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Martin Audio – MA2.8s Amplifier

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9 .1 Ou t p u t Li m i t e r

A n ou tp u t lim iter is includ ed to a vo id am plifier clip pin g. W h en a n a mp lifie r is se ve rely ove rd riven , its o utp ut w ave fo rm

is clip p ed (its p ea ks are squ are d off) – re d ucin g the crest facto r. In e xtrem e cases, the w a ve fo rm ca n a p p r o a c h t h a t o f

a squ are w ave . An a m plifier is n orma lly cap a ble o f prod u cing fa r mo re po w er u nd e r th e se con d itio n s th an its n orma l

u nd isto rte d rated o u tp ut po we r.

T he lim ite r w orks b y m on ito ring th e o utpu t a nd co mp arin g the distortio n p ro du ce d b etw ee n th e inp u t an d o utpu t o f th e

a mp lifie r. If the d istortio n excee ds 1% TH D for a n y re aso n (vo ltag e o r cu rre nt clip pin g), th e lim ite r re d uces th e in p ut

sig na l p ro po rtion ally. N o te tha t, if th e sig na l is disto rted or clip pe d b efore it re a ch es th e am p lifier, the clip limite r w ill n ot

b e activated .

U nd er n o rm al op eration th e clip limiter is ina ud ible. T h e lim iter ca n be tu rn ed “O n” or “Off” by pressin g th e releva nt clip

lim it sw itch . S ee p a ge 5

S om e ma n ufacturers o f lo u dspe ake r pro ce ssors d o n ot reco mm en d the u se of clip limite rs in a m plifiers, a s it can

a ffect the tracking of th e proce ssor's limiters.

If th e a mp lifie r is be i n g u s e d w i t h o u t a n y e x t ern al lim iting , M artin A ud io re co m me nd le avin g the clip limite rs sw itche d

"ON " (b u tton de pressed ).

9 .2 T h e r m a l pr o t e c t io n

W he n th e a mp lifie r is drive n ve ry ha rd in to a lo w imp ed a nce loa d, th e co o ling fa ns w ill run at h igh spe e d. If the se

o pe ra tin g co n dition s con tin ue , the P rotect ind ica to r(s) will illu min ate ind icating th at the am plifier is a bo u t to g o into

the rm al sh utd ow n.

A fter five se co nd s the a m plifie r w ill g o in to th e rm al p rotect b y mu tin g the inp u t sig na l. A fte r 1 5-20 se co nd s the

a mp lifie r will ha ve co ole d do wn en ou g h fo r the a m plifie r to com e ou t o f shu td ow n a nd op erate a s n orma l. If th e lo ad

con ditio ns re ma in u n ch an g ed the th erm al p ro tectio n will be re - initia te d . Th erm al p rotectio n occurs wh e n th e h ea t sin k

tem pe ra ture rea ch es 90

9 .3 VH F p r o t e c t i o n

If a sig na l o f mo re th an 12 kH z, at fu ll p ow e r is de te cte d fo r m ore tha n five se con ds, the V H F pro te ctio n m ute s th e

inp ut sign al. (Th is is ind ica te d o n th e fro nt pa ne l (4 ) b y th e L ED la be le d P ro tect). A fter five se co nd s the o u tp uts w ill u n-

m ute an d retu rn to n orma l o pe ra tio n, un le ss th e o utpu t sig na l h as re ma in e d un ch a ng ed , in wh ich ca s e t h e V H F

p ro te ction w ill re-initia te .

9 .4 Sh o r t c i r c u i t p r o t e c t i o n

A ll M artin A u dio MA Se rie s am plifiers a re co mp le tely sh o rt circuit p ro te cte d. T h e pro te ctio n circuit pe rmits ve ry h igh

p ea k cu rre nts, bu t still ho ld s the o u tp ut d e vice s w ithin the sa fe o p erating a re a . If a sh o rt circuit is ma intaine d , th e

cha nn el affe cte d will eve ntua lly g o into a the rm a l prote ct cycle un til th e sh ort circuit ha s b ee n rem ove d.

9 .5 A C ma in s v o l t a g e pr o t e c t i o n

If th e A C ma ins voltag e is ou tside th e op era tion a l wind o w (o ver o r u nd er vo ltag e ), th e po we r sup p ly w ill a uto ma tica lly

shu t do w n. W h en the ma in s volta g e is ab ove the m inimu m sta rt vo ltag e a nd be lo w its m a ximu m o pe ra tin g vo lta ge th e

a mp lifie r will re sta rt.

T he two gree n ‘ON ’ L ED ’s in dica te wh e n th e p ow er su pp ly is o p eratin g correctly.

It ta ke s a co up le o f seco nd s to se lf-ch eck (th is is kno w n as th e "so ft start" o r "slo w start" se q ue nce), the ga in w ill

slo wly a nd g rad ua lly b e incre ase d ba ck to th e pre viou sly set le ve l, an d the fan s w ill b lo w a t hig h sp ee d b efo re g oin g

into "id le ".

9 .6 D C . p r o t e c t i o n

T he re a re tw o typ es of D C p ro te ction :

• F uses o n the su pp ly bran che s of ea ch ch an ne l.

• D C crow b ar p rotectio n th a t sh orts th e o utpu t if m ore th a n 10 vo lts D C are b eing de te cte d on th e o utpu ts.

B oth th e se circuits co me in to e ffe ct on ce a DC le ve l ha s b ee n d etected o n e ithe r cha n ne l.

CONTENTS

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