Sonic Frontiers Power 3 - $4,500 (Gadsden)

condition: excellent

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The Power 3 is a push-pull, ultralinear design using eight KT88 output valves per monoblock, arranged in four matched pairs operating in parallel push-pull configuration. The circuit topology follows a three-stage architecture: four 6922 dual-triode valves handle input and voltage amplification, two 5687 dual-triode valves act as high-voltage driver cathode followers, and the eight KT88s form the output stage. The 5687 driver stage is a detail that merits particular note — the 5687 runs at considerably higher anode voltages than the 6922 and provides the current drive necessary to control the grids of eight output valves cleanly and without compression, a requirement that less generously specified designs can fail to meet at high output levels. Pearl tube coolers are fitted to the 5687 valves as standard, visible in the photographs, to manage the thermal load on these particularly hot-running devices.

The output transformers are Sonic Frontiers’ own design, wound in-house, and are a major contributor to the amplifier’s measured performance. Stereophile’s measurements recorded an output impedance of 0.17–0.22 ohms across the audio band — exceptionally low figures for a valve amplifier, translating to a damping factor in excess of 50 — and a frequency response that extends from 5Hz to 75kHz at 1W. These are figures that approach or surpass many solid-state amplifiers of the period, and reflect the quality of transformer design rather than simply the output valve configuration.

Rated power output is 220 watts into 8, 4, or 2 ohm loads — the output transformer is configurable for different impedances by the dealer, and this pair is currently set for 8Ω operation. In Stereophile’s measurements, the amplifier was found to produce predominately second-harmonic distortion, which is the character of distortion most commonly associated with valve amplifiers operating in push-pull and is generally regarded as the most musically benign distortion signature. The signal-to-noise ratio is specified at 110dB, and input sensitivity at 2.2V balanced.

post id: 7952330110

posted: 2026-08-08 11:43

updated: 2026-09-16 18:55

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