High Current SS amps with input impedance = 200K

"I don't know why Mapman is reluctant to consider ARC recommendations "

Newbee, what gave you that idea?

I'm not. I would assume ARC to be a most reliable source for recommendations regarding their equipment given their considerable history, experience and reputation, and the fact that their unit has been a home run to-date in my system.

Tvad has been around with a lot of different equipment I believe and has a good attention to sound quality and technical details so I do not discount his observations in this area either.

I agree with your point about validity of apples and apples comparisons between amps based solely on input impedance differences as well, but I do not doubt that higher amp input impedances relative to pre-amp output impedance is one (of several) technically sound measurements that one can attempt to optimize along with but not at the expense of others necessarily as well.

Mapman, Note that I deleted the post you are responding to. Sorry about that. I was really responding to Tvads observations and was not at all pleased about what I was saying especially as it applied to you. I had already communicated all I could really offer to you in previous posts. And I saw no reason to continue the correspondence with Tvad although he is so serious I must admit that I do, sometimes, enjoy rocking his boat. He is a good guy and means well.

But, FWIW, if you can accept the accuracy of ARC's recomendations about amp matching with that pre amp, restricting your search for an amp based upon a desire for higher input impedence will not add to the performance of the amp/pre-amp combo. If the car takes regular gas and the tank is full, that is as good as it gets.

Hope you find the right amp for your Ohms.

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