Repair Needed for Etherwave Pro Theremin

Hello All!

I own an Etherwave Pro theremin, serial number 0024.  A year ago it still played beautifully.  Then it gradually lost its upper octaves and the pitch grew erratic and unstable when playing, especially after warm-up.  I did the E-Pro calibration process very carefully, over and over.  I also tried adjusting the trim pots on each of the two antennas (a unique feature on the E-Pro).

As the problems worsened, I payed careful attention to the circuitry.  I noticed a lot of heat around the "register" knob.  The thick wooden facing on the front of the theremin was actually warm to the touch, and the circuitry inside was really hot - especially the two big black capacitors (I assume they are capacitors) on the circuit panel located just above the power supply.  Someone mentioned the rectifiers, but I am not sure where those are located.

I contacted Moog Music, and they agreed to look at my theremin.  I sent it there nearly three months ago.  There was no communication from them.  I phoned twice, and spoke with "Taylor" both times.  Today I talked with him again.  He told me that no one has even looked at the E-Pro yet.  He said that they must refer it to one of their engineers.  When I asked him how long this all could take, he replied,"I really can't say".  He also told me that they normally don't work on these older, "legacy" instruments anymore.  I told him that I would give them one more month, or they must send it back, unrepaired. But considering the way they are dragging their heels, I probably won't wait that long.

Some of you reading this thread also own Etherwave Pros.  What will you do when you need repair service?  I love my instrument, which is now a fairly rare collector theremin.  It has gorgeous sound and response - the best of any theremin that I've encountered - and I own quite a few different kinds.  NOT repairing is not an option! Either I try to fix it myself, or I find someone who can.

If someone who knows E-Pros would like to look at my theremin and try your hand at fixing it, please reply.  This could be an interesting job for someone!

Thanks for reading!

Jon

Update:

Thierry Frenkel has agreed to do the diagnostics/repairs.  I will have to ship clear to France (at considerable expense!), but I know that the work will be done right and that my theremin won't be sitting in some corner of Moog Music gathering dust.  

We sure need someone here in the USA who can repair our older solid-state theremins like the E-Pros.  I am fine with vacuum tube technology, building solid state from a kit, or doing minor mods on existing stuff.  But we sure do need a repair expert here in America!

Thank you, Thierry, for your willingness to fix my Pro.  I will update this thread later, after Thierry gets the repairs made.

Until then,

Jon

Unfortunately, the actual Moog Music Inc management is not really interested in theremins. Their synths and effect pedals seem to bring more profit, thus we have to accept that the theremin spirit in that company died with Robert Moog.

Most of the people involved in the Etherwave Pro's development, deployment, and service are not longer working there and they do not longer hold spare parts. Thus, someone in France has to do the job... ;) 

Glassman, yours is neither the first nor the last which makes that travel over the big pond. In case you know Thereminist Roger Ballenger from the San Francisco area, ask him about his repair experience at Moog's for his EPro and why he ended up shipping it to France four years ago, that means only 7 years after the last EPro was produced.

Thierry, I've heard that you are currently the main expert on Epros and other similar theremins, and that you have serviced the instruments of a number of performers.  I am grateful, and surely no one minds the expense and effort of getting their instruments into your very capable hands.

I worked 27 years in the piano/organ repair and maintenance business, as my own boss.  I got better and better known, until I was offered the highest level contracts in my field.  My competition died out or moved away, and I never got a good trainee candidate to replace me. When my car crash in 2009 left me with narcolepsy and short-term memory loss from brain injury, and a badly crippled right hand, I had to retire at age 46.  My huge clientele was devastated, but I had no choice but to quit.

Now that Robert Moog is gone, his instruments would be in trouble if you weren't there.  And even though the clientele is very small, your clients would be stuck without you.  I hope that you can be there for us for quite a while!

Thierry,  I want you to do an upgrade on my Epro, while you are fixing it.  I had one of your modules in it before all the trouble started, and it really was nice.  Give it the works, since it probably won't be in your hands again for a while.

Keep up the good work,

Jon

2009 seems to have been a horrible year. I had an accident in September of that year, too, but it was "only" a triple fracture of my right ankle and after surgery and insertion of a metal bar and lots of screws screws into my right leg and foot, followed by a heavy and extremely painful nosocomial infection which was discovered too late, only when they removed the plaster after 2 months. They didn't believe me that there was a problem when I told them before and I was only given stronger and stronger pain relievers... What is left after 7 years now, are still difficulties in walking stairs downwards and occasional pain, especially when the weather changes.

Thus, I can be happy to be operational now, but the question of finding someone to continue my theremin related work (I'm 52 years old just now) is open, too. While there is a huge demand for the theremin academies which I organize for aspiring players, I tried to offer training weekends for aspiring theremin repair techs, but without any feedback. 

Finally, I'm actually trying to further reduce my nicotine consumption (my 4 daughters insist on that!) which should help for continuing my work for at least a few years.

"I did the E-Pro calibration process very carefully, over and over.  I also tried adjusting the trim pots on each of the two antennas (a unique feature on the E-Pro)."

These are variable capacitors...

"As the problems worsened, I payed careful attention to the circuitry.  I noticed a lot of heat around the "register" knob.  The thick wooden facing on the front of the theremin was actually warm to the touch, and the circuitry inside was really hot - especially the two big black capacitors (I assume they are capacitors) on the circuit panel located just above the power supply.  Someone mentioned the rectifiers, but I am not sure where those are located." 

The heat comes from two big (5W) cement resistors located on the control board which carries the potentiometers and rotary switches behind the front panel. These resistors are there as a minimal load for the +15V and the +5V lines of the switched mode power supply block (which had been designed for medical devices - it's not a Moog design), since the theremin circuit itself doesn't draw enough current to meet the stability requirements of that SMPS. Under normal conditions, these get warm but never in a way that the wooden front panel would feel hot... 

I start having an idea what your instrument has. The +/- 15V from the SMPS go through further voltage regulators on the pitch board which generate +/- 12V. Something there must be drawing ways too much current, which makes the pitch unstable (and the volume RF circuit too, but it's more difficult to hear or to sense), and which makes the SMPS regulation derate, followed by overheating the load resistors...

"I contacted Moog Music, and they agreed to look at my theremin. I sent it there nearly three months ago.  There was no communication from them.  I phoned twice, and spoke with "Taylor" both times.  Today I talked with him again.  He told me that no one has even looked at the E-Pro yet.  He said that they must refer it to one of their engineers.  When I asked him how long this all could take, he replied,"I really can't say".  He also told me that they normally don't work on these older, "legacy" instruments anymore."

I wrote my thoughts about that already in a previous posting...

2nd Update:

I spoke with Taylor at Moog Music again today (11/01/16), expecting to have the EPro sent back unrepaired. To my surprise, an engineer had already been in to test it out.  This happens to be one of the men who was around when my instrument was actually built!  Anyway, he found the problem almost immediately.  The circuit board in the pitch antenna went bad (I'll write an update later, pin-pointing the exact problem after I get a written report from Moog). There was a significant current draw from some shorted components there.  They installed a new board, and have my EPro powered on for "burning in" the new circuit.  The problem appears to be gone, and now they are calibrating the EPro and preparing to ship it back.

I would never had guessed that the problem would be in the pitch arm.  I still can't believe it, but time will indeed tell.  I've always thought that the pitch arm on the EPro was excessively complex, and could have been simplified.  The theremin that I am building (my Aria Pro) has a very similar arm.  But I have simply run a well-insulated 18 gauge wire from my aerial straight in to a video connector inside the cabinet.  My antenna functions perfectly, without any added circuitry, and is neither over-sensitive or under-sensitive.

Anyway, the Epro is what it is, with its own idiosyncrasies.  I'll cross my fingers now and hope that Moog has found the actual problem and not just a side-issue.  

Thierry, I know that you are standing by, ready to help.  I think that it is still quite likely that you will see this instrument soon!

Jon

That explanation seems highly improbable or incomplete to me. Since all components in the pitch arm from the beginning to the end are on RF level without ground beneath, nothing can draw too much current. A failing component there, be it the small variable capacitor with a short or one of the inductors having a (partial) winding short would degrade the pitch range and linearity and might have an effect onto pitch stability. But that does NEVER explain the excessive heat behind the front panel...

Hello. I have a Moog theremin that no longer works but perhaps its parts would be useful to you. When I contacted the company for repair, this is what they said: " it is likely that one of the inductors or diodes will need to be replaced on the main circuit board of the Etherwave."

It will be too expensive for my budget to do the repair, and after reading your post I will not send it in! Thanks for that tip.

If this has any interest to you for its parts, let me know.