Q&D VCF on vero - troubleshooting help needed?

[mthibeau]

I built this layout, checked it like a zillion times and still having trouble.

I can hear the filter working, and it can self-oscillate so the output part of the circuit seems OK, just not getting anything from the input to the filter. Weird thing is that it kinda works if I pump audio through the CV in. The actual input just does nothing.

Is there supposed to be cuts under something I am missing here?

Couple of questions:
- Does VR1 trim need to be a 1m? (i'm out), I was going to try a actual pot next (I had a 250k on it) - UPDATE = tried an actual 1m pot in place of the VR, still same problem...
- Any other troubleshooting tips, I think I am close to getting it working, just need to get the input/cv sorted out
- I used a 470pf instead of the 500pf, but I am sure that isn't part of the problem, let me know if you think it could be...
- I used a 5mm green led, should I try something else?

- Thanks in advance,
MikeT

[mthibeau]

Here is the scematic if that helps... I am still new at this, from what I can tell the layout matches the scematic, but I am new at it.. pretty much just been building by numbers (mostly vero, some perfboard).

What I don't get in this layout is row "h", without any cuts isn't the input going to go to ground (the jumper right before the IC?). The input after the trim should hit C1/R1 and hit pin 3 of the IC.

I am going to try to debug with an audio probe tonght, if I hear signal getting to pin 3 but it's still not working, could I have a partially fried IC (like I mention, if audio hits pin 2 (from the CV in) the circuit starts passing filtered audio.

I used an lm741 from radio shack for this one, I have a bunch of TL071's as well, should I swap it and try?

- MikeT

[PRR]

> What I don't get in this layout is row "h", without any cuts isn't the input going to go to ground

Looks that way. Cut somewhere.

If that is not it, post some DC voltages.

[mthibeau]

Wasn't a cut on row H, didn't help. I also connected my input to row I and ditched the trimpot to see if I could get anything, still no dice...

Here are my voltages on the 741

Pin/V
1 = .01v
2 = 1.9v
3 = .01v
4 = 0 - ground
5 = 0
6 = 1.9v
7 = 9.3v (+9v in)
8 = 1.9v

[PRR]

Null -- 1 = .01v
- In -- 2 = 1.9v
+ In -- 3 = .01v
V- ---- 4 = 0 - ground
Null -- 5 = 0
Out --- 6 = 1.9v
V+ ---- 7 = 9.3v (+9v in)
NC ---- 8 = 1.9v

Junction of R7 R1 R2 C2 should be +4.6V, and should NOT be connected to Pin 1.

[mthibeau]

Junction of R7 R1 R2 C2 should be +4.6V, and should NOT be connected to Pin 1.

You rule, a quick cut under R3 made it work like a charm, thanks!

[zhx]

Hi, I know its an old topic but...
I also built this and it works. But my guitar is now microphonic; switching pickups results a big click through the amp. What could be causing this?