Article: M2Tech hiFace Asynchronous USB To S/PDIF Converter Review

[barrows]

Thanks for bringing the thread back to the positive! This is an informative post, I was wondering about the overshoot and ringing (I do not know how to distinguish what might be ringing from reflections?). Perhaps John K. could add an RC network to his Hiface mods to damp the overshoot/ringing and square up the waveform?

[jkeny]

<i><b>I see nothing wrong asking John for his technical background. This is much more than a $12 piece of equipment. He mods this very product.</i></b><br />

<br />

I think you are again mixing up my modified Hiface (which I haven't referred to here, BTW) & the attenuators. I don't do any modifications to attenuators - I simply suggest their use. So asking for my credentials in order to evaluate my suggested use is a bit rich, don't you think?<br />

<br />

This thread is not about my modifications to the Hiface is it?<br />

<br />

I did ask about advertising rates, etc & this is the first time you have responded to this request

[jkeny]

Yes, there is an overshoot in the signal which is coming from the Hiface but the intention of the scope shots was to show the effective reduction in the reflections which are all the other squiggles (to use a technical term ). <br />

<br />

So let's not get distracted - the overshoot is something that can be handled separately. <br />

<br />

The attenuators can be seen to effectively reduce the reflections - can this be seen by everybody?<br />

<br />

Juergen, minicircuits have a UK branch which you will find on their distributors page!

[barrows]

yeah, I saw on the scope shots how the reflections were reduced with the attenuators I also recall seeing some of this at DIYA perhaps. <br />

In any case, I am still curious as to what SPDIF cable was employed in these tests and was it BNC?<br />

I have seen some better looking SPDIF waveforms before, and am wondering if adding an RC network (as suggested by Juergen) would square up the waveform and allow the receiver to operate better.

[JR_Audio]

Ok, only slightly off topic. I have found two German distributors of the RF attenuators, but the selection is large, so JK could you give me a part number, that you have experienced with, together with the HiFace, that should would well.<br />

<br />

Juergen

[jkeny]

You are at it again - deflecting from the point - the point about the shots is to show the attenuators effectiveness not the SPDIF waveform. These shots are, in some instances, deliberately mis-terminated to over-emphasise the reflections & hence to show the effectiveness of the attenuators.<br />

<br />

You haven't answered my challenge to you to try the attenuators?

[jkeny]

Can you post the link & I will PM you the dB units applicable?<br />

<br />

I presume it is the Germany subsidiary of minicircuits you are looking at? You want the fixed attenuators 75ohm precision at the bottom of this page http://www.minicircuits.com/products/attenuators_coax_fixed.html<br />

<br />

6dB, 10dB & 15dB would be the best selection to experiment with.

[barrows]

the subject, which is after all the Hiface (of this thread) and not the attenuators. Just suggesting that you might want to consider Juergen's suggestion as an addition to your Hiface mods.<br />

<br />

"These shots are, in some instances, deliberately mis-terminated to over-emphasise the reflections & hence to show the effectiveness of the attenuators."<br />

<br />

OK, so I would be more interested in seeing results from a set up that was closer to ideal, or to what might be common with a decent SPDIF cable, BNC terminated (yes, I consider the Stereovox/Stereolab cables with BNC "decent"). I would be happy to try one of the attenuators between my modded DL-III and bel canto as transport-I will go back and find the link and order one. Which value would you recommend? Do you know the circuit of the attenuator? I could just add this circuit in series with my DACs digital input.

[jkeny]

Good man - I like somebody who is open to experiment & not just arguing over the technical issues - as I said it's all clap-trap - the real world has a tendency to not follow theoretical exactitude!<br />

<br />

I would suggest a 6dB one on your set-up but you may get away with a 10dB.<br />

<br />

The schematic of the device is given on the datasheet. Specs & graphs of the performance are also given on the minicircuits site. These are precision manufactured devices effective out to 2GHz & I wondered why Gordon asked about them upsetting the impedance of the digital link - it really exposed his lack of knowledge about them (even though he has been using them since before I was born )

[jkeny]

Let's take the overshoot out of the picture & here's a scope with no attenuator & with attenuator overlaid on it. I'm sure you will see what are reflections & how effective the attenuators are:<br />

<br />

I don't need to show my credentials to post these!<br />

<br />

<a href="http://www.4shared.com/photo/uQR5dMxB/att_noatt.html" target=_blank><img src="http://dc192.4shared.com/img/376261915/98e96d79/0.05507015523457515/att_noatt.jpg" border="0"></a><br />

<br />

And here's the technical details of the measurement set-up according to Joseph K:<br />

<i>Here it is the difference before / after the insertion of an attenuator into a deliberately "wrongly" terminated 75ohm transmission line. <br />

<br />

<i>the setup is:<br />

Upper trace <br />

generator - 75ohm line - BNC tee (real 75ohm) - 75ohm termination. <br />

The BNC tee goes into the 1Mohm input of my scope.<br />

Lower trace<br />

generator - 75ohm line - 10dB 75ohm attenuator-BNC tee - 75ohm termination<br />

The BNC tee goes into the 1Mohm input of my scope<br />

<br />

<i>As you see, the only diffeence is the attenuator. The traces are normalized, so as to see the same percentage of the reflections.<br />

<br />

..........<br />

<i>The driver used is a 250MHz Hp pulse generator. The rise & fall times, ~700psec are limited by the scope. <br />

The Hiface is only slightly worse, 1.8nsec rise time.<br />

Last but maybe most important note: I show this setup & graphs again and again, because EXACTLY THIS IS the difference what your dac sees on it's input.</i>

[barrows]

6dB, 75 ohm, BNC, 2GHz attenuator.

[PeterSt]

<cite>On the other hand if John is a Gym Teacher who has picked up some info from the DIY forum I may be more skeptical</cite><br />

<br />

Chris, please allow me ...<br />

<br />

I have said it before (maybe over a year ago), but the best products -in my eyes !- are created in small backrooms or attics, and spring from <br />

a. Motivation on DIY forums from someone with an impossible idea;<br />

b. The huge knowledge of all contributors to such forums amongst which the, say, more known engineers around.<br />

<br />

Undoubtedly people like Gordon, Steve, but maybe even more the here less known Mr Pass and the by now a few times mentioned "Jocko" for his special "negative impact" do all the pre-work, but it really takes someone like John to pick up the real work and do something with it. This is not a negative, but a real positive because in the very end it improves the work of the original "master" like in this case Marco and his company. I don't see anything wrong with the executer of this being even the cloth washer of the gym students. No, it is merely about someone picking up on what everybody thinks it should be picked up, but most don't have the guts to do it.<br />

<br />

Only in very seldom cases this is about self financial interest, because in the DIY areas nobody is about that, at all. It always goes like "can you sell me the PCB please", which in 90% of (good) cases ends up just like that. Maybe people should read back on how John started this, which was nothing more or less than "ideas" on how to improve on the HiFace, next people asking about whether he would sell ready products. It just happens like that. And sometimes one doesn't need to be an engineer with any credentials other than the guts to try *and* to have some responsibility to produce it more or less officially.<br />

<br />

Maybe a bit unrelated to your eyes, but it would be good to investigate the guys at Twisted Pear Audio who were the first to come up with a complete working solution for the ESS Sabre DAC chip. Not McIntosh which may be more known, and certainly not any more known engineer with random name coming up with a 32 bit DAC because again T.P.A. was earlier.<br />

<br />

So, I was bashed before of saying something similar (by the good old Ashley-Tim combo), but development in audio really doesn't happen at the well known companies ... it happens (nowadays !) in the backrooms of the real audio enthusiasts, and next is copied by the large companies. The examples are numerous, and please remember, it takes the guts of nuts to make something out of it themselves.<br />

<br />

The initiatives of these "DIY" guys shouldn't be demotivated at all. It is them who stick their neck out. It is them how we proceed.<br />

<br />

Peter<br />

<br />

PS: And again I wish to refer to the async USB DAC I had running in my room 2 years before anyone even heard of it; Just an idea of an individual nut who was ahead of anyone else and who chose not to make his name known to this world (not me, although I participated in my own backroom :~).

[jkeny]

for your support. I'm an ideas guy - I judge an idea on it's merits irrespective of the credentials of the messenger. I don't hold much store by credentials even though I have a B. SC. degree in Biochemistry & Maths & have spent my working life in computers as owner of a computer company. I'm not giving a CV here as I don't think it has anything to do with what I say. <br />

<br />

If Chris (or others here) are not able to evaluate a concept on it's merits alone then I'm sorry for their lack of objectivity & their lack of analytic capabilities - it's just more evidence of blindjim's assertion of elitism on this forum.

[ar-t]

"Maybe a bit unrelated to your eyes, but it would be good to investigate the guys at Twisted Pear Audio who were the first to come up with a complete working solution for the ESS Sabre DAC chip."<br />

<br />

Just because it is your impression that they were the first, does not make it true.<br />

<br />

No, it wasn't me. Haven't had the time to even look at the data sheet. But I know folks who had working solutions, before TPA even had the first one in their hands.<br />

<br />

(Actually, who it was is not important, and as such, I will not name someone who is unscathed, in this thread.)

[barrows]

Why does horn tooting, and who did what first and ego, etc. matter? Why are people getting all twisted up in feeling like something disingenuous is going on? I've met Chris C. on occasion, and I am certain that he has no "hidden agenda" to promote a certain this or that-he is just another enthusiast who wants to learn and spread knowledge and enthusiasm for computer audio. We do not need to all agree on everything to agree to get along, and trust that people posting here are doing so honestly, and transparently.<br />

If anything, I do understand sometimes when manufacturers might get a little peeved when they have put so much time and effort in producing something (like Gordon Rankins' Streamlength USB Code), from a labor of love (as I know they are not getting rich in this business!) and then some pontificating internet expert comes along and denigrates their work displaying a complete lack of understanding of what their work entails.<br />

Development of new approaches to audio reproduction comes from all areas: established manufacturers (which are often far less "established" than many seem to understand), DIY hobbyists, legendary amplifier designers (Pass)-great! Bring it on, and lets respect everyone, while we agree that we may disagree.

[wushuliu]

John's in a tough position. He's not quite one-off DIY guy, and not really a manufacturer, so the line between helpful suggestions and promotional self-interest (as viewed by others) gets blurred. This has happened on a couple forums already. I believe it's less about the subject of debate and more about personality. Depending on your personality, some forums you can walk right in and it's open arms and let's hear what you have to say. Some you can tell you kind of have to keep a low profile for a while until people feel they know and trust what you have to say. Sometimes there's no love regardless of what you do. It doesn't help that wherever there's a Hiface discussion, John pops up! >. So my 2 cents, John, is don't approach every forum the same way, even though your intentions are good, sometimes it's best to suss out the vibe and take a low-key approach. If you sense a little heat, justified or no, take a time out, hang out in another thread (you know, something NOT Hi-face related!). Shoot the breeze. You get my drift. I've read lots of good feedback on your stuff and your totally available to the public diy mods, so I hate to see you get heat so often.<br />

<br />

That's just my totally unsolicited opinion based on following different Hi-face threads across the net.<br />

<br />

w

[The Computer Audiophile]

Hi wushuliu - Thanks for your comments. I think you've hit at least one nail on the head. Like it or not, intentional or not, the more John talkes about deficiencies of the hiFace and ways to improve the unit the more people learn about him and his products for sale. John may be the greatest most honest guy on Earth but since he has a vested interest in a product based on the hiFace it's going to be a tough road on hiFace-based discussions. <br />

[ar-t]

The only person in a tough situation is the person who runs this site. I submit this thread as evidence.

[sq225917]

Barrows-<br />

<br />

Manufacturers do it for the money. There's no benevolent Saints here.<br />

<br />

Gordon took the TI USB chip and wrote a new driver for it, modding someone else's component to improve it. Jkenny took the Hiface and gave it a better power supply, modding someone else's component to improve it.<br />

<br />

<br />

Neither of them need be sainted or chastised, and certainly not denigrated by some pontificating internet expert.<br />

[jkeny]

I'm outta here - it's the only option as I won't pussy-foot around & I won't shut-up. All your advice is good & I should take some time-out. I can understand how my enthusiasm at the potential of the Hiface could be construed as self-serving but that's just something I can't avoid - maybe I'll stop putting out info & start behaving like a real manufacturer giving no information away except what is in my own interest. <br />

<br />

Maybe Juergens & barrows will report their findings in time & I'll return? Sayonara!<br />

<br />

[barrows]

In my experience this statement is false:<br />

<br />

"Manufacturers do it for the money. There's no benevolent Saints here."<br />

<br />

OK, while I would not say (and did not) that audio designers/manufacturers are Saints, I will ask you what kind of experience you have working in the high end audio industry which allows you to make such a statement, which high end audio manufacturers do you know that are in it the for the money?<br />

In my experience working in this business, the money is not the primary reward, as the money is not that good. Sure, audio designers/manufacturers can make a living (sometimes) but they are not getting rich doing this. Most talented audio designers/engineers could make much better livings working in telecomm, computers, solar, or defense industries.<br />

As consumers of high end audio gear we are lucky to have the talent that we do design products on our behalf, for what is virtually a cottage industry.<br />

I think the point of view that you express here is a root of some of the problems we see in this thread in general-there seems to be some belief that audio companies are "ripping off" consumers/audiophiles, and "laughing all the way to the bank". This is just not true, all the designers/manufacturers of high end gear that I have ever met are audio enthusiasts, and they are in this industry despite the fact that the monetary reward is not all that great, not because of it.

[ar-t]

We <b>used</b> to make a better living, doing telecom and defense. Somehow, "they" got the idea that it would be a good idea to get younger engineers, who understood modern technology.<br />

<br />

If, by modern technology, you mean the practice of working very long hours, for less money, than it would take to get some old guy. That actually knows what they are doing. (Read: analog design.)<br />

<br />

IOW, just like everything else, in the world.<br />

<br />

Yes, we are all greedy capitalists, who work 7 days a week, without time off, no vacation, no health insurance, and no pension/retirement.<br />

<br />

Just like the rest of the world!

[rom661]

Hey Chris<br />

<br />

As I was reading your review I realized the concept you were trying to get across (presumptious, I know). I have only briefly heard the piece and, depending on expectations, context, and/or it being a good way to start when you have an existing DAC, I thought it was fine.<br />

<br />

Let me explain, please, the incredibly important, deep seated meaning of the word fine. This concept originates from the marital relationship and it's understanding is critical to the well being of said relationship.<br />

<br />

If your marital unit (my brother's term; wonder why he's divorced) comes into the room wearing an outfit that she has chosen for the evening's activity, the most dangerous question in the world is "How does it, how do I, etc., etc. look" The worst possible answer is "fine". Trust me. Fine, to her, means: It doesn't suck; it's better than a poke in the eye with a stick; or, worst of all, huh?<br />

<br />

A well done review, Chris and you took great pains to explain your position. All due respect, you could have summed it up, at least to us married guys, by saying it was "fine". Notice I said a well done review, not a fine one.<br />

<br />

Best<br />

<br />

Rick

[The Computer Audiophile]

Hi Rick - Nothing better than a fellow music lover with a great sense of humor. You're just fine in my book :~)

[sq225917]

I don't need to work in the highend industry to know brands are in it for the money, none of them are set up as charitable foundations, ergo they do it to get paid.<br />

<br />

You tell me which manufacturers are not in it to get paid and give all their money away and I'll accept that I'm wrong. Oh, that's right, none of them.<br />

<br />

Maybe you should start a little lower down, rather than trying to explain why they should and could be sainted for their ongoing charitable works of design, maybe you could explain why nearly every manufacturer who repackages 'pro-gear' for consumers charges significantly more for the 'consumer' gear. Is it because they aren't in it for the money?<br />

<br />

As you are 'in the industry' maybe you can explain how your company does it differently to every other brand in the world, I'm sure their 'charitable leanings' will garner them no end of praise and support once you lay it all out for us.