Pioneer PD9700 analogue stage question

paulrerrie · 12th November 2010, 07:13 PM

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.

13th November 2010, 06:41 AM	#3
Mooly diyAudio Member Join Date: Sep 2007	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. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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12th November 2010, 11:03 PM	#2
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	Looks like that. If the 0.0056 is a 5.6nF capacitor...

13th November 2010, 09:31 AM	#4
paulrerrie diyAudio Member Join Date: Jan 2008	Wikipedia calls it a 'multiple feedback topology' and from the corner frequency calculation, it only appears to be filtering at very high frequencies.

13th November 2010, 11:51 AM	#5
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	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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