ModWright Instruments PH 150 Reference Phonostage

Hybrid Delight

Equipment report
ModWright Instruments PH 150
ModWright Instruments PH 150 Reference Phonostage

I first met Dan Wright, President of ModWright Instruments, Inc., at the 2001 CES; introductions were made by Mark Schifter at the Alexis Park campus. At that time, ModWright was still a fledgling company, having only been founded the year before, and one of its first accomplishments was providing mods to the then very popular Perpetual Technologies P-3A DAC, as well as an equally popular power supply for that DAC, the Monolithic Sound P3. What was remarkable to me was that you could order a new PT P-3A with the ModWright upgrades already installed—and they came with a full factory warranty! Aftermarket mods supported under factory warranty by the manufacturer? Yeah, that caught my attention.

By 2003, with everything going very well, Dan took the next logical step of creating his own line of gear. That year saw the introduction of his first product, the 9.0 Series of preamplifiers, including a phono preamp. The trend to offer high-performance audio with an emphasis on quality and value continued with the release of a balanced tube linestage, the LS 36.5. The acclaimed and gorgeous KWA 150 amplifier followed in 2009, and was soon followed by the LS 100 linestage and the KWI 200 solid-state integrated amplifier.

After a long gestation period, a tube-based DAC, the Elyse, and the original PH 150 (2014) were introduced, rounding out a complete ModWright electronics system. With the introduction of the Ambrose EL34 10W SE tube amp, and the remarkable 845 DS monoblock 32W SET amps, first shown at RMAF 2015, Dan’s passion for valve designs has been taken to the next level, and convincingly so.

Over this entire period of evolution and maturation, I’ve had the pleasure of reviewing and owning a fair number of these products (starting with a CD mod in 2001). When Dan asked me if I’d be interested in giving his new PH 150 Reference phono-stage a listen, I didn’t hesitate.

At 17" wide, 12" deep, and 5" tall, and with a 19-pound main chassis, the PH 150 Reference is fairly representative of devices in its category and class. The front faceplate features a cut-out ModWright logo, backlit in blue when the unit is powered on, and centered vertically and horizontally. Two large knobs about 2" in diameter are situated to the left and right of that backlit logo, with recessed pushbuttons, each with its own indicator lamp, just below and between both sets of knobs. From left to right, you have input selection (mm, mute, mc), gain (–12dB, –6db, or 0dB), capacitance (0, 100, 220, 330, 470, and 690pF), and resistance (10, 50, 100, 200, 500, 1k ohms). The left push-button is power, the right is mono/stereo selection. I personally find it an extremely pleasing setup.

Centered vertically to the left on the rear panel are the ground lug and two pairs of single-ended inputs, grouped as right mc and mm, and left mm and mc (they are mirror-imaged). To the right side are the single-ended and balanced outputs, and the umbilical connection for the PS 150’s external power supply. An absolute-polarity toggle-switch is located toward the bottom of the chassis between the single-ended and balanced output jacks, with the output selection (RCA or XLR) toggle-switch located on the same line between the balanced output jacks.

The PH 150 Reference is vacuum-tube design that exploits the advantages of an external power supply, and is ModWright’s most ambitious phonostage to date. The heart of its design is its external solid-state PS 150 power supply. Solid-state rectification and voltage regulation were chosen over the tube rectification and voltage regulation that have been at the core of many earlier ModWright designs. The PS 150 has an 8½" wide, 10½" deep, 5" tall, 15-pound chassis, which houses the power transformer, current-regulating high-voltage choke, and both high- and low-voltage rectifiers. The supply connects to the main chassis via a four-foot-long custom umbilical featuring 8-pin locking connectors (male on the supply side, female on the chassis side). Both the umbilical connection and IEC socket are on the rear panel.

The first gain stage uses a single 6C45 vacuum tube per channel, in a tube/JFET hybrid circuit, for maximum gain and minimized noise. The choke-loaded second gain stage and final buffer stage employ one 6922 (6DJ8/7308/6922) dual-triode per channel. Coupling between the first and second gain stage and input to the buffer stage are achieved using ModWright’s own custom, oil-impregnated, polypropylene M Series Truth capacitors. Chosen because of their weight and body, the M Series caps contribute notably to the ModWright “house sound.”

The PH 150 Reference ships with Sovtek 6C45s and Electro Harmonix 6922s. The 6C45 is an indirectly heated triode that has been designed for wideband amplification of high-frequency voltage, and is arguably the finest and latest expression of small-signal triode technology. Both tubes were selected for their medium-high mu (voltage gain) and low plate impedance, and because they can deliver a lot of current. The 6922 is a heater-cathode type double-triode designed for cascode circuits as a low-noise, broadband audio-frequency amplifier.

In the buffer stage, the output is direct-coupled to a Lundahl gapped output transformer, with a selection of different secondary windings providing either unity gain or 6dB of attenuation. The final 12dB of attenuation is achieved using a simple voltage divider.

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