Super Reverb Variable tonestack lift

[ModMe]

Hi everyone,

was wondering if anyone has a way to make lifting the tonestack variable as I think I'm getting to much signal into the following triode with it fully bypassed.

With it fully bypassed I get loads of gain with loads of his witch I guess is normal considering it is so much louder but when I go to loud the background noise seems to be cancelled out?

I don't have a scope to see the actual signal please help.

Thanks.

[Normster]

Just put a pot in your ground lift circuit. Mine is panel mounted, but you can mount a trimmer inside the amp. The drawing is showing 1MA but I'm going to swap it out for a 250KL for better usable range. (The pot is labeled "Drive")

[Roe]

yes a 250k raw controll works well. I prefer an audio pot

[ModMe]

Thanks Guys

[neon333]

Isn't the 65 "Bump Circuit" a variable RAW control? Why do you suppose they do it on a 6 position knob with a resistor network?

[Super_Reverb]

The circuit I implemented on a 6550 SE amp was to create a boost function with a FMV tone stack that does the following:

boost off: --> bottom terminal of mid pot grounded (NC contacts shorting RC to ground)

boost on: --> bottom terminal of mid pot connected to parallel combination of 5K/0.2uF

Resistor controls the amount of mid-band boost and parallel capacitor value relative to resistor controls frequency at which treble if further boosted. My implemention boosts starting at about 285 Hz and includes a high cut at about 5 kHz because the boost adds so much drive to output stage.

rob

[tubesinside]

Another issue to look out for the the possibility of overdriving the input to the reverb driver tube when the boost is enabled. This causes some very nasty spiking on the reverb driver transformer. This is audible as spiky distortion on the output....even with the reverb recovery pot turned down. The solution is to pad the input to the reverb driver when the boost is engaged. I have had to implement this on Deluxe, Super reverb and Dumble ODS with reverb.
C

[ModMe]

Thanks what would be the best way to do that?

[ModMe]

Also could I test if that is what it is by diconnecting the reverb cables.

[tubesinside]

yep...the simplest way to check if the reverb is being overdriven is to pull the 12AT7 driver tube. If that nasty distortion disappears then I'll give you some hints on how to pad down the reverb drive.
If you are using a relay to lift the ground on the tonestack you may have a contact available or you can use an optocoupler.
C

[Roe]

Another issue to look out for the the possibility of overdriving the input to the reverb driver tube when the boost is enabled. This causes some very nasty spiking on the reverb driver transformer. This is audible as spiky distortion on the output....even with the reverb recovery pot turned down. The solution is to pad the input to the reverb driver when the boost is engaged. I have had to implement this on Deluxe, Super reverb and Dumble ODS with reverb.
C

I just use a 68k grid resistor on the reverb driver tube