AW: Oberheim OB-1 /ca3080e filter question

[Haible Juergen]

	>I think there's a little more to this.  The 'E' just means that
the IC is a
	>DIP, as opposed to the 'A' which is a can.  I suspect that the
3080's were
	>matched, though I'm not sure what for.  Maybe Juergen knows.

Thanks - Juergen "suspects" or guesses as well (;->).

I am quite sure they matched for similar gm - but no idea how close they
matched. (10% ? 5% ? even 1% ?? ... if they are not matched to 1%,
then using 1% divide down resistors would not be of much use ...)
 
They may also have selected for CV feedthru. There are some 3080's
that won't get quiet at short attack times, even if you have offset
trimmers.
But I don't know if they did this or not.

Maybe they also selected for low noise, or bought low noise types (i.e.
selected by the manufacturer (?) ). Again, no idea if they did or not.

My 4 Pfennige ... (Dollar is very high at the moment ...)

Still one big question about gm matching, which I haven't found answered
so
far: *IF* two 3080's are closely matched for gm, are they then
automatically 
matched for input resistance of their Iabc inputs as well, or not ??
(At low cutoff frequencies the ususal 15k resistors loose their effect
of matching two Iabc inputs that are connected in parallel. So if the
impedance
of these inputs isn't matched, and you drive them from the same current
source, gm matching wouldn't be of much use, IMO.)

JH.

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