Rear Panel Features; Gain Switch; Sensitivity; All Material © 2007. Martin Audio Ltd. Subject To Change Without Notice - Martin Audio MA4.2s User Manual

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CONTENTS
9. AC Mains cable. WARNING!
5

REAR PANEL FEATURES

5.1

Gain switch

T he g ain switch loca te d o n th e rea r p an el (the ce ntra l D IP -sw itch ) cha ng e s th e g ain/inp ut se nsitivity o f the am plifier.
T his ca n b e u se fu l w he n u sing lo w or high n o mina l inp ut sign a ls. Mo st pro fe ssio n al m ixing co nsole s op era te a t a
n om in al le ve l o f +4 to + 6 d Bu ; th e 3 2d B g ain p osition e nsu re s the re is p le n ty o f fad er mo ve me n t ava ilab le . Fo r sem i
p ro fe ssion al mixing de sks o pe ra tin g a t a no m in al le ve l o f 0d B o r -1 0 dB th e high e r ga in se tting s o f th e a mp lifie r ca n b e
u se d.
T he D IP -sw itch
5.1.1
There are eight positions of gain selectable, from 20dB to 41dB in 3dB steps. The different settings for the DIP-
switches are listed in the table below. The three switches to the very left are for channel B, and the three to the
very right are for channel A. The two switches in the middle select the operating mode of the amplifier, Stereo or
Link/Bridge A+B.
All material © 2007. Martin Audio Ltd. Subject to change without notice.
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A label just below the mains cable on the rear of the amplifier indicates the selected AC mains
operating voltage. Connect the mains cable only to the AC source referred to on the label.
D iffe re n t ga ins a nd fu nctio n ca n b e selecte d for ch an ne l A a n d B, b y
a pp ro priate setting of th e DIP switch . Se le cting th e ma xim um ga in o f the
a mp lifie r is alwa ys a tra de o ff be tw e en n oise an d h ea dro om . A low g a in
a mp lifie r am p lifies le ss of the no ise o f th e p re ced in g e qu ip m en t (m ixe r,
cro ssove r, e q ua lize r e tc.). A h igh er in pu t level is the n req u ired to a tta in full
p ow er o u tp ut, so th e h ea d ro om w ill b e d ecre a se d o n mixe r o r cro ssove r
o utpu ts. In a n actively d rive n syste m the re is u sua lly a d ed ica te d lou dsp ea ke r
p ro ce sso r or co ntro lle r, fo r th e lou d sp ea ke r system . Mo st lo u dspe ake r
m an ufacturers recom m en d a spe cific g a in for th e a mp lifie rs fo r use w ith the ir
con trollers.
Gain
5.1.2

Sensitivity

Sensitivity is the level in volts (rms) or dBu (referred to 0.775Vrms) that are required to
obtain full output power. As the output power varies with the load impedance, 4 ohms
is usually taken as the reference. Because the MA4.2s is equipped with an MLS-switch
there are numerous variations of output power versus sensitivity versus load
impedance.
We recommend calculating the sensitivity if this is necessary.
As a guide the table below gives the input level in volts rms, and dBu, versus gain for
full power output @1% thd 1KHz sine wave, MLS switches in position 0dB.
Gain dB
Input dBu
Input V rms
Martin Audio – MA4.2s Amplifier
20 23 26 29
+ 22.5 +19.5 +16.5 +13.5
10.40 7.36 5.20 3.69
6
32 35 38 41
+10.5 +7.5 +4.5 +1.5
2.61 1.85 1.31 0.93
GUIDES