Pioneer A-500

Commentary

Pre-main amplifier with non-switching amplifier.

As with A-900 and A-700, a non-switching amplifier is used for the power circuit.
This eliminates switching distortion and greatly reduces high-order harmonic distortion and crossover distortion.

It is equipped with a line straight switch which can directly connect an equalizer amplifier and a power amplifier.
When this switch is on, the tone circuit, balance volume, and mode switch can be passed, and distortion and noise can be reduced by simplifying the circuit.
When the switch is turned on, the Bass, Treble, Loudness, Balance, and Mode indicators disappear to confirm that the circuit has passed.

A DC servo circuit is used in the power amplifier section, and by cutting out the ultra-low range without using a condenser, the characteristics are sufficiently extended to the low range.
This power amplifier has a large gain, and the inputs other than the phono input are amplified only by the power amplifier. Therefore, there is no coupling capacitor from the aux and tuner inputs to the speaker output.

A direct power supply system has been adopted to ensure low impedance power supplies.
This method, in which a dedicated power supply is incorporated into the boards of both the small-signal circuit and the large-signal circuit, realizes significantly lower impedance and reduced mutual interference between amplifier units.

Brass is used for the output terminal, power capacitor and volume terminal, and copper is used for the lead wire of the emitter resistor of the power transistor. By making the signal path completely nonmagnetic, the generation of non-linear distortion is suppressed.
In addition, with an emphasis on how the ground point is set and the material of the ground line affect sound quality, we use a thick copper ground line from the equalizer board to the tone amplifier board.

Equipped with MC position where MC cartridge can be directly connected.
MM/MC can be switched with a switch on the front panel, and the input impedance is also switched to MC.

The Phono input uses a cascade current mirror connection and an FET differential input circuit.
In addition, it is equipped with cartridge load switching for MM cartridge, and load resistance and load capacity can be independently selected by 3 positions each.

The tone amplifier consists of a first stage dual FET, a new current mirror differential circuit, and a last stage emitter follower, and is an NF type configuration.

The power amplifier section consists of an initial stage dual FET, a new current mirror differential circuit, and a final stage two stage Darlington SEPP. The final stage power device uses a group transistor (EBT) with superior high-frequency characteristics.

The subsonic circuit is located in front of the volume and can be used regardless of whether the line straight switch is ON or OFF.

The power supply indicator lights red during operation of the muting circuit and green during normal operation to confirm the operation status.

Model Rating

Type	Non-switching pre-main amplifier
Effective power	80W + 80W (8 Ω, 20 Hz to 20 kHz, both channel drive)
Harmonic distortion factor (20 Hz to 20 kHz)	0.007% (at effective output) 0.005% (8 Ω at 40W output)
Intermodulation distortion factor (50 hz : 7 khz = 4 : 1)	0.007% (at effective output) 0.003% (8 Ω at 40W output)
Output bandwidth	5 Hz ~ 100 kHz (IHF, both channel drive, THD0.05%)
Input Sensitivity / Impedance	Phono MM: 2.5mV/25k Ω, 50k Ω, 100k Ω Load Capacity : 100 pf, 200 pf, 300 pf Phono MC: 0.25mV/0.1k Ω Tuner, Aux, Tape play1, 2 : 150mV/50k Ω
Phono maximum allowable input (1 kHz, THD0.008%)	MM:200mV MC:20mV
Frequency characteristic	Phono MM : 20 Hz to 20 kHz ± 0.2 dB Tuner, Aux, Tape play : 5 hz to 200 khz + 0 to 3 db
Signal-to-noise ratio (IHF, A-network, short circuit)	Phono MM:89dB Phono MC:73dB Tuner, Aux, Tape play : 110 dB
Tone control	Bass : ± 10 dB (100 Hz) Treble : ± 10 dB (10 kHz)
Filter	Low : 15 Hz, 6dB/oct.
Loudness contour (at Volume-40dB)	Low:+6dB(100Hz) High:+3dB(10kHz)
Attenuator	-20dB
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption (Electrical Appliance and Material Control Law)	230W
External dimensions	Width 420x Height 135x Depth 404 mm
Weight	14.1kg