Just going to copy and paste Keiths very informative email response to my question about the Herron phono stage. Obviously he is a true Gentleman as Slaw stated and would not see me disapointed in any way!
Hi Kevin,
Thanks for the note. I like to see, as a general rule in high end
audio, an impedance ratio of at least 1 to 100 (output impedance
to input impedance) when using tubes or solid state as loading the
circuits down generally reduces the quality of the sound. I have
seen similar impedance ratio recommendations from Audio Research
and other high end audio companies.
Solid state circuits generally have much lower output impedances
than tube circuits. 10k Ohm input impedances are a standard
typically used in professional audio, but this does not work as
well for tube based high end audio equipment.
The two 12AX7, three 12AT7 version of our VTPH-2A has an output
impedance of 400 Ohms which performs best into a 40k Ohm or higher
line stage input. Some people are using them with line stage
inputs that are a little less than that with reasonable results,
especially if their cartridge has a lower output voltage. Your
integrated with a 10k or 5k single ended input would likely
restrict dynamics substantially, even with a very low output phono
cartridge. I can't recommend that combination. Audio is supposed
to be fun.
Another thing to watch for is that some line stages (particularly
digital ones) have a very low input voltage limitation which can
cause overload (clipping) with some analog sources. That can sound
nasty.
For the reasons above I design our line stages with a 100k Ohm
input impedance and a wide input voltage margin in order to get
the best sound quality from tube based sources such as phono
stages, tape machines, tuners, and DACs with tube output stages.
I wish everyone would do that.
I hope this short explanation helps.
Best Regards,
Keith
