Luxman P-700u Fully Balanced Headphone Amp

In 2002 Luxman introduced the P-1, their first class A headphone amplifier.

2008 saw the introduction of the P-200—a more modest offering.

2009 saw the introduction of the P-1u, a ground up fresh design with ODNF 2.1.

2013 saw the release of a reference quality, fully balanced pure class A headphone amplifier—the P-700u.

Luxman went back to the drawing board to develop a true reference headphone amplifier. Using the best materials on hand as well as implementing their best technology , the P-700u is the finest headphone amplifier that Luxman have ever made by a wide margin.

The P-700u is a fully balanced design that incorporates four channels of the LECUA 1000-WM high precision electronically controlled attenuator and incorporates the latest revision of ODNF 3.0A audio circuit . This compact version of the LECUA 1000-WM volume control (Luxman Electric Controlled Ultimate Attenuator with Weight Matrix Technology) is configured to electrically block electromagnetic (EMI) and radio frequency (RFI) interferences. The output signal is attenuated without introducing artifacts inherent in conventional volume controls, thereby resulting in constant output impedance, high signal-to-noise ratio, a uniform frequency response and lower distortion.

LECUA Volume Control

This is Luxman’s first pure class A headphone amplifier to benefit from the C-1000f in that they use a variation of the LECUA 1000 volume control. At any single volume setting, only a few resistors are in circuit per channel. The less devices in the signal path, the purer the sound, the cleaner the music.

At low listening levels, potentiometers have trouble keeping both channels in balance, so one channel might easily be 3dB louder than the other. With the volume control made of discrete parts, this is no longer an issue.

The ODNF circuitry is incorporated into the design so that both radio frequency interference and electro-magnetic interference can be blocked and stopped from polluting the delicate audio signal.

There are four discrete channels as it is a fully balanced design, which rejects noise from polluting the audio signal.

Amplifier

The amplifier section has not been ignored either; noise and distortion has been kept to a minimum with the introduction of ODNF version 3.0A. The deep, rich Class A tone is available here is Luxman’s hall-mark sound. More info on ODNF below.

Pure Copper Cabling

Extensive listening was applied to the high purity, oxygen free copper (OFC) cables which are used to transmit the signal throughout the amplifier. These cables have a minimal audible signature and minimal electrical effect on the audio waveform. Linear wide bandwidth frequency response is achieved by the low measured values of both inductance and capacitance. The result, the cables do not color the sound, but pass it through, quickly.

ODNF 3.0

Luxman holds many patents for audio engineering, amongst them is the application of Global Negative Feedback to the output stage, which while widely used throughout the audio industry, they no longer use themselves.

Luxman nowadays use a distortion reduction circuit called Only Distortion Negative Feedback (ODNF). This system works by isolating noise & distortion at the output from the music signal and sparingly applying negative feedback to suppress them. Conventional negative feedback systems can have an adverse effect on the music, introducing phase distortion. “The circuit features such an ultra-wide range, ultra- high slew rate and ultra low distortion that it does not use phase compensation for the music signal amplifying circuits.” This new technology also ensures that need for a DC servo circuit is alleviated, again improving sound quality.

Now with version 3.0 three different monitoring passes are made of the audio signal, to eliminate any noise or distortion in the music signal. It results in a lower noise floor of about 2 dB, giving you blacker silence between the notes and a more dynamic performance.