Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Pegamin on December 15, 2020, 03:06:27 pm
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I'm a theremin player looking to improve my sound.
I am trying to find the tube amplifier design that would suit best the theremin.
The amp would feed a unique 12" Jensen mounted on a pole, perhaps you've heard of the old "diamond" speakers used by RCA in the 1930s.
Having no good technical knowledge, I am having trouble to find the appropriate design for such a project, and I would greatly appreciate your help.
On this subject, the theremin specialists advice the following (in cursive):
"I'm sure that a tube amplifier will sound better with the Jensen chassis. There are lots of schematics on the Internet which use a pair of EL34 tubes in an AB push-pull configuration (or their American equivalents) and readily available input, output, and power supply transformers from Hammond. I would insist on the use of tube rectifiers in the power supply section, too. These increase the inner resistance of the power supply and they have a less sharp cut-off than semiconductor diode rectifiers, both factors will greatly contribute to a good and warm sound."
To me, this is short of Chinese...
Also, to describe the old kind of amplification for this rare instrument, the savants state that:
"Clara Rockmore's amp was integrated in her theremin. On the power supply chassis, there is a push-pull amplifier with two #59 pentodes in triode configuration each (g2 and g3 connected to the plate). The speaker output connector is connected to the secondary, most probably low impedance, winding of the output transformer which would have allowed the use of a purely passive speaker chassis with a permanent magnet."
Again, I really appreciate this great detail, even if I can't say I understand it. But if I had to aim for a tone, it would certainly be Clara Rockmore's. She's the holy grial of tone for us thereminists.
Given the above advice, what kind of amp would you recommend for a built?
There is a great void when it comes to amplifying the theremin, most players using PAs, or powered monitors, or keyboard combo amps. The fanciest ones are playing through Bogen DB10, or Twin Reverbs. All of these are hardly dedicated options. So there's a chance that your two cents here could benefit a great many theremin players, including professionals.
Thank y'all!
Peg
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The Theremin existed before transistors. There are tube schematics on the internet. If you have a SS Theremin, it must have a signal output, or someplace in the circuit from which a signal output can be tapped; then fed into a tube amp. A schematic would be necessary.
The output voltage & impedance from the Theremin must be appropriate for the input of a tube amp. If not, a buffer could be used.
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"Dedicated options"? It is a musical instrument. Use a musical instrument amplifier. Could be sold as guitar or organ or ?? Lightly flavored. Forgiving. Fender Deluxe (early model) would be a fair approximation of what they had then (in pre-guitar days) and a lot easier to source and maintain than a couple '59s.
The high-mount di-pole speaker IS part of the Theremin mystique, do that. The open-back Twin has a similar dispersion pattern, but is a bigger sound obstacle (b/c Therimim does not sing bass as well as a string) and does not fly well. Bipolar high in the room makes the sound soar.
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Theremin ....
Some years ago I've build a Solid State one (it was a kit) for my son and, at that time, I give a look for a tube version finding this pages with nice projects (see the 125 & 126 Theremin)
https://www.theremin.us (https://www.theremin.us)
Franco