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RE: Output impedance of a DAC to input impedance of Power amp??????

Posted by Tre' (P) on August 11, 2014 at 20:23:33

In Reply to: RE: Output impedance of a DAC to input impedance of Power amp?????? posted by georgehifi on August 11, 2014 at 14:18:25:

While a -3db point of 106kHz will yield a (more or less) flat frequency response to about 53kHz it takes a decade for the phase shift to go away.

That means there will be some phase shift all the way down to 10.3kHz

This is why all the tech books talk about bypassing cathodes to 2Hz if you want 20Hz flat and phase shift free (it's the same thing but on the high pass side of the equation) and if we want 20kHz flat and phase shift free, all of the low pass filters (and they are seemly everywhere in a system) need to have their -3db points no lower than 200kHz.

(It's impossible to reach that goal when an audio transformer is involved but that's no reason to introduce more phase shift when you can help it)

You can find good cables with far less than 100pF per foot.

I'm using 1 meter cables that measure 70pF. Not 70pF per foot but 70pF total! Measured on a Sencore LC53.

BTW Don't over look the input capacitance of the power amp, that would be added to the cable capacitance.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 08/12/14

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