Thierry Frenkel Etherwave Pro Wizard!

Posted: 4/3/2012 4:24:01 PM

From: Los Angeles, CA

Joined: 5/18/2007

I would urge anyone wanting their Etherwave Pro Theremin to work expertly, to send it to Thierry Frenkel for calibration. Thierry recently worked on mine and it now plays better and sounds better than it ever has. He is truly the "Mad Genius of the Theremin". Thierry can turn anyone's Etherwave Pro into a work of art.

Off the shelf, the E-Pro seems to have been more or less thrown together without regard to the precision thereminist. This is most clearly demonstrated by the complaints of a 'snappy response' to the volume antenna.

What follows is an account of my recent experiences:

A few weeks ago, I accidentally knocked over my Etherwave Pro. In the fall, the wooden knobs on the front panel had gotten pushed in. This damaged the inside of the cabinet and made my E-Pro unplayable. I was devistated!

I immediately contacted Moog Music to inquire about repair. I was transferred to the repair department and asked about repairing the damage and recalibrating the instrument. The person I spoke to was rather condescending and said, "That's a pretty old product, most of the people who know about it are gone now. I think we might have someone here who can figure out how to do the work."

Well, this comment and attitude destroyed any confidence I had in Moog Music's repair capabilities.

I do know that Carolina Eyck has had Thierry Frenkel work on her E-Pro, and I had installed Thierry's EVPM1345 on my volume board (which is amazing). So, I had a pretty good idea of the quality of his work.

Not to boor you with the details, but, Thierry not only expertly repaired my E-Pro, but he went on to perform calibration magic, transforming my E-Pro into as fine of and instrument as is available today.

Here's a partial list of what he did:

Repaired the crushed front panel

replaced the broken potentiometers in the front panel.

Repaired cracks in the Volume Board.

Fixed problems in the timbre selection and register switches (the timbres are very consistent now)

Calibrated the pitch oscilator, which was about 400Hz to low

Fixed a bad contact in the pitch arm

Added a line out potentiometer

Complete calibration from A to Z, then manual optimization


I simply can't imagine Moog's repair department taking the time or having the expertise to even come close to the wonderful work done by Thierry. I'll be forever grateful. I'd be happy to answer any questions about this post...

Roger Ballenger

(818) 895-6120



Posted: 4/5/2012 12:59:40 PM

From: Colmar, France

Joined: 12/31/2007

Roger, thank you so much for your kind words! 

I understand that it's getting more and more difficult to obtain a qualified service for theremins, even with some manufacturers. Thus I hope that this testimonial will encourage people to seek for help in France.

Posted: 4/5/2012 8:41:06 PM

From: Colmar, France

Joined: 12/31/2007

Excerpt from my repair diary:

The thin wood layer of the front panel behind the pitch and volume tuning knobs was broken and needed to be glued. Add 24h for the glue to dry. Then I wanted to improve its stability by impregnating it with transparent acrylic resin. Add 24h for it to dry.
In the meantime I fixed the obvious damage of the electronics : Replaced the 2 broken potentiometers and fixed several cracks in the control and the volume board. Finally assembled the instrument for the first time. Found that it already worked basically, but the pitch arm showed a very strange behavior. Fixed a contact problem inside and replaced one of the four coils which had a slight crack in the core.
As the instrument fell down, there was a risk of further hidden cracks in the multilayer circuit boards which perhaps would only show up much later. Thus I allowed a few days for warming it up and cooling it down several times, always knocking on the circuit boards in order to detect hidden problems. Found and fixed two of those.
Proceeded to the calibration. Both pitch oscillators ran about 400Hz too low which explains why the linearity was not optimal in the middle of the pitch field. On the EPro, linearity is a complex function of resonance interaction between the pitch oscillator and the tank circuits in the pitch arm. Finally got it tuned for optimal linearity. Let it cool down (calibration should be done on the warm instrument), re-switched it on and heard only a constant extremely high pitch until I approached my hand close to the pitch antenna. Then it started working correctly. 
What happened? When cold, the oscillators ran still somewhat too low which caused the variable oscillator in conjunction with the pitch arm to settle on a false secondary resonant frequency. Thus I turned the pitch oscillators step by step up by finally another 100Hz, always retuning the pitch arm at the same time until I was sure that the oscillators would start on the correct frequency at all temperatures and that linearity and playing range were optimal when the instrument was warm. I didn't want to go too high with the frequency since that would reduce the pitch range and worsen the linearity. Allowed 2 days of repeated warming up and cooling down always checking that.
Calibrating the volume oscillator and the load circuit of the volume loop went without problems.
Then I found that the timbres were not consistent. Some of the presets sounded completely different in the highest register setting. Slight changes are tolerable since in the highest register setting the octave dividers are not in the signal path. Since not only the presets or the waveform/brightness/filter pots play into wave shaping, but also the pitch and volume CVs, I had to re-check the latter although a first rough check with a multimeter at the CV output jacks had shown that the pitch and volume cv circuits were basically operating.
Found that the pitch cv circuit had a slight offset of only -30mV at middle C (always in the highest register setting) which grew up to +600mV four octaves higher. Calibrated the circuit with the 4 potentiometers whose settings influence one another until I obtained exactly 1V/octave +/-2mV and I had entire voltage values (0V, 1V, 2V +/-2mV) for the different Cs. That solved the timbre issue.
Allowed still two evenings just playing the instrument and still tweaking somewhat several settings until the instrument felt not only technically but also musically correct.
And there we are. It's back home at its lucky owner now and as every instrument which has spent some time in my atelier, it leaves a gap...
Posted: 4/6/2012 5:01:55 PM

From: Northern NJ, USA

Joined: 2/17/2012

Wow Thierry, I'm not sure what the world did to deserve such a thorough and knowledgeable Theremin expert, but I'm glad you're here!

Analog Theremins are so complex...

Posted: 4/8/2012 9:24:07 PM

From: Colmar, France

Joined: 12/31/2007

* blush *

Posted: 7/12/2012 9:29:55 PM

From: Hampshire UK

Joined: 6/14/2012


Well it is fairly obvious from all the good things one reads that:- a) you're an ace technician or maybe that should really read ace magician with all things theremin and have a special feel for them which can't be obtained from just setting them up to some specifications provided by a manual (if such a thing exists), b) Moog aren't too hot with their customer service (is just since Bob 'left' us or what?) which isn't too ecouraging and c) your add-on board for the Etherwave Standard is a fantastic addition.

A question or two please. What got you so involved with them Thierry? A love of music? A love of experimental electronics? The need to find out as you damaged one to start with? LOL. I am about to purchase a second hand Etherwave if all pans out as I hope (then I'll solder in your board via Wilco) so what's to check that is obvious? Linearity? What else please? Many thanks in advance,  Chris

PS Find it fascinating to read your techie stuff.......... if only because I have to often go look up some of the items to figure out what you mean!

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