Amp preamp impedance matching...can anyone explain?

Onhwy61, that would apply to situations where the component providing the signal is specifically designed to be able to drive 600 ohms, without a significant increase in distortion or a significant impact on bandwidth or frequency response.

Most consumer gear will not meet those requirements. I believe that Atmasphere is a notable exception. According to posts Ralph (Atmasphere) has made in the past, a benefit that would result from loading the balanced outputs of his preamps with a low impedance like 600 ohms is minimization or elimination of cable effects and cable differences.

Best regards,
-- Al

Onhwy61, I think(?) I remember Jeff Rowland espousing such a philosophy. I also seem to remember(?:-)) past Audiogon contributor Sean suggesting the same thing. Some years ago Dave Wilson writing in The Absolute Sound offered a tiered approach to impedance matching.

Thanks Almarg. What sort of frequency response irregularities?

I have a CJ PV-5 (only thing I found was a post saying 200 ohms output impedence) and Marantz 8B (and Mac MC240 and MC30s but listening to the 8B). I am considering trying a SS amp and considering B&K ST-140 (24Kohm input impedence), Aragon 2004 MkII (22Kohm), and McCormack DNA .5 or 1 (100Kohm).

Regarding:

If, as is often the case, the highest output impedance of the preamp across the audible frequency range is not known, and only a nominal output impedance is specified (perhaps based on a frequency of 1 kHz), I suggest using a ratio of 50 or more, and preferably 75. Many tube preamps, and some solid state preamps, use a coupling capacitor at their outputs, which can cause their output impedance to be much higher at deep bass frequencies than at higher frequencies.

....for the gear I mentioned, do you think I need to worry about the 50:1?

Thanks very much,
Jim

07-11-12: River251
Thanks Almarg. What sort of frequency response irregularities?

If I may be allowed to chime in - like Almarg wrote "Many tube preamps use a coupling capacitor at their outputs, which can cause their output impedance to be much higher at deep bass frequencies than at higher frequencies". So, the preamp output impedance is usually not a constant. It's often lower in the mid/hi freq & higher at bass freq. When higher in the bass freq, you *might* see a loss of signal power from pre to power + the loss of control by the power amp of the bass region. The listener usually perceives this as flabby/bloated bass.
I know that a friend of mine experienced this with a highly regarded preamp that had 600 Ohms output impedance while his power amp had 10K input impedance. It was a bad match & the preamp was sold off immediately.

I have a CJ PV-5 (only thing I found was a post saying 200 ohms output impedence) and Marantz 8B (and Mac MC240 and MC30s but listening to the 8B). I am considering trying a SS amp and considering B&K ST-140 (24Kohm input impedence), Aragon 2004 MkII (22Kohm), and McCormack DNA .5 or 1 (100Kohm).

from my personal experience this should not be an issue. My preamp has 200 Ohms output impedance & my power amp has 10K input impedance. The 2 units mate up very nicely across the entire audio freq range.
FWIW.

Thanks for chiming in, Bombaywalla, and saving me some time :-)

I found some information specific to the CJ PV-5, though. The schematic and parts list can be found here. It can be seen that the output coupling capacitor is two capacitors in parallel, totalling 2.35 uF. At 20 Hz, that corresponds to an impedance of 3388 ohms, based on 1/(2piFC). (That figure will be vastly lower at mid-range and treble frequencies, consistent with the 200 ohm nominal output impedance). It is most likely safe to assume that the overall output impedance at 20 Hz will be just a little higher than the impedance presented by the capacitors at that frequency, so let's call it 3500 ohms.

22K/3.5K and 24K/3.5K are ratios that are between 6 and 7, lower than the ideal of at least 10. So there may be a slight impact on the deepest bass frequencies, which may or may not be perceptible depending on the deep bass extension of your speakers, and on room acoustics. If your speakers have good deep bass extension, my instinct would be to play it safe and avoid the B&K and the Aragon, although it's a close enough call to be debatable.

Regards,
-- Al