Bobtavia unwanted compression problem

[Mick Bailey]

Just been playing around with a Bobtavia and I'm getting a nice distinctive octave using Schotttky diodes and driving it with a Bazz Fuss (Red LED) in the same enclosure. Between the two is a simple variable LPF (47k pot and 22n cap). The main problem is that the first note is loud and clear and then the signal immediately compresses and reduces in attack/volume. It takes about 2 seconds to recover after playing a passage. The attack is very much like a compressor on a hard setting. There is a good deal of promise if the compression could be removed and I'm happy with the overall sound. The problem worsens if I boost the 386 (switchable 10uf cap + 510R series resistor from pin 1 to .

Tried a couple of 386 ICs - LM386N-1 and a JRC386 - both with the same result.

The Bobtavia also compresses when isolated and driven externally from an external distortion pedal such as a Blue Clipper or May Queen.

Any ideas?

[PRR]

I think you are just over-driving it. There's ample gain in the LM386. More gain in front is over-over-kill.

Turn down the input, turn up the output.

[DougH]

Reverse the order. If you want more drive out of the bobtavia, use it to drive the fuzz box instead.

[Mick Bailey]

Spent a couple of hours investigating and putting the fuzz after the Bobtavia. Still no luck and after some considerable experimentation discovered that I'd got the output cap (2.2uf non-polarised electrolytic) between the diodes and the level pot, thus denying the path to ground for the diode bias and inducing the problem described.

Interestingly, I'd replaced the Schottky's with a couple of 'mystery' diodes (2-lead TO92 package - every one out of the pack has a different number but they all have .5v drop) and the result is now even better - easily the best octave pedal I've come across or heard.

The configuration is now Bazz Fuss (MPSA13 + red LED)/100k level/LPF/Bobtavia/47k output level. Needed a 100uf bypass cap on the 9v feed, a 4n7 cap from pin 3 to ground on the 386, and a 850pf cap across the Bazz Fuss input to prevent oscillation - seems to be a problem with running the two off the same supply.

I've socketed the Bazz Fuss diode and transistor for future experiments. Also has a boost switch and an octave on/off switch. Totally wonderful - cleans up ok and has tremendous range of sounds. Will still compress at higher gain, but the levels now need to be distinctly non-musical for this to be a real problem.

Can't recommend this configuration highly enough.....