Advice for a complete newbie

Posted: 12/28/2013 6:41:04 PM

Joined: 12/28/2013

I've recently been thinking about trying to build the EM Theremin. For a bit of background, I'm a second-year physics undergrad; I've most recently finished a class involving a good bit of electronics theory, so I'm comfortable with the basic functions of capacitors/inductors, op amps, transistors, etc., and know my way around a breadboard and an oscilloscope. However, I haven't ever undertaken a serious electronics project, and have pretty much zero practical knowledge of circuit design for something of this level of complexity.

My question is, in short: What skills are necessary for me to develop before I'll be ready to undertake a project like this? I'm sure I'll be in deep over my head if I just jump in right now, but I'm not really sure what I need to know in order to not be in over my head when I do start building. What should I learn, and what resources might any of you recommend for preparing myself?


Posted: 12/28/2013 7:06:14 PM

From: Colmar, France

Joined: 12/31/2007

As for every circuit which deals with RF, you should have some experience with the particularities of RF circuit design (estimating parasitic capacitances etc.). You also should have fully understood the schematic and the principle of operation of all its stages, so that you will not be building it like a blind man in the fog, but understanding what you will be doing.

An oscilloscope and a frequency counter are required tools for building and debugging theremin circuits of the EM's complexity. In case you never built a theremin before, it is highly recommanded to start with a simpler circuit like for example the Jaycar kit.

You'll also have to take into consideration that the EM circuit is now almost 18 years old and that several components are now not so easily available as they were in the time. That's why Moog Music inc modified the Etherwave Theremin's circuit (which was initially based on the EM schematic) several times over the years.

Last hint (which applies to every theremin circuit): Build it step by step and do not continue as long as the previous steps aren't fully functional. That means:

  • start with the internal power supply and make sure that you have stable +/- 12V while the load varies from 0 to 50mA without the integrated voltage regulators oscillating on very high frequencies.
  • build and connect the fixed pitch oscillator. Make sure that it can be adjusted at around 285kHz with the variable inductance L6. Then make sure that the pitch tuning potentiometer allows to vary this frequency by +/- 400Hz and that a frequency which is set once keeps constant +/- 150Hz over several hours.
  • build and connect the volume oscillator. Make sure that it can be adjusted at around 480kHz with the variable inductance L11. Then make sure that the volume tuning potentiometer allows to vary this frequency by +/- 500Hz and that a frequency which is set once keeps constant +/- 150Hz over several hours (all that without the coils L7 to L11 connected)
  • Connect the volume antenna and coils L7 to L11. Tune L11 for a resonance peak voltage of -4V at the cathode of D1. Make sure that this voltage goes slowly and proportionally back to 0V when your left hand approaches the volume antenna.
  • ... To be continued...

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