High Current SS amps with input impedance = 200K

Here are Stereophile's output impedance measurements for the SP16L line-stage preamp, for which the ARC specs are identical to what Mapman quoted:

http://www.stereophile.com/tubepoweramps/901/index6.html

The measurements indicate 262 ohms at mid and hi frequencies, and 549 ohms at 20Hz.

Into a 600 ohm load (sic), they measured a loss at 20Hz of only 2.5db (see Figure 1). By my calculations, into a 10K load the 549 ohm output impedance would result in a loss at 20Hz of less than 0.4db.

So the output circuit, and particularly the output coupling capacitor, of the SP16 appears to be designed more conservatively than in the case of most tube preamps. And the recommendation of a 20K minimum load appears to be conservative as well.

Regards,
-- Al

Al,
c
Thanks for the details.

I can say with confidence that the sp16 sounds very balanced, natural and lively with the MF a3CR I'm using (31K input impedance spec).

There is a larger (>200 w/ch)MF A308CR amp up for sale by a local Agoner. I think the impedance specs are the same as the A3CR but need to confirm. Since I like the current sound an would be happy with more of it, that might be something for me to consider again now that I have a handle on the impedance issues.