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Old 30th March 2009, 08:22 AM   #41
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Hi 454Casull,

Quote:
Significant even through metal shielding?
Yes, it even affects sound quality through RCA and speaker interlinks, as the whole listening room and all equipment installed in it are affected, not only the digital audio source. This would require screening the whole audio set, interlinks included, this isn't very practical.
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Old 30th March 2009, 08:27 AM   #42
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Hi phofman,

Quote:
By AC ground loop do you mean the coupling via ethernet isolation transformers?
Yes I an referring to ac ground loops. The best isolation transformers still have a certain capacitance between both primary and secondary windings (up to a few pF), this provides a low impedance for RF / HF signals.

That's why I decided to use Toslink, as this optical interface doesn't have this problem.
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Old 30th March 2009, 08:44 AM   #43
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Hi soundcheck,

Quote:
Perhaps you should have tried a "quality" Toslink output as it is used on pro-soundcards

My current preference:
As you know I use an optical USB Cable from Opticis (USB 1.1 only) for galvanical isolation.
The receiver is "custom-made" battery powered. This made a great improvement
with your USB reclocker/receiver I used to use.
Toslink (SPDIF) always contains jitter, jitter amplitude isn't the biggest problem, it's jitter frequency spectrum. Using Toslink you have at least 2 jitter sources, source jitter spectrum and PLL jitter spectrum. When (synchronous) reclocking is used, the master clock jitter spectrum is added to the mix. This is basically a no-win situation that always includes making compromises.

Sure improvements can be made by using better Toslink cables (real glass fibre interlinks), and faster optical transmitters / receivers. But performance will always be less than optimal.


Here is a photograph of the recovered master clock from a dual SPDIF receiver (each receiver has different loop filter), both run in slave-clock mode. They are followed by a micro controller-based FFL VCXO. The scope is put on highest time resolution, and the oscillogram shows one of the pulses that follows the trigger pulse. The signal is measured directly at the DAC chip bit clock input. The electron-beam trace is blurred (photo camera). The actual trace thickness is less than a tenth of a millimeter.

This is the (worst case) starting point, this master clock still has way too high jitter, it's barely visible on the oscilloscope, set at maximum time resolution, yet it already has big audible effect on sound quality. I already use a NOS DAC that's least sensitive to timing jitter.

In order to maintain low (bit) clock jitter levels at the DAC chip internal circuits, I attenuate the master clock amplitude to approx. 400mV, and create a low load impedance (approx. 33 Ohm), this is possible with both TDA1543 / TDA1541A as these have TTL-compatible current steering inputs.

Still this doesn't solve the jitter spectrum "issue". Using a single master clock for both source and DAC, that are placed close together, and are connected through I2S is a good starting point.
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Old 1st April 2009, 05:36 PM   #44
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John, whilst I respect your designs I think this project is a bit outdated before it even is in production.

No Flac support "because SD cards can be rewritten many times" will end up in useless time consuming erasing and rewriting the SD cards. A repetative and frustrating experience ! The more data fits on the card the less erasing and copying will be necessary. In this case SD cards will be a kind of replacement for cd's but with better sound quality...

As a sidenote: I just returned to my old friend Hifidelio and despite the fact that it is not a high end player the convenience is terrific. Operation is a breeze and it plays Wav, FLAC and MP3. With a 160 gb disk it is a one time copying action and you're set.

So please rethink this project, it must be possible with a "larger than SD" notebook harddisk or even a SSD.
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Old 1st April 2009, 05:48 PM   #45
agent.5 is offline agent.5  United States
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Quote:
Originally posted by jean-paul
John, whilst I respect your designs I think this project is a bit outdated before it even is in production.Operation is a breeze and it plays Wav, FLAC and MP3. With a 160 gb disk it is a one time copying action and you're set.

So please rethink this project, it must be possible with a "larger than SD" notebook harddisk or even a SSD.
Hard disks and SSDs have controllers in them, which will add latency and jitter. I think the point of this project is to eliminate jitter and all the other craps that modern electronic introduces. I think this project is analogous to playing vinyl. Absolutely pain in the butt, but it sounds great.

On the other hand, and this mostly refers to the DAC connected to the SD player, I like a switch for I2S between the best quality SD mode, and a lower quality auxiliary input from slimserver duet.
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Old 1st April 2009, 06:22 PM   #46
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Those who want to play their music through a SSD or whatever else with 1TB capacity can buy a Squeezebox Duet or a TEAC WAP. The WAP2200 starts at 120 Euros.

I myself don't mind using SD that contains 99 CDs. I don't think I need more. I don't even mind using 2GB SD as Koon's Ultimate Player is restricted to. Large storage capacity is not why I want this player. The only reason for going to this trouble is that it plays original WAV codes without error, and without all the reclocking troubles associated with SPDIF. Simply put, I want the perfect digital source; all solid state, no moving parts, and no lossy codes.

If you want convenience, buy an iPod.




Patrick
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Old 1st April 2009, 06:33 PM   #47
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99 cd's in wav would be around 70 gb. That is a pretty expensive SD card. An SSD will be cheaper and it is also solid state....

My point is that convenience and good sound quality can go together which would make this a truly exceptional product that stands out in the crowd. Why go for something that sounds very good but is a pain to use and that has limited storage capacity ? And which will take months of development for a very small market so it has a big chance to be a time consuming loss creating project. If a project is limited from the start it will be dead when it is finally born. Especially storage capacity is an important factor for user satisfaction.

Good sound quality and convenience also do not exclude eachother. I will stick with my Hifidelio I guess. An Ipod is very convenient and it would be very nice if Apple would make one in 19" format for home use with a very good DAC ( inside ! ). Or if Hermstedt would only have made a HF with a better DAC...

BTW Patrick, FLAC is not a lossy format. It is WAV but compressed without loss.
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Old 1st April 2009, 07:36 PM   #48
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Quote:
Originally posted by jean-paul

No Flac support "because SD cards can be rewritten many times" will end up in useless time consuming erasing and rewriting the SD cards. A repetative and frustrating experience ! The more data fits on the card the less erasing and copying will be necessary. In this case SD cards will be a kind of replacement for cd's but with better sound quality...

As a sidenote: I just returned to my old friend Hifidelio and despite the fact that it is not a high end player the convenience is terrific. Operation is a breeze and it plays Wav, FLAC and MP3. With a 160 gb disk it is a one time copying action and you're set.

So please rethink this project, it must be possible with a "larger than SD" notebook harddisk or even a SSD.
Jean-Paul
Since the bginnings of audio reproduction we have been using some kind of mechanical support: rollers, 78's, 45's, LP, magnetic tapes, CD, DVDs, hard disk, etc.
I always dreamed of getting rid of all this stuff with their associated accessories: needles, phono cartriges, tape heads, laser pickups, name it.
This project may not be perfect, but it shows the way, where we should be heading, not returning in the old footsteps.
I welcome you, John or any other interested EE to push reasearch in the direction of new concepts for audio reproduction where any mechanical support is left out for ever.
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Old 1st April 2009, 08:06 PM   #49
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Hi Jean-Charles. An SSD is a Solid State Disk. A replacement for a harddisk with no moving parts and high reliability. Like a big memory stick with a PATA/SATA connector instead of USB.

If a SSD would be used the less fortunate can use its antique equivalent: a harddisk. Both share the same connector. So two birds with one stone. An expensive version with an SSD with no moving parts and let's say 64 gb. A cheaper version which has the same hardware except for the fact that it has a 2,5 " harddisk which has the added bonus that they are relatively cheap and much larger in size ( up to 500 gb at this moment ). Two versions with relatively small differences but somewhat larger differences in price will attract two different groups of audio afficionados.

Since the hardware and software would be equal more energy can be put in user friendliness and connectivity like LAN ( which should possible to switch off ) and a fancy GUI preferably with a OLED display. Most mediaplayers that can be bought today need a computerscreen ( how sad ) to see the contents of the harddisk.They also sound pretty mediocre but that is another story. A good display for standalone operation is necessary.

Upgrading from harddisk to SSD would be possible. Downgrading from SSD to harddisk too for those that like to run in circles ( or if they need more space for a smaller price )
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Old 1st April 2009, 08:16 PM   #50
phofman is online now phofman  Czech Republic
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I am afraid employing HD/SSD instead of SD cards would increase the project complexity by several orders. In fact, it would be a full-blown computer. I guess ecdesigns is heading for a synchronous player - reading from the SD card would be clocked by master DAC clock.
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