Adding a custom DAC to a CD player

csd · 13th June 2002, 03:55 PM

Hello,
I've been working on a external DAC design, but I'm convinced that a custom DAC and clock upgrade inside of an existing CD player is a better way to go. Avoid all that nasty SPDIF stuff altogether.

I have a Philips CD920, an early 90s unit, that I'd like to use as a test platform. I have the repair manual for it, and it uses a SAA7431 servo/decoder/DAC chip. I don't see any obvious pins for I2C data, only SPDIF out. I attached the schematic that shows this chip. I cannot find the datasheet on the web anywhere, even at Philips.

Any thoughts?

I also have a Marantz CC-67, but it is a relatively recent purchase that still has a warranty...

Craig

Dave · 15th June 2002, 05:05 AM

You need to find a I2s line carrying the 44.1/16 audio data and associated clocks and route that to your custom DAC pcb which I assume will contain a suitable oversampling filter and DAC chips.
You may also want to consider placing the clock on your DAC board and sending that back to the player. This should solve any jitter issues.

guido · 16th June 2002, 10:52 PM

Hi,

Think you said it yourself: "SAA7431 servo/decoder/DAC chip"
There is no I2S out, only the analog signal.

I don't think you can do anything with this player for own development. It's all in the chip.

Greetings,

Guido

Cobra2 · 16th June 2002, 11:50 PM

What about the indicated " Digital Out" on pin-32 ?

Arne K

Thomas · 16th June 2002, 11:53 PM

Since you probably have to get a new CD-player, if you still want to go with your idea, take a look at cambridge audio D300. It's a 350$ unit and is buildt to be modified. Seperate psu, servo controll unit and dacboards. It even has a shielded toroid transfomer. If you want to improve a cheap CD-player, this is it. The factory will introduce their own upgrades later. I can spot a unused HDCD segment in the display just waiting...

I don't know if the drive (Sony) is high enough quality to reach true audiophile quality, though. - Anyone???

csd · 17th June 2002, 02:08 PM

Thanks for the replies!

Pin 32 is the SPDIF output.

The Cambridge Audio D300 sounds like a good machine to start with, especially if it could be found used!

There are a number of test connections on the chip (Test1-9, pins 66-78) which I think are worth a look at, but haven't had the time to dig into yet. The chip is on the backside of the main board, so probing is a bit of a challenge.

I did find that the supply lines are TRASH. How about 250mVpp of high frequency hair on the +5V line? AND, the +/-10V lines to the analog output stage are regulated with a zener/resistor only. I don't need to tell you how bad those lines look.

So far, I think my upgrades to this player will be limited to a better clock (making a Kwak Clock board now), and adding more supply regulation.

Craig

csd · 7th August 2002, 03:55 PM

Well, I finished the following mods to this player:

-Built and installed a Kwak Clock
-Replace all power supply diodes with fast recovery types
-Replace most supply and local chip electrolytics with much larger values
-Replace output opamps with OPA2604
-Remove output muting transistors
-Add +/-8V regulators to analog output stage

For this effort, this player now sounds noticeably better than my Marantz CC-67. The highs are much clearer, cymbals sound much more distinct, and sibilance on voices is much lower.

BUT, there is still some sibilance on vocals that I would like to get rid of. Anybody have any thoughts on what might be the culprit?

Also, there is noticeable amount of 80kHz signal at the output, even when there is no disk playing. This signal is also present at the output of the DAC chip. Any ideas on this?

Craig

csd · 9th August 2002, 12:08 PM

Come on now! Somebody out there must have some thoughts!

peranders · 9th August 2002, 12:48 PM

My suggestion is not to redo the whole CD in order to get better sound.

Think once or twice if you ought to do something about the speakers? What type do you use?

I would say that the biggiest improvement is changing the speakers! I changed my small Infinity to Martin Logan SL3 when I moved (and got better space). My music listning is before martin Logan and after. It's really more fun with cool speakers and not "spitzenklasse" of the signal sources and the other way around (good source and poor speakers).

Elso Kwak · 9th August 2002, 05:23 PM

Quote:

Originally posted by csd
Come on now! Somebody out there must have some thoughts!

Ooh yes, I do have:
Install my asynchronous reclocker; change to Non-oversampling.

16th June 2002, 10:52 PM	#3
guido diyAudio Member Join Date: Mar 2002 Location: diepe zuiden	Hi, Think you said it yourself: "SAA7431 servo/decoder/DAC chip" There is no I2S out, only the analog signal. I don't think you can do anything with this player for own development. It's all in the chip. Greetings, Guido __________________ GuidoB

16th June 2002, 11:50 PM	#4
Cobra2 DIY ! diyAudio Member Join Date: Apr 2002 Location: Stavanger, Norway	Digital out...? What about the indicated " Digital Out" on pin-32 ? Arne K

9th August 2002, 12:48 PM	#9
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	My suggestion is not to redo the whole CD in order to get better sound. Think once or twice if you ought to do something about the speakers? What type do you use? I would say that the biggiest improvement is changing the speakers! I changed my small Infinity to Martin Logan SL3 when I moved (and got better space). My music listning is before martin Logan and after. It's really more fun with cool speakers and not "spitzenklasse" of the signal sources and the other way around (good source and poor speakers). __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Problems adding Digital Out to Laserdisc player (LC78621 chip)	Hybrid fourdoor	Digital Source	9	30th January 2009 08:30 AM
Adding digital out to a CD player with only PCM!	Destroyer OS.	Parts	0	4th June 2006 09:51 PM
Adding Digital Input to CD Player -> low cost DAC for PC	Brent Welke	Digital Source	1	2nd January 2005 04:57 AM
adding balanced output to cd player	cowanrg	Digital Source	6	26th November 2002 08:40 AM
Adding A Superclock To Cd Player	richt	Digital Source	1	17th October 2002 04:58 PM


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

15th June 2002, 05:05 AM	#2
Dave diyAudio Member Join Date: Oct 2001 Location: New Zealand	You need to find a I2s line carrying the 44.1/16 audio data and associated clocks and route that to your custom DAC pcb which I assume will contain a suitable oversampling filter and DAC chips. You may also want to consider placing the clock on your DAC board and sending that back to the player. This should solve any jitter issues.

16th June 2002, 11:53 PM	#5
Thomas diyAudio Member Join Date: May 2001 Location: Right here	Since you probably have to get a new CD-player, if you still want to go with your idea, take a look at cambridge audio D300. It's a 350$ unit and is buildt to be modified. Seperate psu, servo controll unit and dacboards. It even has a shielded toroid transfomer. If you want to improve a cheap CD-player, this is it. The factory will introduce their own upgrades later. I can spot a unused HDCD segment in the display just waiting... I don't know if the drive (Sony) is high enough quality to reach true audiophile quality, though. - Anyone???

17th June 2002, 02:08 PM	#6
csd diyAudio Member Join Date: May 2002 Location: Pennsylvania	Thanks for the replies! Pin 32 is the SPDIF output. The Cambridge Audio D300 sounds like a good machine to start with, especially if it could be found used! There are a number of test connections on the chip (Test1-9, pins 66-78) which I think are worth a look at, but haven't had the time to dig into yet. The chip is on the backside of the main board, so probing is a bit of a challenge. I did find that the supply lines are TRASH. How about 250mVpp of high frequency hair on the +5V line? AND, the +/-10V lines to the analog output stage are regulated with a zener/resistor only. I don't need to tell you how bad those lines look. So far, I think my upgrades to this player will be limited to a better clock (making a Kwak Clock board now), and adding more supply regulation. Craig

7th August 2002, 03:55 PM	#7
csd diyAudio Member Join Date: May 2002 Location: Pennsylvania	Well, I finished the following mods to this player: -Built and installed a Kwak Clock -Replace all power supply diodes with fast recovery types -Replace most supply and local chip electrolytics with much larger values -Replace output opamps with OPA2604 -Remove output muting transistors -Add +/-8V regulators to analog output stage For this effort, this player now sounds noticeably better than my Marantz CC-67. The highs are much clearer, cymbals sound much more distinct, and sibilance on voices is much lower. BUT, there is still some sibilance on vocals that I would like to get rid of. Anybody have any thoughts on what might be the culprit? Also, there is noticeable amount of 80kHz signal at the output, even when there is no disk playing. This signal is also present at the output of the DAC chip. Any ideas on this? Craig

9th August 2002, 12:08 PM	#8
csd diyAudio Member Join Date: May 2002 Location: Pennsylvania	Come on now! Somebody out there must have some thoughts!

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read