Lectric FX Dandy Horse help

[jwyles90]

Hey all,

I just finished putting together this Dandy Horse build and am hitting a bit of a wall in the biasing process. I was able to get the hz dialed in to both 500hz/125hz in the different modes, but I'm not getting any kind of audio output on step 2 (which is coming from IC3). Here's the BOM:
https://lectric-fx.com/wp-content/uploads/2017/03/Dandy-Horse-V.1.0.pdf

I took an audio probe to the board and traced the schematic up to pin 3 of IC3. The audio goes into the chip fine, but nothing is coming out of pin 7, which if I'm not mistaken should be where the audio comes out of the chip? The schematic is on page 5 and 6 of the BOM I linked above. It seems like there's something going wrong with the chip or something around the chip, but I can't seem to figure out what it is. I'm using v3207s as well. Any help would be greatly appreciated!!

[jwyles90]

Oh also here are my voltage readings for IC3 if that helps:
1--5.3v
2--7.3v
3--4.7v
4--14.9v
5--14.9v
6--7.3v
7--9.8v
8--9.8v

According to the list below the voltages should be:
1--15v
2--7.5v
3--7.8v
4--~0
5--~0
6--7.5v
7--8.4v
8--8.4v

https://docs.google.com/spreadsheets/d/1muuyVTsqSNm5fGsh81FYHky85p_sGRMZc4EoyX-2ioM/edit#gid=1299276747

[ElectricDruid]

The voltages are swapped around because you've got the jumpers set for the 3207 not the 3007. The chips have the same pinout, but opposite power supply polarity.

You said you've got the clock range set correctly (KHz not Hz, right?). In which case getting a signal through IC3 should be a case of adjusting the Bias trimmer until you can hear something coming through, and then experimenting to find the best spot for it (that gives you the most clean headroom). The chip won't give you any sound until that trimmer is close-ish.

You're testing in the right place - the outputs are pins 7 and 8, and you should hear the audio there.

[jwyles90]

The voltages are swapped around because you've got the jumpers set for the 3207 not the 3007. The chips have the same pinout, but opposite power supply polarity.

You said you've got the clock range set correctly (KHz not Hz, right?). In which case getting a signal through IC3 should be a case of adjusting the Bias trimmer until you can hear something coming through, and then experimenting to find the best spot for it (that gives you the most clean headroom). The chip won't give you any sound until that trimmer is close-ish.

You're testing in the right place - the outputs are pins 7 and 8, and you should hear the audio there.

I wasn't aware of the opposite supply polarity. Good looking out! Since they have the same pinout I don't need to put the 3207 in the opposite way, correct?

My multimeter only has a Hz setting. I haven't seen a DMM with a KHz setting in my searches. I don't hear any signal at all when I sweep through the bias trimmer, but I haven't tried it while also audio probing the chip.

[ElectricDruid]

I wasn't aware of the opposite supply polarity. Good looking out! Since they have the same pinout I don't need to put the 3207 in the opposite way, correct?

Correct. That's what the jumpers are for, to swap the power polarity around.

My multimeter only has a Hz setting. I haven't seen a DMM with a KHz setting in my searches.

Well, you need to be able to read 500KHz and 125KHz, so check that your meter can manage that. If the clock honestly were 500Hz and 125Hz, there's no way you'd hear anything.

I don't hear any signal at all when I sweep through the bias trimmer, but I haven't tried it while also audio probing the chip.

Get some audio going through it and then fiddle with the bias trimmer with an audio probe on the output. A looper is very handy for this, but I don't have one, so I use a recording of some guitar playing on my phone and play that through the pedal!

[jwyles90]

Well, you need to be able to read 500KHz and 125KHz, so check that your meter can manage that. If the clock honestly were 500Hz and 125Hz, there's no way you'd hear anything.

[/quote]
I don't hear any signal at all when I sweep through the bias trimmer, but I haven't tried it while also audio probing the chip.
[/quote]
Get some audio going through it and then fiddle with the bias trimmer with an audio probe on the output. A looper is very handy for this, but I don't have one, so I use a recording of some guitar playing on my phone and play that through the pedal!
[/quote]

Gotcha. Yea I went back and checked and it was reading KHz. I didn't notice the little "K" on the meter. I'm still not getting any kind of signal on test pad 3. With my audio probe the signal makes it all the way to pin 3 of the first 3207 and then doesn't make it out of the chip. I can hear a bit of hiss that comes and goes depending on where I am in the bias trimmer but that's about it. Do you think adding a jumper between pin 3 and 7 on the underside of the board would do anything?

[ElectricDruid]

Gotcha. Yea I went back and checked and it was reading KHz. I didn't notice the little "K" on the meter.

Ok, good. Looks like the clock is ok then.

I'm still not getting any kind of signal on test pad 3. With my audio probe the signal makes it all the way to pin 3 of the first 3207 and then doesn't make it out of the chip. I can hear a bit of hiss that comes and goes depending on where I am in the bias trimmer but that's about it.

Have you tried swapping the 3207s? It sounds a bit like it might be a dodgy chip. Where did it come from? If you've got alternatives, perhaps a different one will get signal through that part of the circuit.

Do you think adding a jumper between pin 3 and 7 on the underside of the board would do anything?

If you took the chip out, you could jumper from pin 3 to pin 7 (just put a wire in the socket - no soldering required!) and then you'd be able to test that the rest of the circuit was working ok (since now it'll have audio going through it), but it's not going to help fix the 3207!

[jwyles90]

I'm still not getting any kind of signal on test pad 3. With my audio probe the signal makes it all the way to pin 3 of the first 3207 and then doesn't make it out of the chip. I can hear a bit of hiss that comes and goes depending on where I am in the bias trimmer but that's about it.

Have you tried swapping the 3207s? It sounds a bit like it might be a dodgy chip. Where did it come from? If you've got alternatives, perhaps a different one will get signal through that part of the circuit.

So I'm on my second 3207. I was having the same problem when I first fired it up and swapped out the chip to see if that would make a difference. I can't remember which came from where, but all my 3207s and BBD type chips have come from either Cabintech or Stompbox Parts. I know nothing is guaranteed but they generally have been pretty reliable in the past.

[jwyles90]

I also tried reflowing all of the components that are around the chip. That didn't seem to make much of a difference either, as I'm still getting no signal.