EgoDriver high gain squeal

[k.rock!]

Hey guys! (first timer here  )

I recently built two EgoDrivers, one for my friend and another one for me. I decided do build the second one on a protoboard first so I can do come component experimentation but I have a problem. For some reason when I adjust the GAIN pot maybe past three-quarters I get a high pitch whistle sound that persists all the way until I hit the max setting. It doesn't go away until I roll it down. I replaced the 220pF cap across pins 1 and 2 on the IC (C2 on the schematic) with a 470pF and that fixed the problem, however I know that if you replace a higher value cap in there you get less gain out of it.

Have any of you guys seen something similar to this?

I'll be glad to hear any suggestions or ideas from all of you wise people 

Thanks!

PS. Below are some pictures of my first effort for my friend . This one sounds awesome!

[k.rock!]

I received some feedback on the diystompboxes.com forum. I haven't tried this yet, but I thought I could share it in cases there was someone else having the same issues, and if you have another suggestion please post it!

Here's what I got:

"Yup.  I had a similar problem with my build.  The only way I could solve it was to disconnect the cap/resistor to ground coming off the second half of the op amp.  Never figured out the real underlying reason for my squeal, so it's still disconnected, no squeal and it sounds almost the same tone-wise. "

"You don't get less gain, it rolls off more treble so it might just sound like it has less "bite". I had the same problem with an OCD that I built on vero, but the squeal went away when I used shielded cable for the input and output with one end of each shield connected to ground."

[madbean]

I would not go disconnecting any resistors. Definitely shielded cable if you are getting whine.

[k.rock!]

Yeah, my thoughts exactly   I just needed to give him the benefit of a doubt in case somebody else had the same luck doing something similar.


BTW. On another note, I tried replacing the trannies with some diodes for troubleshooting purposes like you suggested and that's what did it! So I just had at least one bad transistor. Swapped them both just for sanity sakes and worked like a charm!  (I had emailed you on a weekend about this )

I'm also experimenting with adding a variety of diodes and even a red LED in series with Q1 (like the diode->Q2 setup in parallel with it) and I really like it! I've found that the red LED gives is a little more grit and just a pinch thicker sound. A germanium diode gives it a similar effect only smoother and I think it handles the bass notes like a smooth fuzz. It sounds pretty cool to me!

Thanks a lot for your help!

-Kaleb

[madbean]

Yep, this one is wide open for diode experimentation. The original (VooDooLabs OD) had 1n914s, IIRC. LEDs would be similar to the Crunchbox, I think.