Quad 405 with current dumping
"Alex Pogossov"
Note that op-amp IC1 is firtually out of the GNFB loop. It is only as a
preamp with gain of 15 and for DC stabilisation.
** IC1 has four jobs:
1. An inverting stage with gain of 15 times making the total gain 56 times.
2. A DC offset servo with C2, R4 & R5.
3. A sub sonic filter, -3dB at 13Hz and -20dB at 5 Hz.
4. With R11 fitted, it clamps the input signal so the max power becomes
half.
These last three together make to 405 safe to use with an ESL57.
.... Phil
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