Crown PIP-AMC Informations techniques télécharger pdf (Page 15)

Macro-Tech 3600VZ Power Amplifier

Page 15

SOLVING INPUT PROBLEMS

Sometimes large subsonic (subaudible) frequencies

are present in the input signal. These can damage

loudspeakers by overloading or overheating them. To

attenuate such frequencies, place a capacitor in se-

ries 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 un-

balanced filters above. Filter D also incorporates the

subsonic 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 levels can also cause your amplifier to prematurely

activate its protection circuitry, resulting in inefficient

operation. RF can be introduced into the signal by lo-

cal radio stations and from the bias signal of many

tape recorders. To prevent high levels of input RF, in-

stall 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 com-

mon sources of hum in an audio system are inductive

coupling 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

fµ

.015

fµ

.018

fµ

1.8 mH

2.5 mH

.015

fµ

1.8 mH

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

1 Hz 10 Hz 100 Hz 1 kHz 10 kHz

–5

–10

–15

1 f

.1 f

.05 f

.01 f

Fre

uenc

4 kHz 10 kHz 40 kHz 100 kHz

Fre

uenc

–10

–20

6 dB/octave

12 dB/octave

Amp

GND

Amp

GND

Amp

GND

Source

1.8 K ohm

.003

fµ

.015

.018

fµ

3.9 mH

5 mH

600 ohm

Source

600 ohm

Source

Note: A low source impedance (R) can be

increased to 600 ohms with an a

riate resistor.

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Crown PIP-AMC Informations techniques Page 15

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