Claravox Centennial- known issues, bugs and quirks

Wow. You guys. Heroes of the week. Absolute legends. I'd have taken you two out for a thank-you pint if it hadn't been for the 3,000 miles of distance! I don't have any oscilloscope or other equipment. But your video convinced me we had the same issue (great video by the way, Moog should buy it off you, it'd save their techie team quite some time!). So I decided to give the red tuning tool a go. Long story short; I had to turn it one entire turn anti-clockwise. For a super-fine-precise-state-of-the-art device, this felt really dirty, and there was a small moment when I was half a turn in when I *might* have cursed you a little bit. But being the stubborn person I am, I kept on going and eventually heard a faint sound (about 3/4 of a turn in). At exactly one full turn, the level of sound was as I expected/wanted. I will add this - the comment of 'making a little flag with some tape' was genuis. Love it. So simple and clever, and provided me with the reassurance that I'd be able to undo it if needed. Thanks again to you two!

Thank you! LOL! I'm so glad it helped. Some people whined that I had the audacity to put up a video that I had the audacity to criticize Moog (oh, the HORRORS!), but hey, even now, Moog is still shipping defective instruments with new complaints on the Internet popping up continually. Anyway, I read elsewhere that a tech from Moog actually advised someone with a defective CVox (aren't most of them?) to do the procedures that Eric and I found (mostly Eric). No, Moog didn't point them at my video - or even mention it or the solution we found. LOL!

Anyway, I'm glad it helped!

"Long story short; I had to turn it one entire turn anti-clockwise. For a super-fine-precise-state-of-the-art device, this felt really dirty..." - Guillaume

Yeah, it felt really wrong to me too when I was doing it.  But the scope was telling me it was improving, so I kept going.  A whole turn is a big deal in an IF transformer, and I believe Jeff's (ContraDude's) Cvox took more than that, maybe two turns.  I think these things get tuned at the factory with varnish insulating the antennas, creating an unintentional series capacitance, and when the varnish wears off they go way out of tune.

Glad you got it working!  Live long and prosper.

dewster > "Long story short; I had to turn it one entire turn anti-clockwise. For a super-fine-precise-state-of-the-art device, this felt really dirty..." -  I think these things get tuned at the factory with varnish insulating the antennas, creating an unintentional series capacitance, and when the varnish wears off they go way out of tune.

As Eric has now quantified turns, I feel more comfortable stating the he turned it two and a half turns - really!

"As Eric has now quantified turns, I feel more comfortable stating the he turned it two and a half turns - really!"   - Contradude

As the turn count inexorably increased, I began to feel a little nauseous "lordy, this can't be right, nothing can be this far out of tune..."

Out of curiosity, you had the scope at hand and were tuning it using Science - do you think me using Magic (‘if it sounds fine, it must be fine’) can have a negative impact on the instrument? 

I’m now wondering if I should have given it a second turn for good measure…

"I’m now wondering if I should have given it a second turn for good measure…"  - Guillaume

My tuning method is:

1) Traditional mode.
2) Volume null knob at 12 o'clock.
3) Stick the plastic tool in the hole and adjust the variable inductor for maximum volume with hand away from the loop.

The scope was mainly there to tell me which direction I should start turning the tool.  With no sound you can't tell anything.

Not saying the above procedure is ideal, it's just what we did and seemed reasonable at the time. I don't own a Cvox so I can't experiment and perhaps improve on the procedure.

Rough & Ready

Over on FB, Lorenz Fish posted an image of his Cvox volume loop straight from the factory (hope he doesn't mind my posting it here):

Kinda amateur looking over-the-top sanding job, but I guess at this point they're leaving nothing to chance.  Soon they'll probably be sanding the whole thing down to a little scratchy brass nub, and you'll have to play it like a Melodia.

There are disturbing complaints of excessive pitch drift from folks who know their Theremins, and this is perhaps the most serious issue (so far) as it is likely a structural problem with the basic design, and not just a stupid SW bug that someone may (or may not!) fix.

Soon they'll probably be sanding the whole thing down to a little scratchy brass nub, and you'll have to play it like a Melodia.There are disturbing complaints of excessive pitch drift from folks who know their Theremins, and this is perhaps the most serious issue (so far) as it is likely a structural problem with the basic design, and not just a stupid SW bug that someone may (or may not!) fix.

Wow! Looks like they’re now using a sandblaster on it!  Perhaps a steamroller will be used for the next “fix!”

A brand new Claravox #832 arrived today as a replacement for my defective #40. It appears to be fully functional. The antenna was sanded down from the factory as depicted above. Subjectively the wood work seems to be of higher quality, with better fitment.
It still chirps when touching the volume antenna, but far less pronounced than the #40.
Kind of relieved even though the initial enthusiasm has faded somewhat.

Claravox Issues / Repairs (roll-call)

Interesting site:

http://aetherwellen-musik.de/Theremin-Instrumente/Instruments/Claravox-Centennial-CV-C-Theremin-Review-Improvement

The length and depth of the Cvox tale of woe is just flabbergasting.  Like every day some new serious issue pops up, it's relentless.

But the case is pretty, and I hear the delay is really nice (/s).