Pioneer SA-420 Amplifier

General:

Pioneer Japan inc. introduced this amplifier in 1981.

 

Special futures:

This amplifier consists of only a RIAA and a power amp section,
tone control is done the same way as in the Luxman L200 series:
in the feedback circuit of the power amp.
The amplifier setup is quite similar to the Luxman L200 series.
It has a peculiar headphone cinch connection at the rear, which is
connected to the speaker terminals the same way as the front jack.
Several different versions were issued with small variations of the schematics.

 

Specifications:

Power output: 21 watts per channel into 8 ohms @ 0.2% distortion.
Frequency response: 5Hz to 60kHz
Total harmonic + IM distortion: 0.08% at half power rating.
Damping factor: 40 @ 1 kHz
Input sensitivity: 2.5mV (MM), 150mV (line)
Signal to noise ratio: better than 72dB (MM), 97dB (line)
Output tape: 150mV (line level)
Dimensions: 420 x 94 x 267mm
Weight: 4.6kg

 

Schematic:

The servicemanual of the Pioneer SA-420 version1 click here

The servicemanual of the Pioneer SA-420 version2 click here

 

 

 

Updating is very rewarding ^

 

Modifications:

The power supply can be improved by using bigger capacitors. Use ie. 10000 uF 35V.

The lamps may be replaced by LED's, with a 3k3 Ohms resistor in series. I used green ones.

You may replace some capacitors in the amp and eventually the coupling caps in the pre-main amp connection.

You may insert a small protection circuit. You may paint the heatsink black. You may upgrade the speakerwiring.

 

Power transistors of Toshiba ^

 

Sound:

Sound is very good due to the fact that there is no tone-amp involved. Heatsinking inside the amp is ok.
The Pioneer SA-420 amp is very well built and the schematic diagram shows a good electronic design.
The parts used inside are of very good quality. After many years of service all parts will be ok.
To improve the sound and specially the bandwidth of the amplifier at half or full power, you can replace some power-rail
capacitors and some capacitors in the main amp to get a more stable sound image.
Specially the lows will benefit from addressing this issue.
Finally you get a fine amplifier of approx. 2x 25 Watts, although moderately powered, of exeptional sound quality, and that for very little money.
This amplifier will be able of driving all big medium and high efficiency speakers and of course bookshelf speakers.
The main amplifier has no protection circuit involved, so be carefull driving this amp at full power
or below 4 Ohms total speaker impedance.

 

 

 

© Hans Hilberink - PE1MMK ® 2003 - Last update: 25-10-2012.