alesis_ra_100 reference manual.pdf

7/29/2019 Alesis_RA_100 Reference Manual.pdf

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ALESISRA-100

Reference Manual


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CH APTER 1 GETTING TO KNOW THE RA-100

1.1 IN TRODUCTION.....................................................................................1

Principal Features................................................................................1

Unpacking and Insp ection .................................................................3

About This Manual.............................................................................4

CHAPTER 2 INSTALLATION

2.1 REAR PANEL CO NNECTIONS............................................................5

2.2 POWER CONSIDERATIONS.................................................................5

Fuse.........................................................................................................5

The AC Cord.........................................................................................5

Electrical Service to the RA-100........................................................6

2.3 OPERATING ENVIRONMENT............................................................6

Therm al Consider ation s in Rack Mou ntin g.................................6

Mou ntin g on a Shelf or in a N on-Rack Enclosur e.......................7

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

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

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

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

Cable Wir ing Tips................................................................................9

Adapting the RA-100 to Balanced Lines.........................................9

2.5 OUTPUTS...................................................................................................11

Connector Options...............................................................................11

Ou tp ut Cables........................................................................................11

Connecting Cables to Push Connectors...........................................12The Importance of Speaker Polarity................................................13

CH APTER 3 USING THE RA-100

3.1 FRONT PANEL CO NTROLS.................................................................14

Volume Controls.................................................................................14

On -Off Switch.......................................................................................14

Mu te Switch..........................................................................................15

Clip Ind icators.......................................................................................15

3.2 CH ECKIN G FOR PRO PER PO LARITY.................................................15

3.3 CHOOSIN G THE CORRECT SPEAKERS.............................................15

3.4 ABOUT GRO UN D LOO PS......................................................................16

CHAPTER 4 TYPICAL APPLICATIONS

4.1 STUDIO MONITOR AMP.......................................................................18

4.2 SOUND REINFORCEMENT..................................................................18


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4.3 KEYBOARD AM PLIFICATION SYSTEM............................................19

4.4 GUITAR AMPLIFICATION SYSTEM..................................................20

4.5 BIAM P SO UN D REIN FORCEMENT...................................................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 Soun d/ Soun d th at Changes Unp redictably in a Room....23

CH APTER 7 SPECIFICATION S

DO NO T REMOVE THE RA-100 TOP CO VER. THERE ARE NO USER

SERVICEABLE PARTS IN SIDE. REFER SERVICING TO A Q UALIFIEDREPAIR TECHNICIAN.


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CHAPTER 1:MEET THE RA-100

1.1 INTRODUCTION

Principal Features

Congr atu lations on you r p u rchase of the Alesis RA-100 Reference Amp lifier.

With all the wond rous ad vances in both analog and d igital electronics in the

past few year s, its easy to forget tha t an au d io chain is only as good as its

weak est link. With low-cost digital devices now offering soun d q ua lity

un heard of only a few years ago, Alesis has applied its expertise toward

creating a sonically accurate, stable, and afford able stereo pow er amp lifierthats suitable for the d igital age. Optimized for stud io monitoring

app lications and mod erate-pow er live performance setups, the amp s main

features include:

100 watts per channel into 4, 75 watts p er chann el into 8

Dual clipping indicators alert you ofany type of non -linear operation, not

just clipp ing

Outpu t short circuit protection to minimize dow n time and p rotect the

am plifiers circuitry

Massive, conservatively rated, custom-designed extrud ed heat sinks

(individual for each channel) for cool operation

No ventilation fan is needed, allowing for quiet operation and reduced

ambient noise in th e studio

Extremely low noise and d istortion; suitable for quiet applications such as

record ing stud ios, church installations, and mu seum s

How ever, some of the RA-100s most imp ortant features are hard to pu t on a

spec sheet. In a quest for a mu sical soun ding p ower am p that can stand u p

to a tough life on th e road as well as continuou s operation in the stud io,

Alesis has m ad e some changessome minor, and some very significantto

the standard power amp .

The RA-100 doesnt produ ce any aud io transients during power-up or

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pow er-dow n. Non etheless, theres a 2-second mu te on p ower-up to

compen sate for any p ieces of equip men t plu gged into the RA-100 that

prod uce transients upon pow er-up , and receive power at the same time as

the RA-100. Also, because the am p doesnt pr odu ce power on/ off thum ps

itself, the m ute circuit can be pre-pow er amp . This allows simp ler circuitry

than wh at would be required for shutting down the pow er amp stages.

The RA-100s pow er supp ly has plenty of reserve capacity to hand le

percu ssive transients, but if someon e kicks the RA-100s plu g ou t of the

wa ll, you wa nt all am plification to cease imm ediately. Therefore, if the

amp senses any loss of pow er, it instantly mutes the au dio.

Because power-up and -down are noiseless, the on/ off switch dou bles as a

mu te or panic button.

The outpu t stage uses full complementary-symmetry circuitry throughout.

Although there are cheap er ways to design an outp ut stage, this time-testedapp roach is generally considered sup erior to non-comp lementary-

symm etry types. The outp ut d evices are rated at 30 Amp s of peak curren t,

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 speak ers; the RA-100 uses several stabilization

techniques to m aintain consistent feedba ck networ k characteristics.

Alesis recognizes that am plifiers will sometimes be dr iven into clipping

even though this is not good p racticeduring a r ecording session or u nd erthe p ressures of live p erformance. As a result, a great of d eal of research

went into creating th e best possible clipping entry/ recovery characteristics.

Amp s with lots of overdr ive and satur ation tend to create overshoot and

ringing d ur ing the clipp ing process, wh ich d egrad es the sound ; the RA-100

has been d esigned so that it exhibits very little satu ration, even w hen

overloaded . As a result, it enters and exits clipp ing very cleanly. Clean

clipping allows the RA-100 to be d riven har der, w hich m akes the overall

perceived sound louder.

Monitoring a sine w ave being clipp ed confirms th is action. With the RA-

100, the am p w ill follow th e original inpu t signal as soon as clipp ing ceases(a). With some conventional amp designs, the signal will hang at th e

clipp ed level for a w hile before catching u p w ith the inp ut signa l (b. This

saturation-caused overshoot can sometimes sound worse than th e clipp ing

itself.

s

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No speaker stress du ring shutdown. With traditional protection circuitry,

the act of clamping th e outp ut devices to a safe value can m ake the am p

un stable with particular notes that interact with the sp eaker resonance,

thu s prod ucing oscillation or motorboating. This could dam age your

speakers. The RA-100 uses an elegant clamp ing d esign that observ es theload at all times bu t also integrates the signal characteristics into the

clam pin g action. Thus, the clam pin g action is gentle and , after clam ping t o

the m aximu m current encountered in norm al operation, will slowly (over

1 to 2 seconds) clamp based on th e load an d sign al characteristics. If the

source of the pr oblem (e.g., a short across the speaker terminals) is

removed , the signal recovers instantly.

Alesis also recognizes that wh atever else, the show mu st go on. As a

result, und er cond itions of extreme abuse (such as ultra-low sp eaker

imp edan ces or mou nting th at allows for no ven tilation), the RA-100 will

limit its signal rather th an simp ly shut d own . Taken to an extreme, thiswill produ ce distortion but sound will still come ou t.

To acqu aint you rself with the RA-100s operat ion, and to u se it prop erly in

various ap plications, carefully read this man ual. Power am plifiers are high-

current d evices that ar e the n ext-to-last link in the au dio chain. Proper

attention to cabling, pow er distribution, groun d loops, and oth er topics

covered in th is manu al is vital to have the RA-100 live up to its full

potential.

As always, we w elcome you r su ggestions and comm ents concerning th is

prod uct, or any other p rodu ct in th e Alesis line.

Unpacking and Inspection

Your new Alesis pow er amp lifier wa s carefully packed at the factory, and the

container was d esigned to protect the unit d uring shipp ing. Please retain this

container in the h ighly un likely event that you need to retu rn th e RA-100 for

servicing.

Up on receiving the RA-100, carefully examine th e shipp ing carton an d its

contents for any sign of ph ysical dam age that man y have occur red in tran sit.

If you d etect any d amage, do n ot destroy any of the p acking m aterial or thecarton, and imm ediately notify the carrier of a p ossible claim for dam age.

Damage claims m ust be m ade by you . If you picked up your am plifier directly

from an Alesis dealer, contact the d ealer.

The shipp ing carton shou ld contain:

Th is ins truct ion 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 ru bber feet (for shelf moun ting, to prevent the RA-100s

bottom sur face from scratching the shelf)

Alesis warranty card. It is important to register your p urchase; if you have

not already filled ou t your w arranty card , please do so now.

About This Manual

The manu al presents information in a logical ord er. Chapter 2 covers

installation, and Chap ter 3, how to use th e RA-100. Chap ter 4 covers several

typical app lications. The man ual closes w ith information onmaintenance/ servicing, trou bleshooting, an d operating specifications.

Please remember th at a p ower amp lifier is a high-curren t, high-pow er d evice

and should be treated w ith respect and care. Even if you are an aud io veteran,

we u rge you to read th e entire manu al to make the best u se of the RA-100.

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CHAPTER 2:INSTALLATION

2.1 REAR PAN EL CON NECTION S

The following diagram shows the various r ear-panel comp onents. Please

refer to this diagram du ring the procedu res described in this chapter.

Fuse:5 Amps(A spare fuse in included inthe fuse holder)

RightInput

Left InputRight PhonePlug Output

Left PhonePlug Output

Left Push CliOutputs

Right PushCl ip Output s

AC LineCord Jack

2.2 POWER CON SIDERATION S

Fuse

Replace with a 5 Amp , slow-blow typ e only; use of any high er amp erage

value will void the warr anty. FUSES ARE FOR YOUR PROTECTION

N EVER SUBSTITUTE A FUSE OF A HIGHER RATING , OR BYPASS IT.

The AC Cord

The RA-100s IEC-spec AC cord (do n ot substitute any other AC cord) is

designed to feed an outlet that includ es three pins, with the third , round pin

connected to grou nd . The grou nd connection is an importan t safety featuredesigned to keep the chassis of electronic dev ices such as th e RA-100 at

ground potential.

DO N OT OPERATE ANY ELECTRICAL EQUIPMENT WITH

UN GROUN DED OUTLETS. PLUGGING TH E RA-100 INTO AN

UN GROUN DED OUTLET, OR LIFTING TH E UNIT OFF GROUN D WITH

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A TH REE-TO-TWO WIRE ADAPTER, CREATES A H AZARDOUS

CON DITION. ALESIS CANNOT BE RESPONSIBLE FOR PROBLEMS

CAUSED BY USING TH E RA-100 OR AN Y ASSOCIATED EQUIPMEN T

WITH IMPROPER AC WIRING.

Electrical Service to th e RA-100

Although the RA-100 has a maximu m au dio ou tpu t rating of 200 watts total

into 4, this does not represent the total current consum ption since there are

certain inefficiencies inh erent in linear am plifier d esign. As a result, the fuse

is rated at 5 Amps, implying that th e maximum current the RA-100 can d raw

is around 500 watts. However, in typical stud io applications the average

pow er consum ption will be mu ch less. How ever, wh en mu ltiple devices are

plu gged into a single AC outlet, the p ossibility of overheated connections can

exist.

Electrical standar ds h ave taken enorm ous strides tow ard increased safety overthe past few d ecad es thanks to circuit breakers, grou nd fault interru pters, and

impr oved w iring and insu lation m aterials. Unfortun ately, some clubs are

situated in older buildings whose w iring m ay not m eet current safety

standard s, or have wiring that has deteriorated over the years. Make sure the

circuit supp lying p ower to the RA-100 can su pp ly enough current to ru n it

prop erly. If the circuit has to supp ly other high-powered consum ption un its

such as refrigerators, coffee pots, toasters, air condition ing, or stage lighting,

plu g the RA-100 into a d ifferent circuit w ith a lesser load.

2.3 OPERATING ENVIRON MENT

Thermal Considerations in Rack M ounting

The RA-100 can be mou nted in an equ ipm ent rack (taking up 2 rack spaces),

placed on a shelf, tucked aw ay in a v ocal booth, etc. When you install it, keep

in mind that heat is th e major enemy of electron ic equipm ent . Fortunately,the RA-100s p rotection circuitry w ill not a llow the u nit to r un hot en ough to

dam age any of the circuitry. How ever, sustained high-temp erature op eration

sufficient to cau se limiting w ill ad versely affect th e soun d qu ality for as long

as the excessive temp eratu re cond itions exists.

The RA-100 has extensive heat sinking to m inimize overheating, as w ell as

eliminate th e need for a ventilating fan. The latter featur e is cru cial for th e

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cramped control rooms typ ically found in smaller studios; any fan n oise

wou ld interfere with the m ixing or m onitoring p rocess. The RA-100 should

be installed so that its h eat sinking is allowed to d o its job. Please observe the

following:

The RA-100 is designed to perform p roperly over a range of ambienttemperatu res from 0 C to +50 C (32 F to 122 F), in up to 80% non-

cond ensing hu midity. These are not absolute limits, but Alesis cannot

gua rantee th at the RA-100 will meet its pu blished specs if operated outsid e

of these ran ges. If necessary, use a fan to blow a ir over th e RA-100 and

prom ote cooler op eration.

Prevent the side heat sink fins from becoming obstructed. There should be

enough airspace aroun d the am plifier for it to breathe.

Always allow adequate ventilation behind th e RA-100. Do not seal any

enclosure th at hold s the RA-100.

Never throw a coat or other flexible fabric or covering over the top of the

amp wh en its in use.

You may w ish to leave an empty rack space above or below the amp to

prom ote good air flow.

Due to th e RA-100s weight (13.5 lbs.), its a good id ea to mou nt it in the

bottom of the rack frame.

Mou nting on a Shelf or in a Non -Rack Enclosure

To moun t the am plifier on a shelf or other flat surface, Alesis recomm end s

using the en closed stick-on feet to av oid scratching th e shelfs sur face w ith th e

amp lifier bottom. To pr operly m oun t th e stick-on feet:

1 Place the amp lifier up side dow n on a clean cloth or piece of cardboard so

the amp top d oes not scratch your work su rface.

2 Clean the bottom of the amp wh ere you p lan to stick the feet. Isoprop yl

alcohol is recomm end ed as a cleaning agen t. This step insu res that n osmall amou nts of oil or other substan ces will inhibit prop er ad hesion of

the feet.

3 When the sur face has d ried, attach th e feet.

Please observe the comm ents on therm al considerations given un der

Thermal Considerations in Rack Moun ting no m atter wh ere or how the

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amp is mounted.

Avoiding Electromagnetic Interference

Because the RA-100 contains a large pow er tran sformer, we recomm end that

you do not:

Place the RA-100 next to an u nshielded video monitor, as the magnetic

fields may d istort the image.

Place tapes, disks, or other m agnetic media close to the RA-100.

Play guitar, bass, or any other instrument with magnetic pickups near the

RA-100. No da mage w ill occur bu t AC fields m ay enter the p ickup s, causing

h u m .

2.4 INPUTS

Inp ut Jack Ch aracteristics

The RA-100 includ es two u nbalan ced, 1/ 4" ph one jack inp ut s. These are

comp atible w ith the low-imp edance, unbalanced, high level outp uts typically

emanating from equipm ent such as mixers, synthesizers, samplers, direct

boxes, crossovers, etc. Guitars, microphon es, and other low-level/ high-

imped ance outp ut d evices require a preamp.

The inpu t jack wiring convent ion is:

Tip: s ignal hot

Sleeve: shield and ground

Cables

Use only high qu ality cables when interfacing equ ipm ent w ith the RA-100.

These should be good qu ality shielded cables with a strand ed (not solid)

internal condu ctor. Althou gh qu ality cables cost mor e, they d o make ad ifference. Route cables to th e RA-100 correctly by observ ing th e following

precautions.

Do not bundle audio cables with AC power cords.

Avoid run ning aud io cables near sources of electromagnetic interference

such as transformers, monitors, comp uters, etc.

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Do not place cables where they can be stepped on. Although stepping on a

cable may not cause imm ediate dam age, it can compress the insu lation

between the center condu ctor and shield (thus d egrading p erformance) or

red uce the cables reliability.

Avoid tw isting the cable or having it make sharp, right angle turns.

Never unp lug a cable by pulling on the wire itself. Always unplug by firmly

grasping the bod y of the plug an d p ulling d irectly outward . If you

experience difficulty in rem oving th e plug , sometim es a slight rotatin g

motion w hile u nplugging will solve the problem.

Keep the cable contacts clean at all time. Oxidation may lead to intermittent

contacts, degrad ed sou nd qu ality, or even d istortion. DO NO T USE AN

ABRASIVE TO CLEAN A DIRTY PLUG. This m ay r em ove so me of the

plu gs condu ctive p lating. Instead , spray contact cleaner on a clean, lint-freecloth and vigorously rub the plu g un til the oxida tion is removed.

Although Alesis does not endorse any specific prod uct, chemicals such as

Tweek and Cram olin, wh en ap plied to electrical connectors, are claimed to

imp rove th e electrical contact between conn ectors.

NEVER PLUG OR UN PLUG INPUT CABLES UN LESS THE RA-100 IS

TURNED OFF, UNPLUGGED FROM THE AC LINE, OR HAS THE LEFT

AN D RIGHT LEVEL CON TROLS TURNED TO MIN IMUM LEVEL. Failur e

to observe these precautions may result in d amage to you r speakers if the

cable being p lugged in to the RA-100 is carry ing a signal, and the level isturned up.

Cable Wiring Tips

If you d ecide to wire you r own cables, Alesis recomm end s that you use tw o

cond uctor shielded cable (even in an installation th at u ses unbalanced

wiring) with either a braid ed or foil-type shield. Connect one condu ctor to the

ph one jack tip connection to carry the h ot signal, and the shield connection to

the sleeve. The oth er condu ctor shou ld also connect to the shield since it is

not good p ractice to dep end on th e shield w ire itself to comp lete the signal

connection. This is becau se the shield wires ar e mor e subject to br eakage,especially in portable installations, than the more protected internal insulated

wires. By u sing a second safety condu ctor for groun d, the w orst that could

hap pen w ith a broken shield wou ld be a rise in noise or hum d ue to the lack

of shielding. If the grou nd connection were comp letely lost, there w ould be

either extremely loud hu m or m ajor loss of aud io.

Adap ting the RA-100 to Balanced Lines

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With long cable ru ns (e.g., over 6 meters/ 20 feet) in noisy electrical

environ men ts, the cable itself can act as an an tenn a and pick up RF fields,

AC hu m, or other types of interference. To avoid these problems, many

professional stud ios and live soun d comp anies use balanced line connections.

The average app lication w ill probably not require balanced lines, so tryun balanced connectors first and convert to balanced line operation only if

warranted.

Balanced lines carry a p air of signals, each ou t of ph ase with respect to the

other bu t otherw ise id entical. To be converted back into a single, un balanced

line, both balan ced lines feed a d ifferential amp lifier inp ut or tr ansform er

that r espon ds to th e difference in levels between signals. Thu s, the out-of-

ph ase signals are recombined into an u nbalan ced signal, but interference

ind uced into the cable will not be out of ph ase. Since there is no difference

betw een these signals, the d ifferential amp lifier or tran sformer w ill reject the

interference to a great d egree. This tend ency to ignore int erference is calledComm on Mode Rejection.

To ad apt a balan ced line out pu t to feed th e RA-100, you have four op tions.

Balanced line to un balanced line transformer. These comm only available

au d io accessories have a balanced line inp u t, usu ally in th e form of an XLR

connector, and an u nbalanced line outp ut, usu ally in the form of a 1/ 4"

ph one jack. The same transformer can also convert u nbalanced signals to

balanced signals.A dvan tages: High signa l carrying capacity, no pow er

requ ired, generates no hiss.Disadv antages: Inexpensive transformers m ay

color the sound du e to frequency response irregularities and can pick uphu m d ue to ind uctive nature of transformers. Very high-fidelity mod els

are expensive.

Active balanced-to-unbalanced converter. This uses an active electronic

circuit to convert balanced lines to unba lanced lines, bu t does not w ork in

the other direction.A dvan tages: Good frequency response sp ecs, no

inherent hu m pickup , less expensive than transformers.Disadv antages:

Requires pow er, generates some noise.

1622 mixer. Inp uts 1-8 of the Alesis 1622 mixer includ e balanced line inp uts

as well as direct-to-tape u nbalanced outp uts and un balanced signal sendpoints. You can p lug a balan ced line signal into th e balanced XLR inpu t,

then patch either th e d irect ou t or send connection to the RA-100.

A dvan tages: Available free if you have a 1622, flat frequency resp onse, no

inherent hum pickup .Disadv antages: Generates some hiss, optimized

pr imarily for low level signals.

Wire your ow n ad apter. It is possible to feed just one of the balanced lines,

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along with groun d, into th e RA-100. The following diagram shows a n

ad ap ter that assum es pin 2 of the XLR connector is hot.

12

3 (no connect ion

Female XLR

Connector

1 / 4 inc hphone jackshield

If pin 3 is hot, then d o not connect pin 2 to anything, and connect the w ire

from th e 1/ 4 phon e jack tip to p in 3 of the XLR female conn ector. If your

system u ses stereo phone jacks to carry balanced line signals (the tip an d ring

shou ld carry the in-phase and out-of-ph ase signals, respectively, althou gh this

may be reversed in some systems), then an ad apt er is not necessary. Simp ly

plu g a stereo cord from th e balanced p hon e jack into the RA-100s inpu t; it

will ignore th e ring connection an d amp lify only the tip connection.A dvan tages: Inexpensive, simple.Disadv antages: No inherent hum and

noise rejection; defeats ad van tages of balanced line op eration

2.5 OUTPUTS

Connector Op tions

The RA-100 is intend ed to d rive loads of 4 or greater. There are tw o speaker

connection outp ut op tions for each channel: 1/ 4" mon o phon e jack, and pu sh

clip termin als (red = h ot outp ut, black = groun d ). Push conn ectors are the

pr eferred choice for perm anen t installations. There is greater su rface area

contact than with ph one connectors, thus p romoting a better electrical

connection betw een the speaker w ire and amp lifier.

Phone jack connections are u sed for soun d reinforcement or an y situation

wh en qu ick setup and breakdown are important. You are also less likely to

accident ally reverse the wires if they are p erma nent ly conn ected to phon e

plugs.

Ou tput Cables

Speaker cables must d eliver large amou nts of peak current to a sp eaker. To

complicate matters further, a speaker represents an inductive load, and is

mor e difficult to d rive than a pu rely resistive load. Speak ers are also very low

imped ance devices. Any resistance between the am p ou tpu t and speakers will

degra de th e dam ping factor, efficiency and u ltimately, the sound quality.

Therefore, the cables you use betw een the RA-100 and its speakers are very

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important.

Alesis recommen ds strand ed, rath er tha n solid, cables for flexibility an d ease

of installation. How ever, solid cables are equ ally usable.

Never use guitar cords as speaker cables. Because they lack sufficient current-carrying capacity, the amp and speakers will not perform p roperly and the

sound may be d egraded . If you make you r ow n cables use electrical zip cord,

wh ich is d esigned to hand le several amps of current, or heavy-gauge speaker

cables if possible/ affordable.

In any event , the thicker the cable, the lower th e resistance and the better the

current-carrying capability. Stand ard hooku p wire is not acceptable; the

minimu m acceptable wire type is the comm on zip cord u sed to connect AC

to app liances. The following table relates the w ire gauge to the h ow m any feet

of cable is required at different imp edan ces to p rod uce a 1 dB pow er loss. . The

lower the resistan ce, the better. For cables run up to abou t 25 feet, 16 to 18gauge w ire is satisfactory.

Cable length th at produ ces 1 dB of power loss

at 4 at 4 at 8 at 8

wire gauge feet m eters feet m eters

6 1200 366 2425 740

8 800 244 1600 488

10 475 145 950 290

12 300 91 600 18314 190 58 375 114

16 120 37 240 73

18 75 23 150 46

20 50 15 100 30

22 30 9 60 18

In recent years, expen sive aud iophile cables of high cur rent capacity have

app eared. These have been somewh at controversial; some feel the extra

expense produ ces an aud ible imp rovement in sound quality, wh ile others

find no sonic difference between aud iophile cables and other heavy -du ty

wiring. While Alesis does not end orse any p articular brand of cable, w esuggest that you investigate d ifferent cable types for your self to d iscover if

they improve the sound of your p articular setup.

Connecting Cables to Push Connectors

The RA-100 pu sh connectors are perfect for stud io installations, especially

near field mon itor usag e, where an effective and reliable connector is

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requ ired tha t still maintains the great cost/ perform ance ratio of the RA-100's

design. In ad d ition, pu sh connectors are very easy to set u p. To connect cable

to the pu sh connectors, remove app roximately 1/ 4" of insulation from the

end of the wire, being careful not to n ick any of the strand s. Twist the stran d s

together, press the push term inal button, and feed the strands throu gh the

exposed h ole in th e pu sh connector. Be careful th at:

The push connector grabs the strands, not the insulation

No stray strands contact any part of the chassis other than the push

connector.

The Importan ce of Speak er Polarity

The speaker cones motion shou ld m imic the instrum ent its reprod ucing.

For examp le, a kick d rum pu shes air toward you, so a speaker reprod ucing a

kick d rum should have its cone pu sh air toward you. If the polarity isreversed, the cone w ill suck air aw ay from you. Even though the same

amou nt of air is moved in either case, man y listeners report su perior soun d

with p roper p olarity as opp osed to reversed p olarity.

An ad ditional pr oblem occur s if the p olarity of one speaker is reversed w ith

respect to the other. This can cause p hase-related p roblems such as th in bass,

poor stereo imaging an d frequency response an omalies.

With th e RA-100, po larity is a fu nction of correctly hooking u p th e outp ut

cables. Usually, for prop er polarity, the tip of the outp ut p hone p lug or the red

terminal of the p ush connector mu st connect to the speakers positive (+)terminal. This will insure tha t p olarity from the RA-100 inpu t to sp eaker

cone motion w ill be consistent. Check your speak ers' polarity, how ever,

because n ot all brand s follow this w iring convention.

Please note that p olarity reversal can occur in d evices (such as m ixers or

effects u nits) up stream of the RA-100. To test for p roper speaker a nd system

polarity, see section 3.2.

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CHAPTER 3:USING TH E RA-100

3.1 FRON T PAN EL CON TROLSThe following diagr am sh ows the var ious front pan el controls, as described

next.

Volume Controls

These regulate the inp ut signa l going into the RA-100. Alwa ys tur n the

volum e controls all the wa y dow n (coun terclockwise) wh en mak ing inpu t or

ou tp u t connections to th e RA-100. Pow er shou ld be off as well. Its also good

practice to turn the volume controls all the way d own wh en turn ing on

pow er just in case a signal sou rce feed ing th e RA-100 is live.

On -Off Switch

Press the up per h alf of this rocker-typ e switch to turn the am plifier on, and

the lower h alf to tu rn th e amp lifier off.

Upon turn ing on th e amp lifier, the green pow er indicator LED will light.

Not e that in d irect sun light, this light m ay not be easily visible.

WHEN TURNIN G O N AN D O FF THE GEAR IN A SYSTEM, IT IS

IMPORTANT TO TURN ON THE POWER AMP LAST AND TURN IT OFF

FIRST. Devices that are am plified by th e RA-100 may g enerate thu mp s or

other tr ansients on pow er-up ; if the RA-100 is on, these transients could be of

sufficient am plitud e to d ama ge your speakers, especially if system levels were

inadvertently set too high. Conversely, some units also create transients

wh en tu rned off. For this reason, the RA-100 shou ld alw ays be tur ned off first.

How ever, Alesis realizes that in ma ny ap plications the RA-100 pow er switch

will be left on and the RA-100, along with other gear, w ill be switched on by a

master AC sw itch. As a result, there is a brief d elay to allow other equ ipm ent

in your system to settle d own after receiving pow er. After this delay, du ring

wh ich the other u nits will have p resum ably mad e all the noises they were

going to m ake, the RA-100 will be ready for op eration.

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Mu te Switch

Because tur ning th e RA-100 on an d off generates no sp ikes within th e

amp lifier, the pow er switch dou bles as a mute sw itch or pan ic but ton. For

examp le, if there is a serious feed back problem, you can simply tu rn off theRA-100, then cha se dow n th e source of the p roblem.

Clip Ind icators

These imp rove on conventional clipp ing indicators by show ing wh enever

any conditions occur t hat could lead to non -linearity, such as an extremely

out-of-spec load (e.g., too ma ny sp eakers connected in p arallel or a short

across the speaker t ermina ls). Even if the p roblem occurs for only a few

microsecond s, a p ulse-stretching circuit w ill allow th e LED to light long

enough for you to see that a p roblem is occurring.

Because of the RA-100s ability to enter an d exit clipp ing w ith as few au d ible

artifacts as possible, you m ay not h ear any d istortion even if the ind icator

flashes. In genera l, a few flashes every now and then w ill not be a pr oblem.

How ever, if the LEDs flash often or remain on for any extended period of

time, then turn dow n the volum e controls to redu ce the signal level going to

the RA-100. If this doesnt solve th e pr oblem, check you r ou tpu t cables and

speakers.

3.2 CH ECKING FOR PROPER POLARITYTo check for correct speaker polarity, briefly conn ect the + term inal of a 1.5V

battery to the speaker cables hot or + lead , and the battery s - term inal to

the speaker cables cold, grou nd , or - lead. You w ill hear a p op from the

loud speaker as you connect the battery, and an other as you d isconnect it.

Observe the d irection of the speaker cone m ovemen t. If the speaker cables are

wired in the common m anner (and th e speakers themselves are not

mislabelled), the speaker cone w ill move forward (toward you) wh en you

connect the battery and away from you wh en the battery is disconnected.

If the sp eaker cone moves in th e opp osite direction, reverse the w ires going tothe speaker an d re-test for p roper p olarity. Alwa ys check you r speakers'

polarity as not all manu facturers follow th e same w iring convention.

3.3 CH OOSING THE CORRECT SPEAKERS

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Near-field m onitoring throu gh reference speakers has become th e p referred

wa y to mon itor and m ix mu sic. With near-field mon itoring, small speakers

are p laced so th at they ar e a few feet from the engineers ears. As a result,

room acoustics become less imp ortan t since the p rimar y acoustic interaction

involves direct sound from the speakers rather th an reflected sou nd s from

the room . Since few h ome an d p roject stud ios have good acoustics, near -fieldmon itors can provid e realistic monitoring in a small space at relatively low

levels.

Near -field m onitors offer other ad vanta ges comp ared to large stud io speakers,

includ ing smaller size, lower cost, and easier tran sportab ility to other stud ios

for reference pur pose.

Because of its mod erate p ow er ratin g, excellent fidelity, and lack of a noise-

genera ting fan , the RA-100 Reference Am plifier excels in d riving r eference

near-field mon itor speakers in smaller stud ios. How ever, you should choose

speakers tha t can han dle the p ower th e RA-100 can gen erate. Speaker w attageratings are often confusing, and stand ard s by which ratings are obtained vary

from m anu facturer to m anu facturer. If a speaker can han dle 100 watts RMS

continu ous p ower, it should be able to hand le the RA-100. How ever, und er

conditions of clipping or other abu se of the RA-100, dam age to sp eakers is

possible. For best results, use speakers d esigned for mediu m- to high-pow er

applications.

3.4 ABOUT GROUN D LOOPS

A hum or buzz may be introdu ced into some aud io systems by a

ph enomenon know n as a grou nd loop. This can occur if a piece of equipm ent

sees two or more d ifferent paths to grou nd , as shown below.

Device Device

shieldedcable

path 2

path 1

To AC powerserv ice

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One path goes from d evice A to groun d via the groun d term inal of the three-

cond uctor AC power cord, but A also sees a path to ground through the

shielded cable and AC grou nd of device B. Becau se groun d w ires have a small

amou nt of resistance, small amoun ts of current can flow throu gh grou nd andgenerate a voltage along the cable shield. This signal ma y end up getting

indu ced into the hot cond uctor.

The loop can also act like an anten na into w hich hum is ind uced, or can even

pick up rad io frequencies. Furth ermore, man y compon ents in a circuit

connect to grou nd . If that grou nd is dirty and contains noise, it might get

picked u p by the circuit. Ground loops cause the m ost problems w ith high-

gain circuits, since massive am p lification of even a coup le millivolts of noise

can give an aud ible signal.

Most ground loop problems can be solved by plugging all equipm ent into thesame groun ded AC source. However, it is importan t to make sure that the AC

source is not overloaded and is properly rated to hand le the gear p lugged into

it.

For really tough cases, you may n eed to break th e conn ection that causes the

loop cond ition. Although some d o this by using a grou nd lifter and breaking

the AC gr ou nd , THIS IS A DAN GEROUS OPTION WH ICH YOU SHOULD

NOT USE because it sacrifices the safety factor the AC grou nd wire prov ides.

In the previous d iagram, a better option wou ld be to interrupt the cable

shield. There are tw o way s to do this: one is to simp ly break the shield at

some p oint, usu ally by d isconn ecting it from grou nd at one jack. (The otherend sh ould r emain connected so that the shielding p roperties are retained,

even if there is no d irect p ath for groun d.)

The other is to use a tran sformer as mentioned in section 2.4, Adap ting the

RA-100 to Balanced Lines, to prov ide isolation in the au d io line betw een the

tw o pieces of gear. Transformers gen erally have no grou nd connection

between the input an d outpu t connections.

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CHAPTER 4:TYPICAL APPLICATION S

4.1 STUDIO MON ITOR AMP

1622 Mixer

RA-100

Near-Field m onit or

Mon i to rOutpu ts

in

out out

in

In the stu d io, the RA-100 is idea l for d riving n ear-field or other r eference

speakers. In th is examp le, an Alesis 1622 mixer feeds th e RA-100, which

pr ovides p ow er am plification. The RA-100 outp ut s feed a set of near-field

monitor speakers.

4.2 SOUN D REINFORCEMENT

For aud itorium and live m usic use, the RA-100 has sufficient p ower to d rive

a set of small-to-med ium size club sp eakers. The hookup diagram is the same

as abov e, with a n Alesis 1622 mixer feeding the RA-100, and the RA-100

driving the sp eakers.

Biamp lification often p rovid es better live sound and greater efficiency by

splitting th e aud io signal into tw o d ifferent chann els. One channel dr ives a

low frequency speaker system an d th e other, a high frequency speaker system.

See Section 4.5.

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4.3 KEYBOARD AMPLIFICATION SYSTEM

in

out out

in

Inpu ts

Output

Quadraver

RA-100

A stereo keyboard feeds the Alesis Quad raVerb, wh ich p rovides reverberation

and other signal p rocessing effects. The Qu ad raVerb outp uts feed the RA-100,

wh ich th en d rives a set of small-to-medium size club sp eakers.

With mu ltiple keyboard setup s, you m ay need a m ixer to combine the

keyboard ou tp uts into a single stereo feed. The Alesis 1622 Mixer is idea l for

this typ e of app lication. The Qua dr aVerb can either process the 1622s out pu ts

on the w ay to the pow er amp as shown, or be inserted into the 1622 and u se

the 1622s send / retu rn effects capabilities. In th is case, the 1622 master ou tputs

wou ld go directly into the RA-100.

Remem ber that synthesizers requ ire full-range speakers to accomm odate th e

extremely low an d h igh frequencies some keyboard s can generate.

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4.4 GUITAR AMPLIFICATION SYSTEM

Speakers

in

out out

in

Inpu ts

Outpu ts

Quadraverb G

RA-100

MIDI InM IDI Foot Pedal

Many gu itarists now u se rack m ount, component systems for greaterflexibility compar ed to all-in-one amp s. In th is system, a gu itar goes

throu gh a Qu adraVerb GT to provide d istortion, chorusing, reverb, and other

effects. Its outputs feed the RA-100, which then drives a set of small-to-

med ium size club speakers.

Note that mono sound sources should plug into the right QuadraVerb GT

inpu t jack, as show in th e diagram .

An op tional MIDI Program Chan ge footswitch calls up d ifferent progr am s in

the Quad raVerb GT.

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4.5 BIAMP SOUN D REINFORCEMENT

High Frequency Driver

in

out out

in

Ins

Crossove

High Frequency RA-10

HighFrequencyOutputs

LowFrequencyOutputs

nsu s

Low Frequency Speaker

Low Frequency RA-10

1622 Mixer

Biamp lification sp lits a signal into t wo separa te lines. One carries low

frequency signals and the oth er carries high frequency signals. Each split feeds

its own pow er amp and set of speakers. The main advantages of

biamplification are greater efficiency and lower intermodulation distortion

since low frequency speakers n eed n ot carry high frequen cies (and high

frequency speakers wont receive low frequencies).

In this setup , an Alesis 1622 mixer feeds a crossover that gen erates the

separate h igh an d low frequen cy splits. The low frequencies go to one RA-100

w hich dr ives the low frequency speak er system; the other RA-100 hand les the

higher frequen cies and d rives a set of high frequen cy speakers.

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CHAPTER 5:MAINTEN AN CE/ SERVICE

5.1 GENERAL INFORMATIONCleaning

Disconn ect the AC cord, then u se a dam p cloth to clean th e amp lifiers metal

and plastic sur faces. For heavy dirt, use a non -abrasive household cleaner

such as Form ula 409 or Fantast ik. DO NOT SPRAY THE CLEAN ER

DIRECTLY ON TO THE FRON T OF THE UN IT AS IT MAY DESTROY THE

LUBRICANTS USED IN TH E SWITCHES AND CON TROLS! Spray ont o a

cloth, then use th e cloth to clean the u nit.

MaintenanceHere are some tips for pr eventive maintenan ce.

Do n ot remove th e RA-100 top cover. Ther e are no user serviceab le parts

insid e. Refer servicing to a q ualified repair technician.

Periodically check the AC cord for signs of fraying or dam age.

If you use the push connector outpu t terminals, check that the cables are

secur ely in p lace and that n o strand s short to the chassis or any other

terminal.

Periodically rotate the volume controls (make sure pow er is off). In manyapp lications the volum e controls will be set to a par ticular p oint and not

ad justed . Occasional rotation of the volum e controls will minim ize build-

up of du st on the potentiometer w iper, thus m inimizing scratchiness as the

un it gets old er.

Place a du st cover over the RA-100 when it is not in use.

Refer All Servicing to AlesisAlesis has sp ent a great d eal of effort researching p ower amp lifier reliability.

We believe that th e RA-100 is one of the m ost reliable amp lifiers that can be

mad e using current technology, and should provide years of trouble-free use.

WARNING: The full AC line voltage, as well as high voltage/ high curren t

DC voltages, are present at several poin ts with in the chassis. Service on this

pr odu ct should be p erformed on ly by qualified technicians. THERE ARE NO

USER-SERVICEABLE PARTS INSIDE.

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CHAPTER 6:TROUBLESHOOTING

Begin th e troubleshooting p rocess by re-reading the m anu al to make su re you

did nt m iss some imp ortant p oint regarding the u nits operation. After that,try th e following t echn iques for specific problems.

Hum

Turn d own the volum e controls. If the hu m goes aw ay, then the source of the

hu m is either in a un it feeding th e RA-100, or in th e inpu t cables feeding the

RA-100. Check your cables and other u nits.

If the hu m p ersists, there m ay be a grou nd loop. Follow th e adv ice given in

section 3.4. Also, check to see tha t the RA-100 is not situ ated near other

devices with large external hum fields.

If a loud hu m continu es, there may be a p roblem w ithin the RA-100.

No Volume

Turn u p th e volum e controls w ith no signal feeding th e RA-100, and listen

very carefully to the speakers. If you hear an y hu m or noise, no ma tter how

low level, then the RA-100 is receiving pow er and the p roblem p robably lies

in the equ ipm ent or cables feed ing th e RA-100.

If the speakers are absolutely dead and mak e no noise whatsoever, check the

speaker cabling.

Distorted or Low Level Soun d

If either of these p roblems occurs after the RA-100 has been on for a long time

and run ning un der a h eavy load, it is possible that the outp ut p rotection

circuitry has kicked in. Let the un it rest for a minu te by turn ing off the p ower

and see if the p roblem goes aw ay. If it does, check for thermal p roblems such

as obstructed air flow arou nd the un it.

Bad cables can also cau se distorted or low level sound yet another argu men t

for using the best cables you can afford.

Thin Soun d/Soun d that Changes Unpredictably in a Room

This is generally the r esult of mismat ched sp eaker p olarity. Refer to section

3.2 for inform ation on h ow to test for prop er polarity.

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CHAPTER 7:SPECIFICATIONS

alesis_ra_100 reference manual.pdf

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