RP4 discontinued

Created to give audiophiles a Hi-End headphone amplifier joining the dynamics of solid state with the silky sound of vacuum tubes. Although its budget price, it is a real Hi-End amplifier: the frequency response is astonishingly flat and the distortion is negligible and mainly 2nd harmonics.

The main board is a printed circuit on which a 1mm silver/copper wire is applied — a technique that joins the solidity of the PCB with the sonic quality of traditional hand wiring. RudiStor calls it SWR (Silver Wire Reinforcement).

The input stage is equipped with a 12AU7 double triode for signal amplification, direct-coupled to the solid state current stage. The configuration is pure Class-A / Zero Negative Feed-Back. The power supply is a compound of capacitance multiplier and RC.

The tube socket and input connectors are gold plated; the box is built in solid aluminium with polished finish and laser-written graphics. It can drive any dynamic headphone from 32 to 300 Ohm.

The RP4 was the new denomination of the RP3-VT mk2. Its design descends directly from the RP3 — the commercial version of the AR3, a headphone amplifier built by many DIY enthusiasts around the world; a version of the AR3 with Japanese semiconductors was the subject of a wide article in the American magazine audioXpress.

Specifications — Maximum Output: 400mW · Inputs: 1 line · Bandwidth: 3–100,000 Hz within 1dB · Gain: 19.8dB · THD: 0.5% (output 100mW) · Technology: Triodes & Bipolar transistors · Input Impedance: 47kΩ · Negative Feed-Back: zero · Output Impedance: 32–600Ω · Amplification Class: Always A-Class · Weight: 5kg · Dimensions: 242×80×282mm

Price (2004): €390. An RP4 Special Edition was also sold via eBay.

Price (2004): €390 in Europe (+ €30 shipment) / US $450 in the US and Canada (+ $50 shipment), delivery 10 days.