Macro-Tech 3600VZ Power Amplifier
Page 16
Reference Manual
SOLVING INPUT PROBLEMS
Sometimes large
subsonic
(subaudible)
frequencies
are present in the input signal. These can damage loud-
speakers by overloading or overheating them. To at-
tenuate such frequencies, place a capacitor in series
with the input signal line. The graph in Figure 3.10
shows some capacitor values and how they affect the
frequency response. Use only low-leakage paper, my-
lar or tantalum capacitors.
For balanced input wiring use one of the examples in
Figure 3.12. Filters A, B and C correspond to the unbal-
anced filters above. Filter D also incorporates the sub-
sonic filter described previously.
Fig. 3.11 Unbalanced RFI Filters
Another problem to avoid is the presence of large lev-
els of
radio frequencies
or RF in the input signal. Al-
though high RF levels may not pose a threat to the
amplifier, they can burn out tweeters or other loads that
are sensitive to high frequencies. Extremely high RF lev-
els can also cause your amplifier to prematurely acti-
vate its protection circuitry, resulting in inefficient
operation. RF can be introduced into the signal by local
radio stations and from the bias signal of many tape
recorders. To prevent high levels of input RF, install an
appropriate low-pass filter in series with the the input
signal. Some examples of unbalanced wiring for low-
pass filters are shown in Figure 3.11.
Fig. 3.10 Subsonic Filter Capacitors
Fig. 3.12 Balanced RFI Filters
Tip:
The P.I.P.-FX included with your amplifier has plenty
of room on its circuit board for input filters.
A third problem to avoid is
hum
. The two most common
sources of hum in an audio system are
inductive cou-
pling
and
ground loops
.
Inductive coupling can occur when input cables are
subjected to a magnetic field from a power cord or
power transformer. One way to prevent inductive cou-
pling is to lace the input cables together along their
length and route them as far away as possible from
power transformers and power cords. The use of
Input Wiring Tips
1. Use only shielded cable. Cables with
higher density shields are better. Spiral
wrapped shield is not recommended.
2. When using unbalanced lines, keep the
cables as short as possible. Avoid cable
lengths greater than 10 feet (3 meters).
3. Do not run signal cables together with
high-level wiring such as loudspeaker wires
or AC cords. This greatly lessens the chance
of hum or noise being induced into the input
cables.
4. Turn the entire system off before changing
connections. Turn level controls down
completely before powering the system back
up. Crown is not liable for damage incurred
when any transducer or component is
overdriven.
+
–
Balanced In
910
Ω
.003
F
µ
.015
F
µ
.018
F
µ
1.8 mH
2.5 mH
A
C
B
.015
F
µ
1.8 mH
D
Balanced Out
+
–
910
Ω
1.8 mH
2.5 mH
1.8 mH
+
–
Balanced In
Balanced Out
+
–
+
–
Balanced In
Balanced Out
+
–
+
–
Balanced In
Balanced Out
+
–
0.47 Film
0.47 Film
1 Hz
10 Hz
100 Hz
1 kHz
10 kHz
dB
0
–5
–10
–15
1 F
µ
.1 F
µ
.05 F
.01 F
µ
µ
Frequency
4 kHz
10 kHz
40 kHz
100 kHz
Frequency
dB
0
–10
–20
A
B
C
6 dB/octave
12 dB/octave
To
Amp
GND
To
Amp
GND
To
Amp
GND
Source
1.8 K ohm
.003
F
µ
.015
F
µ
.018
F
µ
3.9 mH
5 mH
600 ohm
Source
R
600 ohm
Source
R
A
C
B
Note: A low source impedance (R) can be
increased to 600 ohms with an appropriate resistor.
