Etherwave kit pitch un problemo

Hello everyone, new to the theremin game and very excited to get started. I built a Moog Etherwave Theremin kit, followed all the instructions and now it's finished.

When plugged in and turned on, the theremin has a tone. The volume antenna does work, and the knobs seem to work, but the most important problem is the pitch antenna.

The pitch doesn't change no matter what I do with my right hand, touching the pitch antenna or not. I even walked away from the thing and nothing changes. I checked the connections and everything seems right.

Not sure if this is an common problem, but I can definitely take a picture or two if that helps. I really appreciate any assistance, it is really exciting at least that the thing turned on and is making a tone.

Can't wait to play! Thank you!

-Chris

Hi Chris,

please open the cover and take a picture with good resolution so that I will be able to check the wiring and send it by email to theremin(at)tfrenkel(dot)com.

Please answer the following questions:

a) does the tone change if you turn the pitch knob?
b) does the tone change if you take the cover off?

Finally tell us where you live, so perhaps we'll find someone in your neighborhood who could help you if necessary.

OK, here is a link to an album of pictures, let me know if these are good. You can click the magnifying glass (top right) to zoom.
http://picasaweb.google.com/lh/photo/
SdwhAaanLiPkqlHkEMl6pw?feat=directlink (http://picasaweb.google.com/lh/photo/SdwhAaanLiPkqlHkEMl6pw?feat=directlink)

A) The tone does change if I turn the pitch knob, but stays that tone when I stop turning it.
B) The cover on or off has minimal effect on the theremin's tone.

Also, I am from Concord, MA, USA and while we're on the topic if anybody knows a good music/theremin store in Massachusetts please share! Thanks again.

I can recommend you a good theremin repair shop in Colmar, France... *whistle*

I'll have a look on the picture, paint some testing points in and will then let you make further tests. But not immediately, because it's 01:30 AM here in Europe and I need at least 4 hours of sleeping at my age... ;-)

Difficult to tell from the photos - but check the antenna connection (CN3 and L1).. looks like possibly no solder.. I dont know the innards of the EW other than through on-line schematics etc, so this observation may be completely wrong.

If you are able to tune the instrument, then the reference oscillator is likely to be running as it should, and the variable (pitch) oscillator is in the right frequency range, the mixer is working, the volume oscillator and descriminator are working, the VCA is working... These 'facts' apply if you are getting an audio tone out, and the volume of this tone can be controlled by the volume antenna, and the pitch of the tone can be changed by adjusting the tuning knob.

The problem therefore is (I think) likely to be that, for whatever reason, the variable pitch oscillator is not changing its frequency as capacitance 'seen' by the antenna changes -

First check the circuit from the antenna to the board - any break will give the fault you describe.

Since this is the first time I have made a theremin before I wanted to make sure everything worked before soldering the antenna to the CN3 circuit and putting the circuit board in place. I figured that the contact should be enough to test and then after everything works I would solder that wire.

But hey I think you were right on the money Fred with your insight on L1 and the antenna circuit being the problem.

I posted new pictures to the gallery showing that component close up, as well as comparisons to other components. The piece is unglued, and the wiring must have already been broken and I didn't look closely enough. The component even slides off with a light push! Big oops.

http://picasaweb.google.com/lh/photo/
8Mx47tXLlaT2iWL6iEuVOQ?feat=directlink (http://picasaweb.google.com/lh/photo/8Mx47tXLlaT2iWL6iEuVOQ?feat=directlink)

Do you think that component or the rest of the board is salvagable? Maybe Thierry has some ideas too. The Theremin is still under warranty, but I don't know how long it would take to send in and fix. If it will take long I should probably call for the the RMA # tomorrow and try to send it out over the weekend.

Fred has better eyes than me and he is right. Not only is this an obvious problem, but it would exactly explain the false behavior.

Call Moog. Explain them the problem and ask if you shall send in the circuit board or if they prefer to send you a new L1 coil. In the latter case you should find an experienced radio/tv technician or ham radio amateur who will be able to exchange it for you, since that is a difficult task and an unexperienced solderer may easily overheat the new coil.

As the EW is under warranty, your safest bet is probably to send it back to Moog..

However, if you are [b]reasonably skilled[/b] with a soldering iron, you can [b]PROBABLY[/b] fix this easily yourself..

I would contact Moog and describe the situation - giving link to your most recent photo, and ask them to send you a replacement L1.. I would then solder antenna + L1 into place, and repair L1 by soldering a piece of wire to bridge the break.. If L1 has more damage (a possibility) then this will not fix the problem, but you should have a replacement on its way.

It all depends on how long Moog will take to do the repair, and how (im)patient you are! Safest bet is to return the unit.

One other thing - Although working, the connection to the volume antenna also looks dodgy..

You guys were right, I called Amos at Moog and they said they could ship me the L1 part right away. I asked the local Moog authorized repairman to help me since it's under warranty because... well I'm not reasonably skilled at soldering by any means and also lacking in patience. Hopefully it will be ready in the next week or so, I will keep you posted!

At this point, the moral to any kit constructors is to check the circuit board first before doing anything else!