EM/EW Theremin Linearization Coils

Posted: 4/4/2018 2:50:32 AM

From: Tucson, AZ USA

Joined: 2/26/2011

Hello Aerorad,

Here is a picture of the EWS walwart. They are a rare design and hard to find.


The EtherWave Standard works by mixing two Radio Frequency signals. The RF needs a good or even better a direct earth ground or it will distort the RF wave shape, which in turn will distort the audio wave shape. How to get that natural beautiful sound expected of a classic theremin is an interesting trick, has nothing to do with any of the coils which are for linearity. Like anything getting the classic sound is simple once you have the answer. It cannot be found in computer modeling which handicaps many designers.


Edit: If you are a do-it-yourself type then go from a 3-prong power cord into your own separate power box to keep all the components (regulators, etc)that get warm away from the inside of a theremin enclosure, as the solid-state theremin is very sensitive to heat.

Theremin oscillator circuits are also sensitive to noise from the power supply so unless extra circuit filtering is added to compensate for this, stay away from switching type power supplies. I prefer to add extra filtering to an isolated oscillator section so I can use the very available modern switching approach which is cost effective.  If memory serves me, the EWS circuits after the regulators need 12 volts at a max of 30 ma per side.

Visit this webpage - may be an idea here?

Posted: 4/5/2018 1:38:24 AM

From: San Francisco, CA

Joined: 3/31/2018

Ah, thanks for linking that picture Touchless-- I knew the Moog PSU had to have the ground prong, but I had never seen it from that angle to confirm.

The solution you suggest in your edit is an ideal one, in my opinion. Perhaps I would make such a power supply if a qualified person were to lay out the specific steps, but I wouldn't otherwise trust myself to mess with 120vac directly. 

If someone did make such a PSU, could they use a 2-conductor barrel plug for the theremin-side connection, assuming the voltage regulators remain inside the theremin itself?

Posted: 4/5/2018 6:24:07 PM

From: Russia, Saint-Petersburg

Joined: 6/6/2016

If the design is completely homemade, you can do the power unit on your own. But it should be borne in mind that on the Etherwave Board and in its scheme there is already a bipolar voltage stabilizer on the LM78/79 elements. In front of them are the capacitors smoothing the ripple of the rectified voltage. It is to them that you can connect the input bipolar DC power, as well as the common ground contact. I often use this connection when connecting via a 3 pin connector to four 9 volt rechargeable batteries connected in series: 9+9=+18 volts/ ground/ 9+9= -18 volts. This connection provides a clean audio signal and continuous operation for 5-6 hours. The grounding of the theremin goes through the shielded cable to the amplifier.

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