Ecler APA1000, Service Manual

Page: 42 / 138

author:
Queralt
date:
011212
approved:
num:
51.0027
version:
01.02
VERIFICATION PROCESS
title:
APA POWER AMPLIFIERS
ECLER
distortion- and noise-free. Verify that even if the input signal frequency rises up to
50KHz, the output signal level only decreases 1 or 2 dB, but no distortion is noticed.
- Verify the MONO operation mode. Apply a 1KHz 0'5V input signal and set the MONO
STEREO selection switch to the MONO position. The output signals should now appear
in phase opposition one referred to the other, and only the Channel1 input
potentiometer is responding. Connect an 8
Ω
load impedance to the unit's actual active
output terminals of both outputs and verify that the anticlip system switches on easily
when needed. Set the amplifier back to the STEREO operation mode.
- Connect an output load impedance formed by a 4
Ω
resistor shunted to a 2µF
capacitor, and apply a 1KHz square waveform input signal. Monitor the output signal
through an oscilloscope, and increase the input signal level until the output starts
clipping. On the flat sections of the sandcastle output waveform, only two or three
little ringings should be detected.
- To verify the subsonic filter, apply a 20Hz input signal. When the subsonic filter is
active, the output signal should decrease 6.5dB referred to the non-active filter output
level.
- Verify the THERMAL protection. When the thermal probe 1 and 2 leads are shorted,
check that the relay opens, the THERMAL indicator led lights on, the output signal is
cutted off and the cooling fan increases its speed up to the maximum running speed.
PROTECTIONS
- Turn off the signal generator. Select a 1KHz output signal, set the amplitude range to
1V but leave the amplitude control knob down to its minimum position.
- Connect a 0'5 ohm load impedance to the amplifier's output.
- Turn on the signal generator, and slowly increase the amplifier's input signal
amplitude, while watching that the unit's output voltage does not exceed its limiting
value, depending on the type under test, as listed below:
FIRST STAGE SECOND STAGE
- APA1400 13Vpp 22Vpp
- APA1000 20Vpp 25Vpp
- APA600 15Vpp 18Vp
Note: the clipping signal should appear distortion- and ringing-free. The different
stages are obtained by varying the amplifier's mains voltage through the variac's
output.
Sheet 2 of 3