Baldwin Boxall Communications Ltd.
Wealden Industrial Estate, Farningham Road
Crowborough, East Sussex, TN6 2JR
Telephone: 01892 664422 Fax: 01892 663146
Website: www.baldwinboxall.co.uk
Email: mail@baldwinboxall.co.uk
IM2420
Issue 1 03/08/1999
M2420 Amplifier
Operating Instructions
- 2 - Issue 1
Mitre 2420
The Mitre 2420 is equipped with two 0 dBM balanced line inputs per channel which incorporates a
priority switching system. The priority is selected using a two-way dual in line switch. Switch ‘1’
when selected ‘on’ provides input 2 muting when 1 is accessed. Switch ‘2’ when selected ‘off’
enables the first input irrespective of access conditions. When both switches are selected ‘on’ input 1
will override input 2. Therefore it is possible to have both inputs mixing together or cascade priority
depending on the requirements, refer to rear panel drawing.
Input 1 pre-set volume controls are located on the rear and input 2 are on the front panel.
A 200 Hz 12 dB/octave high bass filter may be selected to limit the bass response of any channel.
This is useful if the speakers used have a limited response i.e. horn types.
The output stages are protected against overload and high temperature conditions. If the temperature
exceeds a safe level the output signal is reduced to a low level preventing permanent damage to the
amplifier. When it cools down, it will perform as normal without manual resetting.
The inputs to each amplifier are presented on two separate four-way plug-in terminal connectors, each
connector provides a balanced audio input, ground and access DC control input. The output is
presented on a three-way plug/screw termination connector providing 50V or 100V output.
- 3 - Issue 1
Mitre 2420 Technical Specification
Rated output power
100V line 230V AC supply 4 x 20W - 500 Ohms
THD 1 kHz rated output from all channels
230V AC supply Less than 0.5% typically 0.2%
Typical output power 1% THD
230V AC supply 4 x 25W - 400 Ohms
Output regulation
1 kHz 100V line Better than 1.4 dB
Output voltages obtainable by pin selection 50 & 100V
Supply voltage AC 230V 50-60 Hz
Power consumption @ 230V
Quiescent
Rated output power @ 1 kHz 12VA
180VA
Fuse protection
1 x AC supply 20 x 5 mm
8 x DC (amplifier) auto blade type
1 x DC Aux output 20 x 5 mm
2A(T)
3A(F)
2A(T)
Input type per channel 2 x line balanced with priority gating
Input sensitivity 0.5V @ 40K Ohms balanced
Input common mode rejection ratio
50 Hz - 30 kHz
Frequency response -3dB @
Signal to noise ratio
Selectable high pass filter
Better than 40 dB typically 60 dB
80 Hz - 20 kHz
Better than 85 dB
200 Hz 12 dB/octave
Channel separation @ 1 kHz Better than 60 dB
High pass filter 200 Hz - 12 dB/octave
DC Aux output 30V @ 1.5A max.
Terminations
1 x AC supply input
8 x Line signal inputs
1 x DC Aux output
4 x Loudspeaker line output
3-pin
4-pin
2-pin
3-pin
DIN IEC 6A
Screw terminated connector
Crimp terminated connector
Screw terminated connector
Dimensions (mm) (D x W x H) 340 x 430 x 90
Weight 8Kg
- 4 - Issue 1
40W20W
P17 = CHANNELS 1&2
P18 = CHANNELS 3&4
CHANGE LINK FROM 20W TO 40W
PART VIEW OF PRINTED CIRCUIT
BOARD WITH COVER REMOVED
100V
0V50V
50V
LOUDSPEAKER
100V
100V
0V50V
50V
LOUDSPEAKER
100V
OUTPUT CH1
OUTPUT CH2
CHANNEL 1
CHANNEL 2
40W 250 ohms
CHANNEL 1&2 OR 3&4 OUTPUTS
PART VIEW OF REAR PANEL
100V
0V50V
50V
LOUDSPEAKER
100V
100V
0V50V
50V
LOUDSPEAKER
100V
100V
0V50V
50V
LOUDSPEAKER
100V
100V
0V50V
50V
LOUDSPEAKER
100V
12
0V
ACCESS
INPUT
BALANCED
0VACCESS
INPUT
BALANCED
OUTPUT CH1
OUTPUT CH2
OUTPUT CH3
OUTPUT CH4
CH1-1
CH1-2
CHANNEL 1
12
ON
OFF
ON
OFF
OFFON
ON
12
INPUT PRIORITY SWITCHING
INPUT1 AND 2 WILL MIX WHEN THEY ARE ACCESSED.
INPUT1 WHEN ACCESSED OVERRIDES INPUT2.
INPUT1 ENABLED IRRESPECTIVE OF ACCESS STATE. INPUT2 WILL MIX WHEN ACCESSED.
INPUT1 ENABLED IRRESPECTIVE OF ACCESS STATE. INPUT1 ACCESS WILL OVERRIDE 2
ON
OFF
ON
12
0VACCESS
INPUT
BALANCED
0V
ACCESS
INPUT
BALANCED
ON
12
0V
ACCESS
INPUT
BALANCED
0V
ACCESS
INPUT
BALANCED
ON
12
0V
ACCESS
INPUT
BALANCED
0V
ACCESS
INPUT
BALANCED
ON
CHANNEL 4CHANNEL 3CHANNEL 2
100V OR 50V LOUDSPEAKER OUTPUT
CHANNEL 1
CHANNEL 2
CHANNEL 3
CHANNEL 4AUX 24V DC OUTPUT 1.5A MAX
TO FEED BVMX ETC. FUSED AT T2A
NOTE. INPUT 2 VOLUME CONTROL IS MOUNTED ON FRONT PANEL
BALANCED SIGNAL INPUT
500mV @ 44Kohms
ACCESS CLOSE TO 0V TO
ACCESS INPUT
CH2-1
CH2-2
CH3-1
CH3-2
CH4-1
CH4-2
CH4 I/P1 VOLUMECH3 I/P1 VOLUMECH2 I/P1 VOLUMECH1 I/P1 VOLUME
FIG 1: M2420 REAR PANEL VIEW
CUT FOR 200Hz
HP FILTERCUT FOR 200Hz
HP FILTERCUT FOR 200Hz
HP FILTERCUT FOR 200Hz
HP FILTER
40W20W
40W20W
CHANNEL 1CHANNEL 4
CHANNEL 3
CHANNEL 2
REMOVE LINK TO ENABLE
200Hz 12dB/OCT FILTERREMOVE LINK TO ENABLE
200Hz 12dB/OCT FILTER
200Hz HIGH PASS FILTER
PART VIEW OF PRINTED CIRCUIT
BOARD WITH COVER REMOVED
- 5 - Issue 1
N
E
PSU
24V AUX SUPPLY
OUTPUT 1.5A MAX
+VE
-VE
MAINS
SWITCH MAINS
FUSE
L
230V AC
50Hz-60Hz
+30V
0V
-30V
T2A
T2A
MITRE 2420
BLOCK DIAGRAM
LK1
ENABLE FILTER
REMOVE LINK TO
PRIORITY
LOGIC
200Hz HIGH
PASS FILTER
POWER
AMPLIFIER
100V
50V
0V
F3A
F3A
+30V
-30V
CHANNEL 1
VOLUME
INPUT 2
-
+
I/P
I/P
1
2
BALANCED
INPUT 500mV
INPUT 2
0V
ACCESS
3
4
0V
FRONT
0V
0V
BALANCED
INPUT 500mV
I/P 1 VOLUME
INPUT 1
-
+
I/P
0V
ACCESS
2
3
4
0V
INPUT 1
REAR
LK1
ENABLE FILTER
REMOVE LINK TO
200Hz HIGH
PASS FILTER
POWER
AMPLIFIER
100V
50V
0V
F3A
F3A
+30V
-30V
20W
40W
PRIORITY
LOGIC
VOLUME
INPUT 2
-
+
I/P
I/P
1
2
BALANCED
INPUT 500mV
INPUT 2
0V
ACCESS
3
4
0V
FRONT
0V
0V
BALANCED
INPUT 500mV
I/P 1 VOLUME
INPUT 1
-
+
I/P
0V
ACCESS
2
3
4
0V
INPUT 1
REAR
CHANNEL 2
LK1
ENABLE FILTER
REMOVE LINK TO
PRIORITY
LOGIC
200Hz HIGH
PASS FILTER
POWER
AMPLIFIER
100V
50V
0V
F3A
F3A
+30V
-30V
VOLUME
INPUT 2
-
+
I/P
I/P
1
2
BALANCED
INPUT 500mV
INPUT 2
0V
ACCESS
3
4
0V
FRONT
0V
0V
BALANCED
INPUT 500mV
I/P 1 VOLUME
INPUT 1
-
+
I/P
0V
ACCESS
2
3
4
0V
INPUT 1
REAR
LK1
ENABLE FILTER
REMOVE LINK TO
200Hz HIGH
PASS FILTER
POWER
AMPLIFIER
100V
50V
0V
F3A
F3A
+30V
-30V
20W
40W
PRIORITY
LOGIC
VOLUME
INPUT 2
-
+
I/P
I/P
1
2
BALANCED
INPUT 500mV
INPUT 2
0V
ACCESS
3
4
0V
FRONT
0V
0V
BALANCED
INPUT 500mV
I/P 1 VOLUME
INPUT 1
-
+
I/P
0V
ACCESS
2
3
4
0V
INPUT 1
REAR
CHANNEL 3
CHANNEL 4
20W
20W
20W
20W
P17
P18
/
