harmonic engine guitar pedal

[R.G.]

Smile.

[R.G.]

A bit more info. I looked into the Harmony Generator a bit. They chose the choices for "harmony" to be unison, a third or a fifth. A major third in just intonation is a ratio of 5/4 higher frequency. A fifth is a frequency ratio of 3/2.

They used a frequency multiplier determined by two programmable dividers, to multiply the base frequency by a number set in the dividers, then divided by 64. So they set the multiplier to multiply by  a number that when divided by 64 was the frequency multiple. Oddly, they did it based on the even tempered scale, so the note that resulted was an even tempered fifth or approximate even tempered third. They could have saved some trouble by simply doing a multiply by three, then divide by two or a multiply by five, then divide by four.  That gives the true major third and fifth in just intonation. I still haven't figured out if that's a problem or an oversight.

The setup I was envisioning had the PLL multiplied by 128 to start with, then the unison tapped off at divide by 32, so it had a multiply by 32 at the top of the string. Actually, the VCO on the PLL was running at x64, so it's kind of like what's happening in the H.G.

I'm trying to come up with some easy way to gate in a top divide-by-N at the top of the string, and then tap the harmony generator off down the binary divider chain. A CD4017 is a handy divide-by-N for N=2 through N=10. The H.G. used two CD4526 programmable down counters cascaded to get divide bys of 81 and 96. The CD4526 is essentially unavailable now.

I'm still working the math. My usual answer of "Use a microcontroller" probably won't work without insanely high clock rates.

[slashandburn]

Not meaning to derail this but I've just realised that the Datsuns song "Harmonic Generator" is probably about guitar pedals. 
"I'm gonna push the button, flick the switch today"
"Big yellow eyes lighting up like Xmas, turning tricks baby, Electric Mistress"

Can't believe I've never noticed that before.
Anyway, as you were.