calling jordan bosstone builders...

[swt]

HI. I have just finished mine. It works fine, but when the attack pot is down, i get some kind of a close wah or filter sound. I know this could be solved by adding a bypass cap to the pot as in the guitar volume, but a friend of mine has a voodoo lab bosstone, and it's just as in the schem, but with a 1k resistor added at the top of the first pot. I've used a 2n2222 metal can for Q1 and a 2n3906 for Q2. i'm just wondering if this ckt will benefit of a higher gain Q1, as the voodoo uses a mpsa18, and a 2n2906. Any ideas? Thanks a lot!

[aron]

It's probably a 1K resistor from pot to ground. That would stop the drive/attack from grounding out and probably stop your oscillation/wah/problem.

[brett]

Hi.  IMO this circuit sounds best with a low-to-mid hFE Q1 (which also needs to be low noise).  A 2n3904 is excellent (hFE about 180).  A PN100 is getting "hot" (hFE about 400).  If you like heavy metal and feedback and oscillations, the MPSA18 (hFE about 800) might suit you, but the circuit was designed for low hFE trannies.

The gain of the circuit is about twice the hFE of Q1.

[swt]

OK thanks guys. I've got a low hfe in Q1, as 2n2222 is in the 100 area. The strange thing is this type of nasal tone i'm getting when the pot goes down. I've heard of other guys mention this, but the voodoo is as the schem. Shall i add a small bypass cap?. Thanks a lot!

[p1_ind]

I had the same problem with the one I built so I did away with the pot and put a 10K resistor from the input to the .022uF input cap.

I also change the input and output cap to .047uF, change the diodes to red LEDs.

Then after reading some other posts about the bosstone I added a switch which takes the clipping diodes (or in my case LEDs) in or out of the circuit so I can switch from hard clipping to a very nice, loud overdrive.

Now I am very pleased with it.

Adam