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 :

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.

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.

 

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:

Each pad of the former switch can then be connected to the switch:

 

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!

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.

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!

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:

We can remove all the knobs, and unscrew the 3PDT to have something like this:

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.

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.

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.

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.

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.

Verify that you can indeed put the switch and screw it in the enclosure:

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.

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).

Lets put everything back in the enclosure, and we are done!

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! 

Here is the modded Soul Food! 

 

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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