Martin Audio – MA900 Amplifier
E
NGLISH
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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 u su ally ca pa b le o f p ro du cin g far m ore p ow e r un de r the se co nd ition s tha n its n o rm al
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 . (3 pa g e 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 the y ten d
to up se t the trackin g of th e pro ce sso r's lim iters.
If the amplifier is being used without any external limiting, Martin Audio recommend leaving the clip limiters
switched "ON" (button depressed).
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 tsin k
tem pe ra ture rea ch es 90
°
C .
9.2
VHF protection
If a signal of more than 12kHz, at full power is detected, which lasts for more than five seconds, the VHF protection
mutes the input signal. (This is indicated on the front panel (
4
) by the protect LED). 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.
9.3
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 ,
the cha n ne l a ffecte d w ill e ve ntu ally go into a th erma l p ro te ct cycle u ntil th e sho rt circuit h as be en re mo ve d .
9.4
AC mains voltage protection
If the AC mains voltage is outside the operational window (over or under voltage), the power supply will
automatically shut down. When the mains voltage is above the minimum start voltage and below its maximum
operating voltage the amplifier will restart.
The two green ”ON” LED’s indicate when the power supply is operating properly.
9.5
DC protection
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 is be in g d etected o n the o u tp uts. Bo th
the se circuits co me in to effe ct on ce a DC le ve l is de te cte d o n eith e r ch a nn el.
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MAINTENANCE
Under normal use the amplifier should provide years of trouble-free service. The only maintenance required by the
user is to clean the front grill periodically.
In some extreme cases it may be necessary for authorized service personnel to clean the inside of the amplifier.
These conditions usually occur after prolonged use, e.g. in environments using "cracked- oil" smoke machines.
If you are using your amplifier for heavy-duty use i.e. concert touring or industrial music it is recommended that you
have your amplifier serviced every 3 years, purely as a preventative measure.
All material © 2007. Martin Audio Ltd. Subject to change without notice.
