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 The A-27
Integrated Amplifier was the most expensive component in the Series 20 line,
with a list price of $1250.00. Pioneer clearly intended to incorporate
much of the circuit design from the M-type amplifiers, but have a greater degree
of control than the C-21 pre-amp. It used the "Magni-Wide"
DC power amplifier section, but also used a total of three other
all-DC-configured amplifier stages: a DC phono equalizer amp, a DC flat amp and
DC "head amp" for Moving Coil (MC) type phono cartridges. Like
the M-25, the A-27 used RETs in the output stage. It also used
automatic Class AB switching, operating in Class A mode until the sudden audio
peaks automatically switched to Class B.
The front panel was a very clean design. A 32-step attentuator was used for the large volume control knob. The function selector was all the way to the right for Phono 1, Phono 2, Tuner and Aux. The tone control section could be bypassed completely if desired via one of the toggle switches. All the other control knobs were mounted behind a clear smoked plastic panel. All in all, the A-27 was superb industrial design, as well as "musical"--as audiophiles like to say. The phono equalizer section incorporated dual Field Effect Transistors (FETs) to guarantee a wide dynamic range and a signal-to-noise ratio of 90 dB in the phono section. Selectable load resistance and load capacitance allowed audiophiles to be able to select various different phono cartridges of their choice.
The A-27 used two large power supply transformers, one for each channel, positioned on the left of the chassis, and four electrolytic capacitors. The circuitry employed 206 semi-conductors: four FETs, 122 transistors and 80 diodes. The A-27 was rated at 120 watts per channel into 8 ohms, from 5 hz to 30 kHz with no more than 0.012% total harmonic distortion. Between 20 Hz and 20 kHz, toal harmonic distortion was a mere 0.008%--virtually non-existant distortion! Intermodulation distortion was only 0.006%. The A-27 entire frequency response ranged from 5 Hz to 200 kHz. It measured 17.88 inches wide, 6.63 inches high and 18.44 inches deep. It weighed 56 pounds, 7 ounces. The M.S.R.P. of the A-27 was $1250.00.
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