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paulrerrie 12th November 2010 07:13 PM

Pioneer PD9700 analogue stage question
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Hi. I was just curious to know, do R577 & C567 (see schematic) form a (12KHz) low pass filter? The stage is described as 'Buffer & de-emphasis' & I wondered if this was intended to actually filter the audio signal rather than decouple digital/RF noise.

Thanks, Paul

SoNic_real_one 12th November 2010 11:03 PM

Looks like that. If the 0.0056 is a 5.6nF capacitor...

Mooly 13th November 2010 06:41 AM

The whole opamp stage forms what's called a "multiple feedback" filter and is inverting at DC. The opamp is configured as an integrator (C565) and it's performance is hugely opamp dependant. That may be one reason why the stage uses FET's to boost output stage current delivery.

paulrerrie 13th November 2010 09:31 AM

Wikipedia calls it a 'multiple feedback topology' and from the corner frequency calculation, it only appears to be filtering at very high frequencies.

SoNic_real_one 13th November 2010 11:51 AM

The integrator made with C565 (680pF) is filtering very high. But the one at the input was in question... Is a simple low-pass with 2k4 resistor and 5n6 capacitor. That has -6dB at some 11.8 kHz.

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