DIYHiFi.org

http://www.audioasylum.com/forums/pcaud ... 73401.html

Some of theses guys regularly make pronouncements on how to do PC Audio.

I don't even pay attention to that kind of talk. When you ask the what they are listening you will find mp3's, iTunes and DolbyDigital (or maybe DTS) from movies. One guy actually asked me "what's the big deal about this 'flac' files that I keep seeing talking about?"...

Of course the USB jitter is not their biggest problem.

Actually, stuff posted there by Tony Lauck or John Swenson is correct.

If anything, it's the best thread I've ever read on the asylum

Hi Frank,

I gave up reading the computer asylum. Only few people are readable.

Swenson summed it up in theory, but it still doesn't explain why my Hiface sounds poor compared to my good old PCI Emu0404 transport. Of course I am going to cut off the SMPS feeding the hiface clocks but I don't understand, at some level I fear that USB may just plan be inferior to PCI.

Glen,

Strange, I find Hiface working / sounding definitely better then the SPDIF output of my EMU1616m.
But. ONLY with a slight tweak. While I have ~ never seen a better looking spdif signal than the hiface output, in it's standard form it's simply overloading my dac's receiver input. It put's out 5Vpp, 10 times the standard. AND it does not have a nice output impedance.
I think this is the mostly overlooked factor that might hinder it in properly set up systems. The high level makes it even more essential the proper line termination. Which is almost never existing..

But. This same high level also permits the "Jocko" trick to be applied, that is padding the line. It permits to fit in a 75ohm 10dB attenuator, with still a lot of headroom left. And the 75ohm padding makes simply wonders, at least for me.. It restores the the proper termination at least at one side in the line, so the energy is absorbed much quicker.
I use it at the receiver end. In theory it would need a BNC input on the dac, ( I have it like that) but it works also if you fit a bnc/RCA converter AFTER it.
Like: SPDIF line with 75ohm BNC conn.-> 10dB att. -> BNC to RCA converter -> DAC with RCA socket.

This is something what you simply cannot do with any other dongles, sound cards, players. And a big plus in listening, I would have sold the Hiface without.. And I'm still using it in standard form, no mods.
Last point: my dac has a proper linear input stage before the receiver, I have spent some time in finding a good working solution starting from that of Jocko. In many commercial dacs the high level of the Hiface helps the receiver more than the damage done by the extra level of reflections.

Ciao, George

Interesting stuff George. How exactly is this 10bB attenuation done ..... a 2:1 divider with 75 ohms total impedance? Do you have a link?

by the way, I much prefer the standard Hiface to the s/pdif out of my PCI EMU-0404. The Hiface is sensitive to the quality of ppower coming into it via the USB line. My first try with the Hiface was with a motherboard USB output. Simply changing to a Belkin PCI-USB card with an Oscon across the 5V out gave a significant improvement in sound.

Go for the full body press & power the clocks from an external clean 3.3v supply to find out how good this thing sounds.

_________________
There is a crack in everything, that's how the light gets in!

George,
Some questions:
- Your 75ohm attenuator isn't one of those BNC adaptor types is it? How can this work to match impedance as I thought the output impedance of the SPDIF transformer needed to be taken into account to calculate the correct R so as to get impedance close to 75ohm? Could this not make matters worse?
- what is the output impedance value of the Hiface anyway?
- does the attenuation alone then account for the benefits that you are seeing/hearing i.e does it increase the return loss & reduce the reflected wave energy? And this explains how a BNC to RCA connector after the attenuator is not as much a problem as usual - because the reflected wave is attenuated.

_________________
There is a crack in everything, that's how the light gets in!

Google for H-pad, Pi-Pad & T-pad attenuators

High folks,

To tell the truth, I'm a bit lazy to make new documentation/ photos. Anyway, all of this we had already talked here, many years ago:
This is the attenuator in question: (it's the 50ohm version in the picture, I had at hand that at the time of the photo)
Some posts later I have given the exact part numbers of Suhner.

viewtopic.php?p=7681#p7681

This is an illustration, how to apply to the dac:
viewtopic.php?p=8572#p8572

And this is the result of inserting it:

viewtopic.php?p=8602#p8602

Here it is the situation without it: (two posts earlier in the above thread)

viewtopic.php?p=8598#p8598

Ok, to make it clear: I have only brought up it now, because the Hiface is the special case, where it's really relevant.
Because of the high output level. Padding in the case of standard levels, 500mVpp, only makes it worse, because it makes life even more difficult for the already very critical input receiver sections.

What regards the Hiface output impedance: I have only done an indirect estimation, did not quantify it yet. How did I do it, this could even be interesting to talk about, and was already thinking to open some discussion.
But the point for us now is: the att. trick helps to "balance " the situation exactly in these occasions, when there are problems with the terminations in the transmission line, no matter what the origin is.

for Jkeny:



Yes, this is exactly the case. I have made the test, and have the graphs showing this happening with the Hiface.
The att. increases the return loss, and cleans up the reflections in the line. Exactly as it had been shown in the tests that I had quoted in my post here above.
To answer the other aspect: the impedance imbalance introduced by a transformer is NOT eliminated by this trick, but attenuated to a level that makes it much less relevant.

Ciao, George

I'm aware of that and also of the fact that it is somewhat dependant on what SPDIF receiver is being used in the DAC i.e the CS84XX really works better at higher voltages than the 0.5Vpp standard SPDIF so a certain level of overdriving is probably beneficial in these cases.

It would be interesting to talk about the Hiface output stage. For instance it uses a 2:1 Scientific Conversions SPDIF trafo in the configuration given in the DIT4192 app note (Jocko is spitting feathers at this I'm sure) - would substituting a 1:1 Neweva with the right termination help not only for impedance matching BUT also using 1:1 would give a higher V out & so a higher dB attenuation trick could be used?

Damn good really.

Yes, it's a neat trick & re my point above - the higher the attenuation that can be used, the higher the return loss, the better the clean up of the reflections.

I saw somewhere that you also mentioned using a cascade or series of these attenuators as being more effective - but isn't the VSWR of the devices multiplied together & how does this counteract the attenuation effect i.e more energy is reflected Vs more energy is attenuated?

_________________
There is a crack in everything, that's how the light gets in!

Haven't seen any royalty checks from you. I suggest fishing for design help from some other place.

Guys like you are why I hate DIYers. Always looking for the cheap way to learn something. Only to turn it into something they are selling.

Jocko

_________________
"Because, I hate you guys. I hate you guys so very, very much.

Yours,
General Cartman Lee"

Why should I be paying you a royalty cheque - what have you done for me? Show me where I have used this place for design help? I have started a number of threads some of which may have gotten a bit heated & I'm sorry if you are still bearing a grudge from this or other forums but none of them looked for design information.

I started a thread to discuss the Musiland but that turned into crap until Simmconn posted with some sanity. I started a thread about SPDIF cable length & well .......... None of this was fishing for design info & certainly none was given.

Yes I have modified Hiface & Musiland transports & I have done all the research work & posted what I have done in text & pictures in the public domain. All of this is available to anybody to DIY for themselves. Enough people then asked me to do the work for them so I charge for this. So what's your problem? Is the natural order being upset by all this?

I will probably do what I had already said in my post with the output stage anyway so I was just thinking out loud.

_________________
There is a crack in everything, that's how the light gets in!