Hi, I have a PA amp that has a rotary bass control. Its effective, but its hard to decipher what's going on as there is a hum baffle around it. Before I de-solder the baffle and continue trying to do a proper schematic, I am wondering if anyone can share a schematic for a rotary type bass control that might be in a typical PA amp? The amp has 2 6L6's, 5V4, 6SN7 (PI), three 6AU6 premap tubes, one of which is converted to Triode mode.
So I am running it in wet/dry mode through an AB/Y box. I also have it through an Airbrake and getting some good OD tones. My goal is a complete
schematic (Have not found it - McGohan M20). I am also keen to implement an FX loop which would then use a D-lator. the amp actually sounds pretty good. I was going to strip it out and do a Dirty Shirley, but a blues guy came over and convinced me to leave it as is, just add an FX loop. I also added a NFB switch and variable pot which adds versatility.
I was watching a Peter Thorn vid where he added a .0047uf cap to his 100W lead amp on the vol. pot. It did work well for lower volume grind. I only had a .0022uf and tried that which has really worked well along with the Airbrake for lower volume playing. I will put that on switch that goes
680pf/none/.0022pf
As I have repurposed one of the preamp pentodes to triode mode, the signal into the volume control is behaving very oddly. As I crank volume from 1-4 its normal, then it fades quickly to nothing, as I continue from 6-10 it then behaves normally again picking up from low volume back up to full volume. So soft to loud - nothing - then soft to loud again?
Rotary Bass control
Moderators: pompeiisneaks, Colossal
Rotary Bass control
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Re: Rotary Bass control
Logical spot for passive FX loop? Does this red arrow at the Plate of the 6AU6 to the cap into the PI look like the right spot for my passive loop? So just after the cap coming off of the 6AU6 plate (set up terminal for that), send the signal with a shielded run to the loop, then back to the PI Grid with a shielded run (6SN7) from the other side of the loop (loop input jack). Is that the correct way to do this loop? Any help on this please.
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Re: Rotary Bass control
Occims razor, the simplest thing. Turns out this was a tapped volume pot so that affect for volume rising dropping and rising was due to that tap as a ground on this pot. I removed the tap ground and brought all the associated grounds to a neutral ground....now pot woks fine. Still working on this amp and it is turning into a marvelous OD style amp.
Cheers A
"As I have repurposed one of the preamp pentodes to triode mode, the signal into the volume control is behaving very oddly. As I crank volume from 1-4 its normal, then it fades quickly to nothing, as I continue from 6-10 it then behaves normally again picking up from low volume back up to full volume. So soft to loud - nothing - then soft to loud again?"
Cheers A
"As I have repurposed one of the preamp pentodes to triode mode, the signal into the volume control is behaving very oddly. As I crank volume from 1-4 its normal, then it fades quickly to nothing, as I continue from 6-10 it then behaves normally again picking up from low volume back up to full volume. So soft to loud - nothing - then soft to loud again?"