TO LOAD
SIGNAL IN
BUTTON IN
BRIDGE MONO HOOKUP
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4
Fig. 3.6 Jumper-Wire Location for Bridge-Mono Operation
JUMPER BETWEEN RED
BINDING POSTS
14 GAUGE SOLID OR LARGER
TO LOAD
PARALLEL MONO
SIGNAL
IN
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Fig. 3.7 Parallel Mono Hookup
Parallel Mono Operation
This configuration parallels the two output channels.
Caution: After wiring the unit for Parallel Mono, do not
operate the amplifier in Stereo mode, or you may
damage the amplifier.
1. On the rear panel, push out the "parallel mode"
pushbutton switch.
2. Plug the input line into the Channel 1 input jack,
and adjust the level with the Channel 1 input-level
control only.
3. Do not use the Channel 2 input; otherwise distortion
may result. Unplug the input to Channel 2 when
operating in mono and turn the Channel-2 level
control fully CCW.
4. Connect the output lines according to Fig. 3.7.
Note the jumper between the red binding posts.
Be sure to remove this jumper wheneveryou want
to use the amplifier in 2-channel stereo mode;
otherwise you may damage the amplifier.
3.6 Connecting Input Lines
T h e Micro-Tech's inputs are balanced 1 / 4 " phone
jacks. These inputs may be used either with balanced
phone plugs (tip, ring, and sleeve) or with unbalanced
phone plugs (tip and sleeve).
For loudspeaker-driving applications, the input should
be free of large sub-sonic (low-frequency) signals, a s
t h e y c a u s e o v e r h e a t i n g a n d o v e r l o a d i n g of t h e
loudspeaker. To remove such low frequencies, place a
series capacitor in the input signal line. The graph of
Fig. 3.8 shows how the value of the capacitor affects
the frequency response. Use only a low-leakage paper,
mylar, or tantalum capacitor.
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Fig. 3.8 Effect of Input-Capacitor Value on
Frequency Response
If large amounts of ultrasonic or RF frequencies are
found on the input, such a s bias from tape recorders,
etc., place a low-pass filter on t h e input. While
practically obtainable RF input levels will not damage
the amplifier, they can burn out tweeters or other
sensitive loads, activate the amplifier's protective
system, or overload the controlled-slewing-rate stage
of the amp (which provides RF overload protection).
T h e following filters a r e r e c o m m e n d e d for s u c h
applications (See Fig. 3.9).
A n o t h e r p r o b l e m to p r e v e n t i s g r o u n d loops —
undesirable currents flowing in a grounding system,
possibly causing hum in the output. A common form of
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Fig. 3.9 RFI Filters
3-4
loop is a pair of input cables whose area is subjected to
a magnetic hum field. To preventground loops caused
by magnetic induction, lace both cables together along
their length, and away from the power transformer. Do
not connect the input and output grounds together.
A third problem (with input and output grounds tied
together, a s in testing or metering) is f e e d b a c k
oscillation from load current flowing in the loop. In
industrial use, even the AC power line may provide this
feedback path. Proper grounding, and isolation of
inputs, of common AC-line devices is good practice.
3.7 Connecting Power
The Micro-Tech is furnished with a two-wire, 20A, 120V
AC plug. Use a 20A wall outlet whenever possible.
Voltages above 132V m a y d a m a g e t h e +/- 15V
regulator, filter capacitors and output transistors.
When testing the amplifier, the line voltage must be the
R M S of t h e peak equivalent to a sinusoid of t h e
indicated line voltage when at full load. Line regulation
problems can reduce the available output power.
3.8 Control Adjustments
1 . On the rear of the amplifier, turn down the input
level controls (full CCW).
2. Turn on the front-panel power switch. An amber
LED pilot light will come on, indicating that power
has been applied. This pilot light is powered bythe
low-voltage power supply and is independent of the
main power transformer. The pilot light will stay
on even if the transformers overheat and shutdown
(unless the low-voltage power supply has been
damaged).
3. On the rear panel, turn the level controls all the
way up (full clockwise), or for the desired loudness
from your speakers.
3.9 The Protection Mechanisms
T h e M i c r o - T e c h is protected against all c o m m o n
hazards that plague high-power amplifiers, including
shorted, open, or m i s m a t c h e d loads; overloaded
power s u p p l i e s ; e x c e s s i v e t e m p e r a t u r e , c h a i n -
destruction phenomena, input-overload damage, and
high-frequency overload blowups. T h e unit protects
loudspeakers from DC in the input signal.
3-5
