First impression: Herron VTPH-2A phono preamp

almarg

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

that the manual recommends 50K or more as being optimal