Altec Lansing Stereo Amplifier 4200A User Manual

6125A  
4200A  
Multi-channel power amplifiers  
Altec Lansing Professional  
1000 W. Wilshire Blvd. Suite 362  
Oklahoma City, OK 73116 USA  
A division of Altec Lansing Technologies Inc, Milford PA 18337-0277 Made In USA  
 
Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
10 DESIGN THEORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13  
11 TROUBLESHOOTING TIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13  
11.1 No Audio Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13  
11.2 Distorted Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14  
11.3 Hum or Buzz Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14  
12 DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14  
13 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15  
14 WARRANTY INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15  
Caution:  
This power amplifier can produce dangerous output voltage levels, high  
power levels, and high sound pressure levels in loudspeakers. In order to mini-  
mize the risk of injury, damage, or hearing loss, please read the entire owners  
manual before connecting to a sound system.  
CAUTION  
RISK OF ELECTRIC SHOCK  
DO NOT OPEN  
The lightning flash with arrowhead symbol,  
within an equalateral triangle, is intended to alert  
the user to the presence of uninsulated "danger-  
ous voltage" within the product's enclosure that  
may be of sufficient magnitude to constitute a risk  
of electric shock to persons.  
The exclamation point within an  
equalateral triangle is intended to alert the user  
to the presence of important operating and main-  
tenance instructions in the literature accompany-  
ing the device.  
TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT REMOVE COVER. NO USER SER-  
VICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.  
TO REDUCE THE RISK OF FIRE OR ELECTRICAL SHOCK, DO NOT EXPOSE THIS  
APPLIANCE TO RAIN OR MOISTURE.  
TO REDUCE THE RISK OF FIRE, REPLACE ONLY WITH SAME TYPE FUSE.  
REFER REPLACEMENT TO QUALIFIED SERVICE PERSONNEL.  
WARNING: THIS APPARATUS MUST BE EARTHED THROUGH THE SUPPLIED  
POWER LINE CORD  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
1.  
INTRODUCTION  
The right to any claim against a public carrier can  
be forfeited if the carrier is not notified promptly and if  
the shipping carton and packing materials are not avail-  
able for inspection by the carrier. Save all packing mate-  
rials until the claim has been settled.  
The 6125A and 4200A power amplifiers combine  
the efficiency of a MOSFET high-speed switching output  
stage with the sophistication of modern microprocessor and  
DSP technology to produce a multi-channel amplifier with  
unprecedented versatility and power in a single 3RU pack-  
age.  
3.  
AC POWER REQUIREMENTS  
3.1 Voltage Requirements  
The 6125A and 4200A amplifiers can be operated  
Although similar to other amplifiers with class D  
output stages, the 6125A and 4200A amplifiers employ  
internal microprocessor and DSP algorithms to optimize  
output switching characteristics and eliminate the usual  
harshness associated with high-frequency audio in stan-  
dard class D amplifiers. This optimization results in a  
spread-spectrum switched output that varies with input  
amplitude and frequency, and minimizes radiated emissions  
by eliminating the single-frequency high-energy radiated  
interference normally associated with switching outputs.  
The use of a simple linear power supply removes another  
potential source of radio-frequency interference, an im-  
portant consideration as racks become more and more  
heavily populated with digital signal processing equipment.  
A small switching supply using flyback topology provides  
an efficient power source for logic, protection, pre-ampli-  
fier and indicator circuits.  
from nominal 120VAC or 240VAC, 50/60Hz mains. This  
is user-configurable by changing the insert in the AC Inlet  
(See section 7.9). The power connector on the amplifier  
accepts a standard IEC-320 receptacle.  
For nominal 120VAC operation, the power cord  
should be three-conductor, rated for at least 13A (16AWG).  
The line fuse should be type MDA, 12A.  
For nominal 240VAC operation, the power cord  
should be three-conductor, rated for at least 10A (18AWG).  
The line fuse should be type MDA, 10A.  
3.2  
Current Requirements  
1.) Idle (no audio):  
To assure reliable operation, the usual protection  
from excessive high-frequency, DC offset, and thermal  
overload is supplemented by power supply undervoltage,  
power supply overvoltage, and output overcurrent detec-  
tion, all monitored and controlled by the latest in minia-  
turized microprocessor technology.  
6125A  
120V: 0.81A  
240V: 0.42A  
4200A  
120V: 0.9A  
240V: 0.5A  
2.) With typical audio inputs:  
8loads on all channels  
120V: 4A  
In sum, 6125A and 4200A amplifiers combine the  
best of the new digital technologies with the best of the  
traditional analog technologies to provide a product that  
will supply clean sound at full output from every channel  
while generating minimal heat, thus increasing the reli-  
ability of every other piece of equipment in a rack as well  
as preserving its own.  
120V: 4.6A  
240V: 2.3A  
240V: 2A  
4loads on all channels  
120V: 6.5A  
120V: 7.0A  
240V: 3.5A  
240V: 3.3A  
6125A and 4200A amplifiers consume less than  
12 amps when all channels operate at 1/8 power into rated  
(4 ohm) loads. This condition satisfies the UL, CSA and  
building electrical code requirements for a piece of audio  
equipment not to consume more than 80% of the current  
available when plugged into a grounded 15 amp outlet and  
operated at 1/8 of maximum power.  
2.  
UNPACKING  
As a part of our system of quality control, every  
Altec Lansing product is carefully inspected before leav-  
ing the factory to ensure flawless appearance. After un-  
packing, please inspect for any physical damage. Save  
the shipping carton and all packing materials, as they were  
carefully designed to reduce to minimum the possibility  
of transportation damage should the unit again require  
packing and shipping. In the event that damage has oc-  
curred, immediately notify your dealer so that a written  
claim to cover the damages can be initiated.  
3.3  
AC Grounding and Earth Grounding  
To reduce the risk of ground loop hum, all system  
ground references should originate at the same point in  
your AC power distribution. Do not remove the amplifier’s  
ground pin, as it creates a potential shock hazard.  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
4.  
CABLE REQUIREMENTS  
5.  
RACK-MOUNTING REQUIREMENTS  
4.1  
Input Cables  
5.1  
Mechanical  
Be sure to use shielded cable whether balanced or  
The 6125A and 4200A amplifiers are designed to  
unbalanced. Shielding which is properly grounded will  
protect the signal from outside electrical interference such  
as RF, fluorescent lighting, and computer/display emis-  
sions. As a general rule, unbalanced or single-ended (tip-  
sleeve) lines of less than 10 feet are satisfactory, but greater  
distances or noisy field environments require a balanced  
signal. Avoid running input lines in close proximity or  
parallel to long speaker lines, AC power cables, or power  
transformers, as this may generate hum or oscillation.  
fit in standard 19-inch equipment racks. The front panel  
rack-mount ears are sufficiently strong for most applica-  
tions, however if you desire further integrity for mobile  
racks, we recommend using the four additional holes in  
the back of the chassis for supplemental rear-mounting (see  
dimensional drawing for details).  
5.2  
Cooling  
Be certain that both the front and back of the rack  
have unhindered access to free air flow. Fan direction is  
from front to back. It is not necessary to leave empty space  
above or below.  
4.2  
Output Cables  
These amplifiers are capable of delivering high  
levels of output current, therefore the wire gauge used for  
speaker cables is particularly important. Inadequate wire  
gauge can add significant resistance to the speaker’s own  
impedance, especially over long distances, reducing the  
power which is actually delivered to the speaker. It could  
also result in a decreased damping factor and possible fire  
hazard. Since power at the speaker load is of primary con-  
cern in system design, we have included a table to best  
determine appropriate wire gauge for your application. The  
following table lists the resistance per 100 feet of com-  
mon copper wire gauges, and also gives the percentage of  
the speaker load power which would be lost in an arbitrary  
100 ft run of different gauges of 2-conductor copper  
speaker wire.  
5.3  
Grounding  
In some installations where the sound system is  
sensitive to RF noise or system-induced oscillation, it may  
be necessary to ground the amplifier’s chassis to the rack  
enclosure. This is accomplished using star type  
lockwashers on the four rack mounting screws. These star  
washers will penetrate through the amplifier’s paint to ad-  
equately ground the chassis to the rack.  
Wire Gauge /100ft  
8load 4load  
#8  
.0605Ω  
.1018Ω  
.1619Ω  
.2575Ω  
.4094Ω  
.6510Ω  
0.8%  
1.3%  
2.0%  
3.2%  
5.1%  
8.1%  
1.5%  
2.5%  
4.0%  
6.4%  
10.2%  
16.3%  
#10  
#12  
#14  
#16  
#18  
Table 4.1: Wire gauge resistance/power loss  
This table expresses the power loss as a percent-  
age of the load’s power rather than the total amplifier out-  
put power in order to accurately determine power loss at  
other cable lengths. For example, if you plan to deliver  
150 watts to an 8load through 50 ft of 14 ga. cable, the  
power loss in the cable would be half that of a 100 ft run  
of #14 wire as shown in the table, or 1.6% of 150W, which  
is an insignificant 2.4 watts. However, if you were to run  
200 ft of 18 ga. cable to a 4load, the loss would be twice  
that of the 100 ft run shown in the table, or 32.6% of 250W,  
which is 81.5 watts lost as heat. Always be sure to use  
adequate gauge speaker wire.  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
6.  
FRONT PANEL FEATURES  
operation at an ambient room temperature of 50°C (122°F)  
or less with typical audio program and all channels driven  
into 4.  
6.1  
Power Switch  
When the unit is switched on there is a five sec-  
ond delay, during which time the PROTECT circuit will  
activate, disconnecting the speakers from the amplifier  
output. When turning off the amplifier, the load is removed  
instantly, and the protect LED will briefly turn on as the  
power supply discharges.  
6.5  
Protect Indicator  
The protect LEDs illuminate when the fault moni-  
toring microprocessor has determined that one of the fol-  
lowing conditions exists:  
- Power supply undervoltage  
- Power supply overvoltage  
- Output overcurrent  
- Heat sink overtemperature  
- Unacceptable DC output content  
- Unacceptable high frequency output content  
- AC power interruption  
6.2  
Signal Indicator  
The signal present LEDs illuminate at an input  
level of about 13mVrms (-35.5dBu).  
6.3  
Clip Indicator  
The clipping LEDs illuminate at an input level of  
about 870mVrms (+1.0dBu), with all channels driven by  
1KHz into 8. This indicates that the signal processing  
circuitry has determined output levels to be approaching  
the available power supply rails and has begun to “soften”  
signal peaks. Actual onset of “hard” clipping depends on  
audio program and total load impedance and does not oc-  
cur until the signal processing circuitry can no longer com-  
pensate, which means that signal integrity can be  
maintained even if the clipping indicators illuminate for  
short periods of time.  
Because the signal processing module used in the  
6125A and 4200A amplifiers processes two channels si-  
multaneously, a fault in one channel will result in a pro-  
tect condition for both channels processed by the same  
module, ex. channels 1-2, 3-4, and 5-6 (6125A only). Thus  
there will never be a case where only one of the amplifier  
channels is shown in protect mode. When a pair of protect  
LED's are illuminated, internal relays have removed the  
channel pair's speaker loads from the amplifier output and  
connected the speakers to ground. If the fault is isolated  
to one module (channel pair), the other channels will re-  
main unaffected.  
6.4  
Thermal Status Indicator  
The thermal LEDs illuminate when the tempera-  
ture of any one of the heat sink extrusions reaches 85 to  
90°C. Both channels of the affected amplifier module will  
shut off until the measured temperature drops below about  
70°C. The amplifier should be able to maintain proper  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
* Model 6125A shown - Model 4200A only  
has channels 1-4.  
7.  
REAR PANEL FEATURES  
7.2  
Input Ground Switch  
This switch separates the input signal ground from  
the chassis ground on all inputs. Ground connections from  
an incoming signal float from the chassis ground when the  
switch is out. Unless there are special circumstances which  
require the input signal ground and chassis ground to be  
disconnected, it is best to leave this switch in.  
7.1  
Input Connectors  
The 6125A and 4200A inputs use balanced two  
piece "Euroblock" style connectors. It is recommended  
that balanced input connections be used whenever possible  
to take full advantage of the amplifier's common mode  
rejection properties, and to reduce ground-loop problems.  
If a hum problem persists even though balanced inputs are  
used, try connecting a balanced signal to the Euroblock  
input with the input cable's shield lifted at the amplifier  
end of the cable (ie. no ground connection), but connected  
to ground at the signal source. This eliminates potential  
ground currents through the input cable yet preserves the  
benefits of shielding. If connecting an unbalanced signal  
to the Euroblock input, connect the signal wire to (+) and  
the cable shield to both (-) and ground.  
7.3  
Multi-Channel Operation  
The 6125A is essentially three stereo amplifiers  
in one chassis, for a total of up to six separate channels.  
The 4200A is essentially two stereo amplifiers in one chas-  
sis, for a total of up to four separate channels. Thus, the  
following references to Stereo, Mono, or Bridged opera-  
tion is with regard to each of three or two pairs of chan-  
nels in the amplifier. For example, Channel 1 and Channel  
2 together can provide stereo, mono, or bridged operation,  
completely independent of Channels 3-4 or Channels 5-6  
settings.  
7.4  
50Hz Low Cut Switch  
Each pair of channels has a 50Hz second order  
(12 dB per octave) low-cut filter option which is applied  
to both channels within the pair. When the switch is  
pressed, the audio signal is -3dB at 50Hz, -15dB at 25 Hz,  
-27dB at 12.5Hz, etc.  
G
-
+
G
Euroblock  
Connector  
System  
-
+
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
Model 6125A  
shown.  
Model 4200A  
has only four  
channels.  
7.5  
Input Level Controls  
other input connection, as well as its level control. The  
first channel's input and level control now determines the  
signal to both channels.  
Input Level Controls attenuate input signal from  
0dB down to -. For best performance, Altec recommends  
that the level controls be operated at full level (0 dB at-  
tenuation).  
7.7  
Dual Channel/Bridge Mode Switch  
Bridging a power amplifier is the process whereby  
two channels are supplied the same signal, with the sec-  
ond channel's phase inverted 180°. The speaker is then  
connected across the (+) output connections of each chan-  
nel, resulting in twice the power to the speaker that either  
channel could deliver by itself. Since in Bridge Mode both  
connections have voltage present, never connect or touch  
either speaker wire to ground.  
In STEREO mode, each level control corresponds  
directly to the input signal on its respective channel.  
In MONO Mode, the input signal connected to  
channels 1, 3, or 5 are used to drive channels 2, 4, or 6  
respectively, and the level controls for channels 1, 3, and  
5 likewise control channels 2, 4, and 6. When switched to  
Mono mode, channels 2, 4, or 6 level controls become in-  
active.  
The 6125A is capable of three channels of bridged  
output (two channels on the 4200A). To use bridged mode,  
first press MONO from the Stereo/Mono switch on the  
channel pair to be bridged. This sends the same audio  
signal to both channels. Then press BRIDGE from the  
Dual/Bridge switch on the channel pair to be bridged. This  
inverts the phase of the input signal to the second channel.  
These two channels are now operating together in Bridged  
Mono mode, and the output must be taken from the two  
(+) terminals of the corresponding bridged channel pair  
In BRIDGED mode, the level controls function  
the same as in mono mode.  
7.6  
Stereo/Mono Switch  
The 6125A is comprised of three stereo amplifi-  
ers (two on the 4200A), each operating independently of  
the others, with Stereo/Mono switching available for each  
channel pair. If this switch is set to Stereo mode, the chan-  
nel pair operates as two discrete amplifiers, each with its  
own input connection and level control.  
7.8  
Loudspeaker Output Connectors  
Three terminal blocks (two on the 4200A) pro-  
vide connections for the speaker outputs. In BRIDGE  
mode, the channel 1, 3, or 5 (+) connection is the Bridged  
(+) speaker output terminal, and the channel 2, 4, or 6 (+)  
connection is the Bridged (-) speaker output.  
Switching to Mono mode allows one input (chan-  
nel 1, 3, or 5) to drive both channels of a stereo channel  
pair. Pressing the Mono switch disables the channel pair's  
CAUTION! NEVER CONNECT THE TWO  
BRIDGED OUTPUTS TOGETHER OR CONNECT  
EITHER BRIDGED OUTPUT TO GROUND.  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
Model 6125A  
shown.  
Model 4200A  
has only four  
channels.  
Outputs  
7.9  
AC Inlet  
If the mains voltage is 220-250VAC, the required  
fuse is MDA 10, 250V, and the required power cord is 3-  
wire grounded, 10 Amp (18AWG) minimum.  
The 6125A and 4200A amplifiers can be config-  
ured by the customer for operation at either 115VAC or  
230VAC mains. Switching from one to the other simply  
requires the following steps:  
8.  
SELF-PROTECTION FEATURES  
1.) Unplug the amplifier from the wall and re-  
move the power cord from the rear of the amplifier.  
The 6125A and 4200A amplifiers contain circuitry  
to self-protect during extreme fault conditions. These fault  
conditions are:  
2.) Using a small screwdriver as a lever, unlatch  
the fuse holder in the AC inlet and remove it.  
1.) Power supply undervoltage  
2.) Power supply overvoltage  
3.) Remove the voltage selection insert and ro-  
tate until the new nominal mains voltage level indication  
(115 or 230) is on top and properly oriented for reading.  
3.) Output overcurrent  
4.) Heat sink overtemperature  
5.) Unacceptable DC or high frequency output content  
6.) AC power interruption  
4.) Replace the voltage selection insert in the AC  
inlet, making sure that it is plugged in all the way.  
Except for AC power interruption, the detection  
of any fault will result in the activation of protection cir-  
cuitry on a particular module, which consists of two chan-  
nels. That is, a short circuit on the output of channel 1  
will result in both channel 1 and channel 2 entering pro-  
tect mode. This is because the signal processing module,  
which processes both channels simultaneously, does not  
distinguish between the two channels within a channel pair  
when processing a fault.  
5.) Replace the fuse with the appropriate size (see  
#6 below), and press the fuseholder back into the AC inlet  
until it latches.  
6.) Using a power cord of the appropriate size  
and with the appropriate terminations, plug the cord into  
the rear of the amplifier and then into the wall. The ampli-  
fier is now ready for use at the new mains voltage.  
If the mains voltage is 110-125VAC, the required  
fuse is MDA 12, 250V, and the required power cord is 3-  
wire grounded, 13 Amp (16AWG) minimum.  
An AC power interruption will result in all chan-  
nels entering protect mode simultaneously, just as if the  
amplifier is being turned off.  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
In all cases, the amplifier will restart the signal  
processing module after a short delay and will reconnect  
the speakers after several seconds if no further fault con-  
ditions exist. This allows the servo circuitry to bring any  
residual DC offsets to zero before speakers are connected.  
8.4 Heat sink overtemperature - a measured heat  
sink extrusion temperature of more than 85 to 90 degrees  
C. The three-speed fan will switch to medium speed at an  
extrusion temperature of 45 to 50 degrees C, and to high  
speed at a temperature of 70 to 75 degrees C. The  
overtemperature fault will clear itself when the measured  
temperature is below about 70 degrees C. The fan will  
operate at low speed below about 50 degrees C.  
Specific conditions resulting in a fault are as follows:  
8.1 Power supply undervoltage - less than about  
55 volts on the either supply rail. Possible causes would  
be total load on the outputs exceeding recommendations  
(remove some speakers - 4load min, 8min bridged),  
low AC mains voltage (reduce extension cord length or  
increase wire size, or switch to an AC mains circuit more  
capable of supporting the amplifier's power requirements),  
or improper AC inlet mains voltage setting (make sure  
nominal AC mains voltage matches the number in the view-  
ing window on the AC inlet).  
8.5 Unacceptable DC or high frequency output  
content - a DC offset in the output signal of more than a  
few hundred millivolts indicates module failure, and will  
trigger a DC protect fault. High frequency (20kHz to  
100kHz) in the output at high amplitudes can cause speaker  
damage and causes a fault condition more or less rapidly  
as frequency and amplitude vary.  
These two conditions (DC and HF) are tested by  
the same circuit so the exact cause cannot be isolated. If  
the fault condition persists after disconnecting all inputs  
and outputs from the amplifier, there is probably a module  
failure requiring service. Note: the self-testing circuit may  
take as long as 30 seconds to recover from this fault, so be  
sure to give the amplifier enough time to reset itself. If  
after 30 seconds the module has recovered, begin plug-  
ging in one input and output at a time in an effort to iso-  
late a system high-frequency or oscillation problem.  
8.2 Power supply overvoltage - more than about  
92 volts on either supply rail. Possible causes would be  
high AC mains voltage (change to an AC mains circuit with  
voltage within the amplifier's stated requirements) or im-  
proper AC inlet mains voltage setting (make sure nominal  
AC mains voltage matches the number in the viewing win-  
dow on the AC inlet).  
8.3 Output overcurrent - more than 15 to 20 amps  
being drawn from any output. Possible causes would be  
total load on the affected output exceeding recommenda-  
tions (disconnect some speakers), or a short circuit on one  
of the outputs driven by the affected module (inspect  
speaker wiring for proper connection).  
8.6 AC power interruption - a dropout (or brown-  
out of sufficient magnitude) of more than one half mains  
line cycle and less than one whole cycle in duration.  
9.  
TYPICAL APPLICATIONS  
The above conditions are checked by the signal  
processing module on a switching cycle by switching cycle  
basis and are therefore monitored as often as a million or  
more times a second, allowing protection well before de-  
structive conditions have time to cause part failure.  
The 6125A is essentially three stereo amplifiers  
in one chassis, each with dual stereo, dual mono, and  
bridged mono capabilities, while the 4200A is two stereo  
amplifiers (four channels), but with more power per chan-  
nel than the 6125A. Input connections are hard-wired with  
two-piece Euroblock connectors, while speaker outputs are  
wired to four position screw terminal blocks. Note: The  
6125A is used for the following application details, but  
the 4200A is used in a similar fashion, to a maximum of  
four channels.  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
9.1 Six Channel Setup  
Six Channel Setup (dual stereo)  
Possible Applications:  
Input Section:  
Multiple Zone Systems  
Three Pairs Of Studio Monitors  
Multiple Stage Monitors  
25V Distributed Systems (6125A Only) Stereo Triamplification  
Multi-Media Systems  
Surround Sound  
Three Way Biamplification  
Up to Six Different Inputs  
Stereo/Mono Switches - Out  
Dual Bridge Switches - Out  
Levels Controls - Used Per Input Channel  
Outputs  
1
2
3
4
5
6
1
2
3
4
5 6  
Speaker Outputs  
- Up To Six Different Outputs  
Minimum Speaker Load Per Channel = 4W  
Up To Six Different Amplifier Inputs  
9.2 Dual Mono Setup  
Dual Mono Setup  
Input Section:  
Possible Applications:  
Multiple Zone Systems  
Three Different Stage Monitor Mixes  
Dual-Mono FOH Tri-Amplification  
Up to Three Different Inputs  
Stereo/Mono Switches - In  
Dual Bridge Switches - Out  
Levels Controls - Only Channels 1, 3, or 5 Used  
Outputs  
1
2
3
4
5
6
1
3
5
Channels 1 & 2  
Channels 3 & 4  
Channels 5 & 6  
Amplifier Inputs  
(An Input Can Be Parallel Connected  
From Channel 1 Input From Channel 3 Input From Channel 5 Input  
To Other "Non-Partner" Channels by  
Hard-Wire Jumping the Euroblock Connectors)  
Minimum Speaker Load Per Channel = 4W  
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Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
9.3 Bridged Mono Setup  
Bridged Mono Setup  
Possible Applications:  
Input Section:  
70 Volt Constant Voltage Systems (6250 Only)  
Subwoofers  
High Powered Monitors  
Up to Three Different Inputs  
Stereo/Mono Switches - In  
Dual/Bridge Switches - In  
Levels Controls - Only Channels 1, 3, or 5 Used  
High Powered Full Range PA Speakers  
Outputs  
1
3
5
Amplifier Inputs  
Bridged Channels 1 & 2 Bridged Channels 3 & 4 Bridged Channels 5 & 6  
From Channel 1 Input  
From Channel 3 Input  
From Channel 5 Input  
Minimum Speaker Load Per Bridged Channel Pair = 8W  
9.4 Typical PA Setup  
Typical PA Setup  
Outputs  
1
3
4
5
Subwoofer  
Input  
Full Range  
Inputs  
Monitor  
Input  
Subwoofer  
Bridged Output  
8W Minimum  
Dual Full Range Separate Monitor  
(Bridged Mono) (Dual Stereo) (Dual Mono)  
Outputs  
Outputs  
4W Min/Channel  
4W Min/Channel  
12  
 
Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
10.  
DESIGN THEORY  
11.  
TROUBLESHOOTING TIPS  
No Audio Output  
The 6125A and 4200A amplifiers are based on  
11.1  
stereo driver modules that use digital processing to gener-  
ate a spread-spectrum switching pattern between about  
200KHz and 1.5MHz, depending on input signal ampli-  
tude and frequency. This overcomes the self-limiting and  
inherent weakness in traditional class D fixed-frequency  
PWM amplifiers, and produces an output with THD+N  
numbers comparable to class A and class AB linear ampli-  
fiers. (see Specification Notes at end of this section)  
1.) Power LED not lit:  
Line fuse is blown or power outlet is dead.  
IF LINE FUSE IS BLOWN, REPLACE ONLY  
WITH SAME TYPE AND RATING FUSE.  
2.) Power LED is lit but Protect LEDs stay on:  
In the 6125A and 4200A, the input signal is re-  
ceived by a single operational amplifier configured as a  
difference amplifier to reduce common-mode effects from  
sources located at a distance. This difference amplifier has  
a gain of 2.74 which allows the use of less gain later in the  
system, improving overall system noise performance.  
Amp module is in protect mode. Speakers have  
been disconnected from amplifier output and connected to  
ground until the protect fault is corrected. See section 8  
for a complete explanation of protect fault conditions. Out-  
put overcurrent, overvoltage and undervoltage faults will  
reset in about eight seconds once the fault condition is re-  
moved, while excessive DC offset or high frequency faults  
take about 30 seconds to reset.  
The amplified signal, based on the position of vari-  
ous selector switches, either bypasses or is processed by a  
two-pole high-pass filter with rolloff at 50Hz, and then  
passes through the attenuating potentiometer. The attenu-  
ated signal is buffered and passed to the amplifier module  
along with a zero-volt reference.  
Speaker Impedance: The 6125A or 4200A may  
go into self-protect at high output levels if the actual  
speaker load impedance is much less than 4 ohms. To cal-  
culate speaker impedance for a given combination of di-  
rect-coupled speakers, use Ohm's law as applied to series  
and/or parallel resistor networks, where each speaker (for  
this purpose) can be thought of as a single resistor, using  
DC resistance measurements.  
The amplifier module receives the attenuated sig-  
nal with a unity gain differential amplifier to eliminate com-  
mon-mode interference picked up within the amplifier  
chassis. The signal is then added to a small DC offset sig-  
nal opposite in polarity to any DC offset on the output  
bridge and adjusted by the digital processing module as  
described above. The digital processing module, which  
also generates FET drive signals, has a voltage gain of 11.7  
for a total system voltage gain of 32. The drive signals  
generated by the processing module are fed to a pair of  
high-current MOSFET transistors, and the switched out-  
put of these transistors is filtered and applied to the speaker  
outputs. Fault conditions such as overvoltage,  
undervoltage, and output overcurrent are measured by the  
module and therefore affect a stereo pair of channels re-  
gardless of whether the fault actually exists on both chan-  
nels processed in the module. Since every action applied  
to protect the digital processing module affects both chan-  
nels being processed, other fault conditions are not sepa-  
rated by channel, but rather by amplifier module.  
Simply stated, speakers connected in series will add  
together their impedance. Conversely, two speakers con-  
nected in parallel will result in half the impedance, three  
parallel speakers a third the impedance, four speakers a  
fourth, and so on, assuming the speaker impedances are all  
the same. Don't use mismatched impedances in parallel.  
When using paralleled speakers, the available amplifier  
power for that channel is evenly divided among speakers,  
so 100 watts driving two parallel speakers of equal imped-  
ance provides 50 watts to each speaker, etc.  
3.) Thermal LED and Protect LEDs stay on:  
Amp module is in thermal protect mode and needs  
to cool. The fan will continue to run while in thermal pro-  
tect, and other modules will continue to function. See sec-  
tion 8.4 for details.  
Specification Notes: Due to its spread spectrum out-  
put switching pattern, the output signal of a 6125A or 4200A  
amplifier contains significant dynamic frequency content* far  
outside the audio band, which makes no difference to audible  
performance, but which makes heavily bandwidth-limited** mea-  
surement of amplifier noise and distortion characteristics man-  
4.) Power LED lit but no Signal LED activity  
There is no input signal applied or input level con-  
trols are turned down.  
datory.  
*variable 200KHz to 1.5MHz  
**greater than 48dB/octave above 22kHz  
13  
 
Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
11.2  
Distorted Sound  
11.3  
Hum or Buzz Noise  
1.) Clip LED is flashing regularly  
Amplifier is being overdriven. Turn down the in-  
put level control, or reduce the output level from the sig-  
nal source.  
Be sure that the power cord’s 3-prong plug is con-  
nected to a properly earth-grounded outlet. Lifting the  
grounding third prong may not improve hum or buzz and  
can create a potential shock hazard.  
Hum is usually caused by ground currents flow-  
ing between different pieces of equipment. Ground cur-  
rents can be minimized by using a single point AC ground  
for the sound system, and by using balanced connections  
with quality cable throughout the audio path.  
2.) Clip LED is not flashing at all  
Amplifier input signal may be exceeding input  
headroom, which is greater than +12dBu, or 3.4V rms  
(measured using continuous 1kHz sine wave). Incoming  
signal level higher than +12.8 dBu will cause distortion in  
the amplifier. Turning down the input level controls will  
not eliminate distortion if the input headroom is exceeded.  
Turn down the output level of the device driving the am-  
plifier instead.  
Buzz, as well as certain audible high frequency  
tones, can be caused by environmental emissions such as  
lighting dimmers, neon lights, or computer equipment. Use  
balanced connections, and try moving the amplifier, wir-  
ing, lighting, or other equipment to different locations to  
isolate the source of the noise.  
Additionally, an input signal may already be dis-  
torted before it gets to the amp. Check to see if a piece of  
equipment in the signal chain before the amp is clipping.  
For best performance, the amplifier should be operated with  
input levels fully CW. Also check for damaged speaker  
drivers that could cause distorted sound.  
Sections 3.3, 5.3, 7.1, and 7.2 further discuss is-  
sues related to grounding and noise problems.  
12.  
DIMENSIONS  
2.25"  
(57.2)  
16.9" (430)  
18.5" (470)  
19" (483)  
14  
 
Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
13.  
SPECIFICATIONS  
Typical Idle Current  
6125A  
4200A  
*Power Output  
(Maximum Average Power, 0.1% THD, 1KHz)  
120V: 0.81A  
240V: 0.42A  
120V: 0.9A  
240V: 0.5A  
Rated Per Channel, Two Channels Driven  
Current with Typical Audio Program Material (4 ohm load  
6125A  
4200A  
- all Channels)  
4 ohm:  
8 ohm:  
Mono Bridged (1 Channel)  
250 Watts RMS 400 Watts RMS  
150 Watts RMS 275 Watts RMS  
6125A  
120V: 6.5A  
240V: 3.3A  
4200A  
120V: 7.0A  
240V: 3.5A  
8 ohm:  
500 Watts RMS 800Watts RMS  
Connections  
Input: Euroblock  
Rated Per Channel, All Channels Driven  
Output: Screw Terminal Block  
6125A  
4200A  
4 ohm:  
8 ohm:  
250 Watts RMS† 400 Watts RMS†  
Cooling: Forced Air, Thermal Sensitive 3-Speed Fan, Front  
Inlet/Rear Outlet  
150 Watts RMS  
275 Watts RMS  
Mono Bridged (3 channels)  
8 ohm: 500 Watts RMS  
800Watts RMS  
Dimensions: 19” (483mm) L x 5.25” (133mm) H x 16.5”  
(419mm) D  
(Maximum Average Power, 0.2% THD, 20Hz-20KHz)  
Rated Per Channel, All Channels Driven  
Construction: 14 Gauge All-Steel Chassis  
6125A  
4200A  
8 ohm:  
130 Watts RMS 230 Watts RMS  
Weight  
Shipping  
Net  
6125A  
4200A  
56lbs. (25.5Kg) 53lbs. (24Kg)  
49lbs. (22.3Kg) 46lbs. (21Kg)  
Input Impedance: 10K ohm balanced, 37K ohm unbal-  
anced  
Specification conditions: 120VAC mains at 60Hz, 25° C  
High Pass Filter: 50Hz, 12dB/octave  
* Continuous power limited by power line capacity  
**Total Harmonic Distortion (20Hz - 20KHz @ 8 ohms):  
<0.2%  
**Non-conventional amplifiers require bandwidth limiting  
for all distortion and noise measurements.  
**IMD  
(SMPTE 60Hz/7KHz 4:1)  
@ 8 ohms: <0.2% (throughout power range)  
(IHF) @ 8 ohms: <0.1% (throughout power range)  
† Signal peaks in audio programming may trigger protec-  
tion circuitry at low line voltages. Specifications are subject to  
change or improvement without notice.  
14.  
WARRANTY INFORMATION  
**Hum and Noise: -100dB from full output (A-weighted)  
The unit you have just purchased is protected by  
a limited five-year warranty . For warranty service or to  
obtain a return RMA number, please call Altec Lansing  
technical services at 405-848-3108. Fill out the informa-  
tion below for your records.  
Full Power Input Sensitivity:  
6125A  
4200A  
1.08V RMS (2.9dBu) 1.47V RMS (5.6dBu)  
Frequency Response:  
8 ohm: ±0.5dB 20Hz-20kHz  
4 ohm: ±1.5dB 20Hz-20kHz  
Serial Number _________________________________  
Dealer ________________________________________  
Date of Purchase _______________________________  
Dealer’s Address _______________________________  
Dealer’s Phone ________________________________  
Salesperson ___________________________________  
Voltage Gain: 32X (30.1dB)  
Crosstalk: < -80dB (20Hz - 1KHz)  
Signal Present Signal Sensitivity: 13mV RMS (-35.5dBu)  
Power Requirement: 110-125VAC, 220 - 250VAC 50-60Hz  
15  
 
Operating Manual 6125A and 4200A Multi-Channel Power Amplifier  
Altec Lansing Professional  
1000 W. Wilshire Blvd. Suite 362  
Oklahoma City, OK 73116 USA  
A division of Altec Lansing Technologies Inc, Milford PA 18337-0277 Made In USA  
Printed in USA  
6125A-0 0503  
 

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