Discountinued

The HP 500 SE represents the ultimate evolution of the HP 500 line of preamplifiers signed by Octave. Placed upstream of a power amplifier, it handles source selection, listening level and signal matching. Its production was discontinued after a limited series of one hundred units, making it a sought-after component for systems built around valve amplification.

The most notable evolution of this version lies in its output stage, built around two Siemens D3A pentodes, also known under the designation EF 184. This architecture extends the bandwidth from 0.2 Hz to 2.3 MHz at 6 dB. A low cut-off frequency taken this far down means that no electronic limitation truncates the bottom of the spectrum: the bass retains its density and extension, and the fundamental register on which the intelligibility of voices and midrange instruments relies remains stable. At the other end, the high cut-off, pushed well beyond the audible band, avoids phase rotations and tonal alterations in the treble.

The HP 500 SE also introduces switchable gain. This gain setting allows the useful range of the volume potentiometer to be adjusted to the power amplifier/speaker pairing actually in use, rather than operating permanently at the bottom of the control's travel. On a high-efficiency system, this flexibility avoids abrupt level jumps in the first few degrees of the volume control.

The power supply is housed in a separate unit, which has also been reworked. The high voltage is regulated by MOSFET transistors, rectification uses Schottky diodes and the filtering capacitance has been increased, the whole being complemented by permanent electronic stabilisation. The result can be read in the figures: a residual ripple below 300 µV and a signal-to-noise ratio of 103 dB, giving a noise floor that lets the quietest passages of a recording breathe.

This unit is aimed at the listener building a system around a separate power amplifier and looking for a valve preamplifier capable of driving both sensitive speakers and more demanding loads, thanks to gain matching. Two options were offered in the catalogue and vary the configuration from one unit to another: an MM or MC phono module, intended for analogue listening via a turntable, and a by-pass function. It is therefore worth checking which of these are fitted to the unit in question.