AB763 Normal Channel as Reverb

[atavacron]

There’s a lot of prior art on this, so I’m integrating a few established modifications with some thoughts of my own.

I’m working up a mod for a stock early-70s Silverface Pro Reverb that will get recapped and converted to AA165 (same as AB763 generally in other models) and tested like that first. Then, the drawing below is what I’m thinking for the preamp section. Tone stack curves below that for the fka Normal channel, now dedicated to ‘verb.

The big draw is a highly flexible reverb return, tailored for most common recording scenarios. The mix stage is lower noise than stock, the new Dwell control is as low noise as I could make it, and there’s a wet-only line input.

Am I overlooking anything? Anybody done similar? This is Fender Blackface model agnostic…can easily be adapted for everything from Deluxe to Twin.




That treble cap in the fka Normal tone stack might want to be 390p btw. The bass cap could shift a little too; I stopped subbing in values as soon as I had a perfect HPF shape with both controls at 12 o’clock. There are other tone stack designs, but I’m trying to avoid messing much with the circuit board layout.

 

[musipol]

I recall, back in the day, people doing something similar to this, although simplified, by running the tank output back through the normal channel. I tried it but didn't find any magic compared to the std reverb. Now that I think about it, it may have had something to do with limited mixing adjustability since all you could do was turn up the normal ch vol to get more reverb.
I'm guessing, by adding that 50K pot, you're not so crazy about the blackface scooped mids sound, or you just want a much bigger range of adjustment?

 

[atavacron]

I recall, back in the day, people doing something similar to this, although simplified, by running the tank output back through the normal channel. I tried it but didn't find any magic compared to the std reverb. Now that I think about it, it may have had something to do with limited mixing adjustability since all you could do was turn up the normal ch vol to get more reverb.

Right. The easy way of doing this doesn’t provide much advantage. I’m looking to develop that concept.

I'm guessing, by adding that 50K pot, you're not so crazy about the blackface scooped mids sound, or you just want a much bigger range of adjustment?

It’s 6K8 at center, same as no pot at all. Up above 10K, you’re out of Fender range and it becomes essentially a gain control. Treble and Bass won’t be as effective. That’s ok.

 

[atavacron]

There’s more than one way to skin this cat.

 

[Di_Sousa]

Besides posting here you should post also in the best forum on Tube Guitar amps and circuits:

https://el34world.com/Forum/index.php
A lot of very helpful and knowledgeable people there on these Fender circuits,
you will get great help and ideas over there

 

[atavacron]

Besides posting here you should post also in the best forum on Tube Guitar amps and circuits:

https://el34world.com/Forum/index.php
A lot of very helpful and knowledgeable people there on these Fender circuits,
you will get great help and ideas over there

thanks, yeah i got a little more response over there and it led to this. has some minor errors that i’ll fix in the next version once i can get some insight on whether the 330K NFB solution works once I repurpose the bottom of the P.I. for second channel input.