Rocket Fuzz oscilations

[El Heisenberg]

Just built this

http://www.diystompboxes.com/pedals/rocket.JPG

it squeels and wails though. At unity volume with my amp turned up its almost unuseable. Where could i add a little ceramic cap to keep these out? From output to ground? Or base of Q1 to ground? Or collecter or Q2 to base of Q3? How big would the cap need to be? I would have experimented, but the circuit sounded good to me right away an i went and boxed it all up in an hour. I left the drive and tone control out. I guess i shouldve kept the tone control in it, but i didnt like how weak it was.

[Joe]

Non-inverting circuits are tough, especially one like this with a high input impedance. The problem is caused by the input interacting with the output. (This usually is the worst at the footswitch, where the contacts are close together.) So the rule is to keep the input and output completely separate as much as possible, to reduce the coupling:

-wire the board in a straightforward manner so that the input and output are on opposite ends
-don't twist the input/output wires together, route them separately and twist them together with ground leads
-make sure the box is grounded and that the bottom of the board is close to it
-an input resistor might help, or perhaps a larger resistor before the 2nd transistor
-sometimes 5-10pF caps help across the collector-base junctions, but that's not really the problem
-a single inverting stage can be added to the output, which will eliminate the oscillation completely (will try to post one in a sec here).

The thing to rule out first is the footswitch and wiring issues, and go from there.

[El Heisenberg]

Input and output are on opposite sides of the board. Board is small tho, like less than two inches wide. At the footswitch i didnt use the two outside rows, i used the first two. Ill try and fix that. Ill try to shield them too. I hope you or someone posts a schem for an inverting stage, cus i dunno how to do that.

[Joe]

Here's a quick & dirty one, need to adjust the 1.8K to get 4.5V at the output. Should get roughly unity gain as shown, adjust the input resistor for more or less gain, since it doesn't affect the biasing.

[El Heisenberg]

Thanks, ill add this right away. The thing oscilates when there is nothing even plugged in.

[petemoore]

  Could be that the gain of the circuit is high, causing self oscillations.
  There are a number of ways to reduce gain, if only to determine whether a lower amount prevents jumping into self-oscillation.

[Brymus]

Just curious I have had some problems with my Rocket too.
Does yours hiss?
And does it sound like the clips others have posted?
Mine sounds close but like I am missing something,I still like it very heavy metal fuzz tone,just alot of noise kinda ruins it.
I just wonder what yours sounds like minus the noise issue?
At the very end (very first page)of the members only section there is a Rocket thread Aron started it may help you as well.

[El Heisenberg]

Yea it sounds like all the sound clips. there is hiss. But it's normal type stuff Id expect from something like this.

[El Heisenberg]

I mean I love the sound, but the problems with it are prolly the reasons why EVERYONE isn't building the rocket. Since it's so simple. I just put the thing together for a quick 1 hour build. I'm gunna try my third big muff now, and maybe get some GE trannies for a tonebender or a fuzz face. Im still trying to find my perfect fuzz. I'm sticking with the tychobrahe octavia right now.

[aron]

I built mine and I have built several from perfboard. I have no oscillations at all. I think the "left to right" method of perboard has advantages, one of them being very little oscillation.

Aron

[Gus]

Layout and wire length and power supply and shielding matter with higher gain Si FF type circuits

[El Heisenberg]

I perf up everything from left to right.

[El Heisenberg]

I should add that im playing a semi hollow body guitar. But with my big muff or tychobrahe, i can play at louder volumes, without too much feedback. With my rocket build I seem to get feedback plus this really high pitched squeel. I also usually run a rangemaster before any distortion. With the rangemaster off its not really bad at all. But with my BMP and tychobrahe octavia it doesnt matter that the rangemaster or a compressor is on. 

[Guitar_Ninja]

Could it be the gain of the transistors you're using? I'm breadboarding one right now and I get occasional squealing using 2N5088s with HFEs around 800 apiece. But only with the Drive pot dimed and the volume pot cranked up.

[El Heisenberg]

Dunno. I didnt put the drive pot in. Its just volume control. 2N5088s were around 450 hfe

[aron]

Maybe just too much gain. The booster just adds to the problem - it sounds like you are getting microphonic feedback. It's the treble boost along with extreme hi-gain.

[El Heisenberg]

Im just trying to squeeze too much sustain out of the hollow body I guess. Im givin my rocket to my friend. Its too good to scrap but i cant use it.

[jacobyjd]

Im just trying to squeeze too much sustain out of the hollow body I guess. Im givin my rocket to my friend. Its too good to scrap but i cant use it.

I doubt it has anything to do with your guitar being a hollowbody--fuzzes made with higher-gain transistors often have crazy oscillation problems. If you're getting what sounds like a howling noise, self-oscillation is most likely the culprit.