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Screaming firefly

5/12/2004 6:57 PM
sir Franc of SOSCASTOA
Screaming firefly
I have build an amp based on the firefly design by Doug H. (Rev.3)  
It turned out pretty well. It has an extra switchable gainstage, which I call the boost 'channel'. When the boost is turned off, I get a nice crunch up to maximum volume.  
However when I switch on the boost and turn to full volume, it starts to scream and yell, sometimes a high whistle-like noise.  
It reacts to the tone pot on my guitars, sometimes when I turn it up nicely it doesn't happen until I hit a note. Then it starts screaming and doesn't stop until I turn down the volume...  
I built this this PTP (for pics, see my website:  
When I move the wires around you can hear that it has an effect to the noise, but I cannot get it to stop (yet).  
It's a bit frustrating at times, because when I have almost eliminated the noise with boost on, the sound of the normal 'channel' is choked at full volume. So I move the wires around until sound is okay again, switch on the boost channel and....screams again.  
Now I see a lot of amps with wires all over the place, crossing, lined up in parallel, how come my amp is so sensitive to wire placement?  
Anyone has any suggestions on what particular wires to check? Should I use shielded wire in some places?  

Mark Lavelle [QUOTE]Anyone has any suggestions o... -- 5/19/2004 5:32 PM