SOLVED Help with Total Bender (PCB Guitar Mania)

[neiltheseal]

Hi everyone.

I just put together a Total bender from PCB Guitar mania. I have managed to get the Mk1 and Mk2 working but am having trouble with the Mk3. I'm hoping someone can help.

This is the silicon version and in the Mk3 transistors are 2n3904.

Currently I can get a very faint signal what is very spluttery. Sounds like the transistors are not biased properly, although the trimpot do not really affect this.

Someone in a facebook group suggested I put a 100nf capacitor in c3.4 where the build docs (link here) said to put a jumper. This has helped somewhat and now I get an audio signal (before that there was nothing)

Does anybody know what might be the issue here?

For voltage :q3 collector is 8.48v, base is now -0.01v and emitter is 0v.

Thanks in advance!

 

[neiltheseal]

Is it possible this could be caused by some of the electrolytic caps being reversed?

The build docs had PNP/NPN versions so never specified direction on the PCB. I had to look at the schematic and do my best to ensure they are pointed in the right direction for NPN.

I'm fairly confident c3.8 is the right direction, but c3.2 and c3.6 could be the wrong way around.
- I can see the positive end of c3.6 is connected to r3.5 so that seems right to me.
- The positive end of C3.2 is connected to r3.2 which also seems correct to me.

 

[neiltheseal]

Could this be an issue with the build docs?

C3.3 is 47p in the build docs. However when I look at the schematic, it shows c3.3 as a 220p. Would this be an issue?

 

[neiltheseal]

It could also be an issue with q3. Now I get a signal through the circuit (but very quiet and splattery).

Before putting a capacitor in c.3.4 i did an audio probe and got a signal all the way to the base of q3 but it stopped there.

 

[jesuscrisp]

I would try and put R3.7 in, no idea why that would NOT be needed in the NPN.

Quality product and electronics knowledge by GPCBM hits one more time.

Edit: also cut C3.9, not sure if it would make issues but it's not in the original schematic.

 

[music6000]

Looking at R3.5 - 330r, Yours looks like 33r, Bad lighting?
Check all your resistor values with this Calculator.
Click on Bands for 5 colours:

Resistor Calculator

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.

resistor.cherryjourney.pt

 

[neiltheseal]

Looking at R3.5 - 330r, Yours looks like 33r, Bad lighting?
Check all your resistor values with this Calculator.
Click on Bands for 5 colours:

Resistor Calculator

Resistor Calculator is an App developed by CherryJourney to help the user find the value of a resistor.

resistor.cherryjourney.pt

Thanks. I did check all of the components when it didn’t work hoping I had made a simple mistake.

It’s definitely 330r (orange, orange, brown, gold) must be bad lighting. Thanks for having a look.

 

[neiltheseal]

I would try and put R3.7 in, no idea why that would NOT be needed in the NPN.

Quality product and electronics knowledge by GPCBM hits one more time.

Edit: also cut C3.9, not sure if it would make issues but it's not in the original schematic.

Thanks I’ll try this when I get home from work.

C3.3. The original is 220p (and the schematic) but the build docs are 47p. That’s probably an issue right? I assume a mistake in the build docs.

 

[jesuscrisp]

That capacitor at that spot does NOT EXIST in the original schematic. I'm not sure it would really cause any issue, but it just doesn't need to be there at all. PCB Mania are, from my experience, pretty bad at creating or modifying circuits and sometimes they even mess up copying what is basically other people's work.

Please just try the suggested changes, it will work unless they messed up the PCB even more then the schematic/build docs.

Just to give you a bit of a feel just how useless the PCB/circuit design here is and what is missing from documentation:

• The charge pump chip is not needed if you're doing NPN only.
• They didn't use the opportunity of having a +/-9V charge pump to run the boost at 18V.
• Also the boost adds merely ~7 dB of output at full volume, which is kind of a waste of an op amp.
• Dip switches for voltage: unless you plan on transistor swapping and used bipolar electrolytic caps, you won't ever use the switches. Jumpers would make the build cheaper.
• R2.8, C2.3 and C3.2 are not actually needed, as the power filtering is done at the charge pump already. Mk1 is the only one without an additional power filtering cap, Mk2 is the only one that has an extra current limiting resistor. These do not harm the build, I just don't like the inconsistency and unnecessary parts.
• Jumpering C3.4 as suggested for the NPN build will lead to DC voltage on the pot and ultimately the output jack unless you have the boost engaged. Omitting R3.7 defeats the voltage divider at that spot, which will make Q3.3 not bias properly.
• Apart from C3.9 not actually being in the actual Mk3 schematic, R3.8 isn't in there either and might mess up how the tone pot behaves. I guess they wanted to make it closer to a Big Muff tonestack doing so but without actually knowing what they are doing.

 

[neiltheseal]

That capacitor at that spot does NOT EXIST in the original schematic. I'm not sure it would really cause any issue, but it just doesn't need to be there at all. PCB Mania are, from my experience, pretty bad at creating or modifying circuits and sometimes they even mess up copying what is basically other people's work.

Please just try the suggested changes, it will work unless they messed up the PCB even more then the schematic/build docs.

Just to give you a bit of a feel just how useless the PCB/circuit design here is and what is missing from documentation:

• The charge pump chip is not needed if you're doing NPN only.
• They didn't use the opportunity of having a +/-9V charge pump to run the boost at 18V.
• Also the boost adds merely ~7 dB of output at full volume, which is kind of a waste of an op amp.
• Dip switches for voltage: unless you plan on transistor swapping and used bipolar electrolytic caps, you won't ever use the switches. Jumpers would make the build cheaper.
• R2.8, C2.3 and C3.2 are not actually needed, as the power filtering is done at the charge pump already. Mk1 is the only one without an additional power filtering cap, Mk2 is the only one that has an extra current limiting resistor. These do not harm the build, I just don't like the inconsistency and unnecessary parts.
• Jumpering C3.4 as suggested for the NPN build will lead to DC voltage on the pot and ultimately the output jack unless you have the boost engaged. Omitting R3.7 defeats the voltage divider at that spot, which will make Q3.3 not bias properly.
• Apart from C3.9 not actually being in the actual Mk3 schematic, R3.8 isn't in there either and might mess up how the tone pot behaves. I guess they wanted to make it closer to a Big Muff tonestack doing so but without actually knowing what they are doing.

Thanks for all this. I have heard this about PCB guitar mania but this is my first PCB with an issue.

I added r3.7 and cut c3.9 (left the legs in there and just cut out the capacitor.

I also reversed the diode on Q3.3 because I saw some NPN schematics where this was recommended as the PCB silk was for NPN.. Starting to think I should not have done this?

There is some progress. Now the pedal works but only when I strum very loudly. Here is a video of what I mean.

Do you have any more suggestions? Should I put the diode back the other way?

 

[neiltheseal]

For anyone interested I never got this going as silicon.

I removed the parts and set up the pcb to be PNP. I tested it out with whatever PNP transistors I had lying around it worked! Not well but it worked!

I ended up buying matched germanium transistors and it works perfectly now.

This is a good outcome as I now can switch between germanium and silicon. The mi3 Germanium is now my favourite but it might be confirmation bias.

 

[pliolis]

For anyone interested I never got this going as silicon.

I removed the parts and set up the pcb to be PNP. I tested it out with whatever PNP transistors I had lying around it worked! Not well but it worked!

I ended up buying matched germanium transistors and it works perfectly now.

This is a good outcome as I now can switch between germanium and silicon. The mi3 Germanium is now my favourite but it might be confirmation bias.

Have you tried metal case BC108-9 ,BC186 , GuitarPCB sells BC108-9s reverse caps

 

[pliolis]

Have you tried metal case BC108-9 ,BC186 , GuitarPCB sells BC108-9s reverse caps

If mk1 and MK2 are set for PNP ,set the voltage for NPN on the MK3 reverse the caps etc.,

 

[neiltheseal]

If mk1 and MK2 are set for PNP ,set the voltage for NPN on the MK3 reverse the caps etc.,

Yes I tried metal case BC108 and 109 on the NPN mk 3 but didn't work. I took everything out, reversed caps and used PNP germanium. It works fine now. Votlage set for -9v.

Mk1 and 2 are NPN and they work fine with silicon. I think i have 2n3904 in the mk1 and bc108/9 in the mk 2.

 

[pliolis]

Yes I tried metal case BC108 and 109 on the NPN mk 3 but didn't work. I took everything out, reversed caps and used PNP germanium. It works fine now. Votlage set for -9v.

Mk1 and 2 are NPN and they work fine with silicon. I think i have 2n3904 in the mk1 and bc108/9 in the mk 2.

So NPN does not work in mark 3 ,I have enough NPN and PNP for this project ,I have built all three pedals in I25B will be great to have all 3 in one enclosure ,waiting for pcbs to arrive .I have built a fulltone 69 which is great and a sunface with real NKT275s the needs biasing all the time

 

[neiltheseal]

So NPN does not work in mark 3 ,I have enough NPN and PNP for this project ,I have built all three pedals in I25B will be great to have all 3 in one enclosure ,waiting for pcbs to arrive .I have built a fulltone 69 which is great and a sunface with real NKT275s the needs biasing all the time

So you think NPN does not work in this circuit?

I did not know enough about circuits to say but it would not work for me but the ge pnp works great.

My advice is to make mk3 a germanium pnp. It sounds great.

Mk1 and 2 work fine as silicon.

 

[pliolis]

So you think NPN does not work in this circuit?

I did not know enough about circuits to say but it would not work for me but the ge pnp works great.

My advice is to make mk3 a germanium pnp. It sounds great.

Mk1 and 2 work fine as silicon.

Will go with what you said

 

[idlebydesign]

Hey Neil, I am currently awaiting my Total Bender board from PCB mania. I saw on the forum that you recently built one. I was wondering if you have any advice or insight into building it? I plan on making MKI, MKII, and MKIII all germanium.

 

[debrad]

I'm with you @idlebydesign, my Total Bender board arrived the day I discovered this thread from @neiltheseal. Hoping all the advice here will help put together a full functioning build with this one.

BTW, I just completed PCBGM's "Ultimate Pharaoh" and it had a few issues on the board and in the build docs too (docs have wrong clipping order for the rotary switch and wiring the 5th and 6th clipping options need more tweaks than the build docs indicate). Not a huge deal (and the pedal sounds great) but definitely unfortunate.

 

[neiltheseal]

Hey Neil, I am currently awaiting my Total Bender board from PCB mania. I saw on the forum that you recently built one. I was wondering if you have any advice or insight into building it? I plan on making MKI, MKII, and MKIII all germanium.

Hey. Good luck building this. I really like it now that I have it working.

My main insight is to build Mk3 as germanium as you are. I can confirm it works this way. I had no problem making silicon Mk1 and 2, however I'm sure that germanium will work just as well as that is the original.

The PCB contains no indication what direction you should face electrolytic capacitors so you will have to read the schematic (which was a bit of a challenge for me). I looked at other tone bender schematics and found that for silicon the negative end always pointed to ground and for germanium (PNP) positive always pointed to ground.

You should be able to figure this out too, but you can probably just look at my picture at the top of this post and face the caps in the opposite direction to what I have (as the picture is silicon).