Description

EIZZ LP305 — Reference valve preamplifier

The engineering of the invisible

The EIZZ LP305 is a reference valve preamplifier conceived with a very specific purpose: to preserve the musical signal without imposing an artificial sonic personality.

Its direct-coupled interstage architecture, volume control via relays and precision resistors, and separate 340 V linear power supply work together to deliver transparent, quiet and extraordinarily stable reproduction.

It does not aim to use the valves to add exaggerated warmth. Its purpose is to harness their natural linearity, dynamic capability and second-order harmonic richness to achieve an open, fluid and fatigue-free sound.

Direct-coupled valve architecture

The first stage uses two E180CC valves — also known as 7062 — connected in parallel. This high-transconductance industrial valve was originally developed for broadband and pulse amplification applications.

The output stage employs two E80CCs working as high-current cathode followers. Thanks to this configuration, the LP305 achieves an output impedance of just 15 Ω, allowing it to drive both valve and solid-state amplification with authority.

Direct coupling between stages eliminates intermediate capacitors from the signal path, avoiding phase shifts and the loss of information associated with conventional dielectrics. A 4.7 µF, 400 V polypropylene MKP capacitor is used at the output to protect the power stage against any direct current component.

Volume by relays: precision without potentiometers

The LP305 replaces the traditional mechanical potentiometer with a precision resistor array selected via sealed relays.

Each press changes the volume in 0.5 dB steps, maintaining a channel matching of less than 0.01 dB and a constant input impedance of 100 kΩ.

The slight click heard when changing the volume is the normal operation of its silver contact relays. Once the command has been executed, the microcontroller enters a complete sleep state to prevent the digital clock from contaminating the delicate analogue signal.

separate linear power supply

The power supply is housed in a separate chassis to keep the transformer and main electromagnetic fields away from the audio circuitry.

Its active regulation system provides an extremely stable voltage of 340 V. It incorporates a 150 W EI-type linear transformer, rectification via ONSEMI Schottky diodes, multi-stage filtering and a regulated power supply for the heaters.

Raising the filament voltage to +170 V reduces the leakage currents between the filament and the cathode, eliminating the characteristic 50 Hz hum that can affect certain valve designs.

The result is an exceptionally quiet background, with a stated signal-to-noise ratio of 107.26 dB and a dynamic range of 125.01 dB.

Four inputs and remote control

The rear panel features four RCA inputs selected via high-isolation Panasonic relays. Each time the input is changed, a brief mute is automatically activated to prevent noise or distortion in the speakers.

The LP305 allows remote control of the main functions:

• Input selection.
• Volume up and down.
• Complete silence.

During start-up, the circuit keeps the outputs switched off whilst the valves reach their operating point. Once the initial cycle of approximately 60 seconds has elapsed, the preamplifier is ready to play music.

Mechanical engineering

Both chassis are made from high-density aluminium alloy and are CNC-machined. The structure incorporates asymmetrical reinforcements, decoupled board mounting and damping elements designed to reduce resonance and microphony.

The four valves are supplied pre-selected and matched to maintain symmetry between channels and ensure the correct balance of the direct-coupled circuit.

Key features

• Reference-grade valve stereo preamplifier.
• Configuration comprising two chassis with separate power supplies.
• Two E180CC valves in the gain stage.
• Two E80CC valves in the output stage.
• Direct coupling between stages.
• Output impedance of just 15 Ω.
• Volume control using relays and precision resistors.
• Volume adjustment in 0.5 dB increments.
• Four phono inputs.
• Remote control for volume, input and mute.
• 340 V regulated linear power supply.
• Filament voltage set to +170 V.
• Delayed start-up system.
• Real-time DC current monitoring.
• Constructed entirely from CNC-machined aluminium.

Technical specifications

Performance figures correspond to the measurement conditions specified by the manufacturer.

Transparency, stability and control

The EIZZ LP305 is not designed to draw attention to itself. It is designed to disappear behind the music.

Its combination of industrial valves, direct coupling, volume by relays, extremely low output impedance and regulated power supply makes it possible to recover micro-information, ambient depth and dynamics without hardening the sound or altering its tonal balance.

A proposal for high-end systems where transparency, silence and naturalness take precedence over any transient sound effect.

Discover the EIZZ LP305, a valve preamplifier with direct coupling, relay-switched volume and a regulated linear power supply in a separate chassis.