Q&D Simple VCF Layout

[thedefog]

This is a PCB DIY Layout Creator I did for the Q&D Simple VCF Filter by Tim Escobedo. It is for the non self-oscillating one. This is the first layout I've ever done, so I'm sure there is something wrong with how I approached it, so share comments please! I haven't verified this yet, but I built one on breadboard and then pad-per-hole board from the schematic that works fine. Only issue right now is DC on the pots causes scratchiness. Probably needs a cap somewhere to help that out. Comments? Help?

My pad-per-hole one is rigged up with a simple LFO (Square and Triangle) on the same board going to the CV in. I'm thinking of mounting it inside a broken Wah pedal and installing a switch to go between LFO and manual control of the filter. I still need to tweak it some more, but perhaps I'll add that part onto this layout when I get it right.

[Strategy]

Any luck verifying this layout?
- Strategy

[tiges_ tendres]

Sorry to dig this one up, but better than to make a new posting.

Here is a layout I recently made for this:



Because I'm not that great at layouts yet, the two blue holes should be connected with a wire to provide Vr.  Also, I omitted the trim pot as I will probably wire a regular pot manually to account for different output signals.

Schematic is here:



I noticed the original layout had vanished.  So if someone could give this a quick look, that would be great!

[glops]

Can you post a PNP transfer?  Been interested in this one for awhile....

[tiges_ tendres]

Sure, as noted above it's still unverified.



the real skinny border around the top and sides should be removed or it wont work.

[glops]

Thanks, it's a small enough circuit so I'll double check the tracing before I etch it and report back.  This was something that I would like to bread board but I have been really into taking advantage of all of these wonderful layouts available.....

[thedefog]

Crap, I deleted the hosted files when I last updated my website. My mistake. It was verified working though, as I build a few of them for various pedals.

[wavley]

This looks fun, I'm gonna have to build one!

[Earthscum]

Couple things I spotted... first, no resistor to Vr on pin 1. Secondly, the extra OPA should have the output and neg in tied together, and the positive tied to Vr (Avoiding Noise and Power Problems with Unused Op Amps - AN1957).

You could use this layout by making the connections I mentioned, and carefully putting the 1M to Vr on the back side of the board to the blue holes (I assume that's what was originally going on on the layout. I've made mistakes like that, a Zen layout I made has the feedback cap shorted out at lowest gain).

[tiges_ tendres]

Couple things I spotted... first, no resistor to Vr on pin 1. Secondly, the extra OPA should have the output and neg in tied together, and the positive tied to Vr (Avoiding Noise and Power Problems with Unused Op Amps - AN1957).

You could use this layout by making the connections I mentioned, and carefully putting the 1M to Vr on the back side of the board to the blue holes (I assume that's what was originally going on on the layout. I've made mistakes like that, a Zen layout I made has the feedback cap shorted out at lowest gain).

I made the two holes blue to remind myself to connect a jumper there.  That should provide Vr, right?  R8 is 1M for this purpose.  And then the other stuff I can do on the back of the board.

Thanks for looking over this.

[Earthscum]

If you take R2 down .1", you can run the Vr all the way down to the +In pin, and jump R8 right where R2 is at the moment. That avoids a jumper, and cleans everything up. Also, this will free up a little room, and you can reduce the width a little bit more if you like. (Don't mind me too much... I sit and design PCB's by hand for fun sometimes. It's interesting to me to see how much I can cram into a small space, so I've kinda conditioned myself to spot ways of running traces. Winter time in a Trophy shop is pretty slow.)

[thedefog]

Here's the old one I did. Sorry it was deleted. It has been verified and works. I used it in conjunction with a 555 timer and really simple AR generator with a trigger pulse crudely connected to it in combination with a resistor chain to make a tiny synth for my nephew.

[Earthscum]

Is pin 1 supposed to connect to pin 2 to make a buffer?

NM... just realized it's a single amp, not a dual.

[Strategy]

I am using (I think) defog's layout

part order messed up, got .001uF cap instead of .002.

anyone know what I'm in for if I try the .001 in lieu of the .002?

thanks
Strategy

[frequencycentral]

Higher cutoff. Use two in parallel.

[Strategy]

Higher cutoff. Use two in parallel.

ahh thanks frequencycentral. will sort that out!
Strategy

[thedefog]

I have another one of these that I did in DIY Layout Creator that is a combo of this and an LFO with square and triangle modes. I'll up it soon.

[Strategy]

EDIT: I did use thedefog's layout. Couldn't find any shorts, yet...

Went up to my studio during lunch break and put this together using the earlier layout. I can tell that the filter is filter-y, but it's not working correctly.

- Input is audible at the output but doesn't sound consistently filtered
- A rhythmic pop can be heard at the output and the LED lights up whenever this pop happens
- Resonance pot appears to work correctly
- When I turn the cutoff pot with no audio in the circuit I can hear the cutoff frequency change as expected.

I'm thinking a short somewhere causing feedback somewhere in the circuit? Manifesting as an LFO type regular, but low oscillation?

QUESTIONS..in case it's a wiring error on my part:
1. Are the pots in the diagram viewed as if from front or back?
2. What is the directionality of the LED? Positive towards top of board?

Thanks!
Strategy

I have another one of these that I did in DIY Layout Creator that is a combo of this and an LFO with square and triangle modes. I'll up it soon.

[thedefog]

EDIT: I did use thedefog's layout. Couldn't find any shorts, yet...

Went up to my studio during lunch break and put this together using the earlier layout. I can tell that the filter is filter-y, but it's not working correctly.

- Input is audible at the output but doesn't sound consistently filtered
- A rhythmic pop can be heard at the output and the LED lights up whenever this pop happens
- Resonance pot appears to work correctly
- When I turn the cutoff pot with no audio in the circuit I can hear the cutoff frequency change as expected.

I'm thinking a short somewhere causing feedback somewhere in the circuit? Manifesting as an LFO type regular, but low oscillation?

QUESTIONS..in case it's a wiring error on my part:
1. Are the pots in the diagram viewed as if from front or back?
2. What is the directionality of the LED? Positive towards top of board?

Thanks!
Strategy

I have another one of these that I did in DIY Layout Creator that is a combo of this and an LFO with square and triangle modes. I'll up it soon.

Haven't logged in here in years. Did you ever sort this out?  The top pad is positive for the LED as the gnd rail is the bottom (which also runs to the volume pot). I think the LED is a CV input indicator light, I don't remember. I apologise for not using multiple colors on the wires. This was an early layout for me. I've moved one a good deal since these days. Pots are viewed from the back, but in the case of wiring the opposite way, they would just function backward. Obviously the log tapers would be odd in reverse for the volume.

[Strategy]

I trouble shot this one for quite a while and never got it working, will give it a try again with your notes in mind!
cheers
Strategy