matched transistors

[jhaible]

Hi Ian,

thanks for your answer.
I have sucessfully built VCOs around 3086's, so I see your point.
I was thinking about VCF and VCA applications in the first place,
and I think noise would be an issue here. As for offset, that's most
critical too (VCA and VCF), but one might select good ones from
a bunch of cheap arrays, of course.

JH.

----- Original Message -----
From: Ian Fritz <ijfritz at earthlink.net>
To: <synth-diy at node12b53.a2000.nl>; Haible Juergen
<Juergen.Haible at nbgm.siemens.de>
Sent: Saturday, April 15, 2000 3:21 AM
Subject: Re: matched transistors


> I would propose some softening of this statement. If you just go by the
spec
> sheets, then yes, the inexpensive arrays seem pretty bad. However, as I
have
> mentioned previously, modern parts often far exceed specs. For example I
> recently bought a half dozen CA 3083's. All but one have offset voltages
too
> small to measure reproducibly -- < 0.2 mV. Betas are well over 200. Series
> resistance is only 1.3 Ohm (which can be exactly compensated with a diode
> and a trimpot, anyway). Are you sure you need a lot better than this? Have
> you compared the other sources of error and drift with those stemming from
> using this "cheap" array?  I'm using one of these in the VCO I'm currently
> developing, and I don't see much (if any) difference in performance going
to
> an expensive pair.
>
>   Ian
>
> ----- Original Message -----
> From: "Haible Juergen" <Juergen.Haible at nbgm.siemens.de>
> >
> > Depends on the application.
> > When you're talking about CA3046 and the like, these are fine if you
only
> > need
> > equal temperature for both transistors. In some applications you also
need
> > low offset voltage, low offset voltage drift, high beta, low noise. Then
> the
> > cheap
> > array will not do.
>
>
>
>