Connections: Chapter 2

BALANCED OR UNBALANCED?

With long cable runs (e.g., over 6 meters/20 feet) in noisy electrical environments, the cable itself can act as an “antenna” and pick up RF fields, AC hum, or other types of interference. To avoid these problems, many professional studios and live sound companies use balanced line connections. The average application will probably not require balanced lines, but using balanced connectors between the mixer and the RA150/300/500 means one less possibility for ground loops and hum elsewhere in the system.

Balanced lines carry a pair of signals, each out of phase with respect to the other but otherwise identical. To be converted back into a single, unbalanced line, both balanced lines feed a differential amplifier input or transformer that responds to the difference in levels between signals. Thus, the out-of-phase signals are recombined into an unbalanced signal, but interference induced into the cable will not be out of phase. Since there is no difference between these signals, the differential amplifier or transformer will reject the interference to a great degree. This tendency to ignore interference is called Common Mode Rejection.

To connect a balanced line output to feed the RA150/300/500:

You have two options:

If you have the RA150, which doesn't have an XLR input, you may use an XLR-F to TRS-M cable or adapter. The 1/4" input jack of the RA150 is balanced. (See Figure 5 on page 17.)

To connect an unbalanced source to the amplifier input:

Unbalanced cable

Simply use a standard, shielded 1/4" patch cord. Or, if the source has an RCA/phono output, use a shielded phono-to-phono cable.

Unbalanced-to-balanced cable with telescoping shield

In some installations, you may be able to eliminate a ground loop even though the source is unbalanced by wiring a cable or adapter that has the shield connected at only the unbalanced end, using the inner conductor wires to carry the "hot" signal to pin 2 and the ground to pin 3 of the RA150/300/500. This may keep any ground potential difference between the source and the amplifier out of the signal path. The following diagram shows an adapter that assumes pin 2 of the XLR connector is “hot”; note that the shield of the phone jack is NOT connected to pin 1 (the ground of the amplifier), but is left floating (disconnected).

TRS-to-TRS cable

Most modern mixing consoles, such as the Alesis Studio 32, feature balanced outputs on 1/4" TRS jacks. This is the same balancing connector used by the RA150/300/500. Get a 3-conductor cable with a 1/4" male TRS connector at each end.

XLR-to-XLR cable

Male XLR Connector

2 (hot)

 

 

 

 

 

 

1/4 "

 

 

 

 

 

 

 

 

 

1 (float)

 

phone

 

 

 

 

jack

 

 

 

 

 

 

3 (cold)

A slightly more expensive balanced connector is the XLR type, most commonly sold as a "microphone cable". The main advantage of this is that the connector locks in place, making it more resistant to accidental disconnection. If your mixing console has XLR outputs, and you have the RA300 or RA500 amplifier, you may connect it with an XLR female to XLR male cable. (The mixer will have an XLR male jack, the amp has an XLR female jack.)

If you have an RA150 without an XLR input, then make a 1/4" mono to 1/4" TRS adapter. Wire the "hot" of the input signal to the tip, the shield/ground to the ring, and leave the sleeve disconnected at the RA150.

16

RA150/300/500 Reference Manual

Page 17 Page 19
Page 18
Image 18
Alesis RA300, RA500 manual Balanced or UNBALANCED?, To connect a balanced line output to feed the RA150/300/500
Page 17 Page 19

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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