Tholt, I agree. VAC may state an output impedance of 350, but it doesn't tell
the whole story because output impedance varies with frequency. Output
impedance may be significantly higher in the lower bass frequencies, which
would correspond with weak or rolled-off bass that you're hearing.
If you read the test measurements section of a couple of Stereophile reviews of
preamps (tube or solid state, but particularly tube), you'll see verification of
preamp output impedance changing with frequency. It's common, and it
explains why some tube preamps that have low output impedances published by
the manufacturers sometimes don't match well with solid state amps.
The bottom line is the VAC likely doesn't match your amp based on your
comments. The AH will cost you only shipping to test it in your system. Isn't that
worth the experiment?
