Ecler PAM2000, Service Manual

Page: 11 / 107

8
ZOBEL NETWORK
This circuit tries to get a constant load impedance for the power module, in spite of the amplifier's load
and frequency, to avoid phase shifting of the feedback signal.
The values have been experimentally calculated through a study with square signal by trying to minimize
the power amplifier's ringing with very capacitive loads (2,2µF//4 Ω ).
The Zobel Network eliminates possible oscillations of the MOSFETs between 5MHz and 10MHz, too.
This is why it must be physically placed at the module's output, avoiding long wiring. Great care must be taken for
the signal not to be too shifted at the output, because the feedback could turn negative.
FEEDBACK
The whole amplifier is compensated with just one capacity, which places the amplifier's general pole at:
1
Fp = -------------- = 140KHz
2* π *Rf*Cf
Rf = R106 Cf = C109-C110
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