Last year we were approached by a seasoned audiophile to create our best effort at a phono preamplifier to be used in the high resolution digital archiving of his collection of several thousand classical LPs. A protoype phono preamplifier that used the same basic circuitry as our premium Tube Repro tape head preamp (used by subscribers to eke out the last ounce of musical passion from their Tape Project albums) was sent to the client for audition. A commission was received for a phono preamplifier of the same high standards with the additional flexibility to properly reproduce not only LPs with standard RIAA playback equalization but also LPs from the pre-RIAA days with their various record label specific EQs.
The result was a phono preamp that exceeded our expectations, and we decided that we should make the design available to the high end audio community. The added equalization curves were deemed of interest to a very specialized group of audiophiles and so for this production model we repurposed the space in the chassis that held the very sophisticated multiple EQ switching arrangement to hold instead the very best sounding RIAA network components that we could find (and by the way, we would be happy to build either version for our clients).
The Tube Phono’s hand wired circuit is designed to keep the signal as pure and uncolored as possible, while avoiding the harsh and sterile sound that can come from some gear that claims “great detail and speed”. EF86 pentodes are used at the input, chosen for their high gain, low noise and sweet sound. The signal passes thru a direct coupled passive equalization network to a 6DJ8 type dual triode. From there the signal can be taken at the single ended RCA outputs. To achieve a studio level balanced output the signal passes through a 12BH7 gain stage to balanced transformer XLR outputs.
The power supply utilizes two power transformers and a hybrid tube/solid state shunt regulator for each channel which tightly regulates the high voltage, giving a sense of bandwidth and separation unparalleled by other means of power supply regulation. Each signal tube is isolated from power supply noise by a Camille Cascode Constant Current Source, giving the sound a black background and bringing the dynamics to an elevated level of realism. Premium quality components are utilized throughout, Schottky diodes, premium Panasonic electrolytic capacitors, high quality V-Cap Teflon and polypropylene film capacitors, and a range of premium resistors from tantalum to metal film to carbon composition, each one chosen for optimal performance in the job at hand. Left and right 1/4dB stepped attenuators are accessible from the top panel to allow for fine balance trim between channels to compensate for tube differences. Tubes are socket mounted on the recessed top panel to allow for quick and easy changes to suit the listener’s taste.
And like the Tube Repro, each Tube Phono is hand built to order by one of our senior technicians. Input impedance is 47K ohms, output impedance at the single ended RCA outputs is 4K ohms, output impedance at the balanced transformer XLR outputs is 500 ohms. Gain at the single ended output is 50dB, gain at the balanced transformer output is 64dB. Channel balance trim is adjustable in 1/4dB steps to a maximum of 6dB. Signal polarity is not inverted. Moving magnet cartridges and high output moving coil cartridges of 2mV or higher output are recommended for direct connection to the Tube Phono. Low output moving coil cartridges should be used with a step up device between the cartridge and the Tube Phono input to maintain the lowest possible noise floor.
The Tube Phono is available only by custom order. Call us at 206-451-4275 to discuss pricing and options.