AW: My new VCO

[Haible Juergen]

	>this reminds me of my very first "serious" DIY music project, the
	>Tuenker "Sound Organ". Oscillator was with SCR too, no VCO though.
The
	>four sawtooth footages were generated the same way with resistor
	>networks. No ICs, two frequency dividers on one PCB.

Real saw wave outputs or just staircase waveforms ? (This makes a big
difference)

	>What is the usable frequency range of the VCO itself (without
frequency
	>divider), using the V/Hz input? Are the frequency dividers just to
	>select the footage or do their outputs have to be switched by the
	>keyboard, when a larger (88 keys) keyboard is used?

It runs down to 0Hz. The closer you come to the offset voltage of opamps,
the larger will the relative error be, however. That's why Korg 700 etc
used the freq. dividers, and MS-20 etc switched different resistors for
fottage selection (to change the current, but keep the voltage the same !)

I've tested the circuit over approx 6 Octaves. No problem here. You have
to adjust the offset voltage of the opamps, of course. It's easy: zero
input voltage -> adjust for zero frequency (in practice, adjust for one
click every few seconds for the 2' footage)

LF411 will be better than TL071 in terms of drift.


	[good divider ideas snoípped]

	>Another question: Is the + input of the TL071 really connected to
two
	>caps only?

No. 
The GND connection here.

JH.