Octup revisited

[jmusser]

I took Tim Escobedo's "Octup" circuit to work with me, along with a fresh schematic, and went through it again with a highlighter at lunch. All the wiring was correct, so I checked all the component values, and they were correct. I fired it up today, and started fiddling with the guitar's volume and tone controls, and the 100k effect pot hooked up to 9 volts. My consensus is that it is two different things, but neither of them an up octave. At least for my build, this effect is a stable overdrive, , and an unstable noise maker, if you can adjust the various controls to their sweet spots. I can get touch sensitive fuzz superimposed over the clean signal, smooth muff style fuzz with the amp's bass turned down, different speeds of motor boat sounds, farting, raspberries, various squeals, and intensive Jinx style fizz. All this can be adjusted in different tones with the amp, and guitar. My favorite noise is what I call "dog lapping water out of a bowl". Sort of a blup, blup, blup sound. Now, all this could be because my jfets have some problem, or my bias resistor tolerances caught up with me, I don't know. The overdrive characteristic is the only function of this circuit that is constant. For all the others, if you breath or blink near the controls, it's gone. One other constant thing is your family screaming at you to "turn that thing off because it's giving them a migrain"! If anybody else has any experience with this circuit, let me know. Your's may have work as advertised, but mine is about as unstable as they come. Tim said in his note, that he had just prototyped this, so maybe this is the first hard build, I don't know.

[toneman]

try feeding OctoUp with a (steady)sine wave and watch the
ins/outs with a scope.  U can listen 2 it 2.
Vary the amplitude and watch what output looks/sounds like.
Probable trouble---biasing...
Don't forget to use a stable source of 9V.
A regulated PS is best.
Staytuned
tone

[jmusser]

I don't own a scope, and I'm not so sure how you put a pure sinewave through it either. I would guess you would have to have an oscillator of some kind. One thing I do know, is that I'm using 2 watt 10% 1 megs in there because that's all I had. I'm guessing that the tolerances are just so far off that it's not being biased properly. I believe they are close enough to get "something" out, but are to far off to get what the circuit was designed for. I'll get hold of some decent resistors and replace these old carbon comps.

[jmusser]

Well, I've had luck with this circuit, good and bad. I replaced the 10% 1 meg resistors with 5% parts, and that took care of all the weirdness I was getting from what I'm guessing, was misbiasing of the transistors. That being said, I'm really not getting much more out of it except amplification. the only way I can get an octave up out of it is to do a Townsend windmill on the strings. If I hit them real hard like that, I can get an octave up that immediately dies. Now, I'm wondering if this circuit needs a little something extra to drive it in front, because it appears that the pickups themselves aren't enough. Any ideas? One last question here. On the schematic, it shows the two J201s side by side. I am assuming that the drains and sources are tied together, and that the drains are what are tied to 9v through a 22k resistor. If I'm assuming wrong, that would surely be the problem!