Preamplifiers — Octave Audio HP 300 SE

The HP 300 SE is a line preamplifier from Octave Audio of Karlsbad, Germany, developed as the successor to the HP 300 MK2. Compared with that model it adds an external power supply, a revised amplifier circuit with three gain settings, transformer-balanced XLR outputs and a reworked case. Two front colours are listed, black and silver.

Key specs that matter

The gain switch offers 25 dB (18.5x), 19 dB (8.8x) or 12 dB (4x). Frequency response spans 10 Hz to 200 kHz, within 0.1 dB at the high gain setting, 0.25 dB at the middle setting and 1.5 dB at the low setting. THD ranges from 0.005 % to 0.03 % measured at 3 V into 7.5 kOhm. Signal to noise ratio is -92 dB at high gain, -100 dB at medium gain and -108 dB at low gain. Connections cover two independent XLR inputs and three RCA inputs, with two RCA outputs, one XLR output and a monitor output. The main unit measures 438 x 78 x 390 mm and weighs 9.0 kg, and the separate supply measures 110 x 77 x 277 mm and weighs 3.0 kg.

Engineering and use context

Audio runs through two valves, an ECC81 (12AT7) and a second double triode, and then through a high-gain semiconductor stage that acts as a buffer to drive the power amplifier. Octave lists the ECC88 among the fitted valves, and an optional phono board for MC or MM cartridges uses a further ECC81. The external box holds the mains transformer with a mains filter, while precise, very low-noise voltage regulators sit inside the preamplifier itself. Balancing transformers produce the XLR output, and a ground switch on that output lets the user lift the connection to prevent leakage current between components. Power management with soft-start electronics limits inrush current and spares the valves at every power-up. A home theatre bypass passes the front channels from a surround processor through at a fixed level.

Pairing

The three gain steps are there to match the preamplifier to the efficiency of the loudspeakers and the input sensitivity of the power amplifier, so the low setting suits efficient speakers and the high one suits power amplifiers that need more drive. Thanks to the transformer-coupled balanced output and the buffer stage, the unit can drive long balanced cable runs to a power amplifier placed near the loudspeakers. The bypass input makes it simple to share a stereo power amplifier between a two-channel system and a surround setup.

Alternatives

The Octave Jubilee Preamp is the brand's reference preamplifier, placed above the HP 300 SE in the range.