A pre-main amplifier from Denon’s early 1970s lineup, designed for high sound quality with precision circuitry and reliable discrete components.
Overview
The Denon PMA-350Z is a solid-state pre-main amplifier released around 1973, combining a high-precision preamplifier and power amplifier in one chassis. It delivers 27 watts per channel into 8 ohms when driving both channels, with total harmonic distortion of 0.1% or less at rated output. The unit features a wide frequency response of 8 Hz to 150 kHz (±0.5 dB) and includes dedicated inputs for phono (MM), tuner, aux, and tape playback, with support for two tape decks and a dubbing switch. With an original price of ¥62,000, it was positioned as a high-fidelity component using carefully selected parts for low noise and high dynamic margin.
Design
The power amplifier uses a pure complementary symmetry circuit with Darlington power transistors (PNP-NPN pairs from Motorola, U.S.A.), configured in an OCL (Output Capacitor-Less) design that directly couples all stages. This direct-coupled, dual power supply system ensures low output impedance—0.15 Ω or less up to 10 kHz—enhancing speaker control, especially at ultra-low frequencies. The Darlington transistors are mounted on large heatsinks and stabilized by a temperature compensation circuit for long-term reliability. The preamp section employs high-voltage, low-noise transistors and precision components, particularly in the RIAA equalizer stage, which achieves high-accuracy response within ±0.5 dB (30 Hz to 15 kHz). The tone control circuit uses an NF-type design with FETs in the intermediate stage for low noise, and the volume control is an 11-position click-stop type. Additional features include audio muting (−20 dB), loudness control, and switchable high (9 kHz, 12 dB/oct) and low (40 Hz, 12 dB/oct) filters.
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