How does the theremin instrument work? What's under the hood?

Whatever, it's ingenious. They were all over the
old sci-fi movies, I wonder why they went out of fashion.

--
Rich

On Sunday, December 18, 2022 at 1:14:04 AM UTC, RichD wrote:
> How does the theremin instrument work? What's under the hood?
>
> Whatever, it's ingenious. They were all over the
> old sci-fi movies, I wonder why they went out of fashion.
>
>
> --
> Rich

how they work is based on basic RF circuitry,
as you might learn in RF circuits course.
heterodyning.
one of my favorite documentaries is
Theremin: An electronic odessey (1993)
https://www.imdb.com/title/tt0108323/?ref_=nv_sr_srsg_0
highly recommended
they're hard to play well...

On a sunny day (Sat, 17 Dec 2022 17:13:59 -0800 (PST)) it happened RichD
<r_delaney2001@yahoo.com> wrote in
<4cc4852c-e07f-490c-8280-77b4c605ea14n@googlegroups.com>:

>How does the theremin instrument work? What's under the hood?
>
>Whatever, it's ingenious. They were all over the
>old sci-fi movies, I wonder why they went out of fashion.

Any unscreened RF oscillator that you move your had towards
will chanche frequency due to capacitive effects.

On 18/12/2022 01:13, RichD wrote:
> How does the theremin instrument work? What's under the hood?

Two antennas each with their own RF oscillator and waving your hands
near them alters the pitch for one and the amplitude for the other.

I recall that the amplitude section had to be very carefully isolated
from the frequency or they would entrain. The amplitude was controlled
by rectifying in such a way that higher frequency gave bigger voltage
and modulation of the other oscillator was optically coupled (old days
filament lamp, modern LED) onto an LDR.

Requires 3 or 4 RF oscillators in the same box, f_ref nice and stable
and the variable ones with external antenna. The frequency you hear is
the beat frequency of the oscillator pair. I made one a few years back
for a lecture on sounds (Practical Electronics design from the 1980's).

> Whatever, it's ingenious. They were all over the
> old sci-fi movies, I wonder why they went out of fashion.

They have to be located a long way away from the trombones in an
orchestra. I know someone putting on an Xmas concert next week which
includes both Dr Who theme tune and the Beach Boys Good Vibrations.

I learnt to approximately play mine for the lecture.
Tuning drifts as the room warms up so you have to adapt quickly (or play
by ear which is what I did - a bit of vibrato hides a multitude of sins).

--
Regards,
Martin Brown

søndag den 18. december 2022 kl. 10.41.00 UTC+1 skrev Martin Brown:
> On 18/12/2022 01:13, RichD wrote:
> > How does the theremin instrument work? What's under the hood?
> Two antennas each with their own RF oscillator and waving your hands
> near them alters the pitch for one and the amplitude for the other.
>
> I recall that the amplitude section had to be very carefully isolated
> from the frequency or they would entrain. The amplitude was controlled
> by rectifying in such a way that higher frequency gave bigger voltage
> and modulation of the other oscillator was optically coupled (old days
> filament lamp, modern LED) onto an LDR.
>
> Requires 3 or 4 RF oscillators in the same box, f_ref nice and stable
> and the variable ones with external antenna. The frequency you hear is
> the beat frequency of the oscillator pair. I made one a few years back
> for a lecture on sounds (Practical Electronics design from the 1980's).
> > Whatever, it's ingenious. They were all over the
> > old sci-fi movies, I wonder why they went out of fashion.
> They have to be located a long way away from the trombones in an
> orchestra. I know someone putting on an Xmas concert next week which
> includes both Dr Who theme tune and the Beach Boys Good Vibrations.
>

and afaiu it wasn't a "real" theremin that was used on Good Vibrations
https://en.wikipedia.org/wiki/Electro-Theremin

On 12/17/2022 8:13 PM, RichD wrote:
> How does the theremin instrument work? What's under the hood?
>
> Whatever, it's ingenious. They were all over the
> old sci-fi movies, I wonder why they went out of fashion.
>
>
> --
> Rich

Use Google:
https://electronics.howstuffworks.com/gadgets/audio-music/theremin.htm
Ed

On Sunday, 18 December 2022 at 19:14:19 UTC+1, ehsjr wrote:
> On 12/17/2022 8:13 PM, RichD wrote:
> > How does the theremin instrument work? What's under the hood?
> >
> > Whatever, it's ingenious. They were all over the
> > old sci-fi movies, I wonder why they went out of fashion.
> >
> >
> > --
> > Rich
> Use Google:
> https://electronics.howstuffworks.com/gadgets/audio-music/theremin.htm
> Ed
Theremin made for Lenin had double function:

playing soundds / music

but the primary function was a radio eavesdropping device placed in Lenin's cabinet
to transmit secret talks to remote room