[Russtafarian]

Last year I modified a Pioneer DV-563 by connecting the voltage outputs of the BB1791 dac to a pair of Lundahl LL1527XL transformers.  I’ve notice that PCM (CD, DVD-A) playback off the transformers is dead quiet while SACD is quite noisy with noticeable background hiss and spurious noise.  My suspicion is that the 1791 is simply passing the DSD bitstream along in its native form without filtering it.  That would sure account for noisy SACD playback!

How can I implement a 2nd order passive noise filter that will hinge somewhere between 30 to 50 kHz and provide significant attenuation at the DSD carrier frequency of 2.82 mHz?  Would it be better to put the filter on the input or output of the transformer?  I have some 100 and 1000 pf polystyrene caps.  Can I use those?  Thanks for your help.

Russ

[Gary P]

Hi Russtafarian,

I've done the same mod to my DV563 player using the Sowter 3575 transformers. Very happy with the results.

Question. Do you hear noise during SACD playback?

I ask this as my player is dead quiet during DSD playback but makes all kinds of noise including stop and start pops after stopping from playing a DSD. It keeps making the noise untill you start a new DSD or change modes to PCM.

When stopping from PCM there is no noise. I have not checked the status of the mute circuitry to see if in normal operation the outputs are muted when you stop DSD playback.

For adding a filter a single pole would be easy.  Pioneer's first stage of filtering is a series 1.8K resistor in the + and - outputs of the DSD1791 with 1500pf capacitor across the ouput end of the 1.8Ks.  The series R could be a problem as it is in series with the primary of the output transformer.

I have given thought (but only a tiny bit) to a 2 pole filter using series inductors in place of the 1.8K resistors with the cap across the inductors. This idea has not been developed beyond the initial concept stage.

Hope this rambling heips.

Gary