![background image](http://html1.mh-extra.com/html/martin-audio/ma900-schematics/ma900-schematics_user-manual_1732926009.webp)
Martin Audio – MA900 Amplifier
E
NGLISH
9
O nce co n ne cte d to a su ita ble AC su pp ly, the am plifier ca n be starte d w ith the p o we r switch. Wh en yo u po w er u p the
a mp lifie r it ta ke s a cou p le o f secon d s to se lf ch eck (th is is kno wn as th e "soft sta rt" o r "slow start" se qu e nce), the fa ns
the n blo w at high sp ee d b efore g oing in to "idle". T he tw o bo tto m gre en L E D’s th e n illum in ate to sho w th e a mp lifie r is
o pe ra tio na l.
6.4
Grounding
T he re is n o g ro un d lift switch o n th is am plifier. T he sign al grou nd is a lwa ys floa tin g (lifted ), with re sp ect to ch a ssis
g ro un d via a grou nd lift re sisto r. If a p ote ntia l d iffe ren ce ab ove 0 .6 V is de te cte d b etwe en sign a l grou n d an d cha ssis
e arth , a sho rt circu it is a utom a tica lly introd uce d be tw e en th e tw o, en su rin g ele ctrical p ro tectio n. If o th er eq uipm e nt o r
a mp lifie rs w ith in a syste m sh ou ld de velop a n e le ctrical fa ult to ea rth , the m ain s fu se on th at e q uipm en t sho u ld rup ture
d ue to this a utom atic syste m allow in g a n ea rth fa ult cu rre nt to flo w for protectio n p urpo se s.
If ho we ver yo u wish to p e rm an en tly co nn ect the sign al g rou nd to cha ssis e arth , con ne ct th e X LR -co nn ecto r’s sh ell lu g
to pin 1 . In th e in terest o f sa fety n ever d iscon n ect th e e arth pin o n th e m ains ca ble .
T o co mp ly with CE a p prova l (rad io in terfe re n ce ), th ere is an AC m ain s filte r. T h is filter n e ed s the cha ssis e arth fo r
referen ce, o th erw ise a curre n t lo o p is fo rm ed via th e sig n al g ro u nd .
N ever d iscon n ect (lift) the m ain s sa fety ea rth .
6.5
Power consumption
There are three ways to determine the power/current consumption of the amplifier:
First, the peak current draw at full power output. Under this condition the amplifier will operate for less than 2
minutes before thermally limiting or blowing the mains fuse.
Second, the maximum expected average current under worst case program material, which is 1/3 of full power
according to the FTC-standard. At this level the music will be in the state of constant clip and is therefore the
highest power level one can obtain without completely obliterating the program material.
Lastly, the "normal operating power", as defined by EN 60065 as a measurement level for approval and testing to
this standard. The normal operating power is measured using pink noise, with an average output power equal to
1/8 of full power. The one-eighth power is the maximum volume music can be re- played without continuous
amplifier clipping this corresponds to headroom of only 9dB's, which is very low for normal program material.
6.5.1
Calculation
The current draw can be calculated by dividing the mains input power by the mains voltage.
We recommend that you design the power distribution for at least the required current at 1/8 power, and 1/3 power
for heavy-duty demands such as concert touring and Industrial music etc.
The heat power can be calculated as follows:
If a headroom figure of 9dB is used with a 4 ohms load on each output of the amplifier. The 1/8 power per channel
is 320 / 8 = 40 watts, and the total output power = 2 x 40 = 80 watts.
The mains power consumption from the chart above is then 370 watts.
Power
1/3 Power
1/8 Power
Idle
[W]
note 1
note 2
MA900
8 ohms
2x
200
345
235
60
4 ohms
2x
320
570
370
60
2 ohms
2x
470
930
585
60
note 1
Average power with music as program source. The amplifier driven to clip level.
note 2
Normal music power with 9dB headroom, IEC standard power rating.
MAX OUTPUT POWER
MAINS INPUT POWER
All material © 2007. Martin Audio Ltd. Subject to change without notice.