Alesis RA100 User Manual

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-Rack Enclosure.......................7

Avoiding Electromagnetic Interference..........................................8

2.4 INPUTS.......................................................................................................8

Input Jack Characteristics...................................................................8

Cables......................................................................................................8

Cable Wiring Tips................................................................................9

Adapting the RA-100 to 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-Off Switch.......................................................................................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-100 TOP 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-100 Reference 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. With low-cost digital 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 and moderate-power live 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 of non-linear operation, not
just clipping

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

• Massive, conservatively rated, custom-designed extruded 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’s most 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 some changes—some minor, and some very significant—to
the standard power amp.

• The RA-100 doesn’t produce any audio transients during power-up or

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power-down. Nonetheless, there’s a 2-second mute on power-up to
compensate for any pieces of equipment plugged into the RA-100 that
produce transients upon power-up, and receive power at the same time as
the RA-100. Also, because the amp doesn’t produce power on/off thumps
itself, the mute circuit can be pre-power amp. This allows simpler circuitry
than what would be required for shutting down the power amp stages.

• The RA-100’s power supply has plenty of reserve capacity to handle
percussive transients, but if someone kicks the RA-100’s plug 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-up and -down are noiseless, the on/off switch doubles as a
mute or “panic” button.

• The output stage uses full complementary-symmetry circuitry throughout.
Although there are cheaper ways to design an output stage, this time-tested
approach is generally considered superior to non-complementary­symmetry 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-100 uses 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—during a 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; the RA-100
has 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 the RA-100 to 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-caused overshoot can sometimes sound worse than the clipping
itself.

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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-100 uses 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-low speaker
impedances or mounting that allows for no ventilation), the RA-100 will
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’s operation, and to use it properly in
various applications, carefully read this manual. Power amplifiers are high­current devices that are the next-to-last link in the audio chain. Proper
attention to cabling, power distribution, ground loops, and other topics
covered in this manual is vital to have the RA-100 live 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-100 for
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-100 power amp with the same serial number as shown on the
shipping carton

• Power cord.

• Four stick-on rubber feet (for shelf mounting, to prevent the RA-100’s
bottom 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-power device
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 the RA-100.

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CHAPTER 2:

Right Phone

Plug Output

Left Push Clip

Outputs

INSTALLATION

2.1 REAR PANEL CONNECTIONS

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

Fuse:
5 Amps

(A spare fuse in included in
the fuse holder)

Right
Input

Left Phone

Plug Output

AC Line

Cord Jack

Clip Outputs

2.2 POWER CONSIDERATIONS

Fuse

Replace with a 5 Amp, slow-blow type 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’s IEC-spec AC 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 the RA-100 at
ground potential.

Left Input

Right Push

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

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

Electrical Service to the RA-100

Although the RA-100 has 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 the RA-100 can 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-100 can supply enough current to run it
properly. If the circuit has to supply other high-powered consumption units
such as refrigerators, coffee pots, toasters, air conditioning, or stage lighting,
plug the RA-100 into a different circuit with a lesser load.

2.3 OPERATING ENVIRONMENT

Thermal Considerations in Rack Mounting

The RA-100 can 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 that heat is the major enemy of electronic equipment. Fortunately,
the RA-100’s protection circuitry will not allow the unit to run hot enough to
damage any of the circuitry. However, sustained high-temperature operation
sufficient to cause limiting will adversely affect the sound quality for as long
as the excessive temperature conditions exists.

The RA-100 has 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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