Buffer, working good alone, dies out when connected to the pedalboard

[arma61]

Hi lads

got a problem... need your help

I'm building a pedalboard, let's say 5 FXs in one case, all TB, signal goes from input to Cruch box, HW89, TS808, LBP1.

As a surplus I wanted to add a buffer at the input, so made out a small PCB, 3 jacks, In_buff, Out_buff and another In, so one can connect directly through the In to the FXs, or connect guitar to In_buff then, with a patch cord, connect from Out_buff through the standard In... u now what i mean, isn't it?

Now the problem, every single FX is working alone and chained, the buffer works alone but when I use the patch cord to connect Out_buff to In I get the signal good for ~5 secs then it dies away to a very low level, I bet it loses 80% of level.

Edit: tried to use another jack, connected to the input of the pedalboard, instead of the jack on the buffer's PCB, no change, still dies

What's going on ?  Any clue ? "unfortunately" the case is alrady drilled for the 3 jack!

here is the buffer part


Thx vm

Ciao

Armando

[Mike Burgundy]

Edit: tried to use another jack, connected to the input of the pedalboard, instead of the jack on the buffer's PCB, no change, still dies

If I understand you correctly, you've hardwired a new jack directly to the effects chain, bypassing the buffer pcb, right? The problem is still there - that tells you it's not in the buffer, its after that (the buffer is out of the equation and the problem persists)

[arma61]

Thx Mark,

no, I mean I just skip using the jack socket on the PCB, thinking about a "grounding" problem, so buffer's still connected.

If I connect the guitar directly to the pedalboard input it works fine, but not with the buffer in front.
I did another test with another buffer ckt I've built, it's a double buffer one with gain, from AMZ fantastic site!!, installed it on the pedalboard and, using the one with gain, it works fine , guitar to buffer input, buffer output to pedalboard in.
If I do the same with the other buffer no way.
Probably is a mismatch of impedance (?), or something else relate to the ckts, the single one is uning an LM741, the
double one a TL072, may be... who knows.
Looks like I need to re-design the buffer PCB based on the one from AMZ and using only one part of it, still wonder why this issue.


Thx
Ciao

[Jdansti]

Does the buffer have a bypass switch?  If so, does the PB work fine with the buffer in bypass, but when you switch it out of bypass, the sound dies?  Have you tried turning on each of the PB effects individually when the buffer is on?

The reason I ask is I've had this happen with a Tillman. In my case, the first effect is a tone stack. If the tone stack is in bypass, then the other effects work fine when the Tillman is switched on. But I get no sound when the Tillman and the tone stack are both on at the same time. Does this sound familiar or is it different than what you experience?

[R.G.]

Get your meter out. Attach it between ground and the + power. Verify that the power is good before you insert the cable that causes the problem. Now insert the cable. Does the power voltage change?

If not, repeat the test, this time with the meter on the output at the jack. The DC level here should be zero. Does it change?

If not, repeat the test, this time with the meter on the output pin of the opamp. Does it change?

If not...

You see what to do. Start checking for which DC voltages change when you plug in that cable. That will tell you where to start. Something that works fine, then dies 5 seconds after some change, is having its operating conditions upset by some condition change. This can really only be either one of the coupling caps in this circuit, or the power supply itself. In equipment in general, it could also be something overheating, but I doubt that in this case. So look for what capacitor voltage is pooping out after 5 seconds.

[amptramp]

Some effects may depend on having a DC return path to ground at their input, which yours does not.  If C2 is leaking, you may be forcing something out of a proper bias condition.  "It works for a few seconds" is usually a problem with leakage current charging something.  A resistor to ground at the output may alleviate the problem - try it temporarily and see if it works.

[arma61]

Ciao

@John, no bypass switch for the buffer, the PB works fine using its own input jack, so skipping the buffer PCB

@R.G. thx, yes thought it was time for my meter!! will report back with result

@Ron, that'd be insane!, just one capacitor.... and it'd do all this!! will look at it.


Thx  for replies mates, stay tuned....

Ciao

[arma61]

Hi

first report, did a quick test last night... not much time available 

got 4.2 volts on neg. side of C2 above, though it slowly decrease to 0v, to suddenly rise again to 4V and so on!
Changed C2 same story, installed a 1k res from neg side of C2 to ground and finally got rid of voltages at C2.
All above with nothing connected to the buffer board.

Connected then an mp3 player, it seems the level is the same now at the buffer out and at the pedalboard out, so it seemd this C2 was the culprit... still have to test it with guitar and see if that 1k res is affecting sound.

Thank you so far, will report again with further test results.

Ciao