Foolish question time - is this a Dumble amp? If so, then the bleed-through would be out of phase, no?
This is very much a Dumble ckt (from scratch build, twin iron etc)
I'd want to get rid of that as a matter of principle.
Even when not playing with the volume on 0.
Well there seems to not be much of a consensus on IF it is to be ignored or not. and with my abilities, I'm pretty much at square one when it comes to how to go about getting rid of it. (would the bleed through be out of phase? that wouldn't be a good thing)
Last edited by Pete on Sun May 07, 2006 11:30 pm, edited 1 time in total.
jaysg wrote:
This is usually caused by wiring. Remember there's no volume knob until there's been some gain. The first stage boosts the signal and despite knob settings, a later stage is picking it up. Parallel stretches of wire can behave like transmitter/receiver RF pairs. Study the wires from B+ to the plate resistors and from the plate resistors to the tubes.
Dai H. wrote:
yeah think about that. Which stages are the volume(s) affecting or not affecting in the chain. It should be possible to find the source. Or otherwise, maybe a pot that isn't shorting the wiper enough to ground when in the zero position.
I've checked the resistance between the wiper and the grounded lug (ccw) on both the first pot and the replacement. The first one measured high (30 ohms) the replacement less than 2. That is why I was surprised to find that the condition did not change.
thanks, Pete T
My Dumble clone does this too. Like an earlier post said disconnecting or grounding the 2nd stage with a cap makes the noise go away. I thought the white noise with the volume all the way down was a problem since the problem disappears with the OD stage engaged. I spent days trying to make it better until I check my other amps and they all do it. Guess it's a trait of this design of amp you've just got to live with. it doesn't really affect the performance of the amp in the real world, it's just a nusance.
Pete wrote:OK, I just tried this (grid shorted directly to ground) I got a small decrease in sound (and noise) level, but for the most part, no change.
So, is there room for improvement? I suspect something is "not right"
Pete I suspect something is "not right" could be dressing or grounding, there should be no sound after you ground CL2 grid, some noise is ok.
Pete I suspect something is "not right" could be dressing or grounding, there should be no sound after you ground CL2 grid, some noise is ok.
Teo
Thanks Teo,
I checked one more time and there is definitely sound with the CL2 grid grounded (master on full)
The guitar sound level is like playing a very small amp (about like playing a Fender Champ on 1 or so) much more than I get with any of my old Fenders.
no sound with the master at "0"
no sound with CL1 grid grounded
I have no idea on how to approach troubleshooting this, any thoughts on things to try/check are much appreciated.
I would very much like to see if I can get rid of this and if it improves the overall sound of the amp.
Pete T
I realize this is a very old thread, however I am experiencing this symptom with an old 52 Fender Super. I'd like to solve the problem, and my first instinct was to replace the volume pot, until a few minutes ago: the amp has 4 inputs, 2 instrument, 2 microphone, as distinct 1st stage 6SL7 stages - the same problem is occurring in both channels, if a bit less in the mic channel. Could it be that both pots need to be replace, or is there something else going on??
Head scratcher....
and with my abilities, I'm pretty much at square one when it comes to how to go about getting rid of it. (would the bleed through be out of phase? that wouldn't be a good thing)