Tonnes of Tone Effect Loop Troubles

[jakejoseph]

I have built a 6V6 5E3 power amp connected to a 6SL7 front end. Works great. Had intended to use the Tonnes of Tone Best tubeFX loop, and I have made the circuit.

Despite having decoupled the power supply fo each individual pre-amp tube the thing motor boats, the switchable gain affects the circut when nothing is plugged in and it sounds like doo-doo.

ANyone have any experience with this circuit? It is the one of page 7-16. I am using his values exactly, and have now quad checked the circuit as well as using shielded wire for all hook-ups...

Any other schematics out there for a tube effects loop I can try?

[Matt T.]

Probably not much help here but it seems that there's 3 main ways for there to be some sort of coupling: 1) through the power supply 2) through coupling in the lead dress 3) through the grounds. You said you used shieled cable and separate power supply nodes for each tube so maybe look into some sort of coupling through the grounds. I had one amp (a Bogner XTC lead channel clone) that ran fine until I put a cap from signal-to-ground to chop off some high-end fizzies. Soon as I did that the amp squealed like a stuck pig. I had another amp (Horizontal Input 2204) that sounded different when you 'relocated' some of the grounds from one end of the chassis to the other.

How big are the power supply dropping resistors? If they are low value (say ~1K) then there may not be enough decoupling.

One loop that I think is pretty good is the loop in the Mesa Dual Rectifier. My Send (in the amp mentioned above) is very similar to that one and my Return is the Dumbleator Return stage. One of these days I'll try the Dual Rectifier Return stage for comparison but what I have in there now works really well at the medium volumes I play at.

[jakejoseph]

Thanks for your help. I relocated and shielded one of the PI leads and the oscillations went away. One of the problems is I haven't given the time to understand how that circuit works, so, it may have been the result of moronity on my part.

I just spent two days troubleshooting a nasty hum that was the result of a bad cathode bypass cap in the second gain stage. I am going to shield some more wires, check all the joints, and buton it up - works well.

J