[sdiy] Difficult 2164 behaviour between different sections.

David G Dixon dixon at mail.ubc.ca
Wed Jul 17 18:26:19 CEST 2019


Well, Achim, you may be technically correct, but, to me, an IC that is too
hot to touch indicates a simple design error.  In the process engineering
realm, we have something called "haz-ops" where the engineers get together
and try to find any and all potential weak spots in a plant design.  To me,
a smokin' hot IC would fail the haz-ops test and a suitable design fix
should be applied.

According to the SSM2164 datasheet, its maximum attenuation is 100dB.  This
is achieved at 3.3V on the VC pin.  Presuming the 5k VC-pin impedance of the
"old" 2164s, and further assuming an opamp top voltage of 13.5V in a 15V
supply, then a 7.5k limiting resistor will achieve 3.375V at the VC pins and
full shutoff.  For the "new" 2164s with 10k VC-pin impedance, this resistor
is 15k.

Assuming a 12V supply with an opamp top voltage of 10.5V, then the maximum
resistors are 5.1k for the "old" 2164 (3.45V) and 10k for the "new" 2164
(3.5V).

Hence, my choice of 4.7k covers all the possibilities for achieving complete
shutoff of the VCA, regardless of power supply or 2164 style.



-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of ASSI
Sent: Tuesday, July 16, 2019 11:50 AM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Difficult 2164 behaviour between different sections.

On Tuesday, July 16, 2019 6:14:53 PM CEST David G Dixon wrote:
> It gets so hot you almost can't touch it.  So, I'd say, yeah.

"So hot you almost can't touch it" is actually a rather precisely determined

temperature, about 61°C for a contact time of 2s and 50°C for 10s of contact

time with a digit.  With the junction temperature likely about 20K higher
than 
that, this temperature is well within the specifications for consumer IC, so

no, I don't expect any appreciable reduction in lifetime from temperature 
alone.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptations for Waldorf Q V3.00R3 and Q+ V3.54R2:
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