New Etherwave kit malunction.. help!

[bblumenthal]

Dear folks, I’m a long-time kit builder; Dynaco and Hafler stuff, and have designed and built audio loudspeaker systems for years. The Etherwave kit is a walk in the park; I built it w/ my two sons to help get them started on electronic work. Here’s the problem.. the volume antenna works backwards. No sound is produced unless you’re pretty much touching the antenna, and full volume is not acheived w/out gripping it pretty strongly. When we first powered it up and got no sound at all, I thought the power supply was defective, but taking measurements at various points on the board showed that power was indeed present. It wasn’t until I brushed against the volume antenna by mistake and fiddled w/ L5 and L6 that we finally got “first light.” L5 and L6 were WAY off upon delivery, but we’ve got them pretty close now, although can only get about 2 - 2 1/2 usable octaves. I can NOT solve the reverse sensing volume antenna problem. Additionally, capacitors 31 and 32 are absent from the circuit board, although there are spots on the board to mount them. The IC used on the board does not have a socket as mentioned in the hot-rodding manual, and it is not the same IC,either.

The audio out jack did not have the same pin configuration as the jack shown in the assembly manual. Judging from the schematic, I wired the yellow wire from the multi pin connector to the tip lug. Correct?

Any help folks can give would be most appreciated. My sons are still excited about the project (and both excellent string players; I’m a violinist/violist professionally), but I hate to see their enthusiasm wane due to these technical issues.

Thanks in advance for any assistance.

Barry

[kamal]

Barry-

I’m new to theremins – my wife’s Etherwave kit is about 95% completed at this point – but it does seem to be working properly, and my wife is making real music with it.

First off, yes, there does seem to be an error in the assembly manual regarding the wiring of the audio-out connector. I agree with you that the yellow wire from the multipin connector should go to audio-out tip lug and the green wire from the pot should go to the audio-out sleeve lug (the green wire is circuit ground).

Second, regarding your problem with the volume antenna: I experienced similar problems at first, when I was trying to test the theremin before actually mounting it in its case. I had clamped the antennas to a wooden table and attached the antennas to the circuit board lugs with alligator clip wires. The alligator clip wires were about 1 foot long – considerably longer than the connecting wires should be according to the assembly instructions. In that configuration, the theremin did start producing sounds, but both antennas worked “badly”… The volume antenna acted just as you describe – no audio volume whatsoever until you actually touch the antenna; The pitch antenna definitely controlled the pitch, but the “zero beat” position was about half an inch from the antenna – all crazy.

I realized that the problem was that the antennas were being severely de-tuned by the extra length of the alligator clip jumper wires, so I made shorter jumper wires to test with. They’re still longer than they’re supposed to be, but cutting them down to about 4-inches worked wonders… Now the volume and pitch work as expected (still clamped to the table).

So lesson learned is that the length of the wires connecting the antennas to the circuit board is fairly critical – especially for the volume antenna (?). If the volume antenna wire is too long, it can make the voume appear to behave “backwards”.

As an experiment, cut a piece of wire slightly longer than the length of the actual volume antenna and attach it to the volume antenna’s lug as a temporary test antenna. Bend the wire into vaguely the shape of the volume antenna. Check the theremin. Now clip off an inch of the wire and/or adjust the position of the wire antenna and test again. I found this experiment quite illuminating – it gave me a feel for how the volume behaves when the volume antenna isn’t “quite right”. I did the same for the pitch antenna and determined that it is more forgiving than the volume.

Also, be sure to keep any other wires or cables (power, audio, whatever) away from the volume antenna, as they’ll de-tune it too.

For the record, the reason why I was compelled to perform these tests instead of just assembling the theremin as the instructions dictate was not due to any experienced problems (for all I know it would have worked fine if I’d just assembled it straight off)… But my wife is left-handed and I’m converting the Etherwave accordingly, which requires me to install the circuit board upside down in order to keep the antenna leads short.

Hope some of that helps!

-Kamal

[bblumenthal]

Thanks for the response. I’ve communicated w/ the folks at Moog who’ve been very helpful. Turns out there was a defective coil, L8, on my board; totally open, with infinite resistance. They’ve promised to send a new one to me; I’ve bypassed it in the mean time, and everything’s working correctly now, although the response in the volume antenna is probably not exactly what was intended yet. We’ll get it. The folks at Moog were really great in helping me troubleshoot the circuit. Thanks!

Barry