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lzdiy 20th January 2013 08:02 PM

Choosing a DC storage/rail cap for cmoy like amp

I plan to build a cmoy-like headphone amp for my Grado 225i headphone.

The original cmoy schematic uses two 220uF DC storage caps (C1+/C1-), which I understand serves as buffer to stabilize the power supply:

However, I also found out that Grado's own RA1 amp only uses two much smaller 0.12uF caps (polypropylene film cap) at the same place in the circuit.

Lately, I discovered the schematic of the zenhead amp (ZKIT3) ZKIT3 Personal battery operated headphone amplifier kit from

The ZKIT3 actually uses two caps (one 300uF and one 0.1uF) in parallel, which makes me wonder that the two caps each serve different purpose.

My question is what's the pros and cons of using a larger value (220uf) cap vs a smaller one (0.12uF)?

Also, is there any benefit from using two caps in parallel as in the ZKIT3 amp?

I'm new to amp building. The may be a trivial question and I appreciate any help from the community.

GLooP 28th January 2013 02:11 PM

Small PP caps are put close next to OpAmp power pins to provide filtering and quick on-demand power with small deviations. Larger caps are to provide stable charge and lower power supply impedance (i.e. stable power) for short power-demand peaks. They are not very effective for high-frequency ripple and noise and their qualities are diminished by power rails PCB traces' inductance. My advice - use both.


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