Martin Audio – MA1400 Amplifier
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NGLISH
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5.1.1
The DIP-switch
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 . So m e 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.
T he re a re eig ht p osition s o f ga in se lecta ble , fro m 20 dB to 4 1 dB in 3 dB step s.
T he d ifferen t settin gs fo r th e D IP -sw itch es are liste d in th e tab le be lo w . Th e three sw itch e s to th e ve ry le ft are for
cha nn el B, a n d th e three to the ve ry righ t a re fo r ch an n el A . T he tw o sw itche s in th e m id dle sele ct the op era ting m o de
o f th e a mp lifie r, S tereo or L in k /Bridg e A+ B .
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. The table below gives input volts rms Versus
gain for full output power @ 1% t.h.d, 1Khz sinewave.
5.1.3
Options
A s th e D IP -switch is recessed , A security sticke r can b e p la ce d a cro ss the ba y to preve nt u n au th orize d tam pe rin g
o nce th e g ain h as b e en se t. A no the r o ptio n is to re mo ve th e D IP -switch . T his sh o uld o nly be do ne by a uth orize d
service p erso nn e l ! T his co rre sp o nd s to all switche s set to “OF F ”, i.e. 3 2d B g ain a nd stereo mo de .
5.2
Link switch
T he L in k switch loca te d o n th e rea r p an el (the ce ntra l D IP -sw itch ) is fo r cha ng ing th e op era ting mo de o f the am plifier
(se ctio n 5 .3 ).
5.3
Operating modes
5.3.1
Stereo mode
In this configuration, both channels operate independently of each other. This is used
for all 2-channel operations, eg bi amp and stereo. Stereo mode is selected by
placing the two central switches in the “OFF” position (Down). The attenuators on the
front panel control the respective channel levels.
Never connect either output terminal to ground or in parallel. The recommended
minimum nominal impedance, for stereo or tandem operation, is 2 ohms per channel.
5.3.2
Notes for amplifier testing
NOTE: Channel B is always polarity reversed on the input, and polarity reversed back on the output. On
channel B the positive output voltage with respect to 0V appears on pin -2 of the Speakon connector.
Channel A is connected with normal polarity. By having channel A and B operating in opposite polarity,
the energy storage in the power supply is more efficient. This is significant for signals below 100 Hz (sub bass etc.)
and improves the power bandwidth. Be sure to use balanced inputs on all measuring equipment (including
oscilloscope probes) if you are bench testing.
Gain dB
20
23
26
29
32
35
38
41
Input dBu
+17.3
+14.3
+11.3
+8.3
+5.3
+2.3
-0.7
-3.7
Input V rms
5.67
3.98
2.84
1.99
1.40
0.99
0.70
0.50
All material © 2007. Martin Audio Ltd. Subject to change without notice.
