Ashly SRA-120 Operating Manual - Page 10

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Operating Manual - SRA-120 Power Amplifier

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.

10.

TROUBLESHOOTING TIPS

10.1

No 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.

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.

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).

10.2

Distorted Sound

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

Amplifier is being clipped. Reduce the signal

level at the signal source.