Protection Features; Output Limiter; Thermal Protection; Vhf Protection - Martin Audio MA4.2s User Manual

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CONTENTS
T he Clip /limit ind ic ato r te lls w he n the a mp lifie r o utpu t is clipp in g o r lim itin g . It ha s tw o d ifferen t ind ica tion statuse s:
If th e clip lim iter is e n ga ge d it ha s a sho rt tim e co nstan t a nd it illum ina te s b riefly.
If th e clip lim iter is n o t en ga g ed it h as a n increa se d tim e con stan t a nd illu min ates fo r a lon ge r p erio d .
T he rem a in in g yello w L ED s in d icate if an y p ro tection circu its are a ctiva te d. Th ese a re d e scrib ed o n p ag e
9

PROTECTION FEATURES

E ach Ma rtin A ud io a m plifier h as ma ny ad va nce d pro te ctio n fea tures, p ro te cting b o th th e am plifier an d th e
lou dspe a ke rs co nn ected to it, sh ou ld a fa ult con d itio n a rise . U nd er no rm a l use the se fe ature s are ina ud ible. All
p ro te ction circuits op era te ind e pe nd e ntly.
9.1

Output Limiter

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 pp ro a ch tha 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 "OF F " by pressin g th e releva nt
clip lim it sw itch . Se e p ag e
Some manufacturers of loudspeaker processors do not recommend the use of clip limiters in amplifiers, as it can
affect the tracking of the processor's limiters. If the amplifier is being used without any external limiting, Martin
Audio recommend leaving the clip limiters switched "ON" (button depressed).
9.2

Thermal protection

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

VHF protection

If a signal of more than 12kHz, at full power is detected for more than five seconds, the VHF protection mutes the
input signal. (This is indicated on the front panel (4) by the LED labeled Protect). After five seconds the outputs will
un-mute and return to normal operation, unless the output signal has remained unchanged, in which case the VHF
protection will re-initiate.
9.4

Short circuit protection

All Martin Audio MA Series amplifiers are completely short circuit protected. The protection circuit permits very high
peak currents, but still holds the output devices within the safe operating area. 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

Automatic Fuse Saver, AFS - limiter

T he A FS circu it con tin uo u sly mo n itors the m a in s curre nt draw , a nd e lectro nica lly m od e ls the ch ara cteristics o f a 16
A mp (typ e B) circuit b re a ke r, limitin g th e m ains po we r curre n t draw to 2 0 A (2 30 V ) an d 4 0A (1 15 V). Wh en po we r
testing th e a mp lifie r using test w ave fo rm s it is po ssib le fo r the co ntin u ou s ma ins cu rren t d ra w to activate the A FS
lim iter, u nd e r th ese con d itio ns th e curre nt is re du ce d to a safe op e ra tin g le ve l.
All material © 2007. Martin Audio Ltd. Subject to change without notice.
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Martin Audio – MA4.2s Amplifier
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GUIDES
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