[sdiy] Tempcos a NoGo

[dj hohum]

Hi All,

I'm thinking about temperature compensation and what are the tradeoffs
for each of the basic designs.

1) Tempco resistors.

A pain to get, and expensive when you do.

2) Chip Heaters

Easy to do, not as flexible as (1), uses more power.

3) OTA

Doesn't perform as well? Higher parts count?

Paia uses (3) in their design and I've read criticism that the expo
pair should be attached (glued) to the OTA.  I see a lot of new
designs still using tempcos and certainly a lot of older designs do as
well. Is the performance enhancement over Paia's approach worth the
expense and effort of hunting them down?

I have to say that I'm intrigued by the Paia approach because it
doesn't waste power in a heater and also uses only commonly available
parts. Is the paia schematic about as simple as this type of design
can get?  Are there any other designs also using this approach? EFM
uses either tempcos or heaters, and just about everything else I've
seen, where one can purchase a bare board, uses tempcos.

Why are tempcos, in particular Q81 variants no longer produced? Surely
there were other applications other than music synthesizers? What
other types of industrial applications used expo converters? Have they
all simply moved on to active types of temperature compensation?

Thanks,
Daryl