[sdiy] High-K ceramics and audio

[Richie Burnett]

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,


-- 
This email has been checked for viruses by AVG antivirus software.
www.avg.com