Power amplifiers stereo — Esoteric S-02

Hand-assembled in Tokyo, the S-02 is a stereo power amplifier from Esoteric, the high-end brand of Japan's TEAC Corporation. It sits below the Grandioso M1 monoblocks and uses technology carried over from that line, and its design centres on current delivery and a very low output impedance for driving large woofers.

Key specs that matter

Rated output is 145 W per channel into 8 ohms and 290 W into 4 ohms, with a maximum of 580 W per channel into 2 ohms, which means output doubles with every halving of the load impedance. Frequency response is 5 Hz to 100 kHz (+0/-3 dB into 8 ohms). Signal-to-noise measures 115 dB (IHF-A), THD is 0.003% and the damping factor is 1000. Input impedance is 44 kohm balanced and 22 kohm unbalanced, with a voltage gain of 28.5 dB. Maximum power consumption is 440 W. The chassis measures 445 x 221.5 x 489.6 mm and weighs 28 kg.

Engineering and use context

The main power transformer is a custom EI-type unit with a 940 VA core, individual windings for each channel and a 5 mm steel base plate. Each channel draws on three 4700 uF capacitors in parallel, and the power wiring uses crimped cables bolted together to lower impedance. The voltage amplification stage has its own supply with a separate toroidal transformer, so current swings in the output stage do not reach it. In the output stage, bipolar LAPT transistors twice the size of ordinary power devices, rated for 17 A continuous and 34 A peak, work in a three-stage Darlington arrangement with five parallel push-pull pairs per channel. LIDSC, Esoteric's Low Impedance Drive Stage Coupling circuit taken from the Grandioso M1, keeps the drive stage stable. Nine bus bars per channel take the place of conventional wiring and the output coil is left out, both to bring the output impedance down. A simplified circuit with lower gain in the early stages allows the amount of negative feedback to be reduced.

Pairing

The high damping factor and stability into low loads make the S-02 a match for large, low-sensitivity floorstanders and for speakers with deep impedance dips. Electrostatic and ribbon hybrids whose impedance falls at high frequencies are also within its operating range. The balanced input accepts any preamplifier, including Esoteric's own C-03Xs and Grandioso C1X.

Alternatives

Esoteric's S-05 is a smaller Class A stereo power amplifier in the same range.