[sdiy] matched FETs for phaser

[Jaroslav Lukes]

> From: anthony [mailto:aankrom at bluemarble.net]
> I have a strict policy about trying to use parts I already have.

It is not expensive. I was buy it before few years for 0.1$ per piece.

> Especially
> since I have a huge amount of neat parts that I've scavanged.
> 
> I'm not averse to buying parts, but often my projects take interesting
> detours trying to adapt what I have that would not have occured otherwise.
> There /is/ a pointof diminishing returns though.
> 
> What actually got me thinking about this was my plan to use a matched pair
> -
> something similar to a 2SC3958 that came from a piece of tektronix gear -
> for a clone of MXR's Phase 45. Since I have two of these I wondered how a
> Phase 90 would sound _using_these_parts_.

Okay, use these pairs.

 
> At the heart of these ponderings was a question of theory: do ALL FET's in
> a phaser need to be matched or just matched in pairs?

Try to simulate it. I think that in two transistor cascade it is not as
importatn. And make some measurement with originals of ocurse.

If you want to have best performance, use very powerfull switched phaser
from Elektor which have (I think) 18 cascades. Or try to use phaser from
switched capacitor filter (MF10).

JL.

> 
> ----- Original Message -----
> From: "Jaroslav Lukes" <lsh.synth at seznam.cz>
> To: "'anthony'" <aankrom at bluemarble.net>
> Cc: <synth-diy at dropmix.xs4all.nl>
> Sent: Monday, January 30, 2006 3:01 PM
> Subject: RE: [sdiy] matched FETs for phaser
> 
> 
> >> From: owner-synth-diy at dropmix.xs4all.nl [mailto:owner-synth-
> >>
> >> I know it's not that hard to match FETs for use in a phaser, but I was
> >> wondering if one used two matched pairs that weren't matched to each
> >> other
> >> if you would have good results.
> >>
> >> What I mean is it seems like it would be most important to match each
> >> pair
> >> for two stages for each peak/notch. How do 2 seperate phasers connected
> >> serially controlled by the same LFO sound?
> >>
> >
> > Here are at discount sales 6 matched (ie., 6 on single chip, not matched
> > by
> > measure, but they have very small differences) transistors in single
> chip:
> > MH2009 and MH2009A
> >
> > See http://io.freehosting.cz/166.gif
> >
> > And you can buy it at http://www.mkelektro.com/index_uk.html
> >
> > Origimally, it was designed for switching apps, but at analog apps it is
> > very good too. It was used as signal switchers and mixers, VCA+VCF at
> > famous
> > construction of Dolby B compander by Jaroslav Belza etc.
> >
> >
> > Regards, JL.
> >
> >