RCA THEREMIN

Sort of from scratch.

It's an adaptation of a common guitar overdrive stomp box that's been around for decades. I think the first one was called "Big Muff" or something like that.

They normally use switching diodes for hard clipping. Using LED's gives a softer, more tube like flavor, and using different colors makes the clipping asymmetrical.

Thanks, Fred. That works for me :)

Edit: I just noticed I didn't put a value on R26. It's 100k.

Rob,

Just been making my way through the circuit - It is really nice! - All sorts of unbalanced signal paths and assymetries and frequency related anomolies.. the sort of circuit which one would giv a student to analyse if one was really sadistic! LOL..

I can see why your real circuit produces waveforms which are somewhat "nicer" than the simulations - Diodes (even "normal" ones) often introduce simulation innacuracies. I have seen the LED trick used for "tube" emulation before - but never seen a circuit employing LEDs in the feedback path and as shunts - I like the look of that, its a great idea!

What strikes me about the circuit is the obvious mix of hands-on experimentation combined with competence - there are no potentially destructive configurations, loadings are all fine - It actually reminds me a bit of some of Bob Moogs circuits - One can see that a lot was "designed" using a soldering iron (or these days, simulation alows one to "build" the circuit in much the same experimental way)  - but unlike usual hobbyist circuits 'designed' in this way, it can be put into production and work reliably.

Good stuff!

Fred.

ps - Im a bit puzzleed about the input configuration (in and in1) and these being referenced to -V ?

Is R9 1k? and is the 150k RA to it R7? - Also, what is the value of the resistor on IN1 (R10 I think) ? I see 614.. oh - thats C14 sitting over a 1k ?

R19 and C14 are ground loop breakers. R19 is 10 ohms. They do go to V-

R9 is 1k.

V- is real ground. AGND is bias from the 15k X 2 divider.

The 150k is R7.

I'm sorry for the less than ideal visibility. This was pulled straight from Eagle. I laid out a board with it as a guide for perf board construction and never thought anyone else would see it :)

I'm also suffering from the flu today, so my brain is a bit fuzzy.....

"It actually reminds me a bit of some of Bob Moogs circuits" Fred.

That is the nicest thing anyone has ever said to me!

"R19 and C14 are ground loop breakers. R19 is 10 ohms. They do go to V-" - Rob

Ok - I see it all now.. I was forgetting that you were building this as a seperate external unit for inserting in an "effects" path, and it all makes sense when viewed from that perspective.

Flu? You sure its not something you caught from that "image" you uploaded ?

Joking aside - Sympathies and best wishes ..