peanutbutterjam 0 Report post Posted February 10, 2009 Hi does anyone have experience with making CD transports? I read that you need a PSU, PC CDrom drive and a controller and you're set as far as the internals go. But I know nuts about the mechanics in general, or how to convert the TTL digital signal to SPDIF. Please don't hesitate to throw me any info or links that aren't too boggling Share this post Link to post Share on other sites
peanutbutterjam 0 Report post Posted February 10, 2009 This is interesting. Does someone know how this works? http://www.head-fi.org/forums/f43/fs-cdrom...troller-365981/ Share this post Link to post Share on other sites
eawtan 0 Report post Posted February 10, 2009 There are some TTL->SPDIF conversion circuits at : http://www.epanorama.net/documents/audio/spdif.html Share this post Link to post Share on other sites
wwenze 0 Report post Posted February 10, 2009 Isn't the digital out of CD drives already in SPDIF format? Just that the voltage is higher. Just need a resistor, isolation transformer, or go optical. But hay, when people use expensive SPDIF encoders with their CDP and PC, you're going to trust the cheap thingie in the drive? Share this post Link to post Share on other sites
peanutbutterjam 0 Report post Posted February 10, 2009 Isn't the digital out of CD drives already in SPDIF format? Just that the voltage is higher. Just need a resistor, isolation transformer, or go optical. But hay, when people use expensive SPDIF encoders with their CDP and PC, you're going to trust the cheap thingie in the drive? No it isn't in SPDIF format. Its in some digital format called TTL, and you need to convert that signal. Haha bro you know in many upmarket CDPs most of them use computer drives. The error correction in your PC CDrom drive is way superb, since data generally has far less tolerance than audio. To put it in a nutshell, if your computer CDP can read 800mb of data reliably from a CD without a single bit corrupted at 48x, it most certainly can do so for audio at 1x. Share this post Link to post Share on other sites
wwenze 0 Report post Posted February 10, 2009 (edited) No it isn't in SPDIF format. Its in some digital format called TTL, and you need to convert that signal. Haha bro you know in many upmarket CDPs most of them use computer drives. The error correction in your PC CDrom drive is way superb, since data generally has far less tolerance than audio. To put it in a nutshell, if your computer CDP can read 800mb of data reliably from a CD without a single bit corrupted at 48x, it most certainly can do so for audio at 1x. The data format is SPDIF. Just that the voltage is TTL (5V). That's why simple converters exist. I'm not too concerned about the accuracy of the reading, although I'd like to mention that a bulk of the error correction comes from the file system (100MB of ECC data vs 700MB of actual data on the 700MB disc), which doesn't exists for audio CD. Futhermore data do get wrong at 48x, but they can re-read for data, you can't do that for audio. It's the conversion to SPDIF. The computer or CDP accesses the drive via IDE and the data is sent in PCM format, the combination of this transfer which can be believed as near-perfect. Then this PCM data is sent to the SPDIF encoder. We can assume it's a high-end chip with a high-end circuit. Compare that against what you can get in a CD-Drive. SPDIF is a lossy signal btw. How lossy, I wun know, but definitely depends on the encoder and circuitary. Or you're the type that believe digital signal is always perfect. In that case then there's no need for discussion. Just try it. Who knows, you may discover something good. Edited February 10, 2009 by wwenze Share this post Link to post Share on other sites
peanutbutterjam 0 Report post Posted February 10, 2009 I'm not too concerned about the accuracy of the reading, although I'd like to mention that a bulk of the error correction comes from the file system (100MB of ECC data vs 700MB of actual data on the 700MB disc), which doesn't exists for audio CD. Futhermore data do get wrong at 48x, but they can re-read for data, you can't do that for audio. Hm this is a good point. Agree on the re-read part. But from a data perspective if the drive can read data to 48x, the kind of error at 1x shouldn't be too disgusting right... But this is just pure conjuncture. Compare that against what you can get in a CD-Drive. SPDIF is a lossy signal btw. How lossy, I wun know, but definitely depends on the encoder and circuitary. How is SPDIF lossy? Or do you mean "lossy" as in SPDIF does not have an error check mechanism? Or you're the type that believe digital signal is always perfect. In that case then there's no need for discussion. Just try it. Who knows, you may discover something good. Nope, I don't believe that digital is always perfect, but there are limits to how "audiophile" a digital circuit can be. In any case this looks like a really interesting project, since I happen to have a CD drive on hand. Has anyone tried something similar before? Share this post Link to post Share on other sites
wwenze 0 Report post Posted February 10, 2009 (edited) Yup, lossy in the sense that it doesn't have ECC, but more importantly in the sense that it's actually possible for it to sound bad if you use crappy composite video cable as interconnect, for example. This brings up something interesting to be researched. Somehow I'll need to find info on the on-board SPDIF encoders and compare specs. Who knows, maybe all that's needed to make it sound good are just a few more extra parts. Edited February 10, 2009 by wwenze Share this post Link to post Share on other sites
peanutbutterjam 0 Report post Posted February 10, 2009 Yup, lossy in the sense that it doesn't have ECC, but more importantly in the sense that it's actually possible for it to sound bad if you use crappy composite video cable as interconnect, for example. Well, there's a guy in VRZ that noticed an improvement when he switched from USB -> SPDIF to the on-board SPDIF, maybe u can ask him. Hm offhand I can imagine that this might be due to the sampling rate his music is encoded in. USB only supports up to 16 bit due to transfer speed limitations. The on-board SPDIF would not suffer such limitations. Thus if his audio is orginally encoded in 24bit, it is imaginable why this is so. Maybe you could post the link to that VRZ issue? I think it is interesting, since I do have an on-board SPDIF out but it sucks compared to the USB because I can't use ASIO for it. Stock windoz kmixer is tey pwns. Share this post Link to post Share on other sites
wwenze 0 Report post Posted February 10, 2009 (edited) Here's the thread... http://forums.vr-zone.com/showthread.php?t...ht=spdif&page=2 USB is enough for CD audio, but the conversion of USB -> SPDIF isn't perfect, plus the SPDIF transmitter circuit may not be good quality, lots of small things add up into audible difference. On the other hand, USB is "cleaner", and USB is a better interface than SPDIF, but using USB -> SPDIF converter destroys that advantage and combines the problems of both. Is your on-board sound using AC'97 by any chance? Edited February 10, 2009 by wwenze Share this post Link to post Share on other sites
