VTPH-2A Vacuum Tube Phono Preamplifier

VTPH-2 Front Panel
VTPH-2 Back Panel

Unconventional Magic!

Totally unique circuitry configuration and layout that extracts high end performance from the tubes and extends tube life.

Immediately You Know!

"Pick up an acoustic instrument and the better it is, the greater the sense of life, of energy just waiting to burst forth. This is exactly the quality that the Herron phono-stage captures. All that texture it brings to instruments is built on micro-dynamic definition and the ability to capture the harmonic envelope, the pattern of energy that extends from instruments."

"The colour and ability to reveal each step in the growing intensity of a crescendo mark out the beautiful balance that the VTPH-2 strikes between the instrumental detail that gives music its beauty and the body and presence that gives it its drama and so much of its passion."

"The Herron VTPH-2 gives listeners all the benefits of a tube unit with few of the failings and a text-book technical performance to boot. It offers a level of vacuum-tube engineering (carefully combined with solid-state circuitry) that's rare at any price, unheard of at this one."
- Roy Gregory hifi+ issue 58

The Herron VTPH-2A Phono Preamplifier was created to address the retrieval of musical information from vinyl LPs without any compromise. The original design was only intended for use by a few dedicated music lovers in their cutting edge audio systems. The design was so good, and demand so high, that the unit was refined and engineered to meet the requirements for a more durable unit manufactured in larger quantities. In the process, important refinements were developed and discoveries were made about tolerances and the threshold of human hearing limits.

VTPH-2 loading resistors
external MC load resistor RCA plugs

Separate moving coil and moving magnet inputs

The Moving Coil "MC" Inputs:

The moving coil inputs have an additional 22 dB of gain which is provided by a proprietary FET very low noise linear gain stage connected directly to the MC inputs. The moving coil FET gain section is connected in front of the tube section when the unit is in the MC mode. This moving coil FET gain section has been designed specifically to avoid the sonic artifacts found in many solid state designs.

Moving coil loading RCA resistor plugs can be inserted into the back of the VTPH-2A at the "MC Load" connectors to properly load specific moving coil cartridges. Check with your cartridge manufacturer for recommended loading.

The Moving Magnet "MM" Inputs:

The moving magnet inputs send the cartridge signal directly to the tube section and bypasses the MC FET gain stage. The moving magnet inputs provide all tube amplification of the signal from the cartridge. The moving magnet inputs have an internal 47k Ohm loading resistor for each channel and 100pF "Miller Effect" loading capacitance which is provided by the grid of the first 12AX7 tube.

Cartridge Loading:

The moving coil inputs can be loaded to a particular cartridge specification by externally connecting the appropriate resistors using the "MC LOAD" RCA connectors on the back of the unit, or they can be internally soldered at the MC INPUTS circuit board (this should only be done by a competent technician).

Why loading plugs instead of dip switches?

Reason #1:

When using DIP switches the sound quality will degrade with time and potentially become grainy and bright as unwanted harmonics are added due to contact nonlinearity.

Mechanical switch contact resistance (which is nonlinear with voltage) can be in the order of magnitude of the loading resistor itself particularly at the very low voltages which are generated by a moving coil cartridge. The music information can be down in the range of nanovolts. This problem will be exacerbated with time as the DIP switch contacts which are open and not sealed are exposed to air will develop oxidation and layers of contamination from environmental humidity and air pollution.

Note A: The VTPH-2A uses electronic switching for audio signals when changing from moving coil to moving magnet mode. This is initiated by one mechanical switch which does not carry any analog audio signals.

Reason #2:

So we spent how much on that cartridge and turntable and we load the cartridge with DIP switch contacts and only the resistors that are connected to it?

External loading plugs allow the user to hand pick the resistor brand and type if he or she is so inclined. Yes, resistor brands and types do sound very different. In a way this is comparable to tube rolling.

Reason #3:

The "infinite loading" option.

The VTPH-2A will not load the cartridge at all if no loading resistors are plugged into the MC loading inputs. This is because the moving coil input stage of the VTPH-2 utilizes the electric field generated by the cartridge to amplify the voltage and no current is drawn from the cartridge (there is no load on the cartridge). This can give an extended sense of dynamic freedom and sound stage as it reduces the work done by the cartridge and cartridge/groove interaction.

Note B: Some cartridges will need loading in order to reduce their inherent rise in high frequency response.

Reason #4.

You don't have to get inside the unit to change the loading, you can do it while you are listening in order to get a immediate and real sense of how the loading changes the sound.

The moving coil inputs can be loaded to a particular cartridge specification by externally connecting the appropriate resistors using the "MC LOAD" RCA connectors on the back of the unit, or they can be internally soldered at the MC INPUTS circuit board (this should only be done by a competent technician).

The moving coil inputs have no load resistors installed unless specified by the customer when the unit is ordered from Herron Audio. We recommend trying the VTPH-2 in the no-load configuration as the unit is supplied for most moving coil cartridges. 47,000 (47k) ohm RCA load plugs are supplied with the unit for optional use. Additional user specified loading plugs can also be purchased with the unit.

The moving magnet inputs are factory loaded at 47,000 (47k) ohms, 100pF (standard loading for moving magnet cartridges).

Herron VTPH-2A Vacuum Tube Phono Preamplifier Features

Tube complement (2 x 12AX7, 3 x 12AT7) - most popular, or
(4 x 12AX7, 1 x 12AT7)
Gain MC Mode (2 X 12AX7, 3 X 12AT7) 64 dB
(4 X 12AX7, 1 X 12AT7) 69 dB
Gain MM Mode (2 X 12AX7, 3 X 12AT7) 43 dB
(4 X 12AX7, 1 X 12AT7) 48 dB
Frequency response RIAA 20 Hz to 20 kHz ±0.1 dB
Signal-to-Noise Ratio 88 dB, A weighted
Output impedance (2 X 12AX7, 3 X 12AT7) 400 ohms
(4 X 12AX7, 1 X 12AT7) 500 ohms
Input impedance Infinite with no load resistors connected
Note: load resistors can be connected externally via RCA connectors or soldered internally
Absolute polarity Non-inverting (all modes)
Power Requirements Standard IEC connector - most international voltages available
Overall dimensions 17.6" wide x 4" high (including rubber feet) x 10.25" deep
Warranty 3 years, parts and labor; tubes: 90 days
U.S. Retail Price $3,650 U.S.D.

NOTE: The VTPH-2A is an improved version of the VTPH-1 single input version which was reviewed by Stereophile in March of 2000

Stereophile: March 2000, Vol.23 NO.3 Herron Audio VTPH-1 Phono Stage

"It's competitive with anything I have rated 'Class A.'"
- Michael Fremer

"It was a pleasure to measure such a well-engineered phono stage."
- John Atkinson read the review

Copyright © 1996 - 2017 Herron Audio. All rights reserved.
Herron Audio, div. of Herron Engineering, Inc.
12685 Dorsett Road #138, Maryland Heights, MO 63043 U.S.A.
phone: 314-434-5416