[sdiy] Importance of Matched Transistor Pair

[Alex]

Patchell,

Thanks for the info. It makes sense to me now.


----- Original Message -----
From: "patchell" <patchell at silcom.com>
To: "Alex" <alcratin at hotmail.com>
Cc: "Synth-Diy" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, March 23, 2002 2:09 PM
Subject: Re: [sdiy] Importance of Matched Transistor Pair


>     To keep it as simple as posible...
>
>     In general, the matched pairs are used for the exponential converters
(they
> can also be used for other things, but when it comes to synths, expo
converters
> are the number one job, followed by ladder filter pairs, also found in the
> TB303).  There are quite a few ways that transistors can drift with
> temperature, by using a matched pair, all of these drifting parameters
track
> each other, so if you look at both at the same time, it apears there is no
> drift....
>
>     Generally, what needs to be matched in matched pairs is the Vbe of the
> transistor.  Another important thing about matched pairs is they must be
> thermally connected.  After you match a pair of transistors, you generally
> should glue them together (I use epoxy).  However, the best way is to buy
> matched transistors.  The most common one availiable is the CA3046
(actually
> five matched transistors).  The CA3046 is also the least expensive.  Other
> canidates are MAT02, MAT03, MAT04 (4 transistors), THAT200/220/240, some
> japanese transistors I don't remember the numbers for (somebody else will
come
> up with them, last time I tried, I got them wrong).
>
> Alex wrote:
>
> > I'm kind of new at some of this, can anyone tell me what the importance
of
> > using a matched transistor pair in a synth circuit vs. two individual
> > transistors?
> >
> > I know that the Roland TB-303 uses a matched transistor and there's a
synth
> > DIY site out of Scandinavia, that sites using a matched transistor pair
for
> > his mono phonic synth. I want to build a modular synth and then I saw
this,
> > can anyone provide me with some background on this on why it's used for
> > synth design? There are only 3 or 4 matched transistors that NTE
provides.
>
>     I have purchased these in the past, they are good parts...
>
> >
> >
> > Thanks.
> >
> > Alex
>
> --
>  -Jim
> ------------------------------------------------
> * Visit:http://www.silcom.com/~patchell/
> *-----------------------------------------------
> *I'm sure glad Merry Christmas comes just once a year
> * -Yogi Yorgensen
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>
>