Pioneer M-90a

Commentary

A stereo power amplifier developed using Pioneer's technology.
We pursue three technical themes : direct construction to minimize signal paths in order to eliminate mutual interference of signals, low-load drive capability to improve dynamic drive capability of speakers, and vibration-free and resonance-free construction to reduce vibration and resonance harmful to sound.

Two large power transformers are used independently on the left and right, and a 10,000 μ Fx2 resin-coated electrolytic capacitor is used for each channel. In addition, the positive and negative sides of the power supply are divided into two parts from the winding of the power transformer, and each part is bridge rectified by high-speed low-noise diodes. This makes it possible to supply high-power music signals with low distortion.
In addition, the power transistor is a Pc = 130W 4-parallel push-pull configuration, realizing a large current supply capability of 47A.

In addition to the power input from the normal control amplifier, there are two input jacks, CD direct and line direct. These direct inputs are level-controllable.
The CD/Line direct terminal also has a dedicated output terminal, which can be returned to a control amplifier for copying to tape.

In order to minimize the signal path, direct construction is adopted.
High-quality sound The volume and relay itself are located near the rear panel, near the input terminals, and the volume is controlled via a brass remote shaft.
As a result, the signal path can be minimized without sacrificing operability.

In order to thoroughly suppress internal and external vibrations, we have adopted a casted transformer and a unique honeycomb shape for heat sinks, chassis frames, and large insulators to disperse vibrations in various directions.
The transformer case of M-90a is made of cast iron with high shielding effect. Pitch material with high thermal conductivity is filled between the cast iron case and the transformer body. Heat radiation fins are also provided to prevent internal resistance from increasing due to temperature rise.
A 1.6 mm thick honeycomb structure with copper plating is used for the transformer frame supporting the transformer. In addition, a 1.6 mm thick copper plated honeycomb punching bottom plate is used to firmly hold the frame chassis.
The heat sink is an extruded aluminum honeycomb heat sink that suppresses resonance and vibration of the power transistor and has excellent heat radiation effect.
In addition, four large-size filled type insulators made of special cell polymer are used, and a fifth insulator made of cast iron is also installed to support the heavy transformer.

It employs a non-switching circuit in which switching distortion does not occur in principle. This circuit expands the range of 0 switching distortion to increase the bandwidth. In addition, it stabilizes the idle current that is drifting due to changes in ambient temperature immediately after the power switch is turned on or when a large signal is input, and suppresses thermal distortion caused by this.
In addition, by detecting and correcting the difference between the input and output signals, the nonlinear distortion of the output stage is reduced.

Uses a copper-plated chassis that greatly reduces magnetic distortion. In addition, by using copper plating, different metals are bonded together, and vibration damping is improved compared to the case of using a single metal.

Equipped with a 39mmx98mm large-size power indicator, it can directly read output changes from 2 mW to 300W (at 8 Ω) without switching.
A 0.6 second peak hold function is also built in to make it easier to read peak power.

High-quality parts such as a non-stress power cord using a oxygen-free copper wire with a polarity display that suppresses the influence of external noise, a vibration-proof film capacitor using a soft coating material, a special resin-coated electrolytic capacitor, a oxygen-free copper wire wiring material, a brass capped carbon resistor, a 70 μ m copper-foil substrate, and a gold-plated input / output pin jack are used.

Model Rating

Type	Stereo power amplifier
Effective output (both channel drive)	1 kHz : 200W + 200W (4 Ω, 0.01%) 20 Hz-20 kHz : 200W + 200W (8 Ω, 0.003%)
Dynamic Power (EIA test signal)	800W + 800W (2 Ω) 550W + 550W (4 Ω) 300W + 300W (8 Ω)
Harmonic distortion factor (20 Hz to 20 kHz)	0.003% (200W, 8 Ω)
Intermodulation distortion factor (50 hz : 7 khz = 4 : 1)	0.002% (at effective output)
Input Sensitivity / Impedance	Control Amp, CD Direct, Line Direct : 1V/50k Ω
Output Level / Impedance	CD/Line : 1V/1k Ω
Frequency characteristic	Control Amp, CD Direct, Line Direct : 20 hz to 20 khz + 0 -0.1 db
Signal-to-noise ratio (A network, short circuit)	Control Amp, CD Direct, Line Direct : 125 dB
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law)	410W
External dimensions	Width 457x Height 163x Depth 432 mm
Weight	28kg