[sdiy] Matched Transistor Specs

Tom Wiltshire tom at electricdruid.net
Tue Sep 1 17:15:00 CEST 2020

Alfa’s clones of earlier matched pairs are monolithic. I don’t know how good the specs are compared to other options, but the originals were used reasonably widely, so they must be pretty good! The AS194H is the improved version of the 394, and claims to be twice as well matched.

http://www.alfarzpp.lv/eng/sc/transistors.php <http://www.alfarzpp.lv/eng/sc/transistors.php>

Available at Erica Synths:

https://www.ericasynths.lv/shop/diy/diy-accessories/as194h/ <https://www.ericasynths.lv/shop/diy/diy-accessories/as194h/>

The only other monolithic ones I really know about are the THAT Corp parts.



       Electric Druid
Synth & Stompbox DIY

> On 1 Sep 2020, at 10:28, Steve Lenham <steve at bendentech.co.uk> wrote:
> I seem to remember that many of the general-purpose SMD pairs are not monolithic but are in fact two separate transistor die in a single package. As they come from the same wafer they are probably pretty well matched, but won't track with temperature like a monolithic pair.
> The really good pairs are not just monolithic but interleave the two transistor structures so as to equally share out any minute variations and temperature gradients across the die and make matching even tighter.
> For really good log/expo conformance you also want low base resistance (Rbb) but it is rarely specified except for expensive parts specifically targetted at that sort of application.
> Cheers,
> Steve L.
> Benden Sound Technology
> On 01/09/2020 09:24, Miles Stevens wrote:
>> My experience with dual transistors is mainly the NXP BCM series, they are incredibly handy for tight layouts in general, but I don't find them up to snuff for an expo pair.
>> On Tue, 1 Sep 2020 at 14:50, Aa Bb <alfa.rpar.as at gmail.com <mailto:alfa.rpar.as at gmail.com>> wrote:
>>    Dear Aaron
>>    For exponential circuit must be used transistors for wich some
>>    parameters (H21,...)  are defined in conditions Ucb=0 V.  Number of
>>    available transistors for such purposes is small.
>>    On Tue, 1 Sep 2020, 01:23 Aaron B., <aaron at zadzmo.org
>>    <mailto:aaron at zadzmo.org>> wrote:
>>        I've been looking at dual transistors for exponential circuits.
>>        If I'm
>>        okay with surface mount, there seems to be a bewilderingly large
>>        number
>>        of parts available.
>>        Besides the maximum voltage/current ratings, what should someone
>>        look
>>        for in a good exponential converter pair? Do any of the typically
>>        published specs like Vceo, Is, beta, etc matter much in this use
>>        case?
>>        --         Aaron B. <aaron at zadzmo.org <mailto:aaron at zadzmo.org>>
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