Sony CD XE530 Output filter

[leon]

I am tweaking a Sony CDP-XE530 CD player.

I changed opamps, capacitors, removed muting transistors.

Now I am trying to understand why they use this output filter with the strange response (see image).

This filter is steeper than a butterworth 2nd order but it amplifies the high audio frequencies.

Do they use this kind of response just to make this 2nd order filter steeper or they really want to amplify the high audio frequencies ?

Because if it is only to make a steeper 2nd order filter I can maybe build a higher order but flat in the audio frequencies one.

I already tried a second order butterworth but the highs sounded bad.

[Elso Kwak]

Hi, No high valued resistors in series with the source in the Sony like 9k1??

[leon]

This was the last stage, the filter.

See below a more complete schematic

[Elso Kwak]

Hi leon,
I see clearly now.
How does the NON-UK value for C907 similate? (0.0015µF)
Also try to simulate the whole filter from the 15k resistor...

[leon]

Hi

With C907 1.5nf it is a little better

See below

Blue is with C907=1.2nF
Yellow is with C907=1.5nF
Green is flat with C907=1.2nF and C906=2.7nF