Chapter 3: Operation

SYSTEM SETUP AND TESTING

Before applying power for the first time, double check the wiring to insure that everything is firmly connected and that the proper signals are being fed to the proper places. If a low frequency signal in a multi-amplified system is applied to a high frequency transducer, the transducer can be damaged, and a loose connection can cause noise which can damage any transducer.

Be certain that the amplifier front panel gain controls are set to minimum when the system under test is first powered up. After the power is applied, slowly advance each gain control to confirm that there are no driver-destroying hums or buzzes present—if there are, turn the power off and locate the source of the difficulty.

When first applying program material to the system, it is also advisable to keep the gain controls turned down to confirm, once again, that the wiring is correct. Once the system wiring is determined to be correct, the gain controls can then be set to an appropriate level for the system gain structure.

SETTING THE GAIN PROPERLY

Setting the system gain is fairly straightforward, but if it is not properly adjusted, the system’s distortion and noise characteristics may be less than optimum.

The most common cause of noisy operation, especially in studio use, is that the amplifier's gain controls are left all the way up, while the mixer's output is turned down. This can lead to blown speakers if the mixer is accidentally turned up, but more importantly, it amplifies the noise floor of the mixer output stage or wiring unnecessarily. Keeping the source level as high as possible and lowering the amplifier input gain will keep the noise level at a minimum.

The input sensitivity of the RA150/300/500 amplifiers at the 1/4" input or XLR input is

1.23volts (+4 dBu) for rated output with the amplifier gain controls at maximum. If you're plugged into the phono jacks, the sensitivity is –10 dBV (.316 volts). If the signal at the amplifier input is higher than this, the input gain controls of the RA150/300/500 must be turned down to avoid amplifier clipping. Most mixers output +4 dBu at nominal level/0 VU; that means if you go "into the yellow" on the meter of most mixers, the amp will be clipping its outputs or distorting the speakers unless you turn down the input gain controls.

It is generally best to try to keep the gain of the source device set for best signal-to-noise ratio consistent with distortion, and to then set the amplifier inputs for the desired SPL level.

A good way to set levels is to use a test tone or pink noise with a sound level meter. Set the mixer's controls at nominal levels, increase the test tone until the mixer is exercising its dynamic range without clipping itself. The mixer's meter should read from +10 to +15. Then slowly raise the RA150/300/500's input level controls until the desired peak sound pressure level is achieved.

RA150/300/500 Reference Manual

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Alesis RA150, RA300, RA500 manual System Setup and Testing, Setting the Gain Properly
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RA150, RA500, RA300 specifications

The Alesis RA series of amplifiers—comprising the RA300, RA500, and RA150—have earned a respected spot in the audio equipment landscape, catering to both musicians and audio professionals. With a blend of innovative technology, robust performance, and user-friendly features, these amplifiers offer solutions for various sound requirements.

Starting with the RA300, this amplifier delivers a solid output of 150 watts per channel at 4 ohms, making it ideal for smaller studio setups or personal listening environments. It is built with a lightweight yet durable design, employing a modern Class AB architecture that ensures low distortion and high audio fidelity. The RA300 features comprehensive input options, including balanced XLR and quarter-inch TRS inputs, allowing seamless integration into diverse setups. Additionally, the built-in protection circuitry prevents overheating and damage during prolonged use, ensuring longevity and reliability.

The RA500 steps up the power and performance, presenting a robust 250 watts per channel at 4 ohms, making it suitable for larger venues and demanding applications. It utilizes advanced thermal management technology, which aids in efficient heat dissipation, ensuring the amplifier operates smoothly even under heavy load. The RA500 also boasts significant dynamic range and headroom, making it a preferred choice for professional environments where audio clarity and volume are paramount. The addition of a frequency response that spans from 20Hz to 20kHz means it can faithfully reproduce a wide range of audio frequencies.

Meanwhile, the RA150 serves as a versatile option for various applications, delivering 75 watts per channel at 4 ohms. Despite its compact size, the RA150 does not compromise on sound quality or functionality. Its Class AB amplifier technology results in enhanced audio accuracy, making it popular among beginner studios and educational settings. The straightforward controls and indicators ensure that users can quickly adjust settings for optimal performance.

All three amplifiers in the Alesis RA series share a common goal: to provide high-quality sound amplification without unnecessary complexity. Their combination of solid construction, advanced technologies, and thoughtful features make them suitable for a multitude of audio environments—from home studios to professional gigs. Whether you opt for the RA300, RA500, or RA150, you are investing in a reliable tool designed to deliver exceptional audio performance, catering to the needs of discerning audiophiles and professionals alike.
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