removing the low pass filter from the op amp input seems to work great, there is no DC on the input coming from the DAC and the output DC is now dead zero, with the DC filter it was -0.4 mV and -1.2mV... 
it sounds better of course, this was the main point.
other than it acting as a failsafe in case something goes wrong is the DC filter on the input actually necessary if you know the source is not putting out DC?
The filter values were 2.2uf and 40.2k, 1.81Hz. I could imagine it filtering out infrasonic bass frequencies that could influence the performance of the amp but at 1.81Hz it looks to low to have much impact outside of filtering DC.
it sounds better of course, this was the main point.
other than it acting as a failsafe in case something goes wrong is the DC filter on the input actually necessary if you know the source is not putting out DC?
The filter values were 2.2uf and 40.2k, 1.81Hz. I could imagine it filtering out infrasonic bass frequencies that could influence the performance of the amp but at 1.81Hz it looks to low to have much impact outside of filtering DC.
No, and Im only concerned about the headphones. its just a unity gain op amp driving the headphones so nothing that cant be easily replaced
what is the cause for concern?
The DAC output has a cap to ground and a resistor in series so its actually a low pass filter.
I went to a Jantzen standard z-cap for input coupling shortly after because it sounded more pleasant without much loss of detail compared to no coupling cap. It's still unclear if this cap is smoothing the sound slightly (Jantzen doesnt recommend these for audio, only power supply use) or if removing the coupling cap was introducing some slight harshness.
before removing it again its back to the original question:
''other than it acting as a failsafe in case something goes wrong is the DC filter on the input actually necessary if you know the source is not putting out DC?''
measuring the DAC for DC reads absolute zero
I went to a Jantzen standard z-cap for input coupling shortly after because it sounded more pleasant without much loss of detail compared to no coupling cap. It's still unclear if this cap is smoothing the sound slightly (Jantzen doesnt recommend these for audio, only power supply use) or if removing the coupling cap was introducing some slight harshness.
before removing it again its back to the original question:
''other than it acting as a failsafe in case something goes wrong is the DC filter on the input actually necessary if you know the source is not putting out DC?''
measuring the DAC for DC reads absolute zero
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I have a headphone amp that doesn’t use any coupling caps anywhere. Is very nice, but isn’t sold anymore. It does have a resistor on the output, and pots to zero out any offset. It’s the E5 version, has been used daily for over 6 years.
The schematic is shown here if you’re curious.
My E5 Class A hifi headphone amp
The schematic is shown here if you’re curious.
My E5 Class A hifi headphone amp
Currently building xrk971's amp at the moment which will probably be last one for a good while. this one looks good, the output resistor probably has very little impact on the sound compared to a cap
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