Technical Features of the Artemis Labs PH-1 PhonoPreamp
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V4 |
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6N1P |
1/2 12AX7 |
1/2 5687 |
+160V |
+250V |
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Lundahl |
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Power |
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500H |
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choke |
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Power Supply |
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Right |
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(unregulated) |
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Outputs |
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Right |
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1 |
1 |
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Features: |
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1.5V |
1 |
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Input |
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- Electrostatically- |
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N or AM-5 |
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2 |
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Line voltages |
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2 |
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shielded transformer |
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available: |
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- High-speed rectifiers |
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100V, |
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3 |
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2 |
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- High-temperature |
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3 |
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110V, |
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(105°C) electrolytics |
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47.5K |
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120V, |
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+6V |
220V, |
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230V, |
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240V |
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50 or 60Hz |
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V3 |
V5 |
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V1 |
V2 |
V3 |
V4 |
V5 |
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1/2 12AX7 |
1/2 5687 |
+160V |
5 |
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5 |
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8 |
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8 |
8 |
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8 |
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4 |
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TexTool® |
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Lundahl |
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"ZIF" Socket |
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500H |
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for R or C |
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choke |
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Artemis Labs |
loading |
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Outputs |
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Left |
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6 |
9 |
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+250V |
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40 second |
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PH-1 Phono Preamp |
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Left |
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Delay |
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1.5V |
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1 |
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Simplified Schematic |
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Input |
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7 |
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N or AM-5 |
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7 |
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+163V reference |
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8 |
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2 |
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8 |
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47.5K |
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Muting relay |
4 second |
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control |
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Delay |
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Gain |
RIAA Equalization |
Gain |
Muting & Output |
Low-Gain Regulation |
Power Supply & Time Delays |
Low-noise first preamp stage with battery bias
With typical signals at the microvolt level, the first amplifier stage is extremely critical. Parts are chosen carefully for low noise and minimum low-level nonlinearities. To get around the problems of cathode biasing and the typical electrolytic capacitor, fixed bias using a single “N” alkaline cell is employed. Being in the grid path, virtually no current is drawn, letting the battery last for at least several years. Unlike circuits where the battery is in the cathode, any imperfections or non-linearities in the battery are not manifested by the tube’s current flow.
The plate supply for the first stage is filtered by an R-C filter using a 15µF polypropylene capacitor. This insures minimum noise without the sonic degradation of electrolytic capacitors.
Extended high-frequency response
Many phono preamps’ response drops quickly above 20KHz. The PH-1 maintains its RIAA equalization to above 40KHz, important for high-resolution playback systems and for use with 96KHz digital systems.
Passive RIAA equalization using hand-selected capacitors
By using passive equalization the problems of feedback equalization are eliminated: slew-rate distortion, deviation of equalization curves at high frequencies, and
instability problems. To permit flat equalization to within +/-0.2dB, the capacitors in the equalization network are pairs that are hand-selected on a precision impedance bridge to better than +/-0.5% accuracy.
Single-triode output stage with choke loading
The Artemis Labs PH-1 uses a single 5687 medium-mu, low resistance triode as the final amplifying device for each channel. The 5687, originally designed by Tung-Sol for military and industrial uses, has excellent linearity, and in the mil-spec version, excellent unit-to-unit consistency. Its low plate resistance allows it to drive heavy loads without the use of a cathode follower stage.
The use of an inductor (choke) load instead of a conventional plate resistor offers several significant advantages to the PH-1 design. A good-quality audio choke is essentially a perfect current source, allowing the triode to operate into an infinite-resistance load, giving the lowest distortion. Unlike semiconductor constant-current devices, an inductor is an energystorage device. This allows the plate voltage to swing 100% above the B+ plate supply voltage, doubling the “head-room” and allowing a lower B+ supply voltage to be used, reducing power consumption. This permits an output of over 40 volts rms before clipping.
The audio chokes used in the PH-1 are made by Lun-
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