2040 clone schemos error !

[jhaible]

>A couple more questions regarding the JH 2040 filter clone schemo:
>
>Is this the complete VCF circuit or just the chip? I other words: does it
require some more circuitry to make a >working VCF?
>Maybe an output buffer? Input divider? Something else?
>
>What about Vref? Is it -1V? Can it be supplied by an op-amp? 
>
>What about trimming? How can the 1V/oct tracking be trimmed?

The whole drawing is not a pin for pin replacement of the SSM2040, nor is
it a 
self contained diy project. It's part of of a multimode filter of the JH-4
module,
which is described at 
<www.synthfool.com/diy/jh4_vca_block.gif>.
The whole CV summing stuff (with VCAs for voltage controlled mixing of
modulation
sources) is shared by the 2040 part and the state variable (SEM filter
clone) part.
As with any expo converter, what you need is approx. 18mV / oct between the
bases of the two transistors. (One of the pair actually being 4 transistors
here.)
Same stuff as usual, therefore not explicitely drawn. Tempco resistor if
you need
accurate tracking over temperature range, simple resistor if that's not
important.
I have a 510 R resistor in the circuit simply because I have a few tempco
resistors
of that value. use your usual 100k / 2k + a little trimming here if you
like. Just
make sure that the "common mode voltage" at the transistor bases is
slightly negative
to give the expo converter some voltage drop to work. Sure, it can be
supplied by an
opamp.
If you like CVs centered around 0V, no problem, add a level shifter, either
inverting or
noninverting, just as it fits into your circuit environment. In my JH-4
module environment
this was relatively uncritical, as the "CVs" to be mixed are output
currents of OTAs
anyway, so the absolute voltage level is unimportant.

JH.