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SERVICE MANUAL
DPA 4245 / DPA 4260 POWER AMPLIFIER
MEASUREMENT SPECIFICATIONS: DPA power amplifiers complete appliance
Names of the individual printed board assemblies and their corresponding EDP numbers:
EDP numbers of the main boards
DPA 4245 DPA 4260
84 188 84 189
Board section Index
Main PCB 1
Supply PCB 4
LED PCB 3
Input-PCB (index 1) and Output-PCB (Index 2) are located on the printed board assembly 81340.
Measuring conditions, unless differently specified:
- measuring tolerance: X = 1.5dB
- measuring frequency: f = 1kHz
- all stated levels refer to: U = 775mV (0dBu)
- level controls are set to their clockwise margin:
- XLR connector pin-assignment: PIN 1 = GROUND/SHIELD
PIN 2 = + INPUT
PIN 3 = - INPUT
- source impedance for the induction via the XLR-type connector: R(Q) = 50 ohms
- the AMPLIFIER PCB is provided with service connectors:
CNS1 CNS2 CNRC
PIN Assigned to PIN Assigned to PIN Assigned to
1 -Vcc 1 LIM A Switch 1 LIM Out A
2 BIAS +A 2 -15V 2 LIM Out B
3 BIAS -A 3 LIM B Switch 3 Standby via RC
4 FAN Voltage 4 +15V 4 Standby LED
5 +Vcc 5 AGND 5 -Vss
6 BIAS +B 6 Speaker Out A 6 +Vss
7 BIAS -B 7 Relay/Protect 7 n.c.
8 Temp Heatsink 8 Speaker Out B 8 n.c.
- Pin-assignment of the power amplifiers output connector:
PIN Function Channel
1 + pole of the 100V output and + pole of the 25V output
2 - pole of the 25V output and + pole of the 70V output
3 - pole of the 70V output and - pole of the 100V output B
4 + pole Direct Output
5 - pole Direct Output
6,7 not assigned -
8 - pole Direct Output
9 + pole Direct Output
10 - pole of the 70V output and - pole of the 100V output A
11 - pole of the 25V output and + pole of the 70V output
12 + pole of the 100V output and + pole of the 25V output
Pin-assignment of the Power Remote connector: PIN 1 control voltage -
PIN 2 control voltage +
1
Nominal load impedances
100V output 70V output 25V output
DPA 4245 28,5 14 1,8
DPA 4260 20 9,8 1,25
1. Operation voltage: U(B) = 230V / 50Hz ... 60Hz
2. Deviation limit of the operation voltage: -30% .... +10%
3. Power consumption (both channels driven via the 100V output, f = 1kHz)
DPA 4245 DPA 4260
idling condition power consumption 30-60W 40-80W
nominal power consumption (nominal load) 1580W 1950W
standard power consumption (nominal load) 470W 620W
maximum power consumption (nominal load) 1680W 2180W
power consumption at 1/8 of the maximum output capacity 600W 870W
4. Settings
4.1. IDLING CURRENT ADJUSTMENT
Connect the DC-volt meter at the BIAS measuring points (refer to service connectors) and adjust the idling
current via the trim potentiometer VR101/VR301 (located on the Main PCB). Adjust both channels of the power
amplifier A&B to U(DC) = 7.5mV. Adjusting the idling current has to be performed at normal room
temperature. In case the power amplifier had previously been operated, it has to be given several hours to regain
its normal temperature.
4.2. VCA - OFFSET
Rhythmically open and short-circuit CNS2.1 and CNS2.2 for channel A as well as CNS2.3 and CNS2.2 for
channel B. The switches are located on the Main PCB. Using VR100 or VR300 respectively to adjust the power
amplifier's Direct Output to its minimum offset (with oscilloscope to minimal peak value or to the audible
minimal volume of the interfering pulse).
5. Functioning test
5.1. OUTPUT - offset voltage
DC-voltage measuring at the Direct Output A/B with U(DC) 10mV.
5.2. LIMITER
5.2.1. Voltage limiter
Both channels separately driven without load via the Direct Output with a 1 kHz signal up to U(A) = 38V.
Increase the input voltage by 10 dB. The LIMITER LED lights and the output voltage ascents by approx. 1.5 dB
or 2.5 dB respectively to approx. 44V or 52V, respectively. The distortion rate of the limited signal should not
ascent above 0.8%.
5.2.2. Distortion limiter
Both channels separately driven via the Direct Output at 2 with a 1 kHz signal up to U(A) = 20V or U(A) =
25V, respectively. Increase the input voltage by 5 dB. The LIMITER LED lights and the output voltage ascents
by approx. 1.5dB to approx. 25V or 29V respectively and it is slightly clipping. The distortion rate of the limited
signal is approx. THD = 2 ... 3%. Further increasing the input signal by +10dB should not result in a remarkably
higher clipping of the output signal.
2
5.2.3. Attack- and release times
separately testing the power amplifier channels is mandatory: Test has to be performed at the Direct Output
without load.
1.) Drive the power amplifier's input with a burst signal (f = 1kHz, 10 cycles, rate : 3 sec.) and U(E) = +10dBu.
2.) Monitor the output signal via oscilloscope. After 1 - 2 signal periods, the limiter has reduced the major
distortion to a minor residual distortion (THD 1%)
attack time: approx. 2 ms release time: approx. 130 ms
5.3 POWER-ON DELAY
Feed the test signal to the power amplifier input. Switch the power amplifier ON using the "Power On" switch.
Approximately 2 seconds after pressing the "Power On" switch, the signal is present at the output.
5.4 POWER REMOTE
Switch the power of the appliance OFF. Feed a control voltage of +24V to the Power Remote input. The power
amplifier has to start operation and after disconnecting the control voltage has to go off again.
5.5 FAN CONTROL
Upon powering-on the power amplifier, the fans will run for approximately 2 seconds and stop when the power
amplifier has re-gained its "normal" temperature. In idling condition (power-on, no signal present) the fans are
switched between the SLOW and OFF mode, depending on the heat sink's temperature. Connecting the CNS1.8
via a 5k resistor to +15V lets the fans run in SLOW mode. A FAN VOLTAGE of 16.8V DC can be measured
between pin CNS2.4 and pin CNS1.4. When disconnecting CN5, the fans will run in FAST mode. A FAN
VOLTAGE of 28V DC is measured between pin CNS2.4 and pin CNS1.4.
5.6 SOAR-PROTECTION TEST
Channels separately driven up to 0dB via the Direct-Output, terminated with 4. Parallel connect an 1 resistor.
The protection circuit reacts and tries continuously to re-start! The protect-LED lights.
5.7 SHORT-CIRCUIT CURRENT-LIMITING TEST
separately testing the power amplifier channels without load is mandatory:
- drive the channel with a burst signal (f = 1kHz, 1-3 cycles, rate 1 sec.), at the Direct Output with
U(E) = 0dBu.
- connect a load resistor of 1.
- the short-circuit current-limiter limits the output voltage at the load resistor symmetrically (monitor via
oscilloscope!) to a peak voltage value of 15V or 20V respectively (approx. 15A or 20A respectively maximum
peak output current).
5.8 DC-voltage and HF-Protection Circuit
- Testing the protection circuitry against the occurrence of DC-voltage and HF at the output is only possible
directly via the Main PCB when it is not installed in the appliance.
5.9 INDICATORS TEST
Feed a 1kHz sine signal while slowly increasing the level. At approx. -30dBu the SIGNAL LEDs will light and
at approx. +1.5dBu the Limit LED will light.
3
6. Level CHANNEL A B
6.1. VOLTAGE AMPLIFICATION
Appliance Input U(E) Measuring point vU U(A) Load Frequency
DPA 4245 CH. A/B 0dBu Direct Out A/B 33.8dBu 37.8V 4 1kHz
DPA 4245 CH. A/B 0dBu 100V Output 42.2dBu 99.2V 28.5 1kHz
DPA 4245 CH. A/B 0dBu 70V Output 39.3dBu 71.6V 14 1kHz
DPA 4245 CH. A/B 0dBu 25V Output 30.2dBu 25.1V 1.8V 1kHz
DPA 4245 CH. A 0dBu BRIDGED OUT 39.8dBu 76V 8 1kHz
DPA 4260 CH. A/B 0dBu Direct Out A/B 34.9dBu 43V 4 1kHz
DPA 4260 CH. A/B 0dBu 100V Output 41.8dBu 95.2V 20 1kHz
DPA 4260 CH. A/B 0dBu 70V Output 39dBu 68.8V 9.8 1kHz
DPA 4260 CH. A/B 0dBu 25V Output 29.8dBu 24V 1.25 1kHz
DPA 4260 CH. A 0dBu BRIDGED OUT 41dBu 87.3V 8 1kHz
6.2. MAXIMUM INPUT LEVEL: U(E) = +21dBu
7. GROUND LIFT switch
The circuit ground (at the input or the output connector) is measured versus the common ground of the enclosure
(contact at the ground terminal, located on the rear panel - or common ground of the mains cord).
without input transformer GROUNDED : R = 0 with input transformer GROUNDED : R = 0
NOT GROUNDED: R = 5 NOT GROUNDED: R
8. Amplitude - Non-Linearities
- MBW = 80kHz
- all channels terminated with nominal load at nominal power, Direct Output at 8 or at 4 respectively, at
nominal power
Measurement DPA 4245 DPA 4260 Remarks
100V 70V 25V Direct 100V 70V 25V Direct
THD+N <0.1% <0.2% <0.3% <0.05% <0.1% <0.2% <0.3% <0.05% 1kHz
IMD-SMPTE <0.1% <0.3% <0.5% <0.08% <0.2% <0.3% <0.5% <0.08% 60Hz, 7kHz
DIM 30 <0.2% <0.2% <0.2% <0.03% <0.2% <0.3% <0.3% <0.03% 3.15kHz,
15kHz
9. Frequency Response
The frequency response is linear. (mind the border frequencies)
fU -1dB fO -1dB fU -3dB fO -3dB
100V Output 60Hz 17kHz 45Hz 26kHz
70V Output 60Hz 17kHz 45Hz 26kHz
25V Output 60Hz 12kHz 45Hz 22kHz
Direct Output 60Hz 22kHz 45Hz 30kHz
10. Insert Attenuation
Drive the power amplifier in idling condition via the transformer outputs up to the nominal output voltage.
Connect the nominal load and measure the level changes.
DPA 4245 DPA 4260
100V Output 0,7 dB 0,7 dB
70V Output 0,8 dB 0,8 dB
25V Output 1,1 dB 1,1 dB
4
11. Crosstalk
It is necessary to align the output transformers when testing the crosstalk. Therefore, turn the transformer outputs
by 90