Studio Reference I & II Professional Studio Amplifiers
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 series with the input signal line. The graph in Figure 3.11 shows some capacitor values and how they affect the frequency response of a Studio Reference amplifier. Use only
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1 Hz |
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| 10 Hz |
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| 10 kHz |
Frequency
Fig. 3.11 Subsonic Filter Capacitors
Another problem to avoid is large levels of radio fre- quencies or RF in the input signal. Although 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 protec- tion circuitry, resulting in inefficient operation. RF can be introduced into a signal by local radio stations and from the bias signal of many tape recorders. To pre- vent high levels of input RF, install an appropriate
+ | 470 ohms | + | |
| |||
A Balanced In | .0056 | Balanced Out | |
∝f | |||
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– |
| – |
470ohms
1.8mH
| + |
| + |
B | Balanced In | .015 | Balanced Out |
∝f | |||
| – |
| – |
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| 1.8 mH |
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| 2.5 mH |
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| + |
| + |
C | Balanced In | .018 | Balanced Out |
∝f | |||
| – |
| – |
2.5mH
0.47Film 1.8 mH
+ |
| + |
D Balanced In | .015 | Balanced Out |
∝f |
– –
0.47 Film 1.8 mH
Fig. 3.13 Balanced RF Filters
Tip: The
Another problem to avoid is ground loops. These are undesired currents that flow in a grounded system and usually cause hum in the output. A common source of ground loop problems is the placement of input cables parallel to power cables or near power transformers. The magnetic field that surrounds these conductors can induce the 50 or 60 Hz alternating current into your input cables. To prevent this type of ground loop, it is always a good idea to locate input cables away from
Input Wiring Tips
910 ohms
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| To |
Source | .0056 | Amp |
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∝f |
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A |
| GND |
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| 3.9 mH | To |
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R 600 ohm | .015 | Amp |
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Source | ∝f |
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B |
| GND |
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| 5 mH | To |
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R 600 ohm | .018 | Amp |
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∝ f |
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Source |
| GND |
C |
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4 kHz
Note: A low source impedance (R) can be increased to 600 ohms with an appropriate resistor.
dB
0
6 dB/octave
A
12 dB/octave
B
C
10 kHz | 40 kHz | 100 kHz |
Frequency
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 |
or AC cords. This reduces the chance of |
hum or noise being induced into the input |
cables. |
Fig. 3.12 Unbalanced RF Filters
For balanced input wiring, use an example from Fig- ure 3.13. Filters A, B and C correspond to the unbalanced filters shown in Figure 3.12. Filter D also incorporates the subsonic filter in Figure 3.11.
4. Turn the entire system off before chang- |
ing connections. Turn level controls down |
before powering the system back up. Crown |
is not liable for damage incurred when any |
transducer or component is overdriven. |
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