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Pioneer M-25

Stereo Power Amplifier

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Pioneer M-25


The Pioneer M-25 is a 120W + 120W power amplifier with a wide frequency band and low distortion.

The first stage of the M-25 adopts a dual transistor differential amplifier with a current mirror as the load for a superb stability and gain right from the lowest low frequencies to the highest high frequencies.

The pre-driver stage consists of a voltage amplifier with a constant current circuit as the load, and this makes for a significant improvement in the degree of use of the power voltage, and also for a satisfying gain and linearity.

The power stage features a Class AB pure complementary parallel push-pull circuit with a three-stage Darlington connection.

A newly developed power transistor called a Ring Emitter Transistor (RET) has been introduced into the new Class AB circuitry. This feature guarantees an ultra wide frequency range which turns the attributes of the RET to maximum advantage, and also a superior low-distortion response whatever the power rating - across an ultra-low to full power spectrum.

The M-25 delivers continuous power output of 120 watts per channel, min at 8 ohms from 5 Hertz to 30,000 Hertz with no more than 0.01% total harmonic distortion.

In particular, the Class AB SEPP circuit functions as a Class-A circuit which is highly rated on account of its hi-fidelity sound reproduction capabilities with low power outputs (up to 3W/8-ohms). This means that you can enjoy the final sound as you would from a Class-A amplifier.

Finally, the pre-driver section contains an over-drive limiter and a power limiter for protecting the power transistors. This helps to greatly improve the reliability.

The Pioneer M-25 is symmetrically designed with completely separate heavyweight class power supplies for each channel. Each employs large-capacity capacitors (two 22,000uF for each channel) which not only feature excellent regulation but also have plenty of reserve.

Along with the wide-band frequency response, they ensure a superior channel separation and a reproduction of sound which is both clear and full of latent energy.

There is also a surge-killer circuit to keep the inrush current from the power transformers as well as the high current which charges the electrolytic capacitors to the bare minimum, and this feature reduces the load on all of the related parts.

The M-25 employs a relay type of protective circuit which is equipped with a current detector and an over-current detector. This circuit is designed to protect the speakers from unforeseen accidents caused by the generation of current in the output, or from short-circuiting of the speaker terminals owing to faulty contacts, as well as the power transistors by releasing the output circuitry momentarily.

Moreover, the output circuit relay is for 4-circuit high current uses and all the circuits are connected in parallel for enhanced reliability. This circuitry can also be counted on to perform muting when the power switch is flipped between On and Off.

Each and every part which makes up the M-25 has been singled out for its quality so that only the best is finally chosen. Among the parts employed are gold-plated input and speaker terminals, printed circuit boards of paper epoxy resin with a high insulation resistance, and printed circuit boards using 70u thick copper foil, low-resistance pure copper plates for parallel connections and for the grounding wire, and non-inductive cement resistors.

The visual appeal of the power transistors and heat sinks mounted on a broad-based silver-toned aluminium die-cast chassis is what you would expect from a top-quality power amplifier. Just one look at the M-25 is enough to convince you of its tremendous power and stability.


Power output: 120 watts per channel into 8Ω (stereo)

Frequency response: 5Hz to 30kHz

Total harmonic distortion: 0.01%

Damping factor: 60

Input sensitivity: 1V

Signal to noise ratio: 120dB

Speaker load impedance: 4Ω to 16Ω

Dimensions: 420 x 153 x 370mm

Weight: 23.5kg


service manual   English -

instruction/owners manual   English -

schematic   English -

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This website is not affiliated with or sponsored by Pioneer. To purchase M-25 spares or accessories, please contact the company via their website or visit an authorised retailer.