Vintage Audio
this section covers some restoration work that I did on my vintage HI-FI gear
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Article #1 | 06:00 PM Sunday 01/10/2016

PIONEER SA-9100: Introduction

A Pioneer amplifier that knows how to play music. From my experience, Pioneer gear manufactured during the 1970-1980 decade are refined units that sound full and rich. I had very few Pioneer units during the time because I strongly disliked their sound. I can remember the CT-F950 or the CT-F400 cassette decks. Dull and cold sound. So when I saw this SA-9100 unit on the local market, I decided to give it a chance. It was cheap because it was sold as defect.

And the seller was right. I plugged the thing in and no sound at all. From time to time, the protection would trigger and light the red indicator on the front panel. I opened it up and surprise: it was missing the original supply rail filtering capacitors. Instead some axial capacitors of unknown brand were floating on the chassis, soldered directly to the wire terminals. What a mess. I opened the bottom cover only to find another two capacitors of the same type floating around. So in total there were four short-circuit prone parts floating in the chassis.

I have temporarily insulated the wire leads with electrical tape and decided to try to power on again. This time, the thing started correctly. Relay was acting properly as well. However I was mislead by malfunction due to the front power indicator being burnt out. I plugged some speakers and the signal source and played a few tunes. Despite the supply buzz caused by the semi-leaking axial unknown-brand capacitors, the sound was powerful and warm. Now wait a minute, this one is a keeper.

This is how I decided to restore and keep this unit.

Article #2 | 11:00 PM Sunday 03/01/2016

PIONEER SA-9100: Technical Data

This amplifier has the following technical characteristics.

TECHNICAL PARAMETERS
ParameterValue
Continuous RMS power (both channels)60 W + 60 W (8 Ω at 1,000 Hz)
Total Harmonic Distortion<0.1% (at rated output) and <0.04% (at 1 W + 1 W)
IHF power bandwidth (each channel driven at 8 Ω)5 Hz - 40,000 Hz
Frequency Response (at normal listening level)7 Hz - 80,000 Hz
Load Impedance4 Ω - 16 Ω
SemiconductorsTransistors: 63 / Diodes: 30
Power Voltage110 V, 120 V, 130 V, 220 V, 240 V, at 50/60 Hz
Power Consumption430 W (max)
Dimensions / Weight138 mm (H), 430 mm (W), 341 mm (D) / 13.6 kg

Article #3 | 12:00 PM Tuesday 05/01/2016

PIONEER SA-9100: Parts List

I have assembled a parts list for this amplifier. My restoration touches some of the original transistors. Normally the original transistors contribute to the authentic Pioneer sound. But modern equivalents are better in any aspects. I am also interested in exchanging the electrolytic capacitors. So this is what you will find listed below.

The schematic value corresponds to what normally can be found in the electrical schematics. The recommended value is what I replaced the former part with. Where I found appropriate, I have chosen a film capacitor replacement instead of an electrolytic. My reasons are reliability in time. Less electrolytic capacitors, less time-ticking bombs.

Descriptions and Parts Listings

The power supply rail filtering capacitors are mounted on the chassis. Should they test bad, they need to be replaced. However in my case, they were missing altogether so I am obliged to add them.

Chassis
IdentifierSchematicRecommended
C7115.000 uF / 50 V
C7215.000 uF / 50 V

The Equalizer Amp Assembly is coded AWF-007-0 and implements the Phono preamplifier and the RIAA correction curve. You can find it constructed on dual-mono topology in the front-right part of the steel chassis. In order to operate changes, you need to extract the two printed circuit boards.

The capacitors are listed for only one channels. So double ordering is required.

Equalizer Amp Assembly (AWF-007-0)
IdentifierSchematicRecommended
C12.2 uF / 25 V
C447 uF / 25 V
C73.3 uF / 50 V
C922 uF / 6 V
C10470 uF / 6 V

The Control Amp Assembly is coded AWG-018-A and implements the preamplifier and the tone control circuits. You can find it XXXXXXX steel chassis. In order to operate changes, you need to extract the two printed circuit boards.

The capacitors are listed for both channels.

Control Amp Assembly (AWG-018-A)
IdentifierSchematicRecommended
C11 uF / 25 V1 uF / 50 V FILM
C21 uF / 25 V1 uF / 50 V FILM
C747 uF / 16 V
C847 uF / 16 V
C93.3 uF / 25 V
C103.3 uF / 25 V
C1147 uF / 16 V
C1247 uF / 16 V
C134.7 uF / 25 V
C144.7 uF / 25 V
C1710 uF / 25 V
C1810 uF / 25 V
C21100 uF / 16 V
C221 uF / 25 V1 uF / 50 V FILM
C231 uF / 25 V1 uF / 50 V FILM
C241 uF / 25 V1 uF / 50 V FILM
C251 uF / 25 V1 uF / 50 V FILM
C261 uF / 25 V1 uF / 50 V FILM

The Filter Amp Assembly is coded AWK-021-0 and is located in the XXXXXXX steel chassis.

The capacitors are listed for both channels.

Filter Amp Assembly (AWK-021-0)
IdentifierSchematicRecommended
C14.7 uF / 10 V
C24.7 uF / 10 V
C547 uF / 10 V
C647 uF / 10 V
C74.7 uF / 10 V
C84.7 uF / 10 V
C1122 uF / 10 V
C1222 uF / 10 V

The Power Amp Assembly is coded AWH-023-B is bolted to each of the big black radiators for the output power transistors. You recognize them quickly as they occupy most of the visible area that you see when you remove the top cover.

The capacitors are listed for only one channel.

Power Amp Assembly (AWH-023-B)
IdentifierSchematicRecommended
C10.22 uF / 25 V220 nF / 50 V FILM
C20.47 uF / 25 V470 nF / 50 V FILM
C333 uF / 16 V
C633 uF / 16 V
C12470 uF / 6 V

The Protection Circuit Assembly is coded AWM-025-A XXXXXX.

The capacitors are listed for only one channel.

Protection Circuit Assembly (AWM-025-A)
IdentifierSchematicRecommended
C3330 uF / 6 V
C4330 uF / 6 V
C54.7 uF / 25 V
C6100 uF / 16 V

The Power Supply Circuit-A Assembly is coded AWR-031-0 and is located XXXXXX.

Power Supply Circuit-A Assembly (AWR-031-0)
IdentifierSchematicRecommended
C5470 uF / 63 V AXIAL1000 uF / 100 V AXIAL
C6470 uF / 63 V AXIAL1000 uF / 100 V AXIAL

The Power Supply Circuit-B Assembly is coded AWR-032-0 and is located XXXXXX.

Power Supply Circuit-B Assembly (AWR-032-0)
IdentifierSchematicRecommended
C1100 uF / 63 V100 uF / 100 V
C2100 uF / 63 V100 uF / 100 V
C510 uF / 16 V
C610 uF / 35 V
C710 uF / 50 V
C810 uF / 50 V
C910 uF / 50 V
C1247 uF / 25 V
C1347 uF / 25 V
C1433 uF / 25 V
C1533 uF / 25 V
C2010 uF / 50 V

The Switch-B Assembly is coded AWS-039-0 and is located XXXXXX.

The capacitors are listed for both channels.

The Switch-B Assembly (AWS-039-0)
IdentifierSchematicRecommended
C11 uF / 25 V1 uF / 50 V FILM
C21 uF / 25 V1 uF / 50 V FILM
C510 uF / 16 V
C610 uF / 16 V

The Switch-C Assembly is coded AWS-040-0 and is located XXXXXX.

The capacitors are listed for both channels.

The Switch-C Assembly (AWS-040-0)
IdentifierSchematicRecommended
C90.47 uF / 10 V470 nF / 50 V FILM
C100.47 uF / 10 V470 nF / 50 V FILM
C110.47 uF / 10 V470 nF / 50 V FILM
C120.47 uF / 10 V470 nF / 50 V FILM

The construction of this amplifier is very complicated due to a lot of wires and complicated layout. Thus the restoration is not exceptionally easy. In fact it is on the hard side.

As always, let me throw a piece of advice. Do not hurry, take your time and do the job once. And do it well.

Copyright © 1998- Alexandru Groza