Alesis RA100 User Manual

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ALESIS

RA-100

Reference Manual

CHAPTER 1 – GETTING TO KNOW THE RA-100

 

1.1

INTRODUCTION.....................................................................................

1

 

Principal Features................................................................................

1

 

Unpacking and Inspection.................................................................

3

 

About This Manual.............................................................................

4

CHAPTER 2 – INSTALLATION

 

2.1

REAR PANEL CONNECTIONS............................................................

5

2.2

POWER CONSIDERATIONS.................................................................

5

 

Fuse.........................................................................................................

5

 

The AC Cord.........................................................................................

5

 

Electrical Service to the RA-100........................................................

6

2.3

OPERATING ENVIRONMENT............................................................

6

 

Thermal Considerations in Rack Mounting.................................

6

 

Mounting on a Shelf or in a Non-RackEnclosure.......................

7

 

Avoiding Electromagnetic Interference..........................................

8

2.4

INPUTS.......................................................................................................

8

 

Input Jack Characteristics...................................................................

8

 

Cables......................................................................................................

8

 

Cable Wiring Tips................................................................................

9

 

Adapting the RA-100to Balanced Lines.........................................

9

2.5

OUTPUTS...................................................................................................

11

 

Connector Options...............................................................................

11

 

Output Cables........................................................................................

11

 

Connecting Cables to Push Connectors...........................................

12

 

The Importance of Speaker Polarity................................................

13

CHAPTER 3 – USING THE RA-100

 

3.1

FRONT PANEL CONTROLS.................................................................

14

 

Volume Controls.................................................................................

14

 

On-OffSwitch.......................................................................................

14

 

Mute Switch..........................................................................................

15

 

Clip Indicators.......................................................................................

15

3.2 CHECKING FOR PROPER POLARITY.................................................

15

3.3 CHOOSING THE CORRECT SPEAKERS.............................................

15

3.4

ABOUT GROUND LOOPS......................................................................

16

CHAPTER 4 – TYPICAL APPLICATIONS

4.1 STUDIO MONITOR AMP.......................................................................

18

4.2 SOUND REINFORCEMENT..................................................................

18

4.3

KEYBOARD AMPLIFICATION SYSTEM............................................

19

4.4

GUITAR AMPLIFICATION SYSTEM..................................................

20

4.5 BIAMP SOUND REINFORCEMENT...................................................

21

CHAPTER 5 – MAINTAINANCE/SERVICE

 

5.1

GENERAL INFORMATION..................................................................

22

 

Cleaning.................................................................................................

22

 

Maintenance.........................................................................................

22

 

Refer All Servicing to Alesis.............................................................

22

CHAPTER 6 – TROUBLESHOOTING

 

 

Hum........................................................................................................

23

 

No Volume...........................................................................................

23

 

Distorted or Low Level Sound..........................................................

23

 

Thin Sound/Sound that Changes Unpredictably in a Room....

23

CHAPTER 7 – SPECIFICATIONS

DO NOT REMOVE THE RA-100TOP COVER. THERE ARE NO USER SERVICEABLE PARTS INSIDE. REFER SERVICING TO A QUALIFIED REPAIR TECHNICIAN.

CHAPTER 1:

MEET THE RA-100

1.1 INTRODUCTION

Principal Features

Congratulations on your purchase of the Alesis RA-100Reference Amplifier. With all the wondrous advances in both analog and digital electronics in the past few years, it’s easy to forget that an audio chain is only as good as its weakest link. Withlow-costdigital devices now offering sound quality unheard of only a few years ago, Alesis has applied its expertise toward creating a sonically accurate, stable, and affordable stereo power amplifier that’s suitable for the digital age. Optimized for studio monitoring applications andmoderate-powerlive performance setups, the amp’s main features include:

100 watts per channel into 4Ω, 75 watts per channel into 8Ω

Dual clipping indicators alert you of any type ofnon-linearoperation, not just clipping

Output short circuit protection to minimize down time and protect the amplifier’s circuitry

Massive, conservatively rated, custom-designedextruded heat sinks (individual for each channel) for cool operation

No ventilation fan is needed, allowing for quiet operation and reduced ambient noise in the studio

Extremely low noise and distortion; suitable for quiet applications such as recording studios, church installations, and museums

However, some of the RA-100’smost important features are hard to put on a spec sheet. In a quest for a “musical” sounding power amp that can stand up to a tough life on the road as well as continuous operation in the studio, Alesis has made somechanges—someminor, and some verysignificant—tothe standard power amp.

• The RA-100doesn’t produce any audio transients duringpower-upor

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power-down.Nonetheless, there’s a2-secondmute onpower-upto compensate for any pieces of equipment plugged into theRA-100that produce transients uponpower-up,and receive power at the same time as theRA-100.Also, because the amp doesn’t produce power on/off thumps itself, the mute circuit can bepre-poweramp. This allows simpler circuitry than what would be required for shutting down the power amp stages.

The RA-100’spower supply has plenty of reserve capacity to handle percussive transients, but if someone kicks theRA-100’splug out of the wall, you want all amplification to cease immediately. Therefore, if the amp senses any loss of power, it instantly mutes the audio.

Because power-upand-downare noiseless, the on/off switch doubles as a mute or “panic” button.

The output stage uses full complementary-symmetrycircuitry throughout. Although there are cheaper ways to design an output stage, thistime-testedapproach is generally considered superior tonon-complementary-symmetry types. The output devices are rated at 30 Amps of peak current, and boast a 20 MHz FT (transition frequency) for superior bandwidth.

Extremely good stability with reactive loads (e.g., speakers and crossovers). Stable operation is essential when presented with the changing load characteristics of typical speakers; the RA-100uses several stabilization techniques to maintain consistent feedback network characteristics.

Alesis recognizes that amplifiers will sometimes be driven into clipping— even though this is not good practice—duringa recording session or under the pressures of live performance. As a result, a great of deal of research went into creating the best possible clipping entry/recovery characteristics. Amps with lots of overdrive and saturation tend to create overshoot and ringing during the clipping process, which degrades the sound; theRA-100has been designed so that it exhibits very little saturation, even when overloaded. As a result, it enters and exits clipping very cleanly. Clean clipping allows theRA-100to be driven harder, which makes the overall perceived sound louder.

Monitoring a sine wave being clipped confirms this action. With the RA100, the amp will follow the original input signal as soon as clipping ceases

(a). With some conventional amp designs, the signal will “hang” at the clipped level for a while before catching up with the input signal (b. This saturation-causedovershoot can sometimes sound worse than the clipping itself.

s

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No “speaker stress” during shutdown. With traditional protection circuitry, the act of clamping the output devices to a safe value can make the amp unstable with particular notes that interact with the speaker resonance, thus producing oscillation or “motorboating.” This could damage your speakers. The RA-100uses an elegant clamping design that observes the load at all times but also integrates the signal characteristics into the clamping action. Thus, the clamping action is gentle and, after clamping to the maximum current encountered in normal operation, will slowly (over 1 to 2 seconds) clamp based on the load and signal characteristics. If the source of the problem (e.g., a short across the speaker terminals) is removed, the signal recovers instantly.

Alesis also recognizes that whatever else, “the show must go on.” As a result, under conditions of extreme abuse (such as ultra-lowspeaker impedances or mounting that allows for no ventilation), theRA-100will limit its signal rather than simply shut down. Taken to an extreme, this will produce distortion but sound will still come out.

To acquaint yourself with the RA-100’soperation, and to use it properly in various applications, carefully read this manual. Power amplifiers are highcurrent devices that are thenext-to-lastlink in the audio chain. Proper attention to cabling, power distribution, ground loops, and other topics covered in this manual is vital to have theRA-100live up to its full potential.

As always, we welcome your suggestions and comments concerning this product, or any other product in the Alesis line.

Unpacking and Inspection

Your new Alesis power amplifier was carefully packed at the factory, and the container was designed to protect the unit during shipping. Please retain this container in the highly unlikely event that you need to return the RA-100for servicing.

Upon receiving the RA-100,carefully examine the shipping carton and its contents for any sign of physical damage that many have occurred in transit. If you detect any damage, do not destroy any of the packing material or the carton, and immediately notify the carrier of a possible claim for damage. Damage claims must be made by you. If you picked up your amplifier directly from an Alesis dealer, contact the dealer.

The shipping carton should contain:

• This instruction manual

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Alesis RA-100power amp with the same serial number as shown on the shipping carton

Power cord.

Four stick-onrubber feet (for shelf mounting, to prevent theRA-100’sbottom surface from scratching the shelf)

Alesis warranty card. It is important to register your purchase; if you have not already filled out your warranty card, please do so now.

About This Manual

The manual presents information in a logical order. Chapter 2 covers installation, and Chapter 3, how to use the RA-100.Chapter 4 covers several typical applications. The manual closes with information on maintenance/servicing, troubleshooting, and operating specifications.

Please remember that a power amplifier is a high-current,high-powerdevice and should be treated with respect and care. Even if you are an audio veteran, we urge you to read the entire manual to make the best use of theRA-100.

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CHAPTER 2:

INSTALLATION

2.1 REAR PANEL CONNECTIONS

The following diagram shows the various rear-panelcomponents. Please refer to this diagram during the procedures described in this chapter.

Fuse:

5 Amps

(A spare fuse in included in the fuse holder)

Left Push Clip

Outputs

Right

 

 

 

 

 

 

Left Phone

Input

 

 

 

 

 

 

 

 

 

 

 

 

Plug Output

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Right Phone

 

Left Input

AC Line

 

Plug Output

 

 

 

Cord Jack

 

 

 

 

 

 

 

 

 

 

 

Right Push

 

 

 

 

 

 

 

 

 

 

 

 

Clip Outputs

2.2 POWER CONSIDERATIONS

Fuse

Replace with a 5 Amp, slow-blowtype only; use of any higher amperage value will void the warranty.FUSES ARE FOR YOUR PROTECTION—

NEVER SUBSTITUTE A FUSE OF A HIGHER RATING, OR BYPASS IT.

The AC Cord

The RA-100’sIEC-specAC cord (do not substitute any other AC cord) is designed to feed an outlet that includes three pins, with the third, round pin connected to ground. The ground connection is an important safety feature designed to keep the chassis of electronic devices such as theRA-100at ground potential.

DO NOT OPERATE ANY ELECTRICAL EQUIPMENT WITH UNGROUNDED OUTLETS. PLUGGING THE RA-100INTO AN UNGROUNDED OUTLET, OR “LIFTING” THE UNIT OFF GROUND WITH

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A THREE-TO-TWOWIRE ADAPTER, CREATES A HAZARDOUS CONDITION. ALESIS CANNOT BE RESPONSIBLE FOR PROBLEMS CAUSED BY USING THERA-100OR ANY ASSOCIATED EQUIPMENT WITH IMPROPER AC WIRING.

Electrical Service to the RA-100

Although the RA-100has a maximum audio output rating of 200 watts total into 4Ω, this does not represent the total current consumption since there are certain inefficiencies inherent in linear amplifier design. As a result, the fuse is rated at 5 Amps, implying that the maximum current theRA-100can draw is around 500 watts. However, in typical studio applications the average power consumption will be much less. However, when multiple devices are plugged into a single AC outlet, the possibility of overheated connections can exist.

Electrical standards have taken enormous strides toward increased safety over the past few decades thanks to circuit breakers, ground fault interrupters, and improved wiring and insulation materials. Unfortunately, some clubs are situated in older buildings whose wiring may not meet current safety standards, or have wiring that has deteriorated over the years. Make sure the circuit supplying power to the RA-100can supply enough current to run it properly. If the circuit has to supply otherhigh-poweredconsumption units such as refrigerators, coffee pots, toasters, air conditioning, or stage lighting, plug theRA-100into a different circuit with a lesser load.

2.3 OPERATING ENVIRONMENT

Thermal Considerations in Rack Mounting

The RA-100can be mounted in an equipment rack (taking up 2 rack spaces), placed on a shelf, tucked away in a vocal booth, etc. When you install it, keep in mind thatheat is the major enemy of electronic equipment. Fortunately, theRA-100’sprotection circuitry will not allow the unit to run hot enough to damage any of the circuitry. However, sustainedhigh-temperatureoperation sufficient to cause limiting will adversely affect the sound quality for as long as the excessive temperature conditions exists.

The RA-100has extensive heat sinking to minimize overheating, as well as eliminate the need for a ventilating fan. The latter feature is crucial for the

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cramped control rooms typically found in smaller studios; any fan noise would interfere with the mixing or monitoring process. The RA-100should be installed so that its heat sinking is allowed to do its job. Please observe the following:

The RA-100is designed to perform properly over a range of ambient temperatures from 0° C to +50° C (32° F to 122° F), in up to 80% noncondensing humidity. These are not absolute limits, but Alesis cannot guarantee that theRA-100will meet its published specs if operated outside of these ranges. If necessary, use a fan to blow air over theRA-100and promote cooler operation.

Prevent the side heat sink fins from becoming obstructed. There should be enough airspace around the amplifier for it to “breathe.”

Always allow adequate ventilation behind the RA-100.Do not seal any enclosure that holds theRA-100.

Never throw a coat or other flexible fabric or covering over the top of the amp when it’s in use.

You may wish to leave an empty rack space above or below the amp to promote good air flow.

Due to the RA-100’sweight (13.5 lbs.), it’s a good idea to mount it in the bottom of the rack frame.

Mounting on a Shelf or in a Non-RackEnclosure

To mount the amplifier on a shelf or other flat surface, Alesis recommends using the enclosed stick-onfeet to avoid scratching the shelf’s surface with the amplifier bottom. To properly mount thestick-onfeet:

1Place the amplifier upside down on a clean cloth or piece of cardboard so the amp top does not scratch your work surface.

2Clean the bottom of the amp where you plan to stick the feet. Isopropyl alcohol is recommended as a cleaning agent. This step insures that no small amounts of oil or other substances will inhibit proper adhesion of the feet.

3When the surface has dried, attach the feet.

Please observe the comments on thermal considerations given under “Thermal Considerations in Rack Mounting” no matter where or how the

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