Thierymin pitch only theremin giving nothing but static an high pitched noises.

Hi, I breadboarded Thiery's theremin circuit and all i appear to be getting is static which varies when i touch the antenna. I'm running it through and LM386 audio amp i constructed. When I turn the 10K pot that lies between the audio out of the thierymin and the input of the amp really far, the speaker begins making a sharp shreeking noise. any ideas?

Thank you for anyone who is willing to help.

Thaddeus

The shrieking comes from the LM386 itself which tends to oscillate itself when its power supply is not well buffered and decoupled. The data sheet explains how to place capacitors relative to the IC.

Before putting 2 circuits together, you should test and get working both individually, first. This allows a more systematic diagnostic

First off, I'd like to thank you for your reply and advice.

This is the diagram i am using for the amp. everything is in the right place and all. so what need i do to reduce the shreeking when the pot is turned high?

I see where I have made my mistake, I shall acquire the correct cap for the V+ input.

It's been my experience that IC audio amplifiers aren't such a great idea.  They look good on paper but the sensitive low-level input circuitry is right next to high power high-level output circuitry, so there's not so far to go to find feedback oscillation trouble.  (What's that crazy RC doing hanging off the output?  Killing HF oscillation in the least efficient way I can imagine.)

Thanks for the reply dewster. So would you suggest wiring the theremin output with an audio plug and trying to plug a proper amp into it?

Thanks for the reply dewster. So would you suggest wiring the theremin output with an audio plug and trying to plug a proper amp into it?

Hi there,

dew said: "It's been my experience that IC audio amplifiers aren't such a great idea."

Some engineers are anal like those tube/valve guys that just can't get over it!

In my own design I would not use the 10uf capacitor as the 20x gain is more than enough. This also would make it less prone to self oscillation. This little module below which I rewire slightly to use the earphone jack for pitch-preview is under $2 from China. No wonder jobs are going overseas.

Christopher

Hmmm okay, thanks for the input. So should I just buy a pre built amp?

Breadboarding the LM386 is good, my suggestion is to eliminate the 10uf capacitor at pins 1 & 8 to avoid the extra amplifier gain. The 386 can be a screamer.

Electronics is about constantly learning new stuff. No matter how much I learn dewster always knows more

By choice I do not use 2% resistors because I get confused over the color bands, can't teach an old dog new tricks.

Christopher