[sdiy] Matched MOSFETs - anybody played with these?

[JH.]

I see two applications immediately:

Fast high impedance buffers without offset voltage, as they did it in the
old times before the rise of BiFet opamps. Opamp buffers have
mostly replaced these today, but a discrete buffer with no feedback
loop still has its benefits today.

Second, every time I run a Rhodes sound from the SX WSA-1 thru
my Wasp Filter, I wish it was less noisy. So I'd love to try better
MOSFETs than those in CD40xx packages.

BTW, it's unbelievable what the signal chain Wasp-Filter and Boss CE-1
can make of an artificial Rhodes sound.
The WSA-1 with its sort-of physical modelling puts out a rather nice
and realistic epiano sound, but it sounds a little sterile. The Wasp Filter,
set to a fixed cutoff around 10kHz and low Q, and set to a level
below audible clipping, can dramatically change that. At least in
combination with the old Boss Chorus Ensemble. Switch both to
bypass - sterile. Switch on either CE-1 or Wasp filter, slightly
better. Switch on both, it's pure magic.

But the CD4069's in the Wasp filter are noisy. No problem with constant
level input as from VCOs, but for the Rhodes sounds I'd love to have
less noise. That's why I want to try better MOSFETs.

JH.



> I'm very interested in this, I do hope you'll share anything you learn
> about these.  Not being an EE, I'm not sure I really understand the
> implication of matching MOSFETS other than precision in something like a
> current mirror.  And I wonder how badly (or not) the MOSFETS in something
> like a 4069UB or 4007UB are matched.  I've often wondered about the
> current mirror used in the 4046 VCO, for example over what current range
> does the mirror perform as a mirror?  I think there are limitations to
> this which give rise to the circuit's "linear to a point" operation.
>
> "JH." <jhaible at debitel.net> wrote:
> >> If you dig a bit deeper you'll find that you probably want to talk to
> >> 1stComponents in Germany. http://www.firstcomponents.de
> >
> >Ah yes, indeed, they have a German distributor.
> >
> >
> >> but I haven't found a datasheet
> >
> >The first link I posted _is_ a data sheet.
> >
> >JH.
> >
> >
>
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