Einstein Little Big Phono impedence match with Pass XP20


     The output impedence for the Einstein Little big phono is specified @ 50 ohms; the SE input impedence on the Pass XP20 specifies 48K.
     Will greatly appreciate advice about their compatibility.
rost
No problem whatsoever.

It is commonly stated that to assure impedance compatibility for a line-level interconnection the input impedance of the component receiving the signal should be at least 10 times as great as the output impedance of the component providing the signal. That is a somewhat misleading oversimplification, though. I would state the rule of thumb guideline as follows (I’m quoting this from a post I made in another recent thread):

The input impedance of the amp (or other component that is receiving a line-level input signal) should be at least 10 times the output impedance of the preamp or line-level source component that is driving it, at the frequency within the audible range for which that output impedance is highest. Which in the case of preamps or source components having capacitively coupled outputs (such as the majority of tube preamps) will usually be at 20 Hz. And the output impedance at that frequency will often be far higher than the specified output impedance (which is usually based on a mid-range frequency such as 1 kHz), because the impedance of a capacitor rises as frequency decreases.

That doesn’t mean that there will necessarily be a problem if the guideline is not met. It depends on how the output impedance **varies** as a function of frequency. What it means is that there **won’t** be an impedance compatibility problem if the guideline **is** met.

If Stereophile has reviewed the preamp or source component, the measurements section of the review will usually indicate the output impedance at 20 Hz as well as at other frequencies. But if only a nominal impedance can be determined, such as a manufacturer’s specification that is presumably at a mid-range frequency, to be safe I would suggest a ratio of 50x or preferably even 75x.
In this case the ratio is nearly 1000x (48K is 48,000 ohms), so impedance compatibility is not an issue.

Regards,
-- Al

You´ve been very helpful Al,
thanks.