DanielMacKay is slightly wrong... all the benefits and improvements which he describes come from the ESPE01 upgrade (which is NOT from Moog), not from the Plus upgrade!
An Etherwave Plus is and remains an Etherwave Standard in the first place, the main PCB is 100% identical, and thus the oscillators, the wave shaping, and the volume circuit.
The difference consists in an additional circuit board, designed and added after Bob Moog’s death, which is located vertically behind the front panel and which comprises additional and peripheral circuitry as it was published by Bob Moog himself in the famous Etherwave Hot Rod Manual. With that, you get
- 3 additional outputs at the bottom side which give you a Pitch CV (1V/Octave, centered at C2/130Hz=0V) a Volume CV, and a Gate signal and which allow you to control analog synthesizers with your Theremin as a gesture controller.
- A headphone output with an additional volume control potentiometer which can be transformed into an acoustic pitch preview with the help of a jumper. Due to the very simple and cheap amplifier circuit behind, it sounds just this and ugly. As a headphone output, it is practically useless since one can never play on headphones alone. As long as no suitable amplifier is connected to the theremin, it lacks grounding which makes the sound more ugly (distortion, noise, and ghost tones) and which makes the pitch field highly unstable.
- A red LED which indicates the state of the nearby power switch. The latter is marked with 0 and 1, so that the LED is pretty superfluous.
- Since the main PCB remained unchanged, so did the internal voltage regulators on it and nothing was done to take the additional load of the Plus circuitry into account. The user pays that with an increased time until the instrument stabilizes thermally after switching it on (20min for the Plus vs. 5min for the Standard) and with higher sensitivity to the ambient temperature.
Verdict:
People who want a stable Theremin to play it in the conventional way are better served with the Etherwave Standard and an added ESPE01 module from Ethermagic, since the latter improves the playability by adding additional pitch range, by making the pitch field more linear, and by making the timbre sound more natural.
If one intends to use the Theremin as a gesture controller for analog synthesizers, buy an Etherwave Plus as a second instrument. The only true advantage of its CV and Gate outputs isn’t worth the hassle of thermal problems, and the LED and the useless headphone output aren’t worth the higher price.
