AW: Tempco Update

[Haible_Juergen#Tel2743]

> Regular molded 2K (538Q) :  350 uHenries
> Non-inductive molded 2K (N538Q) : 66-72 uHenries
> Coated 1K (C-2AQ)  - 2 in series for a 2K resistance: 38-42 uHenries
>
> I don't know much about inductance, but we can see that the C-2AQ has 
about

If you put too much inductance into the feedback loop of an opamp (as in
the usual EN circuit, where the tempco resistor is placed there), you
might get some trouble, as the opamp has incresaed gain at higher
frequencies then, and it might not be internally compensated for this
condition. Well, I said "might" - we'd have to calculate this. But
you could easily try if this problem also occurs when you use
a passive resistor divider with the tempco resistor! Just try to build
the adder with a 100k in the feedback, and go with a passive divider
to the base of the antilog transistor!
You could also try and use an externally compensated opamp with
a rather oversized capacitor.

BTW, I asked Stefan where he got his tempcos for the Transistorbass-3,
and he said they were manufactured to order in Japan. Well, I always
was sure he would clone something as close as possible (;->), but
this is surely bad news as I expected to find another source for
tempcos!

JH.