Making the Moog Etherwave theremin roadworthy

07Feb19

Please note that I am not responsible for any damage you do to your theremin as a result of my blog. Hack at your own risk ! If you don’t know how to work on electronics or wood, ask a friend.

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This blog concerns the Moog Etherwave theremin. It deserves credit for being the pioneering modern “professional” theremin. It unfortunately suffers from a few errors in its design.

My girlfriend has played this theremin in her punk band for about 10 years. Experience has proven that the Moog was not designed for use “on the road”. So I had to fix four problems, as explained below, that I did not expect to encounter in a €450 device made for professional use. Boo !!!

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(1) A key problem is that the output is line level, not “guitar level”. So, if you connect your theremin to a guitar amp or play it through guitar effects pedals, the level is much too high, and you will get clipping and distortion. Booooo !!! I suspect many Moog theremin players are not aware of this.

In order to connect properly to an amp or an effects pedal, we need to reduce the output level. I give a big tip of the hat to the Big Briar service manual, which explains precisely what to do. Resistor R33, 4.7K, needs to be replaced with a 47K resistor. I went a step farther and installed a 47K pot in series with R33, allowing adjustment of the level between line level and guitar level so I could experiment. Finally, I wound up leaving the pot at its maximum resistance anyway.

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(2) On this €450 device, Moog saved $1 by not having a power indicator. This is very important for a serious musician on stage to rapidly verify that the power is working. How many times have users set up on stage, found that there is no sound output, and wondered whether it was the power supply or something on the output side ? Booooo !!!!!!

I added a 12 volt LED across the power supply. (Black and green wires to front-panel pots.) I chose a 3mm LED and drilled a hole in the front panel for it. Wonderful ! Now you get an immediate indication on stage when the unit is powered on. Of course you can pay €70 more and get the Moog Etherwave Plus which does indeed have a power indicator.

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(3) The power supply connector is a three-pin DIN, although only two pins are used. Perhaps this was done intentionaly to discourage people from plugging in other power supplies, but a DIN plug, with its small pins, is more fragile than the standard low-voltage connectors. The mating power connector on the theremin is hidden inside the case behind the wood, making it difficult to orient and connect on a dark stage (or even a well-lit one). Boo !!!

Much worse, the power connector on the theremin is simply soldered to the circuit board; there’s nothing to hold it in place except its three wires. So after a few years of constant use, the wires break and the theremin does not work. Booooooo !!!

I replaced the connector with a surface-mounted one that is screwed into and supported by the wooden case, so it is not fragile. And, being on the exterior, you can see the positions of the pins, making it easier to plug into.

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(4) The last area of concern is the wooden case. My girlfriend dropped her theremin off a 6-foot stage, bringing to light certain design deficiencies.

Moog’s design is clever because, with four screws, you can take the upper box off and operate/test the unit when it’s open (see first photo at top of page). But the short sides of the lower box (with the antennas) are not supported by the case, even when it’s closed, so they are exposed to stress when the antennas move, or when it’s dropped. So the side panels crack. Boooooo !

What’s more, the short sides of the lower box are made of wood (rather than plywood) which cracks along the grain. If Moog had chosen plywood, this would be less of a problem.

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Strangely, the front and back of the upper box are attached to the top with special screws and threaded plugs, rather than being grooved and glued. Presumably this was an attempt to make it stronger. The correct way to make the upper box strong is to complete the upper box with 2 more panels with glued dado joints on the inside (see photo below with post-it notes taking the place of these panels). There is room for these to pass on the two sides of the PC board where the metal plates are. These two panels do not have to extend all the way to the base, they could pass above the 2 metal plates. If Moog engineers had paid attention in Wood Shop 101, they would know this. The upper box would be very strong. And they could save money on those funky threaded plugs. Boo !!!

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However, those threaded plugs would find a much better use holding the top part of the short sides of the lower box, which support the antennas. I used wood screws instead. Now the side panels are stable when the unit is closed. I glued the cracked side panels, which seem to be holding up fine. If I had needed to replace these panels I would have done it with plywood as explained above.

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Also, one of the wooden “feet” fell off. They are glued and nailed with tiny nails. A grooved joint (or screws) would have made them much more solid.

There you go ! Now we have a more usable, sturdy theremin that’s ready to take abuse on the road !

 

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