[sdiy] THAT300

Dave Manley dlmanley at sonic.net
Thu May 7 02:26:19 CEST 2015

A while back, THAT replied to an email I sent...you can always try that.


On May 6, 2015 3:51:53 PM PDT, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>"Substrate biasing is not required for normal operation, though the
>substrate should be ac-grounded to optimize speed and minimize
>This sounds like the substrate is electrically insulated from the
>workings (probably by an oxide layer.) So it doesn't matter what dc
>voltage is on there.
>However they are aware that there is still significant capacitance
>between the substrate and various nodes in the workings (probably
>because the oxide insulating layer is very thin.) Therefore they advise
>grounding it at least for ac signals to reduce high-frequency
>crosstalk. Personally I'd just tie it directly to a good *clean*
>analogue ground.
>Sent from my Xperia SP on O2
>---- rsdio at audiobanshee.com wrote ----
>>Did anyone answer this, Crystal?
>>The substrate is typically connected to the source for 3-pin FETs, but
>this is BJT technology so we should disregard FET conventions.
>>The data sheet description holds a clue: "Substrate biasing is not
>required for normal operation, though the substrate should be
>ac-grounded to optimize speed and minimize crosstalk."
>>My interpretation of that is you should connect a capacitor to the
>substrate pins and ground the other end of the capacitor. No idea what
>value it should be.
>>I'm surprised that there aren't example circuits in the data sheet,
>but perhaps there are application notes on the THAT Corp web site. The
>closest I could find is a mic preamplifier based on the THAT120A array,
>but it has a different pinout. They show pin 14 grounded, but its data
>sheet only mentions "grounded" not "ac-grounded," so I think they
>learned something before discontinuing the THAT120A.
>>Have you made any progress since January? Keep us posted…
>>On Jan 2, 2015, at 3:44 PM, crystal <crystals at sonic.net> wrote:
>>> Thanx Tim Ressel for the tip of using a THAT300 for a matched pair.
>Haven't tested my circuit out for tracking accuracy quite just yet but
>i bet it's a significant improvement. my question: what to do with the
>substrate pin?   -V, or perhaps ground?
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