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Old 28th April 2004, 08:28 PM   #11
Bricolo is offline Bricolo  France
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this seems to be very high frequency
try some ferrite beads when you recieve them
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Old 28th April 2004, 08:48 PM   #12
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iīll do

subjectively bass more accentuated than TDA1305.
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Old 28th April 2004, 09:23 PM   #13
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Till,

The noise on all of your scope shot’s is just too high.

Do you have separate ground for analog and digital and you DAC's. What I use on prototypes breadboards is 3M copper tape, it make a great ground plane. In addition, some OSCON's caps close to the DAC will help. If you using 78& &79 series regulators they need more filtering a PI filter will help. However, all is lost if the ground is not a low impedance.

You should have pulse transformers at both ends on your SPDIF. If you have a CAP to ground at your CD player or on the DAC that connects to your shield that will introduce noise, big time into the DAC. It causes circulating ground currents.

Make sure that your scope probe has a very short ground lead. A longer lead will make the reading look higher.
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Old 28th April 2004, 09:38 PM   #14
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I made ground like Analog Devices told me in the datasheet: separate at the DAC and connected at the power supply board.

The ground clip of my probe is 150mm long. Its a 150MHz Testec probe, i have no better one. All the noise shown is only visible with the 7904, the slow 25MHz bandwith 7313 does not shows this stuff. In the CD player i did not change anything, only a BNC socket instead of the corroded old RCA for SPDIF. I have no pulse transformers, so i have to use what they call "consumer interface" in the CS8412 datasheet until i find something better.

I use 7805 for the digital supplys only, not the DACs analog. All supplys are filtered. The Analog with the circuit as shown in the thread for the power supply board linked above. At the DAC board with 100nF + 100uF at connector, 100uH/ 1.7Ohm series, 10uF + 100nF at DAC.

The 7805 at PS board with 330nF at in and out blocked, some electrylytic at in, at DAC board with 100uF, 100uH+1,7Ohm series, 10uF+100nF at each IC pin. Of corse i can make some additional RC into this.

The CDP has no real ground, only two pin mains plug. The DAC i also have not connected to real earth ground - only 2 pin mains plug.

I understand i will have to make a groundplane from all unused area on the board with some copper foil, but i will do this when everything works and iīm sure i donīt change parts anymore.
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Old 29th April 2004, 01:53 AM   #15
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Till,

If you plan to integrate the DAC into the player maybe this is not such a big deal since the DAC and Player will be command or stared to the same ground.

If you do not then will should consider changing to 75-ohm SPDIF interface that has transformer at both ends. Burr Brown makes some isolation chips that you can put between the digital hardware and the DAC to isolate the noise I will have to look for the part number. It is kind of like using an isocoupler but has lower noise

What kind of transport are you using and does it have a transformer? It really not to hard to change the receiver the output player may be a little harder. A lot of this noise is common mode noise and can be reduced with a differential inductors or a common mode filter for the supply and ground.
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Old 29th April 2004, 03:35 PM   #16
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thanks jewilson,

At the moment i use a Philps CD670 spdif output, i have to look inside how spdif out is made.

I did not find oscon at the parts supply i ususaly buy, whats the speacial thing about oscon?

I use the spdif at the moment because its less money to kill a CS8412 while prototyping than kill a CD transport. My plan is to build a CD player with balanced DAC and CD PRO2 or any DSA transport. I donīt see the advantage of external DACs , and integrated i will be able to make short connections, do not use the reciver IC , and have a hopefully better clock than spdif. To me all the reclocking is some kind of dubios, i would prefer to use only one clock that is allready there (the transports), and have everything near to each other. The reason for all this is i want a balanced out CD player as without a balanced source it doesnīt make to much sense to me to go for balanced preamp and amplifiers.

I will use this unit,
http://www.daisy-laser.nl/homeoptics/
and try to tell it to give me the data in the format the analog devices dac wants. So i donīt need reciver chip for converting the signals format anymore.

I split this "project" into some parts, first power supply, now DAC working, next I/V stage. I will need to get a controller for the DSA CD transport working,some assembly language coding necessary, and then mate CD transport with the DAC.

The isolation amplifiers i found at TI had not much bandwith?
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Old 29th April 2004, 04:13 PM   #17
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The OSCON or a Organic type of electrolytic cap, they are very low ESR, good for removing switching noise. Of course, you should have some .01 ceramics to decouple the higher frequencies.

One of the main reasons to get the DAC out of the CDP box is due to digital switching noise. However, if the SPDIF interface is implemented poorly the performance will be bad, as you seen.
You can implement the SPDIF 75ohm interface with transformers it is not that big of a deal. I use a PS audio Lambda transport, which has a balance digital drive output using 74ALS74's with some resistors and pulse transformer.

If you want to check out the OSCON the one's I use are make by www.vishay.com and can be found with their electrolytic caps. The only better cap for this application is a low ESR tantalum which cost about 5x the price of the OSCON's also Sanyo makes the too.

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Old 29th April 2004, 04:22 PM   #18
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Thumbs up DAC out of the CDP Box

Quote:
Originally posted by jewilson
One of the main reasons to get the DAC out of the CDP box is due to digital switching noise. However, if the SPDIF interface is implemented poorly the performance will be bad, as you seen.
Hi, At least someone understands why............
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Old 29th April 2004, 04:44 PM   #19
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So you say converting to spdif, cable out of box, in the other box, converting back to to I2S is better than direct connection I2S to DACs?

What about shielding between transport and DAC, and of corse separate power supplys?
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Old 29th April 2004, 05:32 PM   #20
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Question ???

Quote:
Originally posted by till
So you say converting to spdif, cable out of box, in the other box, converting back to to I2S is better than direct connection I2S to DACs?

What about shielding between transport and DAC, and of corse separate power supplys?
Hi Till, You are addressing me?
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