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Mornin' Folks,
Again I dive into the viscera of my venerable Vibrolux with a mission of madness in mind. The model is the "mysterious" AA864 (all copies of whose schematic must have been eaten by senior Fender personell to prevent CBS executives and technicians from gaining acess) which I've found to be identical to the AA946. The reverb return consists of the RCA phono "jack" (really this should be called "jenny" - a "jack" is a male mule) feeding the control grid of section 2 of the 7025 with a 220K grid return resistor in parallel with the reverb footswitch RCA "jenny" <grin> - the footswitch turns the reverb on/off by shorting the 220K resistor thus shorting the return signal to ground.
Now I really love the reverb of this amp for the style of stage madness I currently play but instead of being able to turn the reverb on/off I'd like to be able to set different levels for rhythm and lead (the current set up is still the Martin D-25K using a Fishman "Rare Earth" soundhole humbucker - more or less sounds like an electrified full hollow body archtop).
So, has anyone experimented with adding a resistor in series with the "switch" in the footswitch to provide a different level reverb level instead of simply shorting the 7025 input?
Off the top of my cranium simply adding another 220K resistor should cut the reverb input in half but I was also considering using a 0.5 meg linear taper pot to the footswitch to be able to "dial in" a set lower reverb level. Other considerations were to increase the value of the original 220K resistor to perhaps allow more variation (assuming that the original carbon comp resistor is still anywhere near 220K - the amp was made in 1967). Since my whacked out reverb experiments are now over ten years in the past - I cobbled up one of my Bogen M60A as a reverb test bed using the 9 pin input transformer socket as tube sockets. Then I experimented, using cap coupled reverbs, with driving tanks with the stages in series and parallel - fun and funky stuff but nothing so earth shattering that I bothered to permanently incorporate the results in any later build. Anyhoo, as my memory isn't that great and I can't find my experiment notes from the reverb work I wondered if anyone had thought about the effects of changing the recovery stage input impedance on the resulting reverb tone?
While I know that I could just easily experiment so far I've not been switching the reverb and don't have the original petal - but I do have a similar one that uses a 1/4" plug. So I've decided that rather than adapt or change the pedal plug I would change the V'lux's "jenny" to 1/4" as I truly dislike the little RCA jobbies.
Rob
Again I dive into the viscera of my venerable Vibrolux with a mission of madness in mind. The model is the "mysterious" AA864 (all copies of whose schematic must have been eaten by senior Fender personell to prevent CBS executives and technicians from gaining acess) which I've found to be identical to the AA946. The reverb return consists of the RCA phono "jack" (really this should be called "jenny" - a "jack" is a male mule) feeding the control grid of section 2 of the 7025 with a 220K grid return resistor in parallel with the reverb footswitch RCA "jenny" <grin> - the footswitch turns the reverb on/off by shorting the 220K resistor thus shorting the return signal to ground.
Now I really love the reverb of this amp for the style of stage madness I currently play but instead of being able to turn the reverb on/off I'd like to be able to set different levels for rhythm and lead (the current set up is still the Martin D-25K using a Fishman "Rare Earth" soundhole humbucker - more or less sounds like an electrified full hollow body archtop).
So, has anyone experimented with adding a resistor in series with the "switch" in the footswitch to provide a different level reverb level instead of simply shorting the 7025 input?
Off the top of my cranium simply adding another 220K resistor should cut the reverb input in half but I was also considering using a 0.5 meg linear taper pot to the footswitch to be able to "dial in" a set lower reverb level. Other considerations were to increase the value of the original 220K resistor to perhaps allow more variation (assuming that the original carbon comp resistor is still anywhere near 220K - the amp was made in 1967). Since my whacked out reverb experiments are now over ten years in the past - I cobbled up one of my Bogen M60A as a reverb test bed using the 9 pin input transformer socket as tube sockets. Then I experimented, using cap coupled reverbs, with driving tanks with the stages in series and parallel - fun and funky stuff but nothing so earth shattering that I bothered to permanently incorporate the results in any later build. Anyhoo, as my memory isn't that great and I can't find my experiment notes from the reverb work I wondered if anyone had thought about the effects of changing the recovery stage input impedance on the resulting reverb tone?
While I know that I could just easily experiment so far I've not been switching the reverb and don't have the original petal - but I do have a similar one that uses a 1/4" plug. So I've decided that rather than adapt or change the pedal plug I would change the V'lux's "jenny" to 1/4" as I truly dislike the little RCA jobbies.
Rob
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