Troubleshoot no sound Big Muff

[Outlaws]

Doing a Green Russian from a Tonepad board.  Bypass works, but the effect is dead.  I can hear the tone knob moving with the effect volume cranked.

http://www.tonepad.com/getFile.asp?id=94

Only mod is a 100k log pot for Volume.

Any ideas where I should have what voltages?  Or since the volume needs to be cranked to hear the mechanics of the tone pot, how to probe the guitar input after it hits the board?

Polarized caps are all good, and I have continuity from the input tip to the boards input.

[bluebunny]

Build an audio probe (see GeoFEX) and trace your signal from left to right through the schematic.  Take voltages from your active components - basically follow the sticky debugging thread.

[duck_arse]

mostly big muffs are the same transistor stage three time, two with added clipping diodes, which we don't care about for DC. and an extra easy-to-work-out final stage, which is mostly ohms law pencil and paper. so the first three stage base voltages should all be similar, the collectors similar and the emitters, well, similar.

you can inject signal to the first stage input, and listen at the collector for signal, then each collector following. or lift the interstage resistors and inject signal into the base of each transistor in turn, listen at its collector. this is if your voltages measure ball-park, and will confirm/eliminate the interstage parts.

photos of what you have built, please, and as bb says, the debugg page.

[Outlaws]

Well my collector voltages on Q1 C is a little different... assuming the first three stages are considered Q1-3 on this board.  Q1 is by the input so I presume yes.

8.75v in.

Q1: C 1.54v  B .84v  E .24v
Q2: C 4.41v  B .72v  E .14v
Q3: C 4.30v  B .71v  E .13v
Q4: C 4.26v  B 1.47v  E .89v

I see what is meant by the first three are similar. The resistor from source voltage to Q1C is the same 12k value as used for the resistors to Q2C and Q3C, all with a 470K and 470pf between the C and B, yet the voltage is quite different. Q1 is faulty? Or maybe the Cap is at issue?

[Outlaws]

Just measuring the resistance in the circuit between the Collector and Base of the first 3 stages...

Q1: 330k
Q2: 145k
Q2: 136k

But oddly, the same traces, but at the 470pf cap leads on the top side of the board, the first is 465k while the other two are the same as the C and B trace measurements.

I don't feel like this should change.

[whoisalhedges]

The first three stages share the same value collector and emitter resistors; shouldn't DC collector voltage be more or less the same at each?

edit: I'd measure the 12k at Q1's collector. And maybe the 100R at the emitter (probably irrelevant, unless you put in a 100k or something by mistake). Something's off.

[GibsonGM]

That first stage looks buggy.   Al is right, the collector at Q1 should be similar voltage to the others.   I suspect something went wrong when soldering up the feedback stuff at the collector, perhaps a short somewhere.

Like they said, if you try to audio probe you may find no signal at Q1, except perhaps the base.  Then, if you INJECT a sine wave (low voltage tone, even your guitar will work in a pinch) into the next stage, you may see the following stages work.  But as Duck said don't forget to lift the input resistor to the base of the next stage, or a short previous to this would render your injected tone inaudible.

Your homework: examine the first transistor and all its R's and C's...make sure they are all connected properly!!  And are the RIGHT VALUE parts for where they are!   

[duck_arse]

we love looking at photos ......

[Outlaws]

we love looking at photos ......

I would but it's a hassle and a half since I have to get them from a phone, to a desktop, resize, and then upload to an FTP.  I cannot find a decent photo hosting means to access from my iPhone.  Suggestions?

[Outlaws]

But I solved it.  Every trace was clean and shiny and no wrong values.  I started wiggling stuff.  That 470pf (that had different resistance between the C and B traces on the cap leads bs under the board) I could feel a movement in the pad.  Desoldered and the pad came right off with it.  Not good for something that was soldered once and right.  Oh well.  I used a scrap lead to run a trace for those three points right there.
Effect works perfect now.

Thanks everyone for narrowing down where I needed to be.

[Fndr8875]

damn big muff is the only effect i havent been able to make work...just build 2 phasers and worked first time both of them...tried like  5 big muffs and none of them work.... i mean theres like 23 or 24 resistors, 4 transistors, 14 capacitors, 4 trannys,  4 clipping diodes , 1 rp diode, 3 pots....phaser has way more....build some delays to same thing no probs, way more parts...who knows


i havent done a phase 45 before but came upon two pcbs, anyone have any idea what two phase 45s together would sound like, i dont know wwhat the wiring options would be just one going out into the other , never done any combo pedals, but have no need for another phaser, thought maybe could get something diff or interesting out of doing it differently. Prob start a new thread since this is totallly off topic

[duck_arse]

nice work, outlaws (except for the lack of pics).

I dunno about "phone", but imgur is a fairly trouble-free pic host.