2040 filter clone with unmatched transistors ?

[Haible Juergen]

Hi,

I was wondering lately how precisely the transistors in my SSM2040-style
filter must be matched. (http://www.synthfool.com/diy/jh2040.gif, or
http://www.it.kth.se/~e93_mda/synths/friends/haible/jh2040.gif)
What I have written in the schemos is what I have *done* when I built mine,
i.e. matched the transistors in pairs to delta Vbe < 1mV @ Ic=100uA.
But I am wondering if this is really necessary.
Think of this: both transistors of each npn differential pair are working at
very different Vbc. So far, I have ignored this effect, but Spice
simulations
tell a different story. With one collector near 15V, and the other one
near 0V, the whole thing must be rather unbalanced. A Vbe difference
as high as 10mV would cause a similar effect. One could possibly
cure this "problem" with some additional transistors to form a cascode,
but I'd rather look at the whole thing from this point of view now:
It does work in spite of this effect, so why shouldn't it work with
unselected
transistors, too ??
I have not tried this on the real thing, and probably don't find the time to
do it
in the near future, so I'd like to hear comments if you can confirm this
from
theory, or even better, from building such a filter with unmatched
transistors.

Any ideas ?

JH.

PS.:
The SSM2024 aparently solves this problem by using a much smaller internal
positive supply voltage for the pnp current mirror ...