[sdiy] mached transistors

[patchell]

    It is kind of funny, but for what ever reason, transistor voltage matching
is generally expressed in mV...not too sure why, but most likely because in
diff amps you are interested in the input offset voltage...but anyway...

    I generally try to match to 1mV.  What I do is set up to measure a whole
bunch at one time.  I try to do this when the temperature in the room isn't
changing (as this will through the voltage value off).  I write down the
voltage for each transistor.  When I am done, I look at the list and start
matching.  Transistors with the "same" value get matched.  Generally, I have
found that in a batch of 30 transistors, I can generally get at least 13 pairs,
sometimes I even get 15 pairs when I am lucky.

Terje Winther wrote:

> Hello,
> I am measuring some transistors to get "mached transistors" needed for some
> VCFs (moog-ladders) and VCAs.
> How close do they have to be to be called "matched"?
> totally equal? 1% apart? 2% 3-5%?
> Also, for the moog-ladder filters; do they have to be matched between the
> ladder "staps", or is it enough to have the two transitors of each "step"
> to be matched?

    The only transistors that have to be matched are the two at the bottom and
the two at the top.  All the rest can be randomly selected.  But it is the
pairs in the rungs that need to be matched, if you want to do it that way.

>
>
> tw.  :)

--
 -Jim
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