Martin Audio – MA1.3s Amplifier
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NGLISH
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T he D IP -sw itch
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 D IP switch . S electin g th e m axim u m ga in of th e
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.
5.1.1
Gain
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.
5.1.2
Sensitivity
Sensitivity is the level in volts (rms) or dBu (referred to 0.775Vrms) that is required to
obtain full output power. As the output power varies with the load impedance, usually 4
ohms is usually taken as the reference.
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.
5.1.3
Options
As the DIP-switch is recessed, a sticker can be placed across the cut out to prevent unauthorized tampering.
Another option is to remove the DIP-switch.
This should only be done by authorized service personnel.
This
corresponds to all switches set to “OFF ”, i.e. 32dB gain and stereo mode.
5.2
Link switch
The Link switch located on the rear panel (the central DIP-switch) is for changing the operating mode of the
amplifier (see below, section 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, e.g. 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 channels 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
Gain dB
20
23
26
29
32
35
38
41
Input dBu
+16.7
+13.7
+10.7
+7.7
+ 4.7
+1.7
- 1.3
- 4.3
Input V rms
5.30
3.75
2.65
1.88
1.33
0.94
0.67
0.47
All material © 2007. Martin Audio Ltd. Subject to change without notice.
CONTENTS
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GUIDES
