Class A Power Amplifier
CONGRATULATIONS on your decision to become the proud owner of this Plinius SA-250 Power Amplifier. This manual has been prepared to help you understand the operation of your amplifier, and to provide information about its design and the variety of ways it may be used. We have designed and manufactured this amplifier to reproduce faithfully and accurately, your favourite music.
Introduction ........................................................................................................................................Page 3 Precautions ........................................................................................................................................Page 5 Amplifier Features - FRONT PANEL .....................................................................................................Page 6 Amplifier Features - REAR PANEL ............................
Please take special note of the following precautions before operating your new amplifier: • The Plinius SA-250 Power Amplifier can be operated in bridged mode and may deliver in excess of 900 watts into 8 ohms. This amplifier is also capable of a very large peak current delivery. • The Plinius SA-250 Power Amplifier operates in Class A. It is capable of generating temperatures that could have an adverse effect on other equipment, furniture etc.
The front of the Plinius SA-250 Power Amplifier incorporates a small panel fitted with three switches. These switches control the functions most used on the amplifier. A BIAS MUTE FRONT PANEL LAYOUT SHOWING MUTE, MAINS AND BIAS SWITCHES 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 loudspeakers, so a Mute switch is fitted to interrupt the input signal.
BIAS SWITCH This switch on the right of the panel alters the operating bias of the amplifier. The switch operates on a pulse system and lights the Bias LED when the amplifier is switched to Class A. In Class AB the LED is off. BIAS AB: This 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 fidelity amplifier designers for their products.
This panel incorporates all the terminals for connecting the input signals from your preamplifier, and output to the loudspeakers, and mains supply. A reasonable understanding of this amplifier and a logical approach should ensure that you are listening to this amplifier without any difficulties at all. Please remember that your Plinius SA-250 Power Amplifier is a high quality electronic instrument capable of an exceptional level of performance.
INPUT TERMINALS Input terminals for your Plinius SA-250 Power Amplifier are easily accessible and fitted to the top centre area of the rear panel. A brief summary of connection possibilities is listed below, while a more detailed explanation follows later in this instruction manual. RCA INPUTS LEFT & RIGHT: These standard RCA terminals are for use with unbalanced signals from most signal sources such as audio preamplifiers.
RCA BRIDGED MONO: This option configures your amplifier to drive one loudspeaker from one unbalanced signal fed to the RIGHT RCA input. The loudspeaker is connected to both channels positive (+) output terminals, giving an available power in this mode four times the rated output of the amplifier, approximately 900 watts into 8 ohms. Special care must be taken in connecting the input signal and loudspeakers to ensure safe operation and best possible performance.
Please note that in order to achieve STEREO performance in either of the Mono modes, it will be necessary to use two Plinius SA-250 Power Amplifiers - one amplifier each for left and right channels. GROUND LIFT SWITCH This switch is located adjacent to the Mains Input Socket, and allows the signal ground to be disconnected from the chassis. In some installations a hum loop may exist due to duplicate ground paths from different equipment.
PLACEMENT AND VENTILATION Your Plinius SA-250 is designed to operate at a moderately high temperature, even more so when used in Class A. The ideal location is on a rigid stand or floor mounted away from direct contact with any temperature sensitive materials or deep pile carpets. The flow of air around the amplifier should also be kept unimpeded, so ensure that the heat sinks (cooling fins) are not covered or restricted in any way to ensure adequate ventilation.
RIGHT INPUTS LEFT INPUTS RCA STEREO RIGHT OUTPUTS XLR BALANCED MONO RCA BRIDGED MONO XLR STEREO LEFT OUTPUTS AMPLIFIER CONFIGURATION SELECTOR REFER TO OWNERS MANUAL FOR USAGE INSTRUCTIONS REAR PANEL SHOWING LOCATION OF INPUT/OUTPUT TERMINALS It is important that you connect your loudspeakers (outputs) and preamplifier (inputs) to the Plinius SA250 Power Amplifier correctly to ensure the amplifier is not damaged, and sounds it’s best with your system.
RCA STEREO Connect your preamplifier or input signal to the two RCA inputs at the top of the amplifier back panel. Make sure you connect the red coded cable to the red RIGHT RCA input and the black (or white) cable to the black LEFT RCA input. Also make sure the RCA connectors are a snug fit and are inserted all the way in. Next connect your loudspeaker wires to the output posts on either side of the rear panel.
Now turn the ACS switch fully clockwise then two positions counter-clockwise so that it is in the XLR Stereo position. It is now safe to switch on your amplifier. XLR BALANCED MONO As with RCA Bridged Mono, this option configures your amplifier to drive one loudspeaker, but from one balanced line input connected to the RIGHT XLR Input. In balanced mono mode the only input made to your preamplifier is to the RIGHT channel XLR input. The LEFT channel XLR input is not connected.
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 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.
ERROR DETECTION The Plinius SA-250 Power Amplifier has in-built error detection. This will function under the following conditions: • • When the amplifier is overdriven/clipped If any internal fuse is damaged Should either of these circumstances arise the amplifier will disconnect both channels and mute the input. This condition will remain until the input signal level is reduced or the damaged fuse replaced. When error detection is triggered the power LED will turn off and the mute LED will pulse.
LED BRIGHTNESS CONTROL Your Plinius SA-250 has an internal LED brightness control that will adjust all three front panel LED’s. A small flat bladed screwdriver can be used to adjust the brightness. The LED brightness control is a small multi turn potentiometer and is located on the front of the main circuit board within the top cavity of the amplifier, and is labelled VR5.
Your Plinius SA-250 Power Amplifier is designed for use with high fidelity loudspeakers. It should not be used to operate any other type of appliance or equipment. Choice of loudspeakers is one of personal taste, providing the chosen loudspeakers are suitable for use with your amplifier. Be certain that your loudspeakers can handle most of the rated output power of this amplifier.
Class A has always been regarded as the perfect operating mode for audio amplifiers. Many leading amplifier designers and manufacturers world wide recognise that a well designed Class A circuit has inherently lower distortion than any other design. Class A circuit topology is one in which the total current the amplifier is capable of delivering, is kept flowing in the circuit regardless of demand. In a conventional or Class AB amplifier circuit this current flow varies when demand varies.
250-WATTS RMS PER CHANNEL INTO 8 OHMS. 450-WATTS RMS PER CHANNEL INTO 4 OHMS. BOTH CHANNELS DRIVEN FROM 20Hz TO 20kHz AT 0.05% TOTAL HARMONIC DISTORTION. S BRIDGED OUTPUT: 900 Watts RMS 20Hz to 20kHz into 8 ohms (Mono). S DYNAMIC HEADROOM: 1dB or greater at 8 ohms with music. S FREQUENCY RESPONSE: 20Hz to 20kHz ±0.2dB. 0dB at 0Hz and -3dB at 70kHz. S DISTORTION: Typically <0.05% THD at rated power. 0.1% THD and IM worst case prior to clipping.
ACS (Amplifier Configuration Selector)...........................................................................................Page 9 Balanced Signal ...........................................................................................................................Page 10 Bias Class A............................................................................................................................ Pages 7,20 Bias Class AB....................................................................
All operational, technical and descriptive material published here is subject to change at any time without notice. For further product information or queries, please contact us at the address below. PLINIUS products are designed and manufactured by: Audible Technologies Ltd. P.O. Box 1836 1836 Palmerston North New Zealand Phone: Facsimile: Email: Internet: 64 6 354 8583 64 6 354 8586 info@pliniusaudio.com www.pliniusaudio.com ©2000 Audible Technologies.
