Some pics of a build... the Silicon Chip Thermin.
https://www.siliconchip.com.au/Issue/2018/January/Make+your+own+Theremin+%E2%80%93+then+make+music%21
This kit has been stuck in a draw for over 10 years ??
This design is from 2009.
A friend recently asked for some help in building a thermin using Bob Moog's design.
In the 1960s Moog had 4 designs :
The Vangard, (Vacuum tubes)
The Professional (Transistors)
The Melodia (Kit & built vesions)
The Troubador
The Melodia could be purchased as a kit.
I though before I embark on that project I'll build this and see what I can learn.
This is the inside of a Melodia.
This
old instrument seems to be made up of transistors, oscillators, coils
and wires which create electromagnetic fields around the instrument's
two antennae.
Thermin's
rely on the human body's capacitance. When you move your body in and
out of that electromagnetic field, you change the frequency of the
oscillating circuit.
You are actually making a variable capacitor with your hand being one plate, and the antenna, the other.
What a thermin contains are basically two primary circuits:
1) a pitch circuit.
2) volume circuit.
These two circuits are connected to individual antennas.
Vol antenna is on the left. pitch on the right.
The antennas need to be separated by at least 20 inches & be about 3.5 feet from the ground.
According to the build guide these antenna coils are machine wound by a special method called
"progressive universal" and cannot be duplicated by hand wiring.
It looks like though the original circuit is quite simple, its full of hard to find parts.
The most difficult to obtain being the inductors.
More about inductors are here:
Inductors are also called coils or chokes.
They are passive two terminal components.
Like capacitors, they store energy.
However, in this case, energy is stored as a magnetic field.
They are usually made up of a insulated (copper) wire, wound round a core (magnetic ... iron or ferrite).
The schematics indicate (L4) 10mH volume and (L1) 75mH pitch antenna inductors.
These are wound coils that I think were only available only from Moog.
I can't find any manufacturer’s part number.
They might be custom-made for Moog ????
According to the vintage DIY manual:
"satisfactory substitues for the antenna coils can be made by connecting
three 25mhy ferrite chokes in series
and
for the volume: connect two 10mhy chokes in series.
It seems like the rest of the inductors (the 4 within the metal case) can be hand wound.
The pitch circuit used two oscillators:
A variable oscillator and a fixed oscillator.
The variable oscillator produces a range of frequencies and is connected to the vertical antenna.
The fixed oscillator generates waves at a static frequency.
Signals from the fixed and variable oscillators were mixed together
and then amplified and output as sound.
The second circuit (the volume circuit) controls the volume of the pitch circuit.
To do this it uses an oscillator connected to an antenna.
Disrupting the electromagnetic field around this antenna changes the volume of the tones from
the pitch circuit.
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Some Links:
how to make your own inductors
This webpage is really useful:
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I'll start the silicon chip thermin build in another post
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