AETHERPHON, global theremin family

Quoting David VanHorn <microbrix@...>:

>> The tone oscillators are around 190 KHz, the volume circuit is running
>> in the neighborhood of 400 KHz. I haven't checked recently. I almost
>> threw this thing in the lake Saturday. The oscillators were literally
>> driving me crazy. They would stop working if you touched the antennas
>> or even looked at it crooked.
>
> Ok, you may see second-harmonic energy from the tone osc getting into
> the volume osc..  That could cause some interesting effects.  On the
> schematics I've seen, the tone osc is normally the higher one.
> Would it be really hard to move the volume circuit to say 300kHz?
> I'm thinking to put them in places where they don't have any direct
> integer harmonic relationships.
>
> Decoupling the power supplies is really important too, and star-grounding.
> I'd use R-C decoupling in series with each oscillator's supply, and
> try hard not to share bias voltage supplies, or anything else.
> Basically, make the oscillators three independent (or four if that's
> the design) modules that have only B+, Ground, and output connections.
>

Yes, however Philip keep careful notes and make each change one at a time.

The timbre modulation is likely the result of interference / coupling  
tendency between the oscillators.  So, if you completely isolated the  
pitch and volume oscillators (if such is possible) you might also  
loose the timbre modulation. A subtle tweak to the frequency of the  
volume oscillator might be enough to do the trick.

There is very little energy above 7000hz in a theremin tone.  You  
might consider a low pass filter after after the amplifier.  I know  
that is kind of a "cheap and dirty" solution however it might get the  
job done.

Alas, I don't know much about tube circuits -- however my ears are  
telling me that you are on the right track.

I've messed around with my Paia Tube Preamp and I am convinced that  
the "magical timbre change" must be related to interference/coupling  
tendency between the oscillators.  The sound is different than a basic  
"overdriven tube" sound.

Hope you can find a way to get rid of the audible interference (I  
agree -- it is likely a harmonic of the (fixed?) pitch oscillator  
interacting with the volume (variable, perhaps?).  Perhaps you could  
low pass filter one of the oscillators (before it goes into the  
mixer/detector)??

Well, if you can preserve the nice timbral modulation while  
eliminating the audible interference well... what an instrument it  
will be!

-- Kevin