[sdiy] Dual Matched N JFET from Linear

[Michael E Caloroso]

In the early days of opamps, ARP placed a matched FET IC at the inputs of
Teledyne and LM301 opamps to increase the input impedance.  That was a
Dennis Colin innovation, which he carried to the Aries modular after he
left ARP.  There's a lot of circuit design conventions between Aries and
ARP products.

ARP used this technique in analog synths all the way from the 2500 to the
end of the company.  I don't think this was used in the Chroma though, by
then FET input opamps were mainstream.

MC

On Sun, Jun 22, 2025 at 9:05 AM Paul Perry via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Electrometer design is one application for matched fets, but there is also
> a VCA that requires a matched pair:
>
>
> https://www.edn.com/op-amp-linearizes-response-of-fet-vca/#:~:text=FETs%20find%20common%20use%20in,C%20is%20the%20control%20voltage
> .
>
> paul perry Melbourne Australia
>
>
> On Sun, Jun 22, 2025 at 6:21 AM Mike Bryant <mbryant at futurehorizons.com>
> wrote:
>
>> One place you do see FETs quite a lot is the muting output of mixers -
>> they kill thumps well without distorting the output signal.
>>
>>
>> ------------------------------
>>
>> On 2025-06-21 12:53, René Schmitz wrote:
>> > FETs have large unit to unit variations, good for one-off hobbyist or
>> > space mission work, but
>> > annoying to show-stopper for mass production. So you'll not see them
>> > that often in the wild.
>>
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