INPUT/OUTPUT IMPEDANCE

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

I love the way people remove posts after asserting something truly ridiculous creating "plausible deniability"...lol