Headphones amplifiers — Allnic Audio HPA-15000 OTL/OCL

The Allnic Audio HPA-15000 OTL/OCL is the valve headphone amplifier that the Korean company presents as its flagship, and it keeps both the output transformers and the output capacitors out of the signal path, so the output valves couple straight to the headphones. Allnic says the model was engineered from scratch with a new valve topology and a valve complement different from the HPA-10000. Pre-outputs let it also work as a line-stage valve preamplifier. In Italy it was offered at EUR 19,800.

Key specs that matter

Maximum output is 10 W, and Allnic rates the amplifier for headphones from 15 to 600 ohm. Voltage gain is 32 dB at the headphone outputs and 16 dB at the RCA pre-out. Five analogue inputs are provided - three RCA and two XLR. Headphones plug into two 6.3 mm TRS sockets for unbalanced cables and two 4-pin XLR sockets for balanced ones, so two listeners can plug in at the same time with either type of cable.

Engineering and use context

Two ECF802 triode-pentodes handle voltage amplification in the first stage together with the feedback loop, a dual triode performs phase inversion and drives the output, and four 6C41C triodes form a single-ended push-pull (SEPP) output stage. Allnic describes the circuit as true balanced, with its positive and negative halves working in a cancellation arrangement. A Harmonic Balance Mode adds an analogue filter intended for ribbon and planar magnetic headphones, which Allnic lists alongside dynamic designs as loads the amplifier was made for. Volume is set by a 61-step Constant Impedance Attenuator of the type fitted to the top Allnic preamplifiers. An optional Direct Ribbon Headphone Terminal, a male 4-pin XLR, is available on order without a surcharge. It is wired with PC-silver wire to nickel permalloy matching transformers with a 0.2 ohm output, so this one output is not OTL/OCL, and RAAL ribbon headphones then connect without their usual interface box.

Pairing

The wide impedance range covers most dynamic headphones, from low impedance portable models to high impedance studio types, and the power reserve suits current-hungry planar magnetic headphones. DACs and players with XLR outputs keep a balanced connection into the amplifier, and the pre-out can also feed a power amplifier or powered speakers, making it the control centre of a compact speaker system.

Alternatives

The Allnic HPA-10000 is the earlier OTL/OCL headphone amplifier of the brand, listed at USD 15,000 when launched.