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In Reply to: RE: Output impedance of a DAC to input impedance of Power amp?????? posted by Astrostar60 on August 11, 2014 at 02:32:48:
It's not the output impedance of the source, it's the output impedance of the passive attenuator that causes the problem with long cables.As long as the source is "happy" with the input impedance of the attenuator that will not be the problem but the output impedance of the attenuator vs. the total shunt capacitance that has to be driven is where the problem lies.
That capacitance includes the cable capacitance plus the input capacitance of the power amp.
The output impedance (of the attenuator) vs. the total shunt capacitance creates a low pass filter and if you don't want the volume control to "change" the sound of the system then that low pass filter's -3db point needs to be at or greater than 200kHz otherwise there will be phase shift at or below 20kHz.
P.S. I started by saying that it's not the output impedance of the source but in a way it is.
If your DAC's output impedance is really 10 ohms then there's no reason you can't use a very low impedance attenuator.
10 ohms can drive 1k ohms all day long without causing any problems at all.
A 1k attenuator will have a worse case output impedance of 250 ohms and that would drive long cable just fine.
Tre'
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Edits: 08/12/14
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Follow Ups
- RE: Output impedance of a DAC to input impedance of Power amp?????? - Tre' 08:19:41 08/12/14 (0)
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