Amp preamp impedance matching...can anyone explain?

Thanks for clearing this up here...

07-19-12: Dracule1
I have a tube DAC that uses a single 6SN7 tube with 1 microfarad coupling caps. I was told it has 8 kohm output impedance.

that is correct. impedance at 20Hz = 1/2*pi*20Hz*1e-6 = 7957.7Ohms, which could be rounded up to 8KOhms. The manuf wasn't lying! ;-)

I wanted to get this integrated SS amp but the input impedance is 10 kohm. So this is a horrible match, so I stayed away.

right again! a horrible match down the in bass region. Your system would have sounded tinny. So, good thing you stayed away.

But I really wanted that SS integrated.

better put a lid on that desire while you have this particular tube DAC! ;-)

Does the voltage gain play into this at all? The amplifier I am using is a McCormack DNA-125, which has 30db of gain. Its input impedance is 100 kOhms. I am using an Audio Research SP8 MkII preamplifier with it which has an output impedence of 1,000 ohms.

I had Audio Research lower the gain in my SP8 recently, but needless to say, the volume through my Vandersteen 3A Signatures still gets loud in a hurry.

I was wondering if someone could please recommend a low gain, solid state Audio Research amplifier that is rated between 100-200 watts per channel? I do not want a tube amplifier, and I do not want to get rid of the wonderful SP8 MkII.

07-24-12: Distortions
Does the voltage gain play into this at all?

No, gain and impedance compatibility are two separate issues, although if the amplifier's input impedance is too low in relation to the preamp's output impedance (which it is not in this case) there will be a very slight reduction in overall gain.

I see that in stock form, prior to the recent modifications, your preamp had a line stage gain of 26 db. That in combination with the amp's 30 db gain, as you realize, is way too high, especially if you are using a digital source having the typical full scale output of 2 volts or so.

I see that you have another thread in progress on amplifier replacement and other possible approaches, and you've already received an intriguing input from Steve McCormack himself!

Regards,
-- Al

I have a Pass X250.5 amp whose input impedance is 22 kOhms. I've been reading about tube preamps, specifically the ARC Ref 3 (output impedance 600 ohms balanced) and Cary slp-05 (output impedance 500 balanced), both of which seem to draw comments that they wouldn't be good matches with Pass amps because of the low input impedance of the Pass amps.

So I went on the Pass website and see that the XP10 and XP20 preamps have output Impedances (for balanced) of 1,000 ohms! Presumably, these two preamps are ideal matches with my X250.5 amp, but if I do the math, how is an XP10/XP20 with 1000 ohms output impedance a good match for the X250.5 when an ARC Ref 3 with 600 ohms output impedance is considered by some to be a bad match? 22000/600=37 for ARC and 22000/1000=22 for Pass XP10/XP20

What am I missing or not understanding?

Lpw