[sdiy] opto compressor project

[JH.]

> Just the other day I showed a friend of mine (experienced professional
power
> supply designer) the VCS-3/Synthi-A Mk I PSU schematic and asked him find
the
> flaws, he spotted them almost all, but he wasn't paying attention to the
> shunting action of the regulations. The mixed-mode loading in there helps
to
> confuse things. Your heater design is so much like the Mk I PSU design
that
> it is scary. You should know better... ;O)

Actually it was the MK1 Synti (and its PSU overload problems at today's
slightly higher mains voltage) that made me use a constant current source
instead of
a simple high power resistor to feed the shunt regulators ...

First I wanted to build just a 300mA current source (no shunt regulators)
for
serial feeding, but a friendly list member pointed out that many modern
tubes don't
follow the data sheets in terms of current consumption. (Thank you, Rainer
Meergans!). I measured the voltage of a few different 12AX7 and 12BH7 tubes
@ 300mA, and I got huge variations not only during warm-up, but also for the
static case. More than 2V difference!
So I decided to make the tubes work at their nominal voltage (not current),
and
instead of soldering in some fixed shunt resistors, I went for a variable
shunt
that will self-adjust even when I have to change a tube.


> But, how is the LDRs modulated? I can't see that from the schematics...

Scott already answered this. The NIght Light foil is directly driven by the
amplified
audio signal. There is no rectifier and threshold circuit: The EL panel does
both
all by itself, and the attack/release time constants are created by the LDR.

JH.