Denon PMA-300 (1973–1987, three variants)

Name: Denon PMA-300
Brand: Denon

Three amplifiers share this badge - the original 17W-per-channel OCL design and a CD-era 60W successor that barely resemble each other.

Overview

The Denon PMA-300 is three amplifiers, spread across roughly fifteen years of Denon's engineering. The earliest, the PMA-300Z, appeared around 1973 at ¥42,800. The improved PMA-300ZA followed at ¥49,500 in 1974. Circa 1987, Denon revived the name for the PMA-300V, a fundamentally different machine built for the CD era, priced at ¥44,800. Treat them as distinct models that share a badge. The specification sheets read like two different companies.

The original PMA-300Z and its ZA successor are modest integrated amplifiers by modern standards: 17W + 17W into 8 ohms with both channels driven, or 19W per channel with a single channel operating, at 0.1% total harmonic distortion. The numbers look small, but they leave out the topology. These are OCL (output capacitor-less) designs with direct-coupled circuitry from input to speaker terminal, which was advanced for 1973. The PMA-300V delivers 60W + 60W into 8 ohms and 80W + 80W into 6 ohms, with total harmonic distortion rated at 0.008%.

Key Features

Pure Complimentary OCL Circuit with Motorola Transistors

The PMA-300Z and PMA-300ZA use a pure complimentary output stage with paired PNP/NPN silicon power transistors sourced from Motorola in the USA. Denon's documentation says why: these transistors offered excellent characteristics and durability, and in a complimentary Darlington configuration the symmetry of the push-pull stage is nearly perfect. All stages from input to speaker terminal are directly connected OCL circuits, with no coupling capacitors in the signal path. The ZA adds a driver stage with Darlington connection. The power supply uses a two-rail system with direct coupling, so damping does not degrade in the ultra-low frequency range. The rated damping factor of 70 or more holds across 5 Hz to 30 kHz, which is wider than the audible band.

Dual Phono Inputs with Switchable Gain

The original models have two moving-magnet phono inputs, each with different sensitivity. Phono1 accepts 2.4 mVrms at 60k ohms with 32 dB of gain, which suits lower-output cartridges. Phono2 takes 8 mVrms also at 60k ohms with 22 dB of gain, for higher-output pickups. The equalizer amplifier is a 3-stage direct-coupled E-E negative feedback design using a low-noise NPN transistor, and the sensitivity is set by changing the amount of negative feedback. Maximum allowable input at 1 kHz is 240 mVrms for Phono1 and 600 mVrms for Phono2. RIAA deviation holds within ±0.8 dB from 30 Hz to 15 kHz. A high collector voltage of +38V gives a wide dynamic range, and the signal-to-noise ratio is rated at 70 dB or more for Phono1 and 77 dB for Phono2 (IHF-A).

Stepped Volume Control and Tone Circuitry

The volume control on the ZA uses a special resistance curve with an 11-position click stop. It gives a stepped feel and keeps the advantages of a continuously variable attenuator. The tone control section is a 2-stage direct-coupled design with a low-noise NPN transistor in the first stage and an FET in the second, and tone adjustment works by changing negative feedback through the volume. Bass control offers ±11 dB at 80 Hz, treble ±9.5 dB at 12 kHz. A low filter cuts at 100 Hz and a high filter at 7 kHz, both at 6 dB per octave. There's also a -20 dB muting switch and a loudness control. The ZA's preamplifier section can deliver 9V or more from the equalizer stage and 5V from the tone control stage at 0.1% THD, which is plenty for the power section.

Pre Out / Main In and Protection Circuitry

The Z and ZA both have Pre Out and Main In jacks, so the preamplifier and power amplifier sections can be separated for external processing or bi-amping. The protection circuit uses a current-limiting method at the final stage. It is designed to keep the power transistors within their safe operating area even if the speaker load is short-circuited, which has kept many of these units alive into the present day. The rear panel has a switched and unswitched power outlet, with a total rating of 350W.

PMA-300V: The CD-Era Rebuild

The PMA-300V shares almost nothing with its namesakes beyond the badge. Denon built it for digital sources, with a Pure Dynamic power supply featuring a 160VA toroidal transformer, a big step up from the conventional supply in the earlier models. The circuit aims for thorough simplicity and straightness, getting low distortion and low noise through minimal signal path complexity. It has a built-in MC/MM equalizer amplifier, so moving coil cartridges work directly without an external step-up transformer. Phono MC input sensitivity is 0.25 mV at 100 ohms, while Phono MM takes 2.5 mV at 47k ohms. The input selector uses electronic switches rather than mechanical contacts. A subsonic filter at 16 Hz with -12 dB per octave rolloff protects speakers and amplifiers from warp-induced cone excursion. The V also adds a loudness control delivering +7 dB at 100 Hz and +6 dB at 10 kHz, and its headphone jack produces up to 230 mW into 8 ohms, suitable for headphones from 8 to 400 ohms.

Historical Context

Denon's documentation describes the PMA-300Z as "a pre-main amplifier that has taken over the quality of PMA-300 as it is, and is more complete." The PMA-300ZA, introduced the following year at ¥49,500, was an improved version on the same platform. Both were built on the design policy of "excellent bare characteristics and moderate negative feedback," using a genuine complimentary Darlington circuit with Motorola transistors and a differential amplifier using a carefully selected monolithic IC for DC stability. The 40V power supply voltage provided efficient dynamic range and linearity.

The PMA-300V arrived in a very different audio landscape. Circa 1987, Denon positioned it as an integrated amplifier aimed at full-fledged CD playback. The specification sheet shows it: a 160VA toroidal transformer, 0.008% THD, and line inputs for CD, DAT, Tuner, and AUX/Video at 150 mV / 30k ohms. Its dynamic power rating is 120W into 2 ohms. The original Z's OCL circuit was advanced for its day, but the V's current delivery into difficult loads is in another class.

Collectibility & Value

Both the PMA-300Z and PMA-300V appear in the used market, with eBay listings confirming working units. A service manual for the PMA-300V was listed at C $27.75. No current market prices for the units themselves are documented, so condition and functionality will drive whatever a seller asks. The Z and ZA models are now over five decades old. The electrolytic capacitors in the power supply are well past their design life, and the current-limiting protection circuit, while good, does not excuse a unit that has sat unused for years. Budget for a recap and a check of the DC offset if you buy one untested.

The PMA-300V is the more practical daily driver, with 60W per channel and an MC phono stage. The earlier models are more collector's pieces, interesting for their OCL topology and Motorola output transistors, but their power ratings will struggle with anything but efficient speakers.

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