The VTPH-2 has, essentially, two gain sections: a FET front-end used only by the MC circuits, and tubed gain stages used by both the MC and MM sections. "But there's also a passive RIAA section that constitutes an equalization stage between the tube stages," Herron said. He came up with the idea a dozen years ago, but then it was a matter of designing a circuit and finding good parts for it. He goes through thousands of capacitors for his phono stages, using perhaps two out of every hundred to get the RIAA equalization precisely right. For the tube gain stages, Herron looked for suppliers that could provide tubes in decent quantities, then printed out several hundred pages worth of tube layouts in order to document the comparisons of different tube combinations and circuits. Only then did he decide on which tube complements to use.
The VTPH-2 has two basic complements of five tubes each, meaning that the model is produced in two versions. The 69dB version uses four Ei 12AX7 and one Ei 12AT7 output tube, and the 64dB version uses two Svetlana 12AX7s, two Electro-Harmonix 12AT7s, and one Ei AT7 as the output. (My review sample was the 64dB variety.) This is why Herron doesn't recommend tube-rolling for his gear: he chose his stock tube types to work together to create the exact sonic balance and quality of transparency he's looking for -- "the sound of no sound," as it were.
The cartridge plugs come in pairs -- my sample came with two sets, in values of 47k ohms and 100 ohms. The VTPH-2 is delivered with no load resistors installed; Herron recommends that it be run wide open for the first 100 hours or so. After doing that, I tried both sets of loading plugs and found the 100-ohm value to be best for my Shelter 501 Mk.II cartridge and for many of my recordings, especially those saturated with upper-mid and high frequencies, such as choral music, or orchestral music with massed strings. The 47k ohm plugs had little effect, though they didn't seem to harm anything either. In general, jazz and pop seemed to need the 100-ohm plugs to tame the highs so they didn't sound overdriven, but classical LPs could sound good run wide open or with the 100-ohm plugs, depending on the recording. Herron will send you a set of 47k ohm plugs, or a set based on the recommendations of your cartridge's manufacturer.
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