random number generator pedal

[timd]

Hello! I just built the random number generator pedal and it produces an oscillation that can be controlled by the volume pot. The guitar signal is faint and never gets louder than the oscillation at any setting. Does anyone have an idea about what might be wrong. I built this on vero.
Also, if I wanted to keep the oscillations and turn them off via a mini-switch, would I use a cap? I built a ring mod in the past that used a small electro cap tied into the output to kill the unwanted noise, but the volume drop was severe. Ideally, I just want a RNG pedal that works like it should.
   

[Taylor]

That circuit will behave very different depending on the specific transistors used. IIRC Doug Deeper said he would audition transistors in sockets before soldering them in. When I built one, it was very crazy, noisy, and relatively uncontrollable. Yours is likely working, but you might get less crazy results with different transistors - just use sockets and try several out.

You can't simply turn off the oscillation, as this circuit is basically designed to feedback. But you can get less oscillation again with different transistors and by changing the feedback resistor from the last stage to the third to a bigger value (as I recall - haven't looked at this schematic in a couple of years).

[timd]

I think I'll try changing the transistors. I do have all of them in sockets from now, and it'll be easy. Thanks for the tip about the feedback resistor - off the top of my head, I think its a 100K. I've also heard that people have put a pot in place of this too. For the 2M2 resistor, I had to use a 1/8 watt. Could this be an issue? I usually use only 1/2 or 1/4.

[Taylor]

No, 1/8w resistor should be fine.

[timd]

Thanks again, I'll report back when I have some results.

[timd]

I found a couple interesting things -

1. I had the 47uf cap in a socket and took that out to replace it with a different value, and it didn't make any difference in sound when removed and I don't know why.

2. The transistors did make a huge difference, especially the last one. I kept it stock except for the last transistor (stock were 4401, 2222, 3094, 3904). The transistors that were greatest to my ear were a 5088, 5089 and a random one from my parts bin that I couldn't read the markings for the last transistor.

[Taylor]

Here's the schematic so we know what we're talking about:

http://i52.tinypic.com/2r2ulp0.jpg

And the layout I assume you're using:

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=18731&g2_serialNumber=1

That 47uf is connected between 9v and ground. It's a power supply filter, so it's job is to clean up noise that might be in your power supply. It won't make a difference in the sound of the pedal other than to clean up hum/buzz that might or might not be there.

[timd]

Thanks again. Yes, that is the schematic and layout I'm using.