Ashly manual Operating Manual - SRA-120Power Amplifier, Design Theory, 10.2Distorted Sound

Operating Manual - SRA-120 Power Amplifier

9.DESIGN THEORY

Ashly engineers set out to design a single rack space stereo power amplifier delivering a minimum of 120 watts total with the sonic excellence, mechanical rug- gedness and unsurpassed reliability Ashly amps are known for. These qualities were upheld while containing other important parameters such as weight, depth, serviceabil- ity and cost.

The result of this design philosophy is a superior sounding all-discrete bipolar power amp section at the heart of the amp. The voltage gain stages of the amp are totally discrete transistors operating "class A" for low distortion. The output section is a full complementary bipolar push-pull stage. The active balanced input and level control stages utilize low-noise op-amps for con- stant input impedance with accurate, low noise level con- trol. All integrated circuitry was kept outside the feed- back loop of the power amp section to maintain excellent transient response.

A toroidal power supply transformer is used to minimize induced hum noise and to reduce overall weight. Epoxy sealed output relays are used to protect speakers and the amplifier from turn on transients, excessive load current and overheat conditions. A unique rear-panel sen- sitivity switch (0dBu or -10 dBu) is provided to interface the amp with professional line level equipment or directly with low line level tape machines and CD players.

The SRA-120 is packaged in an extremely rug- ged one piece welded 14-gauge steel chassis. The power transformer is located near the front center of the amp to minimize front panel torsion. Channels 1 and 2 circuitry are on separate plated-through glass epoxy circuit boards with plug-in connectors for all wiring to ensure ease of servicing. Each channel has a large, extruded aluminum heat sink with vertically oriented fins for maximum con- vection cooling action.

10.TROUBLESHOOTING TIPS

10.1No Audio Output

• Power switch is on but not illuminated:

Line fuse on rear panel is blown or power outlet is dead.

IF LINE FUSE IS BLOWN, REPLACE ONLY WITH SAME TYPE AND RATING FUSE.

• Power switch is lit but no signal present indicator activity:

There is no input signal applied or input level controls are turned off. NOTE: In MONO mode, channel two input is disconnected and channel one input is sent to both channels.

• Protect LED remains lit:

Amp is in thermal protect mode. Loudspeakers have been disconnected until the amplifier returns to a normal temperature. The amplifier relies on convection air currents to move vertically through the side fins to keep cool. If the protect indicators come on because of overheating, mount the amplifier with air space above and below to allow convection cooling action to occur.

Amp is protecting speakers from ultrasonic signals. Disconnect input cables to see if ultrasonic signal is coming from audio source.

• Protect LED remains lit and relay clicking is heard:

Output is short circuited or load impedance is too low. Check speaker cables for shorts, increase load impedance by disconnecting some speakers.

A high frequency oscillation in the sound system is occurring when the relays close. Turn down the input level controls to verify that the amplifier alone is not causing the problem.

Be sure to use good quality shielded and balanced input cable. Do not run input cables alongside output speaker wires over long lengths (i.e..through the same conduit).

10.2Distorted Sound

• Output level meters indicate 0dB level (red CLIP LED on):

Amplifier is being clipped. Reduce the signal level at the signal source.

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