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RE: BTW- Vintage Power Amp with Passive Pre

Posted by Bold Eagle (A) on July 14, 2012 at 17:11:18

In Reply to: RE: BTW- Vintage Power Amp with Passive Pre posted by Eli Duttman on July 14, 2012 at 13:11:20:

Eli,

With the buffer in an existing active preamp, there is already an output cap for the preamp, so all the buffer needs is one additional cap for the output.

The two Sony CD platers were an ES model and one of the regular line. Both were measured at 1100 ohms at 1 kHz.

Both were also sensitive to the capacitance of the interconnects, so I used 12" interconnects made from low capacitance coax. Capacitance was in the 25-30 pF range. With typical 3' interconnects with a capacitance of 100 pF, they both developed a hard, bright edge. My old, and dear departed Onkyo DX230 CD player and my Rotel RCD971 don't seem to care about cable capacitance; but the earlier Rotel RCD955AX does. With short, low capacitance cables the RCD971 and 955AX sound identical; but use 3' long, 100 pF cables with the 955AX and the difference is quite noticeable.

I have no idea what the root cause is; but my friend, the analog circuit guru, thinks it might be oscillations in the output circuit caused by the extra capacitance.

Jerry

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