Plinius SA-50 User manual

Plinius SA-50 instruction manual. Page 1
CONGRATULATIONS on your decision to become the proud owner of the
Plinius SA-50 power amplifier.
This manual has been prepared to help you understand the operation of your amplifier and
to provide some information about its design and the variety of ways it may be used.
We have designed and manufactured this amplifier to faithfully and accurately reproduce
music. This hand built instrument should give a lifetime of pleasure and with a little care
and a full understanding of the operating recommendation in this manual the Plinius SA-50
should provide trouble free performance.
THE PLINIUS SA-50 STEREO POWER AMPLIFIER
PLEASE TAKE TIME TO READ THIS MANUAL THOROUGHLY BEFORE
USING YOUR AMPLIFIER.

Plinius SA-50 instruction manual. Page 2
LIST OF CONTENTS
Warnings and precautions. Page 3
Amplifier Facilities and Features. FRONT PANEL. 4
Amplifier Facilities and Features. REAR PANEL 6
Amplifier Configuration Selector (ACS) 9
Installation and operation. 12
Mains / Line power connection. 13
Changing the Mains / Line voltage congfiguration 14
Connections for stereo operation. 15
Connections for Mono / Bridged operation. 18
Loudspeakers. 20
Why is Class A better.21
Specifications 22
Index. 23

Plinius SA-50 instruction manual. Page 3
WARNING
The SA-50 power amplifier can be operated in bridged mode and may deliver in excess of
200 Watts into 8 Ohms. This amplifier is also capable of a very large peak current
delivery.
This SA-50 power amplifier operates in Class A and is therefore capable of generating a
moderately high temperature which requires careful placing to avoid any effect this heat
may have on other equipment, furniture and fittings etc.
DO NOT remove the top cover from this amplifier. Hazardous voltages are present.
Any repair work should be referred to a suitable qualified and experienced service person.
DO NOT attempt to connect any input of this amplifier to any of its outputs.
DO NOT earth any output terminal or connect any of these terminals together without
following the instructions in this manual or seeking qualified assistance.
DO NOT place this amplifier in any position where liquids or any foreign
material may accidentally enter it.
DO NOT connect any voltage source, short circuit, earth / ground or appliance ( other
than suitable HiFi quality loudspeakers ) to any output terminal.
Some preamplifiers, processors, CD players etc, produce large switching pulses when
switched on, causing a loud click through the loudspeakers. For this reason, turn on all
other equipment in your system and operate the
MUTE circuit of the amplifier before turning on the SA-50.
NOTE: Plinius preamplifiers do not cause this problem.
Plinius SA-50 instruction manual. Page 4

AMPLIFIER FACILITIES AND FEATURES FRONT PANEL
The front panel of the SA-50 power amplifier incorporates a small panel fitted with three
switches. These switches control the day to day functions of the amplifier. The operation
of these switches is, from the left;
MUTE SWITCH. It is not recommended practice to interfere with the input cables while
the amplifier is switched on and connected to the loudspeaker/s. Therefore we have fitted
a MUTE switch to interrupt the input signal (by shorting it to ground). This allows the
user to connect and disconnect the input cables without the necessity of turning the
amplifier mains power off. The switch should be on OPERATE (down) for all normal
listening situations. Switch this switch to MUTE (up) to disconnect the input signal.
NOTE. This switch does not isolate , mute or disconnect the OUTPUT of the power
amplifier. Observe all normal precautions when handling or changing the output
(loudspeaker) leads.
MAINS SWITCH. This heavy duty rocker switch in the centre of this panel switches the
MAINS / LINE Power to the amplifier ON or OFF. A LED immediately above the switch
illuminates to indicate that the power is ON.
This amplifier draws a moderately high current when switched on.
It is not good practice to repeatedly active this switch ON and OFF rapidly.
FRONT PANEL LAYOUT SHOWING MAINS, MUTE & BIAS SWITCHES
Plinius SA-50 instruction manual. Page 5

FRONT PANEL FACILITIES AND FEATURES CONTINUED
BIAS SWITCH. This switch on the right of the panel alters the operating
Bias of the amplifier. Switch UP is BIAS A/B while switch DOWN is BIAS A.
BIAS A/B position reduces the bias on the output stage to operate the amplifier in class
aB. This is a bias configuration used by the majority of High End amplifier designers for
their products. In "Class AB" the SA-50 produces a very high quality of sound suitable
for all occasions where "super" critical listening is not a priority. The quality of
performance in this mode may exceed that of many other amplifiers so a dual benefit exists
in that this facility provides the user with a much cooler operating temperature and a much
reduces demand on electricity particularly at idle,
(ie. while the amplifier is not reproducing music). This unique feature allows the user to
leave the SA-50 switched ON at all times rendering the amplifier READY for use and
requiring only a few minutes of WARM UP in "class a" before the very best of the
amplifier's sonic qualities may be experienced.
BIAS A position provides a true class a bias to the output stage, therefore ensuring the
optimum performance of the amplifier during all critical or casual listening events. Class
A amplifiers run hotter that class AB amplifiers hence our specially designed and
distinctive heat sinks. Operating the amplifier in BIAS A creates a small number of
precautions that should be observed.
1. On switching the BIAS A the temperature of the amplifier will quickly increase and
the amplifier will become quite hot. Be certain that you have left adequate space around
the amplifier for ventilation. Ensure that no objects are resting on the amplifier and check
that the heatsink (cooling fins) are not obstructed in any way.
2. The current required from the mains / line supply by the amplifier in BIAS A is
now approximately 650 Watts.
This amplifier should not be connected to a wall outlet that is shared with other heavy
current appliances such as heaters or electric motors. If you are in doubt, check with your
Plinius dealer for advice.
Plinius SA-50 instruction manual. Page 6

FRONT PANEL FACILITIES AND FEATURES CONTINUED
REAR PANEL
The facilities on the rear panel of the SA-50 may seem complex. The rear panel incorporates all of the
terminals for connecting the input signals and output to the loudspeakers. A reasonable understanding of
this amplifier and a logical approach should ensure that you are listening to this amplifier in a very short
space of time without any difficulties at all.
Please remember that this Plinius SA-50 power amplifier is a high quality electronic instrument capable
of an exceptional level of performance. Be sure that you understand your requirement fully before you
make any connection to this amplifier or adjust the ACS ( Amplifier Configuration Selector )
REAR PANEL OF THE SA-50 SHOWING ALL OF THE AVAILABLE FACILITIES INCLUDING
INPUT AND OUTPUT TERMINALS, THE ACS (AMPLIFIER CONFIGURATION SELECTOR),
MAINS INPUT AND MAINS FUSE.

Plinius SA-50 instruction manual. Page 7
FRONT PANEL FACILITIES AND FEATURES CONTINUED
INPUT TERMINALS STEREO
Input terminals for this SA-50 power amplifier are easily accessible and fitted to the top
centre area of the rear panel.
RCA INPUTS LEFT & RIGHT. These standard type RCA terminals are for use with
unbalanced signals from most signal sources such as audio preamplifiers.
XLR BALANCED INPUTS LEFT & RIGHT. XLR connectors fitted to the amplifier
are for use with balanced line signals from audio preamplifiers etc. Balanced signals are
carried via a three way cable that
connects all three pins at each end of the interconnect cable. XLR pin wiring information
is discussed on page 15.
DO NOT Operate this amplifier with both RCA and XLR cables connected at the
same time.
INPUT TERMINALS BRIDGED / MONO
RCA. Connect to RIGHT channel RCA INPUT only.
XLR. Connect to RIGHT BALANCED XLR INPUT only.
DO NOT Operate this amplifier with both RCA and XLR cables connected at the
same time.

Plinius SA-50 instruction manual. Page 8
FRONT PANEL FACILITIES AND FEATURES CONTINUED
OUTPUT TERMINALS STEREO
OUTPUT CONNECTIONS For the loudspeakers are provided on the left and right
hand side of the rear panel.
A pair of heavy duty, gold plated five way binding posts for each channel are supplied.
CONNECT your Right hand loudspeaker positive terminal to the amplifiers Right
channel + output terminal. Connect your Right hand loudspeaker negative terminal to the
Right channel - output terminal. Signals for the LEFT channel should receive
corresponding attention.
PHASING (or Polarity). It is important to achieve good stereo imaging in your listening
room. By observing the wiring instructions above, each power amplifier / loudspeaker
combination should be in phase. If you experience a poor stereo image and / or a lack of
bass, check that the loudspeaker wiring has been connected correctly. We recommend
that you use one of the easily obtainable "test discs" to help you ensure both phasing and
channel orientation are correct. If in doubt, consult your Plinius / loudspeaker dealer for
advice.
OUTPUT TERMINALS BRIDGED / MONO
CONNECT the loudspeaker positive terminal to the amplifiers Right channel + output
terminal. Connect the loudspeaker negative terminal to the amplifiers Left channel +
output terminal.
DO NOT MAKE ANY CONNECTION TO ANY OF THE AMPLIFIERS NEGATIVE
OUTPUT TERMINALS.
QUALITY of the connections must be examined to ensure a high performance trouble
free operation is enjoyed. Check that the connections
are tight, but do not overtighten with excessive use of spanners etc. If bare wires are
used, make sure that no loose strands of wire short across to the other terminals or the
amplifier chassis.
When using plugs such as Banana, be sure to use good quality one's with a firm fit.

Plinius SA-50 instruction manual. Page 9
AMPLIFIER CONFIGURATION SELECTOR (ACS)
The Amplifier Configuration Selector (ACS) is a unique switching method that exploits all
of the operation features of this amplifier. By using this switch it is possible to operate
this amplifier with either balanced or unbalanced signals and achieve a stereo or mono
output.
Stereo or Mono use of this amplifier will depend on the type of ancillary equipment
employed with your system. If you wish to use this amplifier as a single channel (mono)
power amplifier in a stereo Hi Fi system, then another amplifier the same as this will be
required for the other channel. This will provide an extremely high performance option.
STEREO. This SA-50 is a dual channel or stereo amplifier.
Both left channel and right channel signals are amplified and output to a stereo pair of
loudspeakers. This is the most common use of this amplifier.
MONO. Using the built in switching facility (ACS) both channels of this amplifier
combine (electronically) to form one single amplifier channel. Special input and output
wiring requirements apply and are explained throughout this manual.
Balanced or unbalanced input options will depend on the type of signal available from
your preamplifier or other equipment.
The SA-50 provides both options to allow you to choose the most suitable preamplifier
for your purpose.
Plinius preamplifiers offer both balanced and unbalanced output options.
BALANCED LINE is normally used to transmit signals in a professional environment.
Because balanced line effectively reduces or eliminates noise pickup by the cabling, it has
become increasingly more important in high quality domestic HiFi systems.
Plinius SA-50 instruction manual. Page 10

AMPLIFIER CONFIGURATION SELECTOR CONTINUED
UNBALANCED or single-ended or RCA or coaxial leads are the most common of all
and are used in the majority of audio signal systems. The terminal plug and socket are
most commonly called RCA and can be found on the SA-50 for use as the standard input
terminals for both Left and Right inputs.
DO NOT Operate this amplifier with both RCA and XLR cables connected at the
same time.
Now that you will have a basic knowledge of the two types of input and two types or
output, we will discuss each of the options on the ACS.
THE ACS OPTIONS ARE AS FOLLOWING:
RCA STEREO This option provides a stereo output via both left and right output
channels from a stereo signal connected to both left and right RCA inputs. Connect the
input as discussed in pages 7 & 14 and the loudspeakers as discussed on page 8 & 16.
Plinius SA-50 instruction manual. Page 11

AMPLIFIER CONFIGURATION SELECTOR CONTINUED
RCA BRIDGED MONO. This option configures the whole amplifier to drive one loudspeaker from one
unbalanced signal fed to the RIGHT RCA input. See page 7 & 17. The loudspeaker is connected to both
channels + (positive) output terminals. DO NOT CONNECT ANYTHING AT ALL TO THE -
(NEGATIVE) TERMINALS.
See page 8 & 17 - 18. The power available in this mode is approximately four times the rated output of
the amplifier. Approximately 200 Watts into 8 ohms.
XLR STEREO This option provides a stereo output signal from a BALANCED input stereo signal
connected to both the left and right XLR inputs. See pages 7 & 14. All the advantages of Balanced line
transmission will be realised with good rejection of noise and some freedom from earth or ground loops
(hum). Connect the loudspeakers to both channels as discussed in "OUTPUT TERMINALS STEREO"
page 8 & 15 - 16.
XLR BALANCED MONO. The SA-50 operates as a true balanced mono amplifier, from input to
output. This configuration provides the highest quality mono performance from a balanced line input
connected to the RIGHT BALANCED XLR INPUT. See page 7 & 18. The loudspeaker is connected to
both channels + (positive) output terminals as discussed in OUTPUT TERMINALS BRIDGED MONO
page 18.
The power available in this mode is approximately four times the rated output of the amplifier.
Approximately 200 Watts into 8 Ohms.

Plinius SA-50 instruction manual. Page 12
INSTALLATION & OPERATION
MAINS VOLTAGE.
CHECK that the mains voltage printed on the rear of this amplifier is similar to the mains voltage
normally supplied to your area.
If in doubt, please consult your Plinius dealer.
PLACEMENT AND VENTILATION.
This SA-50 is designed to operate at a moderately high temperature.
The ideal location is on a rigid stand or floor mounted away from direct contact with any objects,
materials or deep pile carpets which may be effected by the heat or which may interrupt the flow of air
around the amplifier.
When operating the amplifier in Class A quite a lot of heat is generated which should be allowed to
dissipate without restriction. Make sure that no objects are placed on top of the amplifier and that the
heat sinks (cooling fins) are not covered or restricted in any way. Always ensure adequate ventilation.
The Plinius SA-50 design incorporates a very high level of mechanical decoupling of the input and
output. It can however still be influenced by acoustical feedback in the operating environment. The use
of acoustic cones or a suitably spiked amplifier stand or table may further enhance the performance of this
amplifier. Consult your Plinius dealer for further advise if required.

Plinius SA-50 instruction manual. Page 13
MAINS / LINE POWER CONNECTION
MAINS / LINE POWER connection is via the supplied plug-in lead.
The standard IEC socket connects the mains power at the amplifier end while a local mains plug is
required at the wall end. In the event where a "local" plug needs to be fitted to the wall end of the lead,
ensure that the plug is wired correctly by a suitably qualified or experienced person.
The wiring code is;
Green to Earth,
Blue to Neutral,
Brown to Phase or Live.
Ensure the mains switch on the front of the amplifier is OFF before attempting any modification of the
mains connection.
Depress the left hand side of the MAINS switch. See page 4.
MAINS / LINE FUSE.
A Mains / Line fuse is fitted within the IEC Mains / Line socket on the rear of the amplifier. A small
draw at the bottom of this socket may be removed ( after the IEC plug is removed ) by levering it out with
a flat blade screw driver. The fuse fitted should be rated at no greater than 10 Amps Slow-Blow.
In the unusual event that this fuse should blow, you must first establish the cause of this failure, cure the
fault and then replace the fuse with one of the same type.
DO NOT FIT A FUSE WITH A HIGHER RATING without consulting your Plinius dealer first.

Plinius SA-50 instruction manual. Page 14
CHANGING THE MAINS / LINE VOLTAGE CONFIGURATION
In the event that your Mains / Line voltage is different to that printed on the back of the SA-50, it may
altered by a suitably qualified or experienced person.
There are only two options, 110V - 120V or 220V - 240V Operation
Firstly disconnect the lead from the IEC socket on the SA-50 and make sure the MAINS switch is OFF.
Turn the SA-50 over so the base is facing up.
Carefully remove the 12 cross-head screws, and the 2 large flat screws.
This will allow the base to come free.
Locate the terminal block with a clear perspex guard, remove the guard by undoing the M3 nuts.
The ring terminals can be moved by undoing the cross-head screws.
Use the layout label stuck to the base of the SA-50 to ensure correct orientation of the wires.
DOUBLE CHECK THE WIRE ORIENTATION BEFORE RE-ASSEMBLING THE SA-50.
Re-assemble the SA-50 and verify correct operation, by attempting correct operation.
If there are any resultant problems consult your Plinius Dealer.
Plinius SA-50 instruction manual. Page 15
CONNECTIONS FOR STEREO OPERATION.
Connect the input and output cables to the amplifier. The use of high quality cables and connectors is
highly recommended.
DO NOT Operate this amplifier with both RCA and XLR cables connected at the same time.
INPUTS

SECTION OF REAR PANEL SHOWING RCA AND XLR INPUTS
RCA inputs are the most commonly used and are found on virtually all preamplifiers or other ancillary
equipment. For normal STEREO use, connect the left channel output of the preamplifier to the left
channel input of the SA-50 and the right channel output of the preamplifier to the right channel input of
the SA-50
SELECT "RCA STEREO" on the ACS
( Amplifier Configuration Selector ). See page 9.
XLR inputs are becoming more popular and provide a professional quality of wiring. XLR inputs allow
the use of fully balanced or quasi balanced signals from preamplifiers, CD players and other ancillary
equipment to be fed directly to the amplifier.
The technical advantages of this system of wiring may be fully realised here because of the dedicated
"BALANCED" input circuit facilities provided. Input XLR sockets are provided for the termination of
each left and right channels.

Plinius SA-50 instruction manual. Page 16
CONNECTIONS FOR STEREO OPERATION CONTINUED
SELECT "XLR STEREO" on the ACS ( Amplifier Configuration Selector). See Page 9.
CONNECTIONS to the XLR sockets are;
Pin 1 - Earth Pin 2 - + Signal Pin 3 - - Signal
To achieve a sound performance that is correctly aligned in your room, it is important that all of the leads
carrying signals for the RIGHT channel loudspeaker ( this loudspeaker will be the one which is located to
the right of the listening position ) are connected to the RIGHT input or output from signal source ( CD,
Phono etc ) to loudspeaker. Signals for the LEFT channel should receive corresponding attention.
The use of low quality preamplifiers or CD players "direct" should be treated with caution and advice
sought from your dealer about the compatibility of these items before connecting them to this amplifier.
DO NOT Operate this amplifier with both RCA and XLR cables connected at the same time.
OUTPUT
Output connections are provided to allow the use of most types of high quality loudspeaker cables.
The terminals are very robust 5 way binding posts which allow the use of banana plugs, bare wires, pins,
spades and looped wire or terminals. The hexagonal nut is provided where extra tightening of the
terminal is needed or desired and may be used with a suitable spanner. This is often necessary with some
of the stiff speaker cables used today. Do not over tighten these terminals.

Plinius SA-50 instruction manual. Page 17
CONNECTIONS FOR STEREO OPERATION CONTINUED
CONNECT the RIGHT hand loudspeaker to the RIGHT CHANNEL OUTPUT terminals on the
amplifier. Connect the LEFT hand loudspeaker to the LEFT CHANNEL OUTPUT terminals.
Connect the Positive (+) or Red loudspeaker terminal to the + (Positive) terminal on the amplifier.
Connect the Negative (-) or Black loudspeaker terminal to the - (Negative) terminal on the amplifier.
Repeat this process for each loudspeaker.
PHASING (or Polarity). It is important to achieve good stereo imaging in your listening room. By
observing the wiring instructions above, each power amplifier / loudspeaker combination should be in
phase. If you experience a poor stereo image and / or a lack of bass, check that the loudspeaker wiring
has been connected correctly. We recommend that you use one of the easily obtainable "test discs" to help
you ensure both phasing and channel orientation are correct. If in doubt, consult your Plinius /
loudspeaker dealer for advice.

Plinius SA-50 instruction manual. Page 18
CONNECTIONS FOR MONO / BRIDGED OPERATION
MONO / BRIDGED operation of the Plinius SA-50 amplifier is a very high quality method of achieving
very high power output without any compromise of performance. Both channels of the SA-50 combine to
form a single channel or Mono amplifier. The output power available is
equal to four times the rated output of this amplifier and is typically 200 Watts RMS into 8 Ohms.
Special care must be taken connecting the input signal and loudspeakers to ensure safe operation and best
possible performance.
To achieve a STEREO performance in MONO / BRIDGED mode, it will be necessary to have and use
TWO (2) SA-50 power amplifiers. One amplifier for each LEFT and RIGHT channel.
SECTION OF REAR PANEL SHOWING LOCATION OF RIGHT CHANNEL INPUT AND
OUTPUT TERMINALS..
INPUTS
RCA AND XLR INPUTS FOR MONO / BRIDGED OPERATION USE ONLY RIGHT
CHANNEL INPUT TERMINALS.
RCA input for BRIDGED / MONO use is the RIGHT channel RCA INPUT.

Plinius SA-50 instruction manual. Page 19
CONNECTIONS FOR MONO / BRIDGED OPERATION CONTINUED
SELECT "RCA BRIDGED MONO" on the AMPLIFIER CONFIGURATION SELECTOR (ACS).
XLR balanced line input for the MONO / BRIDGED option use RIGHT channel XLR INPUT.
SELECT the "XLR BALANCED MONO" option on the AMPLIFIER CONFIGURATION
SELECTOR (ACS). See page 11.
DO NOT Operate this amplifier with both RCA and XLR cables connected at the same time.
OUTPUT
Output connections are provided to allow the use of most types of high quality loudspeaker cables.
The terminals are very robust 5 way binding posts which allow the use of banana plugs, bare wires, pins,
spades and looped wire or terminals. The hexagonal nut is provided where extra tightening of the
terminal is needed or desired and may be used with a suitable spanner. This is often necessary with some
of the stiff speaker cables used today. Do not over tighten these terminals.
Both sets of loudspeaker terminals are used in a special way when the amplifier is BRIDGED. As the
amplifier is now operating as a MONO or single channel amplifier, you must be very careful to attach the
loudspeaker correctly.

Plinius SA-50 instruction manual. Page 20
CONNECTIONS FOR MONO / BRIDGED OPERATION CONTINUED
CONNECT THE POSITIVE (+) OR RED TERMINAL OF THE LOUDSPEAKER TO THE RIGHT
CHANNEL + (POSITIVE) TERMINAL ON THE AMPLIFIER
CONNECT THE NEGATIVE (-) OR BLACK TERMINAL OF THE LOUDSPEAKER TO THE LEFT
CHANNEL + (POSITIVE) TERMINAL ON THE AMPLIFIER.
DO NOT CONNECT ANY WIRE OR LEAD TO ANY - (NEGATIVE) OUTPUT TERMINAL.
LOUDSPEAKERS
This amplifier is designed for use with HiFi quality loudspeakers. It should not be used to operate with
any other type of appliance or equipment not intended or designed for use with this amplifier.
Choice of loudspeakers is one of personal taste, providing the chosen loudspeakers are suitable for use
with this power amplifier. Be certain that your loudspeakers can handle most of the rated output power of
this amplifier. Your may find loudspeaker specifications confusing or misleading therefore you should
discuss these fully with your audio dealer prior to purchase. The use of medium power (50 Watts RMS or
greater)
loudspeakers are recommended for this amplifier in stereo mode, while the use of high power (150 Watts
RMS or greater) loudspeakers are recommended for this amplifier in mono mode. Our experience
indicates that low power loudspeakers are quite often suitable for use with this amplifier in either mode,
provided the volume is maintained at a level where no distortion is audible.
Impedance of the loudspeaker load is important to ensure the rated performance of this amplifier. Any
combination of loudspeakers may be used but the total average impedance load for each channel should
be within a range of 4 to 8 Ohms in stereo mode and 8 Ohms in mono mode.