L-7000 Preamplifier

The 300B has justly won the reputation for being a superb output tube in single-ended amplifiers. But it will take some rethinking to imagine this great tube in a non-audio role. The benefit the 300B brings to as a voltage regulator is its ability to pass a fair amount of current at low cathode-to-plate voltages, the result of having a low Rp.

The L-7000 offers world class, holographic sound-staging combined with incredible resolution, clarity, micro-dynamics, and drive. Instrument and vocal tone and timbre are lifelike; placement of instruments and bodies in three dimensions startling, life-size, and addictive. The L-7000 has no voice of its own. It is silent, except for the music emanating from the blackest of backgrounds. The outstanding sonic quality is matched by the simple elegance, flexibility and ergonomic functionality of the casework and connection options. Few pre-amplifiers can compete. The L-7000 is, simply, a revelation.

The L-7000 is Allnic Audio’s reference line stage pre-amplifier. Like all Allnic Audio products, it uses permalloy (iron and nickel alloy) for its transformer cores. Allnic is grateful to Mr. G.W. Elmen of We stern Electric for inventing permalloy for transformer core use, and in so doing, providing an enormous service to recorded music listeners everywhere.

The L-7000 has the following features:

• DHT 300B as a series voltage regulator. The benefit the 300B brings to a voltage regulator is its ability to pass a fair amount of current at low cathode-to-plate resistance, the result of having a low voltage drop.
• True Dual-Mono design. Each of the two channels operates completely independent of the other. The chassis, attenuator control and the AC power connection are the only parts of this pre-amplifier that both channels share.
• Single gain stage. A single gain stage circuit uses only one tube for amplification (“gain”). This reproduces a purer, more detailed, more spacious and more dynamic sound than multiple gain stages.
• Line output transformer coupling. The L-7000 is “transformer coupled”. In tube amp circuitry, there are two coupling methods; one is capacitor coupling and the other is transformer coupling. Capacitor coupling is the traditional, low cost method. It is somewhat stable but transfers only voltage, not wattage (i.e., not real energy). With transformer coupling, about 90% of real wattage is transferred (there is still a transformer loss of about 10% of wattage, while voltage is not affected).
• In-house transformer manufacturing and transformer/tube matching. While transformer coupling is superior to capacitor coupling, all the advantages of transformer coupling depend on the quality of the transformer and on the choice of tubes. Allnic Audio manufactures its own transformers and uses what it views to be the best core material, permalloy. Allnic Audio’s unprecedented, wide (16 Hz ~ 50 kHz, -3db), low distortion, and ultra-flexible (up to 20 kHz square wave response) output transformer helps Allnic Audio to realize the ideal transformer coupled pre-amplifier. Of course, gain tubes are also carefully selected for three critical factors for function with the permalloy output transformers: high gm, low internal resistance and high mu.
• Power supply circuit with under 1% voltage regulation. The voltage regulation of the transformer is the percentage change in the output voltage from no-load to full-load. To get the best performance out of your transformer, you need the lowest possible voltage regulation. The voltage regulation of Allnic’s power supply circuit is under 1%. It yields an improved power transfer and lower regulation factor, resulting in increased current speed and better dynamics.
• Constant and low output impedance. One of the benefits of transformer coupling is that it facilitates constant low output impedance. Low output impedance is critical to the design of a good pre-amplifier. The L-7000 has a 150ohm (150Ω) constant output impedance at all frequencies. In capacitor coupling (C-R coupling), a “cathode follower circuit” is usually used to lower output impedance. Unfortunately, this method of lowering output impedance is accompanied by high distortion and has an “L” shaped output impedance curve.