Ampeg R12R Reverbarocket, need to dump treble from the reverb

[Hugo]

I have a vintage 1961 Ampeg Reverbarocket, the short-lived version with the 6V6 power tubes.

I love the amp, but the reverb is a bit too bright/metallic for my taste. Could anybody here give me some advice on what I could change in the reverb circuit to make the reverb darker and less "surfy"?

Schematic:

https://tubeamplifierparts.com/schem..._schematic.gif


Thanks!

[nevetslab]

I have a vintage 1961 Ampeg Reverbarocket, the short-lived version with the 6V6 power tubes.

I love the amp, but the reverb is a bit too bright/metallic for my taste. Could anybody here give me some advice on what I could change in the reverb circuit to make the reverb darker and less "surfy"?

Schematic:

https://tubeamplifierparts.com/schem..._schematic.gif


Thanks!

You could place a small cap across R21, which is the grid bias resistor for V3B @ Pin 4 to ground. 2.2nF would give a corner at 3.3kHz, 3.3nF would be at 2.2kHz. You could also increase the size of C21 or C24, both being HF rolloff caps following the plate circuits of V3A and V3B. You could also increase the size of C22, being the cathode bypass cap across R22, currently yielding a corner frequency of 2.4kHz, maybe set it to 100nF, which would be close to 500Hz.

[Hugo]

Thank you, nevetslab, for your detailed answer. I will give your suggestions a try and report back.

Your help is much appreciated!

[Gaz]

Cap across R21 like Fender did on the Silverface amps actually makes the reverb brighter. @Hemholtz explained to me in another thread that because the reverb recovery transducer is inductive, you get an LC low-pass with a resonant peak that actually boosts high mids. And it's quite helpful too if you are using a a darker 3 spring tank!

[Helmholtz]

Cap across R21 like Fender did on the Silverface amps actually makes the reverb brighter. @Hemholtz explained to me in another thread that because the reverb recovery transducer is inductive, you get an LC low-pass with a resonant peak that actually boosts high mids. And it's quite helpful too if you are using a a darker 3 spring tank!

That's right. Knowing the inductance of the recovery transducer would allow to calculate the peak frequency.

[HaenC]

Hi there,
I'd change C24 for a bigger capacitor or add one for more high frequency roll-off on the reverb return signal.
Another way which follows a different approach is to reduce the amount of signal going in to the reverb tank - reducing the dwell of the reverb to make it more room or hall-like and get rid of the surfy splashy reverb sound.
To do so I would place a resistor in series (after) with C17 to form a voltage devider with R18, which is 47k if im not wrong. I'd start with 22k-47k on the new resistor to see how things turn out. Higher value, less dwell.
I personally really like the hally reverb sounds, much more then those splashy fender-like reverbs.

Let me know how it sounds

Cheers