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Old 11th December 2003, 12:31 AM   #21
pieris is offline pieris  United States
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Direct I2S definitely prevents PLL-induced phase noise but no link is jitter-free. I would venture to guess that your signal at the other end of the cable still exhibits significant jitter, a significant portion of which is DDJ (data-dependent jitter, the harmonic-producing bad kind). But, not as much as what you'd get from PLL based reclocking.

As for whether source-generated jitter can be completely eliminated, yes it can be, but you have to buffer the entire contents of your data (eliminating the time domain) and then reclock it with a perfectly clean clock. Buffering any less than the entire contents will necessitate adjusting the (now, not so) clean clock to match the source clock every so often. And, there's no such thing as a perfectly clean clock anyway.

I'm not sold on non-OS DACs, maybe some matlab simulations would be an entertaining way to make a theoretical comparison between OS and non-OS.
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Old 6th January 2004, 03:04 PM   #22
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Hi all

I've looked at doing DAC mods on some old CD players. I want to do the I2S direct thing, but so far, on all the players I've messed with, the I2S output carries a 2 or 4 times oversampled signal. This is no good because I want to use a AD1955 DAC chip, which has its own OS built in.

So my plan B is to use the SPDIF output with a CS8412 receiver. To try and reduce line jitter, I was thinking of getting rid of the transformer, RCA cable, etc, and driving the CS8412 input pin directly off the raw logic level signal. Or maybe using ECL differential drivers and receivers.

Can anyone comment on this? Is there any point in doing it, or does the CS8412's PLL introduce enough jitter to make the line jitter insignificant?
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Old 6th January 2004, 05:46 PM   #23
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Quote:
Originally posted by CurrentFeedback
Hi all

I've looked at doing DAC mods on some old CD players. I want to do the I2S direct thing, but so far, on all the players I've messed with, the I2S output carries a 2 or 4 times oversampled signal. This is no good because I want to use a AD1955 DAC chip, which has its own OS built in.

So my plan B is to use the SPDIF output with a CS8412 receiver. To try and reduce line jitter, I was thinking of getting rid of the transformer, RCA cable, etc, and driving the CS8412 input pin directly off the raw logic level signal. Or maybe using ECL differential drivers and receivers.

Can anyone comment on this? Is there any point in doing it, or does the CS8412's PLL introduce enough jitter to make the line jitter insignificant?
If you do use the SPDIF, make sure you remove the spdif digital output circuitry and take the raw signal into the CS8412 (ie, do not use the 75ohm-ish output circuit that usually has a pulse transformer and buffers. You should also look at the CS8412 datasheet and look how they connect to it when using TTL. I don't know if it going to add or subtract jitter, but it is worth a try.

-Vinnie
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Old 6th January 2004, 05:46 PM   #24
pieris is offline pieris  United States
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Definitely re-doing the driver and receiver will help a lot. I'm developing an add-on SPDIF driver for DIY people, currently using a direct-coupled output, and experimenting with different transformers. A problem with not using transformers is ground loops and EMI pickup. If you have no ground loops, and no EMI nearby, then a transformerless solution might be better, just use the shortest length of (twisted pair or coax) cable you can find.

Read the papers on scientificonversion.com for why transformers are good (they have a vested interest, but it's good reading)

You could replace the transformer on the receiving end, or change the topology. A lot of receivers have caps to ground which will work against a fast slew rate. You will most likely need a line driver of some sort on the transmitter, because the capacitance of even a short cable will be significant, and termination to reduce ringing will require more drive current.

Of course, the PLL produces a lot of jitter. Most PLL circuits attenuate jitter down to 1kHz or so, and everything below 1kHz is coming through loud and clear. The best solution is I2S or a DAC that doesn't use a PLL. But line jitter is not insignificant, and you will hear big improvements with even simple changes to the SPDIF output stage.

Are you sure your I2S is already oversampled?
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Old 7th January 2004, 09:23 AM   #25
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Quote:
Are you sure your I2S is already oversampled?
Yup! These are old cheap and nasty players, not the more modern or higher end type, which I suppose have a separate oversampling filter chip, or the OS is built into the DAC, or they have no OS at all because it isn't cool any more

One of the players (actually an old 24x CD-ROM) gave a 4x oversampled output to the DAC, in EIAJ format rather than I2S. The other one, an old Goodmans player with a Sony chipset, used 2x oversampling, again in EIAJ format.

I still have a newish TEAC CD-ROM and a Harman/Kardon CD player that I haven't tried yet. I like the TEAC because it has a SPDIF out and plays even the oldest and most scratched discs no problem. I didn't mess with the H/K because it's the one I listen to while I'm hacking up all the other ones
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Old 26th January 2004, 10:48 PM   #26
Lyra is offline Lyra  Norway
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Default Re: Re: IIS direct/ASR

Quote:
Originally posted by Elso Kwak

I have only practical experience with a Philips CD650 and a CD931 using I2S Direct on a NON-OS TDA1543 DAC.
It also worked with a Sony CDP-X333ES and the same DAC but the TDA1543 replaced by the TDA1543A
I have a CD-player with this Sony control chip onboard. I have had a hard time to get this player to play MUSIC!!!......it just end up with something hard, and harsh, with terrible sss-sounds.

If I want to go the I2S way I must probably choose the TDA1543A chip, or a combination of cm's EIAJ to I2S converter, and a standard TDA1543/1541 chip.
Will the simplest way be the way to go ?

Would it be wise to go for/try the TDA1543 tower for increased linearity, conciderering this mod is intended to be carried out inside the CDP-box ?
The fact that it is a TDA1543A chip doesn't change the possibility to piggyback these chips, do it ?

I also read somewhere in the forum that it was the C4M (pin 57) that decided if the signal should be oversampled or not.....does this mean that i could turn the OS on and off ?
If I want it permanently off I just connect it to ground...yes ?

And finally (for now... ): will a player with a really! decent drive, and this Sony chip be able to play as good as a player with a CDM-drive when going the I2S way ????????

Many questions, but I would really like to know what to do before I do it............
Lyra

BTW: what are the pins that I have to use to get this work named. Seems to me like little different markings compared to the TEAC VRDS (CDX2500AQ) unit in another tread ( my chip is named CDX2500Q )

Ooooops!!! I just looked inside the CD-player an the chip is actually a CDX2500AQ !. Does this mean that the pins have different names, just because this is a Denon-player, and the other one was a TEAC ????, or is it me that need some sleep ????
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Old 27th January 2004, 08:14 AM   #27
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Default oversampled i2s

The oversampled i2s need not be a problem if you are using one of the newer DACs with build in filter. I know that the ad1853 is capable of taking in a 2x or 4x oversampled signal (same as 96 / 192 khz). It has control pins for that. On the ad1955 you will probably have to use a microcontroller to program the relevant registers.
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Old 27th January 2004, 12:42 PM   #28
Lyra is offline Lyra  Norway
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Default Re: oversampled i2s

Quote:
Originally posted by Joachim_b
The oversampled i2s need not be a problem if you are using one of the newer DACs with build in filter. I know that the ad1853 is capable of taking in a 2x or 4x oversampled signal (same as 96 / 192 khz). It has control pins for that. On the ad1955 you will probably have to use a microcontroller to program the relevant registers.
What I was hoping for was some way to get my player play wihtout harschness. The player now uses the built-in AD1862 DAC's.

Don't know if theese could be unsoldered and still be working, and use theese. But then again, i'll need something between the CDX2500 and the DAC. I was hoping to make it simple.

Anybody with a really GOOD schematics regarding a simple DAC with theese AD1862's ??

Elso Kwak:
I know (read) You have used the TDA1543A in combination with CDX2500.
Witch pins do You use ?
What about the sound compared to Your Philips CD930 I2S sollution ??
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