Boosters in Series

[Khas Evets]

So I figured I'd slam the front end of my Vox booster with a cranked Brian May Booster, because you can't have too much gain. With both boosters at full volume, it produces a very shrill feedback sound (I think the term is oscillation?). If I back off the volume of either, it produces what I expected, a louder more saturated sound - pretty nice actually.

Anyway, I was wondering what is happening to cause this oscillation and what can I do to control it?

[petemoore]

What you did or similar.
 If it's a high freq oscillation, you can kill some highs trying caps to ground from SP in different areas.
 Could be the gain gets so over the top it just turns it into an oscillator.

[Alpha579]

could be layout of the pedal...keep all wires as short as possible, and dont let input or output wires get to close...

[petemoore]

Yupp, if they're spread out on a bench...they'll be different in a box...probably.
 Not that boxing/neatening will necessarily defeat osci. ...can't hurt.
 Maybe put a limit on voltage going into the second circuit...tune around a tweek asound...I find once they're in the box they're harder to mod, hard to know what it'll do when it's in the box...I think that's also called debugging...you have to work through this when experimenting with seriesing effects.
 Does that first booster have a volume control?

[Khas Evets]

They both have volume controls.

I put one pair of boosters in an enclosure today and have the others on the breadboard. They both do the same thing. I think it's just a case of too much gain.

[Khas Evets]

Follow up...

Putting a 50K resistor between stages tames the problem. I experimented with caps to ground, but it didn't help. I also tried various diode pairs to ground, but didn't care for the harshness added. Anyway, thanks for the help.

[bean]

I'm running the Fat Boostered at the top of my chain and a Mosfet Booster at the end. Works really well, except right at the point where I set the levels and gain for best breakup it starts to clip and let out a little distortion. But, that's at bedroom volume....haven't tried it with the amp cranked. Pretty good combination, though.

[petemoore]

Voume knob on the first stage/input gain control before the second stage do/are basically the same thing/.
 The reason I like a pregain control is so that I can have 'two adjustments' of how much that gets out of the first stage goes to the amp [bypassing the second stage] or...into the second stage [through the pregain]...I don't have to reset the 1rst stages volume control [the pregain is in the second stages ByPass loop] to get 'optimum' performance or dialed in sound for 1 then both stages.
 Of course if you're not putting a bypass for the second stage, the first stages volume control is' the second stages pregain.

[Khas Evets]

Good point. What I'm basically doing is setting a fixed volume reduction between stages, so I won't (through user error) have too much gain.

[Steben]

Actually guys, check my fat germs pedal (search in forum). The basic of it IS two boosters in series.