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VOX solid state amps, UL700 and later, used a very odd reverb circuit to avoid paying royalties.
The reverb spring was connected to two crystal phono cartridges instead of the usual transformer or driver transistors. Problem is that the setup is almost impossible to find replacements for. I was thinking that the Amp-Verb might be a perfect replacement for the whole circuit. Just have to figure out how to drop the 16vdc to 9vdc. Any thoughts on whether it might work.
I am going to refer this to our resident reverb guy who was a designer for the Intersound RV100 back in the 80’s among many products Wilkie1. I am sure he will be with you in the morning.
Thanks, Barry. Although I was working at Intersound, I was not the designer of that reverb.
The Add-Verb might work as a replacement in that Vox depending on the send and receive levels and impedance. Without the schematic and testing, I can’t say for sure. However, the Add-Verb would work as an effects pedal at the front as an input to the amp.or in the pedal chain.
The sound will be different since the AddVerb is an analog circuit and not a spring reverb. You might also try the Ancestral Apparition.
I’m building a UL730 using R. G. Keen’s redesign of the circuit board for the preamp. He did some updates on the VOX circuit but it isn’t a full replacement for the one using the phono cartridges. (See http://www.voxshowroom.com/uk/amp/730_hood2.html) for the original setup.
With the new board and clearly laid out Reveb section I thought that I could just set it up as a “daughter board”, use trimmers for the Tone and Volume controls. I’ve Inserted the updated schematic from R.G.’s manual. It looks as though it should connect pretty well right into the overall preamp circuit – the hardest part may be getting the voltages right. The “Reverb In” come right off the “Signal Out” line of the 2nd pre-amp channel and then hooks back into the Signal Out summing to go to the Power Amp circuit. In a modern amp it would be sitting right at the Preamp out and Power Amp In junction.
Originally I had hoped just to use one of the new “bricks” with the circuit but could not figure how to do it correctly with the very old circuit. The consensus seems to be that a replacement of the whole circuit is the best way to do it.
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