Martin Audio – MA900 Amplifier
E
NGLISH
7
!
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.
Reverse operation of Channel B.
5.3.3
Tandem mode
In tandem mode channel A input is linked to channel B input, either input socket may then be used to provide the
input signal. Tandem mode is activated by placing the two central switches (4 and 5) in the "ON" position (UP).
Bo th input attenuators' are active, allowing you to set different levels for each channel. Note that only the inputs are
connected in parallel. This is NOT a parallel output mode. Never connect either output terminal to ground or in
parallel.
You can use the remaining input connectors to parallel off “Daisy – chain” signals to other amplifiers.
NOTE: Always turn off the Link switches when using the amplifier for Bi-amping.
5.3.4
Bridge mono mode
B ridg e m on o m od e is used to d elive r incre ase d po w er to the lo ud sp ea kers. Usin g
the M A9 0 0 in brid ge mo de re du ce s the nu mb er of o u tp ut ch an ne ls from tw o to on e.
T he n om ina l imp ed an ce of th e lo a d mu st be m o re th an 3 o h ms. S et the Link/Brid ge
A +B switch es to "ON " (UP ) a nd u se eithe r of th e inp ut co nn ectors A o r B. Yo u ca n
u se the re ma ining in pu t con ne cto r to ca rry a p ara llel sign al to o th e r am p s. B oth A
a nd B le ve l a tten ua tors m ust be at th e sa me po sitio n. W e reco mm en d the y a re
u se d in th e 0 dB fully clo ckwise po sitio n. T h e lo u dspe ake r sh o uld no w b e con ne cte d
to C ha nn el A ou tpu t S pe akon . (+1 sh ou ld be co nn ecte d to the [+] po sitive te rmina l
o f th e lou dsp ea ke r, an d -2 to th e [-] n eg ative te rm in al of th e lo ud spe ake r.
5.3.5
Bridge mono mode features
Bridged mono mode combines the power of two output channels into one. This results in twice the voltage swing,
four times the peak power and just less than three times the full power of a single channel.
This is because the coil is driven with positive voltage at one pole and an equivalent negative voltage at the other
pole. So, if an 8 ohms load is connected in bridged mode, one channel shares one 4 ohms part of the load, and the
other channel shares the other 4 ohms part. The power into 4 ohms from an MA 900 is 700W. So, the total bridged
power into the 8 ohms load will be 2 x 700 = 1400W
All material © 2007. Martin Audio Ltd. Subject to change without notice.
