Problem with Theremax.

Okay, so here's the deal:
After a couple of problems, I got my theremax back up and running. But now, the volume antenna very faintly acts like the pitch antenna. It still mainly does volume, but very faintly has a pitch to it that I didn't notice it having before. When its loud enough, normal playing partially masks the tone, but its still annoying. Even when the volume is completely down on the Control Panel, it still emits a high frequency pitch that changes if you move you hand closer or farther away.
Thanks everyone! (these sure are finicky instruments!)
Ethan.

Ethan, I may be able to help you resolving this problem. But I'm actually at my day job and can't act as I would like. Please wait until this evening (will occur in about 10hours here in Europe) and I'll do my best to help you.

Now, I'm ready to attack this problem.

This ghost tone appears when one of both volume oscillators interferes with one of both pitch oscillators. Paia made a change in the circuit in order to prevent this. Please make sure that C6 and C10 have 100pF while C14 and C18 have only 68pF.

If that is the case, we should re-tune your Theremax in order to solve the problem. Do you have the tuning instructions? They start by turning all 4 slugs counterclockwise. Then they say you should turn L1 and L4 one turn clockwise. I recommend to turn L4 only a half turn and L1 one plus a half turn clockwise. Then continue the adjustment procedure as written.

My "recommendation" for L1 and L4 increases the frequency difference between the volume and the pitch oscillator, so that the risk of interference will be decreased. Take care when slowly and carefully adjusting L2. There are several points where you may hear a tone. The correct point is where the tone is loudest and where there is no influence from the volume loop.

Don't hesitate to post once more if that doesn't work as expected.

Good luck!

Thierry
Theremingénieur franco-allemand

I'm actually having a similar problem... When I touch the lop antenna I get a very low volume variation. Sort of like a European police siren (low tone, high tone).

I've turned the volume way up to try and hear any tone when I tune coil L# but there's nothing...

>Please make sure that C6 and C10 have 100pF
>while C14 and C18 have only 68pF.

I hate to sound like an idiot but how exactly do I do that :-} I have a Radio Shack multimeter. I know how to use it to test continuity but that's about it :-}

I had this exact problem with my Etherwave Standard. I had a feeling it may have something to do with oscillators interacting in some strange way. Mine would only happen every now and again after it was on for a while (more then an hour or so). I discovered it could be cleared up by adjusting the volume tuning knob a hair. I don't think its happened since I retuned it internally.


On a side but similar note:

Thierry, I seem to recall you had posted a run down on tuning the E-Standard to achieve maximum linearity. I went searching for it but could not locate it. You wouldn't have a quick link to that would you?

Okay, so that didn't seem to work. When I am in a 0 pitch zone (for pitch obviously ;) and move my hand to and from the volume antenna, i can hear the faint pitch that the volume loop is producing.

I, as well, don't know how to check the "pf." of the capacitors. What do I need in order to do that?

and actually, I just though: I have my volume setting for "controller mode" i think (when the volume gets LOUDER as you move your hand toward the volume loop). Would that make any difference?

Thank you Thierry for your time! It is much appreciated!
Godspeed.
Ethan.

Such small capacitance differences can not be measured with standard equipment. But in our case it's enough to look if there are these different values written on the capacitors. Older circuit releases had four identical values or two and two values which are nearer to one another.

The so-called controller mode should not change anything on the problem.

Please check also if the ghost tone is audible in all positions of the "timbre" pot. If it is not audible in the leftmost setting but becomes stronger when turning clockwise, there is most probably another problem.

Hmm, well I don't know what I can tell you now!

On C6 and C10 is the NPO (the black-tipped) capacitors labeled "101". On C14 and C18 are NPO's labeled "68." Everything should be fine on the circuit board.

And also, I replaced the stock antennae with 1/4 in. copper tubing. Would that make a difference? That's the only thing i've changed on it.

And finally, I noticed that when I turn the Velocity to half way (its usually set to min) the sound is still there, but the Gate/Trig light comes on when my hand nears the volume antenna (when in the 0 pitch area.)

Thanks again!

Ouch!

Please allow me to think deeper about this problem, it is not standard...

Capacitors and antennas seem to be fine.

The behaviors of the velocity knob and the gate light are correct. The volume oscillator/mixer/cv-converter/slope detector work totally independent from the pitch section.

Please check the timbre knob. What happens with the ghost tone when it is set fully clockwise? And fully counterclockwise?