Pioneer A-700
¥ 82,000 (released in 1979)
Commentary
Pre-main amplifier with non-switching amplifier.
In the non-switching amplifier, the bias value of the final stage is changed according to the input signal, and the transistor is not switched, so that a sufficient power can be obtained.
Equipped with a line straight-through switch, it can pass a tone circuit, a loudness switch, a balance volume switch, and a mode switch. When the switch is on, the Bass, Treble, Loudness, Balance, and Mode indicators turn off to confirm that the circuit has passed.
The DC servo circuits of the equalizer amplifier and power amplifier respectively cut out the unwanted ultra-low frequency components (power amplifier 1 Hz or less, equalizer 0.2 Hz or less). This eliminates the need for a coupling capacitor and enables sound quality with less coloring.
A direct power supply system is adopted in which each power supply is incorporated into a power amplifier board and an equalizer amplifier board. This reduces cord routing and greatly reduces impedance, while reducing interference between large signal circuits and small signal circuits.
The circuit configuration of the power supply uses inverted Darlington to obtain low impedance characteristics over a wide range. In addition, a thick copper plate is used to connect the ground from the MC circuit board to the tone amplifier board to further reduce impedance.
Capacitors and resistors that affect sound quality are made non-magnetic, and copper lead resistors are used for the emitter resistor of the power transistor, and copper terminal low-impedance type is used for the volume.
In addition, an electrolytic capacitor for audio is used for the capacitor to suppress the inductance component and eliminate the non-linear impedance to the current change.
The MC head amplifier has a 3-stage direct-coupled DC configuration with a low-noise transistor in the first stage, and high gain (28 db) and low distortion factor are achieved by improving the circuit configuration.
In addition, in order to bring out the performance of the MC cartridge to be used, it is equipped with MC cartridge load switching of High / Low stage switching type.
The equalizer amplifier uses a dual FET input DC servo circuit to eliminate coupling capacitors for both input and output. Moreover, Pioneer's new current mirror differential circuit (PAT. P.) and final stage SEPP enable ultra-low distortion that cannot be measured in the audible band from 20 Hz to 20 kHz.
For cartridge load switching, the additional resistance and load capacity can be switched independently in 4 stages each.
The tone control circuit is an NF type with first stage dual FET, new current mirror differential, and last stage emitter follower.
In addition, it is equipped with a subsonic filter that can be activated even when the line straight switch is ON. This subsonic filter does not pass through the active element above the cutoff frequency, thus reducing the effect on sound quality.
A new current mirror circuit is also employed in the front stage of the power amplifier, and a group transistor (EBT) with superior high-frequency characteristics is employed in the final stage to reduce distortion over a wide range.
The power indicator lights red when the muting circuit is in operation and green when the muting circuit is in normal operation. The operation status can be confirmed.
The Phono input terminal is gold-plated.
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Model Rating
| Type | Pre-main amplifier | ||||||
| Effective power | 90W + 90W (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 45W output) |
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| Intermodulation distortion factor (50 hz : 7 khz = 4 : 1) | 0.005% (at effective output) 0.003% (8 Ω at 45W output) |
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| Output bandwidth | 5 Hz ~ 100 kHz (IHF, both channel drive, THD0.05%) | ||||||
| Input Sensitivity / Impedance |
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| Phono maximum allowable input (1 kHz, THD0.005%) |
MM:300mV MC:12mV |
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| 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 |
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| Signal-to-noise ratio (IHF, A-network Short circuit) |
Phono MM:90dB Phono MC:73dB Tuner, Aux, Tape play : 110 dB |
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| Tone control | Bass : ± 10 dB (100 Hz) Treble : ± 10 dB (10 kHz) |
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| Filter | Low : 15 Hz, 12dB/oct. | ||||||
| Loudness contour (at Volume -40dB) |
Low:+6dB(100Hz) High:+3dB(10kHz) |
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| Attenuator | -20dB | ||||||
| Power supply voltage | 100 VAC, 50Hz/60Hz | ||||||
| Power consumption (Electrical Appliance and Material Control Law) | 250W | ||||||
| External dimensions | Width 420x Height 135x Depth 404 mm | ||||||
| Weight | 14.7kg |