Power Consumption; Grounding; Calculation - Martin Audio MA4.2s User Manual

< >
CONTENTS
6.6

Grounding

T he re is n o g ro un d lift switch o r te rmina l o n th is am plifier. T he sign al grou nd is a lwa ys floa tin g via a resistor to cha ssis
a nd the grou n ding system is a uto ma tic. If a po te n tial d iffere nce ab o ve 0 .6V is d etected b etw ee n sig na l g ro un d a nd
cha ssis grou n d, a sh ort circu it is a u to ma tically in trod u ce d b etwe en th e two , en surin g e le ctrical protectio n. If o th e r
e qu ip me n t or am plifiers w ithin a system sho u ld d e ve lo p a n ele ctrica l fau lt to e a rth, th e ma ins fu se o n tha t e qu ip me n t
sho uld rup tu re du e to th is au to m atic system , a llo wing a n e arth cu rre nt to flo w for p rotectio n pu rpo 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 g ro un d for
referen ce, o the rw ise a cu rren t loo p is fo rm e d via the sign al grou nd .
N ev er d isc on n ec t (lift) the m ain s sa fety ea rth .
6.7

Power consumption

There are three ways to determine the power/current consumption of the amplifier:
First, the peak current draw at full output power. Under this condition the power amplifier will operate for less than
2 minutes before thermally limiting or blowing the mains fuse, and is an unrealistic "normal" use condition. To
design a mains distribution system based on the current draw at full power would result in an over specified
system. No music programme material requires the full steady state continuous power of an amplifier, this
operating condition is only valid during amplifier bench testing. *
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 a state of constant clip and is therefore the highest
power level that can be obtained without completely obliterating the program material.
Last, the "normal operating power", as defined by EN 60065, IEC 65/ANSI/UL 6500 as a measurement level for
approval and testing to these standards. The normal operating power is measured using pink noise, with an
average output power equal to one-eighth of full power. The one-eighth power is the maximum level music can be
re-played without continuous amplifier clipping; this corresponds to a headroom of only 9dBs, which is very low for
normal program material.
*If operating the amplifier at sustained full power into low impedances, the MA 4.2s has a mains current limiter,
AFS (Automatic Fuse Saver), which will limit the long-term current draw. Read more about AFS-limiter under
Protection on page 15.
MA4.2s
note 1
note 2
6.7.1
The current draw can be calculated by dividing the mains input power by the mains voltage.
We recommend you to design the power distribution for at least the 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 5dB(1/3 full power) is used with a 4 ohms load on each output of the amplifier. The 1/3
power per channel is then; 2300 / 3 = 767 watts, and the total output power = 2 x 767 = 1534 watts.
The power consumption according to the chart above is then 1975watts.
All material © 2007. Martin Audio Ltd. Subject to change without notice.
PRINT
MAX OUTPUT POWER
Power *
8 ohms 2x
4 ohms 2x
2 ohms 2x
* will be reduced by AFS limiter
Average power with music as program source. The ampli f ier driven to cli p level.
Normal music power with 9dB headroom, IEC standard power rating.

Calculation

Martin Audio – MA4.2s Amplifier
MAINS INPUT POWER
AFS activated 1/3 Power
[W] [W] note 1
1300 1300 1230
2300 1450 1975
3200 1850 2950
11
1/8 Power Idle
note 2
575 105
900 105
1290 105
GUIDES