Front Panel Description
1. Gain Controls
These two knobs are the level controls for each channel of the amplifier. The gain increases as the knob is turned clockwise. The SA5500 features detented gain controls with dB calibrations to simplify set up.
2. Limit LED
If an audio signal is amplified beyond the limit of the amplifier, the extremes of the signal will not reach the appropriate levels, giving the appearance of being clipped off when viewed on an oscilloscope. The audible result is distortion, which in small amounts can lead to rapid ear fatigue, and in larger amounts a harsh and unpleasant breaking up of the sound which can damage speakers.
The SA5500 has a built in limiter on each channel to prevent clipping. Should the signal reach a level high enough to cause clipping, the limiter momentarily reduces the level just enough to prevent it. The limit LED lights whenever this occurs.
If your system has a dedicated compressor, you may decide to use the limiting function of this instead. Although the limiting function of the SA5500 has no noticeable effect on the sound quality below clipping, some users may seek to disable it. See feature 11.
3. Protect LED
The SA5500 features several types of protection to prevent damage to the circuitry during turn on or fault conditions. The power on protection relay prevents damaging thumps to the speakers as the power comes on. When the amp is switched on, the protect LED will light for a few seconds and then go out, indicating that the relay has closed, connecting the speakers to the amplifier.
The protect light will also come on if the speaker terminals are short circuited, or the impedance of the load between them is too low. In these circumstances, the protect LED will stay lit until the fault condition is rectified.
The amplifier’s large heatsinks, vents and fan should provide enough cooling even with a high ambient temperature. However, if the amp overheats, thermal shutdown protects the circuitry until the temperature is reduced to a safe level. Should the amp shutdown for thermal reasons, leave the power connected to the amp, try to improve ventilation, and reduce the gain. Without power, the fan cannot operate, and the amp will require longer to reach a low enough temperature to restart.
4. Signal LED
Each channel of the SA5500 features a signal LED to show that there is an audio signal at the input to the channel. The threshold for the indicator is
5. Power Switch
This turns the amp on and off. Although the SA5500 features power on muting, it is nevertheless good practice to reduce both the gain controls before turning on the amp. The turn on procedure for powering up an audio system should be to start from the instruments and mixer, and verify operation before moving on to the power amps. Once the amps are on, verify they are receiving a signal and then slowly increase gain.
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