INPUT/OUTPUT IMPEDANCE

Although the output impedances of the AV7705 appear to not be specified by the manufacturer, according to a post I found at another forum those numbers are 800 ohms (RCA), and 200 ohms per leg (XLR, which means 400 ohms for the XLR outputs per the usual way of defining balanced impedances).

Those are the kinds of numbers I would expect for this type of product. And given that it is solid state the output impedances are unlikely to rise significantly above those numbers in the deep bass region (as happens in the case of many tube-based preamps, which can result in rolloff and/or undesirable phase shifts at low frequencies when the load impedance is too low), or at any other audible frequency. So given the input impedances of the power amp you stated the bottom line is no problemo!

Enjoy! Regards,
-- Al

Thanks to both for the quick response! Much appreciated. Now, I just need a head shrink for the Audiophelia Nervosa I have... 

The 1:10 ratio does matter as you want to minimize voltage loss at the load input. With most amps/preamps on the market this isn’t an issue because they conform. But to claim this should be completely ignored or best forgotten is nonsense. Last year I was discussing with Keith Herron whether he felt the VTSP-360 would be a good match with my amp and the FIRST thing he wanted to know was the input impedance of my amp. Why would an audio component designer/manufacturer ask a question like that if it didn’t matter at all and was completely unimportant?

antho768 OP
I don’t want to over think this, but I just pulled the trigger on a power amp rated at 10k(RCA) 15k(XLR) input impedance. Problem is I don’t know the output impedance of my pre/pro(Marantz av7705).

The 7705 being solid state "should" be fine into that 10kohm load.

Cheers George

The 1:10 ratio does matter as you want to minimize voltage loss at the load input.

Very true, of course. However in itself that voltage loss would only result in a very slight reduction in overall system gain. A much more significant issue arises if the output impedance varies significantly as a function of frequency, AND does not satisfy the 1:10 ratio at all frequencies. In that situation the result can be both frequency response irregularities and undesirable phase shifts at some frequencies.

As George alluded to that is most likely to be an issue in the case of tube-based components, many of which use a coupling capacitor at their outputs. The impedance presented by a capacitor increases as frequency decreases, so the output impedance in the deep bass region can be much higher than the specified output impedance, which is usually based on a mid-range frequency such as 1 kHz.

To cite some examples, Audio Research recommends a minimum load impedance of 20K for almost all of their line stages and preamps, and 60K in the case of a few older designs. And the manual for the fantastic Herron phono stage recommends a minimum load (line stage input impedance) of 50K "for optimum performance," although I recall a member here stating that Keith Herron verbally indicated that 20K is likely to be satisfactory for most users.

Regards,
-- Al