Input Capacitor on cmoy headphone amp

[lawfreak]

Questions have been asked here before regarding this circuit. http://tangentsoft.net/audio/cmoy/misc/cmoy-tangent-sch.pdf

The 0.1 uF input capacitor seems to be far too high an impedance in the audio range to be an appropriate choice.  Simply testing the input pre/post cap suggests significant attenuation of any audio input. I hope there is a reason for the choice of 0.1uf given the thoroughness of the site, but it seems counterproductive to attenuate the entire audio signal before amplification. To caveat this, I had trouble trying to observe any significant difference pre/post cap using a scope.

Two questions now...  Capacitors in the 10uF range seem better suited to the task, but are there other issues to consider?  What drove the original design decision of 0.1uF capacitors?

[daveshah]

The difference will only be noticeable at low frequencies: in combination with the 100k input resistor a RC low-pass filter with a cutoff frequency around 16Hz is formed. This is unlikely to make much difference listening to actual music with actual headphones.

I suspect 0.1uF was chosen because the original creator wanted to avoid electrolytics and 0.1uF is one of the largest readily available non-electrolytic and non-MLCC capacitor sizes.

[ciccio]

You can buy film capacitors in small sizes and low voltage up to 2.2 uF, but there is no need to increase the suggested value.
On the other side, the power supply section is too simple... you can design a better virtual ground circuit.

Best regards

[danadak]

Use a charge pump for the split rail solution.

http://www.ti.com/lsds/ti/power-management/buck-boost-inverting-or-split-rail-products.page

Or do design as a single supply design.

Regards, Dana.