Hey all, I'm working on a theremin, specifically the beat frequency oscillator, which subtracts out the frequency difference between a variable pitch oscillator and a fixed pitch oscillator. For the fixed pitch oscillator, it just needs to generate an analog 260kHz signal. Can I use a crystal oscillator? Is that cheaper? Is there a better method for this? Want it to be very stable.

This is the document I'm working off of, but it's from the 90s. Pg.3 and 6 have the circuit diagram. https://www.cs.nmsu.edu/~rth/EMTheremin.pdf.

 

You're still going to need the same capacitors, inductors and resistors, which just leaves the transistors. You can buy two matched 2N3904s in a single 6-pin package, if you think it's worth it.
The SA602 might be worth a look.

 

You're still going to need the same capacitors, inductors and resistors, which just leaves the transistors. You can buy two matched 2N3904s in a single 6-pin package, if you think it's worth it.
The SA602 might be worth a look.

Thanks for the advice. I've already got a handful of those transistors anyways, just was wondering if a crystal oscillators or something would be easier, but it seems like this is the best strategy then.

 

Hello,

Did you notice figure 4 on page 97? location of components can influence the working.



There are more theremin schematics on theremin world:
http://www.thereminworld.com/schematics

Bertus

 

Hello,

Did you notice figure 4 on page 97? location of components can influence the working.

View attachment 281748

There are more theremin schematics on theremin world:
http://www.thereminworld.com/schematics

Bertus

Yes, I understand that positioning is important. My question is if there is a more effective/compact/cost effective way to produce the 260kHz signal from the fixed pitch oscillator, as I know other options like crystal resonators exist.

 

Thanks for the advice. I've already got a handful of those transistors anyways, just was wondering if a crystal oscillators or something would be easier, but it seems like this is the best strategy then.

A Colpitts or Hartley need two inductors and a capacitor or two capacitors and an inductor for the tuned circuit. Use a crystal and you still need two capacitors with it.
Crystals between 32768Hz and 1MHz are exceedingly rare! You'll find 455kHz resonators for radio IF.

 

A Colpitts or Hartley need two inductors and a capacitor or two capacitors and an inductor for the tuned circuit. Use a crystal and you still need two capacitors with it.
Crystals between 32768Hz and 1MHz are exceedingly rare!

Thanks! Didn't know that

 

Hello,

As for the inductors, have a look at the IF transformers of some AM radio.
Those are likely tuned in the range of 455 kHz to 462 kHz.
As long as the frequencies of the fixed and variable oscillators are in the same frequency range, you will be fine.
An other advantage of those inductors is that they can be tuned.

Bertus

 

Yes, I understand that positioning is important. My question is if there is a more effective/compact/cost effective way to produce the 260kHz signal from the fixed pitch oscillator, as I know other options like crystal resonators exist.

I suspect that two oscillators using similar components will approximately drift in a similar way with changes in temperature, supply voltage etc. If you use a crystal oscillator its frequency drift will not match the other oscillator.