[Pedal] Guild Rotoverb Design

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Guild Rotoverb Design

Postby enorbet2 » Mon Jun 04, 2018 11:56 pm

I'm new here because I stumbled onto this forum from Googling "Guild Rotoverb" schematic and a photo was actually displayed. Much to my disappointment no threads seem to exist on this subject. Way back in the 60s I worked on several of these units as the most common failure was some component in the final output stage "letting the smoke out" resulting in a vastly reduced output that still had the effect and only a bit of distortion. I "fixed" a few by adding a moderate gain single transistor preamp circuit in the switch housing that switched in when the effect switch was engaged. It was a dirty fix at best and probably caused by the very thing that made it impossible to properly service, the epoxy dumped into the "bathtub" chassis which I imagine was to protect it's "secrets".

So I bought one and later was given a few once it got around I was attempting to find a way to workaround the epoxy. I dremel'd around one but it took forever to make even slight headway once I confirmed no solvent would dissolve the goop. By this time Guild had stopped selling them and when I asked a Guild Rep who made them he said, "CEI in Bologhna, Italy". I got a phone number but nobody there spoke English and I don't speak Italian so all could say was "Scuza" ;)

A friend of mine had an interesting inspiration saying "maybe if you cozied up to a hospital lab tech or something you could XRay it". I tried that too to no avail, never getting an opportunity to put it under the "scope". So I began to brainstorm at how an Italian company might have come up with the design (everything is derivative, right?) and made what is entirely a guess but possibly a good one. I found that Hammond licensed an electronic version of a Leslie-type effect from an Italian organ company that used a rotary switch powered by an electric motor that ran through successively tuned tone filter circuits creating a fairly powerful phase shifting effect AND because of the actual physical motor and mass of the rotor, displayed a real start up and slow down speed !!! just like the pedal does/did. Plus, the pedal is quite heavy, easily containing an electric motor and of course was AC powered so easily handling a motor. There was even a detectable vibration when the unit is plugged in that is reminiscent of a motor and the epoxy gets quite warm in that area. So for all these years, since I've never been able to confirm it, I'm now wondering if the wide-ranging contacts of the Interwebz may locate someone who has XRayed or otherwise knows if my sleuthing was accurate or not.

It may be of extremely limited interest these days but I just can't let it go. I'd really like to know how CEI did it. Anyone with comments or contacts is most welcome to post here and let me know what ya got :) Thanks
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