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Old 7th October 2004, 08:06 PM   #1
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Default Sony CDP players mod's.

I am working around the output stage of a Sony CDP player XB940 SACD, the XA50/30/20 and XB940/920/720 are similar (VC24+ CXD2562Q or CXD8735N - DAC chip’s). If someone is interested I can go further in this thread. I tested various configurations (OP-AMP’s / discrete) the last one uses a trans former to unbalance the output, but it can be used in balance mode. The sound is really very "natural" and the design is quite simple.
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Old 8th October 2004, 12:23 AM   #2
lpm76 is offline lpm76  Denmark
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I for one would be highly interested. I have long thought the 940 to be a bargain, and I am always interested in new tweaking possibilities.
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Old 9th October 2004, 02:29 PM   #3
Davet is offline Davet  United States
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Default Please continue!

I am interested in your mods as well as any photos you might post.
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Old 9th October 2004, 07:35 PM   #4
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At once I have some problems with my ftp pages and with my provider, so I can’t post the schematics now.

For the moment I can tell you the evolution of the improvements :

The first and easiest way to improve this player is to bypass the “current pulse chips”, so you get the DSD directly from the dac in a differential voltage mode, both at 2.5V dc, I think you have already seen this in a few sites (VSE, LC-Audio etc...) For the output stage, there are various possibilities : Op-Amp, discrete differential to single ended, transformer…
The goal was also to unbalance the dac outputs, to make it compatible with my preamp/crossover or at least to get the choice between balanced or unbalanced outputs.

In order to “try” the signal directly at the output of the dac, and to achieve a smooth filtering, the first simple way, was to use a “good” op amp. The AD826 or AD828 are among the best ones for this application in my knowledge and the less tricky to implement. I prefer the AD828 (Gv>2) but the AD826 with a current sink of 5mA to V-. will give you about the same results. I didn’t tested the most recent ones from Analog Devices…
This simple mod, bypassing the current-chips and a few Burr Brown op amps improved greatly the sound in all the ways !

Well I hope tonight or tomorrow my provider will solve the problems !
Keep in touch.
Questions or suggestions are welcome… while waiting debugging !
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Old 9th October 2004, 10:18 PM   #5
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HOOOUUUUUFFF !!!
Well after working hard, (with a big help from my wife !, she is my blind listener too...), I find another way to post my diagrams.
Below the first ones.
They may appear not really original, but the improvement taking into account simplicity is worth.

XB-output1

The DAC output offset between +out and –out, is not 0V but a few mV, and moreover, change according to the playing mode CD (pcm) or SACD (bitstream).

DC-servo add here.

XB-output2
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Old 10th October 2004, 01:19 AM   #6
EUVL is offline EUVL  Europe
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Default DAC Out

Richard,

If I am correct, VSE is not using the signal from the DAC output, but rather uses the differential bit-stream output directly from the VC24+ before the DAC and then low-pass filter / buffer.

Have you tried this, or are there reasons why you prefer to tap after the DAC ?

Also would you have datasheets for the VC24+ / DAC chips ?
Or some pin assignments would already be a GREAT help.

Many thanks in advance,
Patrick
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Old 10th October 2004, 05:42 AM   #7
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Default Re: DAC Out

Quote:
Originally posted by EUVL
Richard,

If I am correct, VSE is not using the signal from the DAC output, but rather uses the differential bit-stream output directly from the VC24+ before the DAC and then low-pass filter / buffer.

Have you tried this, or are there reasons why you prefer to tap after the DAC ?

Also would you have datasheets for the VC24+ / DAC chips ?
Or some pin assignments would already be a GREAT help.

Many thanks in advance,
Patrick
No, I do the same way as VSE or LC audio. If you refer to the XB940, the VC24+ is under the PCB, and this is the “real” DAC. What you see on both sides in skew and lengthened, with a “copper tape” are the current pulse converters. These chip’s are very sensitive to their supply (+7,-7V) and their reference. I tested in this way, after the current pulse converters, with battery power supplies and batt for the reference, (battery for the reference was the biggest improvement), this modification is not as effective in the reproduce sound quality as the one I describe here, and is more complicated and difficult to implement. Well… I must say that I didn’t test it with a jocko homo I/V converter... By the way, if someone here remember the thread where he speaks about it, I am curious to see his design, well maybe just a simplified one, I saw so much people in this forum speaking about it !

I get from Sony the service manuals of the SCD XB 940, CDP XA-50 and CDP XB-920.
I don’t have a scanner or a digital camera for the moment, maybe next week…but you can take a look at the VSE or LC-audio (Zap filter) sites, for their photos. I hope that Allen Wright or Lars Clausen will not be annoyed.

Davet, EUVL,
I can try to draw a simpified diagram for the output assignements pins of the VC24+, or the input pins of the current converters, I think maybe it’s easier to get the signal at the input of those chips.

(Maybe someone in this forum has them in computer file ?)
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Old 10th October 2004, 06:52 AM   #8
EUVL is offline EUVL  Europe
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Default Very useful information

Richard,

Your information is and will be most useful for someone like me who is thinking of doing the same modification (on an XB940). So any picture or sketches of your work is very welcome indeed. If you would be kind enough to take the trouble, please send me a copy of the manual and datasheet by post. I'll reimburse your costs. Send me a email so that I can let you have my postal address.

Many thanks for sharing with us.

Patrick
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Old 10th October 2004, 07:20 AM   #9
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Just have a look at:
http://www.diyaudio.com/forums/showt...161#post255161

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Old 10th October 2004, 07:30 AM   #10
EUVL is offline EUVL  Europe
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Default Great Tip

Elso,

Great tip. Many thanks.

I know that you have done a lot on DAC's, etc. So what do you think of the idea (Zapfilter directly from VC24+) ?

Patrick
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