Mono/Poly (was: beating a dead DAC )

[jhaible]

Hi Osamu, and list,

> The big (1W or 2W) resisters on SSM2033s are for heating the chips.
> I've read an interview of the designer of Mono/Poly in a Japanese
> book.
>
> Mono/Poly and Poly6 are the first V/Oct synths for KORG.
> He said that they were used with the great stability of Hz/V VCOs and
> was not satisfied with the stability of 2033 itself, so he added that
> big resisters (heaters) to get sufficient stability.

This becomes even stranger now.

First of all, Poly6 and Mono/Poly had very different VCOs:

The Poly6 still has V/Hz VCOs, plus one multiplexed expo converter for
all 6 VCOs. This was neither heated nor was a simple tempco resistor
used. Instead, they used a 7th multiplexer channel to derive an error
voltage
for a known input voltage, and the expo converter's gain was adjusted
by a optoelectronic device.

The Mono/Poly, OTOH, used integrated VCO chips (SSM2033) which
already had a heater *on chip*. It's too long for me since I last looked
into a real Mono/Poly, so I can't be totally sure about these external
resistors.
When I built my MidiMini years ago, I used the Mono/Poly VCOs
as a scheme to start with, but I've taken it from the schemos, so I might
have missed the power resistor part. Maybe they placed an unregulated
heat source (power resistor) next to the thermostated chips in order to
decrease the temperature gradient from the chip to the ambience ? That's
the only thing I could think of. It would reduce the 2033's power
consumption,
and in case it also improoved the regulation, it must have been very clever.
But that's the first time I heard about that. Time to look into a real
Mono/Poly
again !

JH.