PAiA overtone -- HELP!

A friend constructed and gave me a PAiA Theremax. What a sweet gift! Then I took it to a local electronic music repair shop and paid boo-coup bucks to have it properly wired (i.e. grounded, volume control fixed, etc.). Played great for awhile.

But soon enough, the tone in the middle registers (either side of A 440) developed a nasty diminished-fifth overtone below the note. And when I took it back to the store, they said it was a new problem and wouldn't cover it under their 90-day warranty. They also wouldn't give me any idea of how much it might cost to fix, and once again wanted a sizeable deposit to look at it.

Well nuts with that.... I found someone on craigslist who repairs amps and has an oscilloscope. Took it to him, and he didn't make any promises, but he also didn't charge to keep it and attempt to fix it. Which he was unable to do (although he did install a jack for the AC adaptor so it doesn't have to be permanently attached to the Theremax).

To make a long story short: I went to the PAiA website, and I cannot make ANY sense of their troubleshooting guide. I'm a pianist, not an electrician! Does anyone here have familiarity with the PAiA Theremax to tell me what might be wrong? Does anyone here live near Portland, Oregon, who could give me a hand with this?

If it's something I can re-tune if/when it produces this overtone, I'd like to be able to fix it myself. Meanwhile, I can't stand listening to this miserable discordant dual tone. [big sigh] Please help me get back to playing it without *again* paying more for its repair than it originally cost!

--

The exact same thing happens with one of the presets on the Etherwave Pro. Apparently, it's due to electrical interference. I don't really understand it, but if this is the case, there may be a chance this is due to whoever did the re-wiring for you.

Hrrrrm.... it did play just fine when I got it back from the repair shop. The overtone occurred several weeks later. When I took it back to the shop, we plugged it into a different amp, in case the problem was with the amp -- but the overtone was still there.

Most frustrating!

There are a few things you can check:

To check for electrical interference, turn on your Theremax and set the pitch control so that it plays a tone (and the offending extra tone). Now, one by one turn off any other electrical equipment in your room. In particular, light dimmers and computer equipment. If you turn off a piece of equipment and the tone clears up, then you have found the source of the interference.

The next question: does the pitch of the extra note change as you move your hand to and from the volume antenna? If so, then the volume oscillators are tuned close to the frequency (or a harmonic) of the pitch oscillators. The solution is to adjust coils L3 and L4.

If you are ever near the Kansas City area I would be pleased to look it over for you. Barring that, if you have a friend that has some familiarity with DIY electronics such a person would be able to make sense of the troubleshooting information.

Hope you can fix your theremin soon and enjoy playing it.

[i]-- Kevin[/i]

Thanks for the suggestions, Kevin. Here are my results:

I plugged the T-max into a living room outlet with nothing operating (besides the amp) -- no lights on, no other electronic equipment. The overtone is still there, no difference. It was also present in the repair shop, and at the place where the craigslist fellow had a go at it.

Just now I listened to it more carefully. Actually the *interval* of the overtone to the pitch *increases* as I *lower* the tone on the pitch antenna. It becomes clearly audible as a major third below E~660 Hz, and increases to become a minor seventh below middle C~260 Hz. There is also a fainter second overtone, about a sixth lower. By the time I drop the primary pitch into the tenor/baritone registers, an unpleasant buzz gets added to the overall tone -- this is while there should still be good tonality (I'm not talking sub-bass).

"The next question: does the pitch of the extra note change as you move your hand to and from the volume antenna?"

Interesting.... actually the primary pitch changes at the same time as the overtone, the combined sound going up anywhere from a half-tone to a whole tone as I lower the volume. I anchored my pitch hand to make sure it wasnt moving. Sure enough, the last inch of distance on the volume antenna makes the sharpest rise in pitch. But the overtone doesn't change its interval relationship to the fixed primary tone.

"If so, then the volume oscillators are tuned close to the frequency (or a harmonic) of the pitch oscillators. The solution is to adjust coils L3 and L4."

I see the four little silver square boxes (L1-L4) which appear to have red straight-screw heads set inside of them. Does "adjust coils" mean to turn those screws? Can you tell me a little more about the function of those coils, and what it means to be turning screws 1 through 4? I sure as hell don't want to break anything!

"If you are ever near the Kansas City area I would be pleased to look it over for you."

KS or MO? :o) I'll keep that in mind....

"Barring that, if you have a friend that has some familiarity with DIY electronics such a person would be able to make sense of the troubleshooting information."

Well, the friend who put it together has a limited understanding (which is why I had to get it fixed in the first place), and I'm not sure how to go about courting potential DIY electronics friends in this city.... but anything's possible....

Again, thanks for the suggestions. And if you can tell me more about L1 to L4, I'll thank you some more!

From your description you may be getting interference from the volume oscillators.

Check out this thread:

http://www.thereminworld.com/forum.asp?cmd=p&T=1132&F=3

A jumper is simply a wire with an alligator clip at each end (radio shack sells them). The jumper is simply to hold the volume circuit "open".

Did your friend give you the manual that comes with the Theremax kit? If, yes, then I can find mine and we can do a little troubleshooting.

The good news about the Theremax is that its internal voltages are low -- around 9 volts -- so there is no danger for you to work on it.

I am on the Missouri side north of the Missouri river.

Well, check out the link above (you will have to scroll down a few messages) and see if the explanation there makes any sense to you.

[i]-- Kevin[/i]

"From your description you may be getting interference from the volume oscillators."
--Okayyyyy......

"A jumper is simply a wire with an alligator clip at each end (radio shack sells them). The jumper is simply to hold the volume circuit "open"."
--Yes, and I can't find the one that came with the Theremax. Went to Radio Shack and they didn't have one. So I called around, and found an electronics store that does. I'll go there this afternoon.


"Did your friend give you the manual that comes with the Theremax kit?"
--Yes. And I also printed some troubleshooting stuff off the PAiA website.


"Well, check out the link above (you will have to scroll down a few messages) and see if the explanation there makes any sense to you."
-- [sigh] I went to the library and picked up Electronics for Dummies. But they don't have Electronics for Cretins. I'm smart in the liberal arts arena, but hard science is beyond me.
I need a seven-year-old's version of this stuff.... I'm not sure if I can grasp the principles, but I *can* follow basic instructions. And I'm completely willing to be patient and plug away at possible solutions, even though my hair is already standing on end *without* any static in the room. (It's the "What in the Hell Do I Think I'm Doing?!?" Syndrome. :o)
What's next?

Eureka! Found the jumper in the kitchen junk drawer. OK, let's get down to business!

Absolute-Pitch,
KKissinger is the man for the job on this Theremin site. He should work for PAiA. When matters of a mistuned There-Max arise he is the guy to which to speak.
teslatheremin

Haha! Well, a little knowledge is dangerous, so that make me a hazard!

Sorry I didn't respond sooner... when I get home I will dig up my schematics.

In the meantime, have you figured out how to use the jumper? (it forces the volume circuit to the "loud" setting.)

I'll write more later with schematic in hand and my Theremax in front of me.