Connections: Chapter 2

OUTPUTS

Warning: Be sure that the AC power is off prior to connecting or disconnecting any signal wiring.

WHAT'S THE LOAD IMPEDANCE?

Alesis amplifiers can reliably drive 4 Ω loads in Stereo mode and 8 Ω loads in Bridged Mono mode. However, the impedance of a loudspeaker varies with frequency, and its nominal rated impedance is not necessarily its minimum impedance. Some loudspeakers carry both nominal and minimum impedance specifications, and some are supplied with impedance curves. When connecting multiple loudspeakers or systems to any amplifier, care should be taken that the actual load impedance does not drop below the amplifier’s rated output load. The RA150/300/500 amplifiers will not be damaged by excessively low output load impedances, but they will not be able to provide full output power and their protection circuits may automatically cut off their outputs until the low load condition is removed.

CONNECTORS

Each channel features a standard binding post connector (red = “hot” output, black = ground). The binding post or "banana" connectors are the preferred choice for permanent installations. There is greater surface area contact than with phone connectors, thus promoting a better electrical connection between the speaker wire and amplifier.

SPEAKER CABLES

The cables you use between the RA150/300/500 and its speakers are very important. Speaker cables must deliver large amounts of peak current to a speaker. To complicate matters further, a speaker represents an inductive load, and is more difficult to drive than a purely resistive load. Speakers are also very low impedance devices. Any resistance between the amp output and speakers will degrade the damping factor, efficiency and ultimately, the sound quality.

Alesis recommends stranded, rather than solid, cables for flexibility and ease of installation. However, solid cables are equally usable.

Never use shielded guitar cords as speaker cables. Because they lack sufficient current-carrying capacity, the amp and speakers will not perform properly and the sound may be degraded.

If you make your own cables, use electrical zip cord, which is designed to handle several amps of current, or heavy-gauge speaker cables if possible. In any event, the thicker the cable, the lower the resistance and the better the current-carrying capability. Thin hookup wire is not acceptable; the minimum acceptable wire type is the common “zip cord” used to connect AC to appliances. The table below relates the wire gauge to the how many feet of cable will lead to a 1 dB power loss at different impedances. The lower the resistance, the better. For cables run up to about 25 feet, 16 to 18 gauge wire is satisfactory.

Cable length that produces 1 dB of power loss

wire gauge

 

at 4Ω

 

at 8Ω

 

feet

 

meters

feet

 

meters

6

1200

 

366

2425

 

740

8

800

 

244

1600

 

488

10

475

 

145

950

 

290

12

300

 

91

600

 

183

14

190

 

58

375

 

114

16

120

 

37

240

 

73

18

75

 

23

150

 

46

20

50

 

15

100

 

30

22

30

 

9

60

 

18

18

RA150/300/500 Reference Manual

Page 19 Page 21
Page 20
Image 20
Alesis RA500, RA150, RA300 manual Outputs, Whats the Load IMPEDANCE?, Connectors, Speaker Cables
Page 19 Page 21

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.
Top Page Image Contents