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

[Matias]

John, where can I buy this cheap attenuator and test it myself? eBay?<br />

<br />

Edit: already found it here.<br />

http://www.minicircuits.com/products/attenuators_coax_fixed.html

[jkeny]

Correct - you want the precision 75 ohm ones at the bottom of that page - get a few values to experiment with - I would suggest 6, 10 & 15dB ones. They only come in BNC style so you may need an RCA to BNC adaptor if you have an RCA cable. You can use these adaptors, which would normally cause more reflections on the line, because the attenuators remove these reflections effectively. Also you can use them at whatever end of the cable you want - again experimentation is recommended!<br />

<br />

The conclusion the group at that meeting came to was that the attenuators were a fantastic bang for the buck & somebody said that the effect was better & more clear-cut than a high end cable. What we were using was a cheap SPDIF cable.<br />

<br />

It would be interesting to do a high end SPDIF cable Vs cheap SPDIF cable with attenuators review!<br />

<br />

Edit: The glaring differences between the output impedance of the Hiface reported on the Audiophileo site (is that 0.3 ohms?) & the 73 ohms reported here is also something that is of interest - can anybody throw some light on this? I'm presuming it is a typo on the Audiophileo site?

[barrows]

Thanks for your input here, I appreciate your efforts to get the most out of the hiFace. For those who might object to John's posting, re hiFace Mods, I suggest to allow John to continue to post his observations and findings: John continues to keep his mods "open" that is he details how one can mod the hiFace themselves, and shares his findings for those who do not want to pay for a modded unit-this open approach is quite generous in my mind.<br />

Re the hiFace, it seems that the manufacturer should revisit the design of this product; having a product where the SPDIF output is so far out of spec that it causes some DACs to clip really seems like poor design implementation, regardless of cost (there is no reason a within spec SPDIF should cost anymore to produce). And to consider hiFace with mods vs. competing products (like the Halide Designs Bridge, or Audiophileo) one must consider that the price advantage of the hiFace dissappears when considering modded units (hiFace mod+SPDIF cable, vs. Halide Bridge no cable necessary, vs. Audiophileo 2 includes cables). <br />

John, have you managed to extract I2S successfully from your modded hiFace units?

[jkeny]

Thanks barrows, I'm glad you have taken my post in the spirit it was intended. You are correct that the mods (if not DIYing them) + SPDIF cable (if not using a cheap one) is perhaps equivalent price-wise to a Halide or Audiophileo. The question then becomes how does it compare to these other products. As I said a review is coming out shortly <br />

<br />

Of course, with the attenuators a cheap cable can be used, I believe & this claws back some savings

[Purite Audio]

Has anyone else apart from myself and Chris C compared the Halide Bridge and the M2Tech 'Hiface'?<br />

Keith.

[barrows]

I have seen a few comparisons between the hiFace and Halide bridge on the headphone sites (head-fi, etc.). A quick Google search will find the relevant threads. As I recall most (if not all) comparisons agreed quite strongly with Chris C's opinion.

[jerryt]

Hello there,<br />

<br />

does anyone have experience with running the Hiface from a powered usb-hub? Theories about this? As I see it, power should not be a problem anymore and the device remains un-modded. I saw this site http://www.aqvox.de/usb-power_en.html and it appears interesting.<br />

<br />

I'm running a Squeezebox Duet into a Lyngdorf TDAI 2200 into Dynaudio Focus 140 speakers. The sound from my cd-player - Cambridge Audio Azur 640C (II) - seems fresher than the Duet and I'm hoping that a Hiface solution with my netbook (Win7) could sound better.<br />

<br />

Anyone?<br />

<br />

Juergen

[jkeny]

Does that "anyone" include me or will my post be considered self promotion?<br />

<br />

You will only get some improvement from running it off an external 5V supply (which is what the USB powered hub should provide) depending on how good this 5V supply is & how bad your PC USB 5V is.<br />

<br />

However, you still have a single internal 3.3V regulator supplying power to the two clocks & to the Xilinx chip - this is not the best PS configuration for supplying power to very sensitive clocks. I have written about this on other forums where I describe the details of these PS mods.<br />

<br />

Believe it or not, you will probably get a better sonic benefit from the attenuators.

[Purite Audio]

I am only aware of three people in the UK who I know have made the comparison, ( I am sure there must be more )I would be interested to hear from any others?<br />

Keith.

[jerryt]

also includes you, John. I don't have a problem with that.

[barrows]

I believe I read somewhere that the onboard regulator(s) on the hiFace were also DC/DC converters (these are switching regulators), if this is true they would also be rather noisy on their own in comparison to a low noise linear regulator like the LT 1361. If I am correct, the DC/DC converters would still be rather noisy, regardless of whether a powered USB hub was used.

[jkeny]

You read it in Chris's review above, also <br />

<br />

You are correct that the self-noise generated by these regulators is one of the major issues especially where the clock supplies are concerned. There are other considerations also but these will be revealed when the review is published - measurements & scope shots were taken for this review & they are interesting!

[barrows]

I hope that you will be able to point us to this review upon its publication.<br />

Personally, I am just about finished with my Buffalo DAC project, and am going to be looking for a computer interface to pair with it. I am hoping that Twisted Pear's upcoming USB-I2S interface board will be up to snuff...<br />

John: my understanding is that your mods power the clock circuit with an unregulated LiFePO battery, with nominal voltage of 3.3 volts. I know the LiFePOs are more voltage stable than many batteries, but their output voltage still varies quite a bit over time with respect to discharge state-does this varying voltage supply to the clock create any problems, or are noise and output impedance really the only relevant factors?

[calameda]

Since Chris took note of the Hiface's excessive output and is intent on "pulling every ounce of sound quality out of the hiFace" I am sure he will post a follow-up with attenuators in line. I think we'd all be very interested in those observations.

[JR_Audio]

Just a very short explanation (otherwise you have to look at the SPDIF Bi-Phase Specification and some Julian Dunn work).<br />

<br />

For example for 44.1 kHz, die Bi-Phase signal just change between 1.411 MHz and 2.822 MHz, so not a huge difference, to introduce additional jitter.<br />

<br />

But every FS / 192, there is the Frame Sync signal which has a violation of the Bi-Phase status in order to be recognized as the start of the Frame.<br />

<br />

So when you do a FFT of the complete SPDIF Signal, you will see 1.411 MHz and 2.822 MHz and multiple of that, but you will see also 229 Hz.<br />

<br />

So this FS / 192 is the lowest signal that is in the SPDIF Signal, so this signal has the largest variation to the 64 FS of the logic 1 of the SPDIF signal.<br />

<br />

Exact for this reason, Julian Dunn has taken this Frame Sync frequency with 1 LSB in his J-Test signal, to force the maximum sensitivity to jitter.<br />

<br />

Juergen<br />

<br />

PS: I have seen, that there is also another Juergen posting in this threat, but we do have different avatars ;-)

[jkeny]

will be well publicised, I'm sure <br />

<br />

The initial full charge of 3.7V quickly settles to a fairly steady 3.3/3.2V output. At the low current draw of the Hiface, this remains a very stable output. However, I believe that low noise is the most important aspect of this supply, as far as the clocks are concerned, anyway.<br />

<br />

Yes, I would hope Chris does try these attenuators. I posted about these on CA back in June but it was pretty much ignored http://www.computeraudiophile.com/content/Just-received-M2Tech-Hiface-USB-interface<br />

<br />

Thanks Juergan2 - a lot of good technical detail but can I ask, does this Frame sync jitter actually effect the sound or is it just a worse case jitter number? i.e. does jitter really only matter when it effects the sound that is when it occurs at the DAC's decision stage (transition point)?<br />

<br />

BTW, I emailed Phillip from audiophileo to check their output impedance for the Hiface & he has pulled this 0.3ohm figure as he used a wrong method to measure it.

[labjr]

While I think Jkeny may have done a good service to the audiophiles by finding flaws in a product, I'm not counting on reading reviews of his modded Hiface. A product should be reviewed on it's own merits or shortcomings. I want to buy a whole product which is ready to rock out of the box and has all the major bugs worked out.<br />

<br />

[jkeny]

Quote from the review "Internally the hiFace uses three DCDC converters to power the Cypress USB controller, the dual oscillators, and the SPDIF converter."<br />

<br />

My findings are different - the Hiface uses only two DCDC step down converters: <br />

<br />

a 3.3V to supply the USB receiver chip, Xilinx FPGA chip & clocks<br />

a 1.8V to also supply the Xilinx FPGA chip.<br />

<br />

The 5V supply to the digital audio transmitter chip DIT4192 comes directly from the USB 5V supply.

[jkeny]

I understand your viewpoint & I presume you have similar views & statements about the Bolder Cable Squeezebox Duet Modification Review that appeared here in March 2008? <br />

http://www.computeraudiophile.com/bolder-cable-company-squeezebox-duet-review

[MarkM]

<i> "I am only aware of three people in the UK who I know have made the comparison, ( I am sure there must be more )I would be interested to hear from any others?<br />

Keith" </i><br />

<br />

Hi Keith. I purchased a Hiface from you a few months ago. In an attempt to upgrade this (based on reviews on this website) I have bought a Halide Bridge which is currently in transit. I will post my thoughts when it arrives.

[JR_Audio]

Jitter does care during the whole chain of digital playback (and recording), so during envelopment, one has (and I do) to look at every stage, but finally they sum up at the output, so that's the reason why I checked mainly the “summary” when looking at a device.<br />

<br />

The jitter due to the frame sync signal is always there in the AES/EBU and SPDIF signal, no matter if you do have digital silence or full scale signal. Using the J-Test signal (invented from Julian Dunn, who has done a incredible amount of work on jitter), you can compare the results from for example John Atkinson (Stereophile) or from Paul Miller (in the UK) or the results, given in this review.<br />

<br />

Just my opinion on testing modded versions:<br />

<br />

The HiFace has a far too high digital output voltage, why should Chris mod this with a 75 Ohm voltage divider, because this is a fault from M2Tech. Sure it would also be good, if a DAC does have a good handling capability of this high voltage, and I do know some DACs, that can handle very well over 10 Volt on the SPDIF input, but first, M2Tech is responsible to be not compatible with the level.<br />

<br />

The same is with the non galvanic isolation. Why should Chris test this device with additional isolators? It is a fault of the HiFace that the output is not isolated. Sure, I also know a lot of DACs, that have isolated digital inputs, but in the SPDIF spec, only the output must isolated, the input must not, but can.<br />

<br />

I am pretty sure, that the jitter of the HiFace is small enough for the “average” HiFi listener and that only the two above mentioned points have a main influence, whether a regular listener is satisfied with this device or not.<br />

<br />

Juergen<br />

[michael123]

I did not see any 'major bugs', any bugs actually.<br />

Albeit testing BNC, which has better galvanic isolation than plain RCA model, the sound I got was far more exceeding cheap sound card you can buy for 180$. More like a CD in 2000-4000$ range..<br />

<br />

[ I was using Foobar with Kernel Streaming module for all my auditions ]<br />

<br />

Also, trying to picture M2Tech as a newcomer is misleading.<br />

Marco was a founder and owner of North Star, and having met him in Munich High End Show in May, surely he is not a newbie.<br />

<br />

[blueixus]

Mr JKenny<br />

<br />

AS a matter of interest is the Mini Circuits Attenuator transformer based or resistor based?<br />

<br />

My interest is whether I could 'DIY' an attenuator inside my Dac rather than have another set of connections hanging about on my rig?<br />

<br />

Any thoughts or is this idea off the mark <br />

<br />

Regards

[jkeny]

I'm only passing on here what I have discovered & not defending the design of the Hiface or it's flaws. I was simply responding to Chris's quote of "The only reason for such an extended period of time was so I could try every way I knew to squeeze the last ounce of sound quality out of the unit."<br />

<br />

One point that you overlook in my suggestion to use RF attenuators is that they pretty much kill dead any reflections on the digital link between transport & DAC. This not only includes reflections generated on the SPDIF cable but also at the transport output stage & the DAC input stage. As you are a technical guy you will know the implications of reflections & that they cause jitter at the DAC. Removing this is beneficial to the sound. The attenuators do this effectively.<br />

<br />

It just so happens that the high SPDIF output flaw of the Hiface allows a high level of attenuator to be used & therefore a better removal of reflections! So by exploiting this flaw it actually proves to be an advantage!<br />

<br />

I agree with you about the galvanic isolation of the digital output but there are also lots of SPDIF output stages whose SPDIF transformers are tied to ground on the output side. So this flaw is not unique to the Hiface by any means & it hasn't caused a problem that I've seen reported anywhere. Who said anything about Chris testing with additional isolators on the output?<br />

<br />

Edit: BTW, the crystal CS84XX line of SPDIF receivers work better with a higher than spec SPDIF signal so this isn't a universally agreed spec that all manufacturers abide by!

[jkeny]

They are resistor based & you could DIY it - in fact attenuators (or T-pads, H-pads as they are also called) are sometimes found in the output stages of digital audio devices. I'm not sure if you will get the same result as a precision made device but DIY is fun so why not!