First impression: Herron VTPH-2A phono preamp

Keith has said the majority of the improvement in the VTPH-2 compared to the VTPH-1 is in the MC circuit of the phono amp. For users of high output pickups (moving magnet and moving iron)---whose signal does not pass through the MC circuit---the improvement provided by the mm-2 in relation to the mm-1 is not as pronounced. That's purely academic, as the VTPHmm-1 is no longer offered, and mm-1 owners don't sell theirs!

@almarg, if you would, please help me understand your math.....I though 3 db was equivalent to 1 doubling; if that is correct(?), than I do not see how 66 db is a multiplication of ONLY 1995....my math suggests 33 db would be a multiplication of 2056....
Thx for helping me understand
J

@jw944ts
Al’s math is right. A doubling of output power to your speakers corresponds *approximately* (not exactly) to +3 decibels of increased SPL. But the gain from a phono stage is not amplifying power - it is amplifying the source signal’s voltage. When you double the voltage signal input to your power amplifier (e.g. from 0.5 V to 1.0 V), a linear amp responds by outputting twice the voltage AND necessarily twice (approximately) the current - because the speaker load (represented by R in ohms) remains constant and the law is: V = I * R. Since power is V * I (voltage times current), you end you with 4 times the output power from the doubling of signal voltage! Therefore a doubling of gain in your phono stage corresponds to (approximately) a +6 dB increase in SPL. This is also why bridging a stereo amplifier to mono nets you up to 4 times the output power, not just 2 times (assuming the power supply and heatsinks and output stage are up to task). It’s not "magic" or free power - the amp is working all that much harder to push the extra current (and be very wary of hooking a bridged amp into 4 ohm and less speakers)!

This means 60 dB of phono gain is approximately equivalent to an amplification factor of 2^10 (a 6 dB voltage doubling, 10 times) or 1,024. More exactly, 60 dB of gain is exactly equal to 10 ^ 3 = 1,000 - since 20 dB corresponds exactly (not roughly) to a voltage multiplier of 10x. The 3dB / 6 dB doubling rules-of-hand are a (close) approximation to make the math easier by tossing out some nasty decimal digits.

In short, a doubling of voltage (in most applications) results in a SPL increase of approximately +6dB; a 10x voltage amplification factor is exactly +20dB. You can mix-and-match these two shortcuts to approximate a wide range of gains. E.g. 32dB = 20dB + 6dB + 6dB = 10 * 2 * 2 = a voltage amplification factor of 40 times (decibels are added as amplification factors are multiplied).

A doubling of *power* is an SPL increase of approximately +3dB; a 10x power amplification factor is exactlyequal to +10dB. Use these shorthand rules to impress your friends with Rainman-like quick calculations :) 

Also, the VTPH-2A is a very nice sounding phono stage :)