[sdiy] What do people use for matched transistors these days?

Spiros Makris spirosmakris92 at gmail.com
Mon Sep 11 13:37:37 CEST 2023


The 4 transistor ICs offer the possibility of forming a thermal oven, which
can be exceptionally stable if shielded from air breeze. I have built and
evaluated a version using THAT-320 and it tracks very well regardless of
season (indoor use). It's been a few years, but I remember that there's a
tradeoff between Rbe and temperature; higher oven temperature offers more
stability against ambient temperature changes (I picked 50C in my version),
but increases Rbe, messing with high-frequency tracking.
In any case, the stability of the expo pair essentially depends on the
temperature matching of the transistors, and thus, having them on the same
die is the optimal solution, even if you go with thermistor compensation
instead.

On Mon, 11 Sept 2023 at 07:47, brianw <brianw at audiobanshee.com> wrote:

> Does anyone here have access to a thermal chamber where the temperature
> drift of a given circuit can actually be assessed?
>
> My assumption is that things will probably work fine under "normal"
> conditions, but as soon as a musician brings gear in from a cold climate to
> a warm venue, or even starting from comfortable climes and then
> temperatures inside climb to sweaty, humid heat, there might be problems
> that didn't show up in the home studio.
>
> Brian
>
> On Sep 10, 2023, at 6:22 PM, crys <crystals at sonic.net> wrote:
> > I acquired a bunch of THAT 320 and 300 and used them for quite a few
> ircuits. Sometimes it was likely overkill, like when i built a ladder
> filter with them. I found them to be easy to work with and quite stable.
> They do cost but i think i either got a deal or bought a quantity. It was a
> decade ago. I did score about 20 LM394 cans but it was just as i packed up
> my lab to storage, I'm interested in what's what now.  I have made a tester
> and matched them myself, as already menioned quite easy these days. I
> started matching resistors, too, which was quite easy. I also built plenty
> of modules with just transistors from a new lot that sounded just fine.
> >
> > On 9/9/2023 6:21 PM, Paul Glass-Steel via Synth-diy wrote:
> >> I’ve had good results with those too.
> >>
> >> On Sat, Sep 9, 2023 at 4:20 AM Mike Bryant <mbryant at futurehorizons.com>
> wrote:
> >> Nxperia also do dual transistors without the base resistors e.g.
> BC856S.  They are on the same die so will be well matched.
> >>
> >> From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Scott
> Bernardi via Synth-diy <synth-diy at synth-diy.org>
> >> Sent: 09 September 2023 00:33
> >> To: SDIY List <synth-diy at synth-diy.org>
> >> Subject: [sdiy] What do people use for matched transistors these days?
> >>
> >> Right now I'm looking at matched pnp's, suitable for a VCO.  Something
> like the THAT-320 quad pnp would be ideal, but they are kind of pricey. The
> quad is nice because you have an extra matched transistor you can use for
> high frequency tracking adjustment.
> >>
> >> I ordered some BCM856's to see how they will pan out.  I think the VBE
> match will be good enough, I'm wondering about the base resistance that
> causes deviation from ideal log conformance.
> >>
> >> For npn's, THAT-300 or MAT14 are the best, also pricey.
>
>
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