My brother passed away recently and I received his Theremax 1909b Theremin. Looking inside, the unit has a daughterboard attached. it has flying wires going from C1+ to C38+ and then goes to the Audio Out jack. I assume that it is some sort of amplifier/pre amp. Anybody ever see this mod before. Some of the wires have become loose, so Im looking for help to put it back together. I will probably remove it and build it like the instruction manual said and then add this mod daughter board afterwards. Anybody ever seen anything like this in a Theremax?/Users/ken/Desktop/theremin/ed theremin - 1.jpeg/Users/ken/Desktop/theremin/ed theremin - 2.jpeg/Users/ken/Desktop/theremin/ed theremin - 1 (1).jpeg
Identify this Theremax Mod
Posted: 3/8/2024 4:50:33 PM
Yeah, looks like a home cooked amp of some sort. I'm going to remove it, hook it up as god intended and then see what I have. Ed was a much better cabinet maker than a solderer. The cabinet is beautiful, prettiest one I've ever seen. I will try to draw a schematic of the "amp" and post it. Meanwhile, If anybody has an idea...
Theremax has different flavors of circuit boards from the 9505, the 9505a,b,c,d,k. the instruction manuals all look the same but components move around. I don't know if a 9505b, which I have is any different than the 9505c. I will trust the install manual.
Posted: 3/10/2024 3:25:17 AM
Pretty scary layout! I have no idea what the IC is - sorry! - though the large caps make me wonder if it's an audio amplifier?
Looking at this plate: https://photos.app.goo.gl/DYM1UKRSCGrZwGR16
The Theremax plate is white and it has a large volume knob for headphones and an added headphone jack. The daughter card is a preamp for headphones and has the plate also shows an additional light and jack for a foot switch! Since it is a 9505b circuit board, I found this posting showing a Theremax with a daughterboard and a gate/mute jack for a foot switch. The plate is black but the plate on my brother's Theremax is screen printed on white and Professional looking. Here's the link: http://www.thewhistleshop.com/misc/auctions/theremax.htm
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