put the plug back together, verify one last time with your multimeter that everything is well connected, and you are done!
     Guitar cable DIY

    There you go, here is a perfect lead guitar cable, which is worth the 50 euros cables that you can find in stores! With the choices I made (1,5 meters of Sommer Tricone MKII XXL, Amphenol ACP M-GN), the cost was less than 10 euros for this cable!


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    Any questions? Post a comment!

    Ditto Looper repair (how to fix a broken switch)

    The Ditto looper from TC Electronics is a good looper - in theory-. Easy to use, no audio quality loss due to the high sample rate of the recorded signal, true bypass... Everything to make it the best looper for guitarists!

    However, practically speaking, it has downsides: no stop button, which makes loops hard to synchronize, and it is really fragile! Mine did stop working after 6 months of intensive use (I bought it used so I guess it makes more than 6 months total). LED is still working, but I have to press many many many times on the switch before anything happens. Impossible to record loops! It was thus really useless as is.

    First, I contacted TC Electronics customer service, and I have to say that they were not helpful. I bought my Ditto used, so I did not have any invoice. However, when the problem happened, it was less than 1 year and a half that the Ditto was issued, and it was guaranteed for 2 years!TC electronics did not agreed and suggested me an exchange, which more expensive than buying a new Ditto in a shop... Thanks TC!

    It was try or die then: I tried to repair it!
    Here is the step by step guide if you ever need to repair yours.
    The main problem seemed to be the switch, which just needed replacement. I dismounted the pedal. First, you need to remove the knob by pulling it with pliers, and unscrew the potentiometer. Then unscrew the backplate. You have to separate the 2 circuit boards that are in the pedal. Indeed, to gain space, the Ditto is composed of two PCB, linked by connectors, allowing to fit such a complex system in a small enclosure (1590A size!). You have to pull up gently the top part of the circuit, holding the jack connectors. Then, you have two screws to remove to be able to pull the top part of the PCB. You should have something like this :
    Ditto looper repairing
    The "naked" Ditto. We can see the connectors linking the 2 PCB

    On the top of the circuit, we can see the LED and the chips which allow recording of the audio signal. Everything is SMD, except some big blue 100uF electrolytic capacitors. If we look at the bottom PCB, we can see that the switch is not a classic switching system, but a spring which activates a microswitch on the PCB.
    Ditto looper repairing microswitch
    The culprit: a microswitch (round button on a square),
    next to a 100uF electrolytic capacitor

    This is the same system than in the Line6 DL4, famous for switch failure! The faulting component is therefore very likely to be this microswitch. Microswitches are fragile compared to a classic footswitch, and cannot resist as many activations. There are 2 solutions:
    • Either replace the microswitch by the same component (which can result in other failures later)
    • replace the spring + microswitch system by a real 1PST footswitch, more resistant and easier to replace later.
    The second solution was the best for me.

    First, we have to dessolder the faulting microswitch. However, the capacitor can prevent us from reaching all the bottom lugs of the switch, so we have to remove it first. I have to say that soldering is fun and easy, however dessoldering is really a pain in the a...! Commercial components are soldered with very little solder, which is dry and on both sides of the PCB... You have to eat it quite a bit before it melts, yet do not heat too much because SMD components are very sensitive to heat! So take your time while doing this job, and wait times to times for everything to cool. You can see that there are 2 very fragile SMD IC just near the switch, so be careful, and dessolder only by the bottom of the PCB. A dessoldering pomp is the best for this kind of job. I managed to dessolder the two bottom legs of the microswitch that way. Top legs were impossible to reach from the top because of the jacks, and I did not want to overheat the circuit. So I just broke it by twisting the switch up and down. The 2 legs got stuck in the holes, so impossible to replace the microswitch. This is clearly the most difficult part of the repairing job. Once you did it, the rest is easy.
    Ditto looper switch 
    The PCB once you removed the capacitor and the microswitch.
    The two lugs near the jack are still visible

    We can see 4 pins for the microswitch. In fact, they are connected 2 by 2 vertically. We can the traces connecting the two holes vertically. There are also 4 pads to mount as SMD microswitch. 1PST footswitch has two lugs, so you have to cennect each lug to one hole on the left, and one hole on the right. Do not forget to use a classic "normally opened" footswitch.

    The problem is that a classic 1PST soft footswitch is too big to fit in the enclosure. In facts, it is too high to fit between the 2PCB, and too long at the base. There are 2 solutions:
    • either doing a rehousing of the pedal in another enclosure. This is difficult because you have to adapt the jacks input/output and power supply, which means more dessoldering, which means more risks of breaking the pedal.
    • Using a different type of switch that would fit the enclosure
    After a bit of research and help of people from madbean pedals forum, I found that a "arcade" type of switch would perfectly fit in the enclosure!
    We can then remove the old switch (unscrew it from the top), and remove the flange in the switch hole. We can then place the switch in:

    TC electronics ditto fixing switch not working
    Each pad of the former switch can then be connected to the switch:
    Ditto looper switch repair not working 


    Lets put it back together and boom! We are done! Everything works again like a charm, and with this system, I am almost sure that the pedal will stay functional a bit more. Moreover, this type of arcade switch is easier to replace if it broke.


    It is also easier to use, as there is no more latency between the moment when you press the switch and the activation of the effect. It is thus easier to have loops with the right tempo, or not to fail by pressing the switch too softly.
    And moreover, it has a really cool look!

    Ditto looper switch repair
    The new arcade switch on my functional-again Ditto looper!

    Every single pedal of TC Electronics have this switching system, so they are expected to break a lot... You can use this guide to repair them.

    Electro Harmonix Soul Food diodes mod (step by step)

    So I decided to mod my EHX Soul Food. As you may know, the Soul Food is a pedal "heavily inspired" by the famous Klon Centaur. The Klon is a rare overdrive pedal, which sells around 1500 euros today! This stompbox, created by Bill Finnegan in the 90s, is an overdrive with 3 controls: gain, volume and treble. It has been used and abused by many guitarists, including some famous ones like Jeff Beck. The Centaur is also known for its good quality buffer, like the Pete Cornish pedals. Thus, the Soul food is a cheaper version of the Klon.

    However, when looking closer to the pedal, we can see that the diodes ("essential" says Bill Finnegan on the PCB of the new version of the centaur, the KTR) are not the same as in the Klon. Indeed, the klon centaur's diodes are germanium, whereas the Soul Food uses Schottky silicon diodes! The diodes are hidden on the top part of the PCB, in order not to scare the klon maniacs I guess. Diodes are indeed essential to generate saturation generally speaking, and germanium and silicium diodes have different properties, so changing it seemed a good idea.
    Klon KTR diodes
    Today, lets see how the diodes can be changed by adding a simple switch to choose between the stock diodes and the original centaur germanium diodes.

    Disclaimer:
    I will not be held responsible if you break your Soul Food by doing this mod. The Soul food is fragile: potentiometers are cheap, everything is surface components which are sensitive to heat ... etc. The modification is not difficult nor risky in theory, but be careful and cautious in order not to damage it!

    Something else: as we will see later, this mod is after all quite anecdotal. There are no big differences between the stock version diodes and the centaur diodes, and I guess it would be quite difficult to distinguish between the diodes in a blind test... So it is more like a test to prove that sometimes, importance of some components just results from the musical "hype" around it! Learning how to do this will allow you to do mods like this on other pedals like tubescreamer, where the effect of diode selecting is much more pronounced. But do not expect great changes on the overall sound of your soul food!

    I noticed that East River Drive form EHX has almost the same design than the soul food, so you probably could do the same mod on the East River Drive following this tutorial. This would also be a much more useful mod on the East River Drive, much more sensitive to diode clipping.


    What do you need to do it?

    To do this mod, you will need a few things: a Soul Food of course, germanium diodes and a DPDT switch. The original Klon diodes are still unknown, however the DIY community did determined that the diodes were really closed to D9E russian germanium diodes. If you want the closest diodes to the original, get these ones on ebay. Anyway, germanium diodes have really close properties between them, so classical germanium diodes like 1N34A, BAT41, OA1160...ect. will perfectly do the job!
    Diodes mod soul food EHX
    You also need everything to solder: soldering iron, solder, tweezers. A third hand can be useful too.
    Ready? Lets go!

    First step: dismounting the pedal
    Diodes are on the top part of the PCB. So to have access to it, we have to entirely dismount the pedal. To do that, we need to remove the knobs first. Beware ! Knobs are really difficult to remove, and the pots are really fragile (60 dollars pedal, here you go...). Be gentle, or you can easily break a pot. A good working way to do this is to use two spoons as levers both side of the knob. Place the spoon under the knob, one by each side, and press both gently at the same time to remove the knob:
    knobs soul food
    We can remove all the knobs, and unscrew the 3PDT to have something like this:
    EHX removing knobs
    We can then remove the backplate, with a screwdriver or a driller. We can see the circuit, all with SMD, some film and electrolytic capacitors. We can also see the switch allowing true bypass or buffered mode.
    Soul food EHX mod
    We can remove the circuit from the box, by pulling gently the jack inputs on both sides.



    Second step: removing the original diodes and assemble the DPDT switch

    Once the circuit pulled out, we can see the diodes on the top part of the circuit:
    To remove them, do not try to dessolder them. There is solder on both sides of the PCB, and these commercial solders are really dry / hard to melt. Moreover, fragile SMD components are on the other side of the board (heat sensitive !)... So my advice would be to simply cut the legs of the diode with pliers or a cutter. Try to keep as much metal legs possible, so we can add some length later by soldering legs of other components to it later. I did that way, and by twisting a bit the diodes, I took them off quite easily.
    diodes EHX soul food
    We can then solder the germanium diodes on the DPDT. You have to solder them in an opposite polarity, on the top (or bottom) part of the DPDT.
    Then, we can do the same with the original diodes from the Soul Food. First, we can improve the length of the legs by adding some cut resistor legs. I just soldered it on the diode, using a third hand.
    We can then solder it on the bottom of the DPDT like the germanium diodes.
    Soul food diodes
    We can then insert the DPDT in the enclosure.


    Third step: drilling the enclosure

    We have to insert the DPDT in the enclosure. There is not much room for it, so we will have to sacrifice the battery compartment. You can also put it next to the switch, but then when you activate the pedal you can just move the setting with your foot... I decided to place it vertically on the bottom side of the enclosure. For me it is better if you want to squeeze your pedals on your pedalboard than a side switch.
    With a hammer and a nail, we can mark the spot where the hole will be drilled.
    diodes soul food mod
    We can see the mark of the nail. It prevents us from skidding with the driller. We start with a small diameter, and increase progressively the size until the DPDT fits in.
    Soul food mod switch
    Verify that you can indeed put the switch and screw it in the enclosure:
    diode mod soul food
    We are nearly finished now, last step!


    Last step: soldering the DPDT to the PCB and mount the pedal back

    So we are going to solder 2 wires, one for each lug of the DPDT (in and out). To have the good length of wire, try to see approximately how much lenghth will be needed in the enclosure. Do not make it too short, it is better to have a little more than a little less in those cases! Do not forget to put a bit of solder on the naked wires before soldering them to make it easier.
    Soul food mod
    Then, we can solder those wires to the PCB, where the diodes were. Just put one wire to each side of the diode D3 for instance (or D4, they are connected on both sides anyway).
    Soul food EHX mod
    Lets put everything back in the enclosure, and we are done!
    soul food diodes mod
    For a more professional looking, I just used letter stamps to engrave which side of the DPDT was which diode: "K" for Klon diodes (D9E), and "SF" for Soul Food (original diodes). A bit of China ink and voilà! Finished! 
    EHX mod soul food
    Here is the modded Soul Food! diodes soul food mod

     

    How does it sound?

    I have to say that I am quite disappointed... Differences between the 2 types of diodes are really minimal! Maybe the germanium diodes sounds a bit better at higher gain settings ("maybe"), a bit brighter... But nothing that really stands out really. I am not sure that the difference could be heard in a blind test. I tried to change the germanium diodes for classis 1n4148 diodes, and it was the same... Then, I tried with a soft clipping with 4 diodes (2 on each side), and the changes were minor.... Changind these diodes seems to have very very little influence on the overall tone and gain of the pedal!
    Desperate, I tried to remove the diodes! And very surprisingly, there was almost no influence on the sound! 
    Most of the saturation comes from the distorting OP-amp and not the diodes... So maybe the "these are essential" is finally quite a joke from Bill Finnegan!

    So my advice would be to stay with the stock version!
    But, if you are curious, you can do this mod to ear it yourself!
    I am really surprised that some builders (JHS...) still do this mod, I do not get the use of it, apart from being closer to a real klon circuit.... Musically speaking, there are almost no differences!


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