[sdiy] High-K ceramics and audio

Mike Bryant mbryant at futurehorizons.com
Wed Nov 29 18:51:52 CET 2023


Most standard ceramics aren't suitable, due to both reasons you mention.

However Samsung Electro-Mechanic do a range of special automotive grade ceramics that eliminate the microphony problem.   These are used extensively in the automotive industry for sensors and audio applications, as you can imagine a car is a never ending source of thumps and thuds to the electronics no matter how much damping you put in.

There is also a TI paper examining how you can use X7Rs in most critical audio pathways by careful design.  Google for it.

Electrolytics are the usual solution though.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Richie Burnett <rburnett at richieburnett.co.uk>
Sent: 29 November 2023 16:20
To: synth-diy mailing list <synth-diy at synth-diy.org>
Subject: [sdiy] High-K ceramics and audio

I'm assuming the use of small high dielectric constant ceramic capacitors
like 0805 4.7uF X7R for audio coupling applications is a bad idea due to the
voltage coefficient?

Most of the audio gear I've opened up seems to have surface mount
electrolytic capacitors providing AC coupling between amplifier stages, or
in places like the DC-blocking at the audio inputs and outputs of CODEC
chips?  Given that electrolytic capacitors are larger, heavier, more
expensive and will eventually dry out, they must be superior to high-K
ceramics in these applications?

Is the problem with ceramics distortion caused by the non-linear dielectric?
I can see how the change in capacitance with applied voltage could lead to
distortion in applications where there is a large voltage swing across the
ceramic capacitor.  However, in cases where a DC-blocking (coupling)
capacitor is sized quite large there wouldn't be that much voltage swing
across it due to audio even down at 20Hz surely?

Or is the issue microphony?  I have certainly observed DC-blocking caps at
the front end of a high-gain amplifier (not audio related!) that caused a
very significant disturbance at the amplifier output when the PCB was tapped
with a pen!  (This seemed worse when there was DC bias across the
capacitor.)

I'd be interested to hear your thoughts.  (I hope I haven't opened a can of
worms with this topic !?)

-Richie,


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