exponential VCO problems

[Eric Barbour]

>You have built an expo converter without linearity problems
>with tubes ?!?

No, I didn't. As someone else pointed out, it is not possible
with tubes. (Actually it is possible but very difficult--it 
requires a special tube made by Raytheon in the 1950s, a 
square-law tube called a QK329. Very rare today.)

At no time did I apply all the tired old paradigms of solid-state
synth design to my circuit. The VCOs use thyratron tubes, which
vary considerably from unit to unit in their zero-point switching
thresholds. The only practical way to control them is with a keyboard
having adjustable pots in its resistor ladder, allowing an
arbitrary voltage for each key (in ascending order).

A nice side benefit is that you can tune it for ANY scale.....

Although it is very difficult to make various modules (VCO, VCF
etc.) track each other, at very least it is possible to get VCOs
to track by using matched pairs/etc. of thyratrons. I don't even try
to make hi-Q filters anyhow, so why bother making them track with
the VCOs?

Anyone who is interested in more information can wait for Kevin Lightner
to finish putting the schemos on the Synthfool page. If you can't wait,
send me US$5 cash and I will be happy to send you copies of the
schematics.

-- 
Eric Barbour
Metasonix
1095 East Duane, Suite 106
Sunnyvale, CA USA 94086