[audioferret]

I am ordering mine today.  I chose the balanced output package so I can eventually have a totally balanced system.  The pre reportedly sounds better balanced, so I wanted that capability eventually.

AF

[jb]

It is generally accepted that clock jitter below 200ps rms is inaudible; although there are some who claim to hear as little as 2ps. Most S/PDIF receivers have <200ps jitter. So, the question is: Why would a DAC designer deliberately increase clock jitter by orders of magnitude, as is the case with asynchronous reclocking, and why doesn’t anybody hear it?

Asynchronous reclocking interposes latches in between the S/PDIF receiver and the DAC chip to reclock the data, bit clock, and word clock signals. The presumed purpose is to reduce jitter but that is preposterous. Asynchronous reclocking actually increases jitter.

In simplest terms, a latch or flip-flop is a digital circuit with two inputs, CLK and D, and one output, Q. Whatever binary value is present on the D input when CLK changes from low to high, is transferred to the Q output and held there until the next low to high transition of CLK. Regardless of the timing of changes at the input D, the output Q will change only when CLK transitions from low to high.

The usual implementation of asynchronous reclocking connects the CLK inputs of three latches to the reclock oscillator, the three D inputs to the data, word clock, and bit clock outputs of the S/PDIF receiver, and the three Q outputs to the respective data, word clock, and bit clock inputs of the DAC chip. (In actual practice, the latches have to be doubled, making six latches in total, to avoid an undesirable phenomenon called the meta-stable state. Conceptually, each double latch operates as a single latch.)

Ideally, the sample clock should be exactly 44.1KHz and the period of each and every clock cycle should be exactly 1/44100 seconds. But all oscillators have jitter, some more than others. With 200ps rms jitter expected in the S/PDIF sample clock, most clock periods will be too long or too short by 280ps rms. With asynchronous reclocking, each sample period will be an integral number of reclock periods and will be too long or too short by as much as a full reclock period. Because the clocks are asynchronous, an integral number of reclock periods will never equal the desired sample period. Reclocking with 100MHz, as the Prometheus DAC does, increases sample clock jitter, as seen by the DAC chip, to more than 5.7ns rms. 5.7 nanoseconds is considerably larger then 200 picoseconds!

Forcing the sample clock to be an integral number of asynchronous reclock periods will increase the granularity of the clock jitter. Instead of 22.675736961ns, the sample period is either 22.67ns or 22.68ns, +/- a few picoseconds. As a result, the effective sample rate jumps between two different frequencies, 44.09KHz and 44.11KHz, with a very predictable pattern. When the sampling frequency changes so does the frequency of the reconstructed audio signal. In other words, the changing sample frequency modulates the frequency of the audio signal.

It’s like wow and flutter. Perhaps that’s why some listeners report that asynchronous reclocking sounds more ‘analog-like’, meaning it sounds like a cheap turntable. Pitch stability is one area where digital audio is superior to analog. Why negate that benefit with asynchronous reclocking?

One more thing: I think the Prometheus web site is a real hoot. They make a big deal that the “clock module is place below the PCB to prevent spraying the board with noise.” That’s nice, but chances are the clock module is a ready-made oscillator hermetically sealed in a metal box. It’s hard to imagine a better electrostatic shield. Meanwhile, the reclocking latch, which is directly clocked by the reclocking oscillator, is mounted on top of the PCB and located a few centimeters from the DAC chip. The latch is encapsulated in plastic and its long bond wires, which traverse the entire length if the chip package, act as antennas spraying the DAC chip with RFI. What’s more, the eight latches, clocked simultaneously with only single VCC and ground pins located at diagonal corners and the decoupling cap located at the wrong end of the chip, will produce considerable ground bounce, which will add significant noise to the ground plane.

I can’t tell from the photo but I’ll bet the reclocking latch is a 74AC374 or equivalent. The 74AC logic family is well known for ground bounce and noise. When 74AC was developed, ground bounce was not well understood. More recent CMOS logic families are specifically designed to minimize ground bounce and noise that plagued earlier high-speed logic.

If all you golden ears think the Prometheus DAC is the best you have every heard. What can I say? Ignorance is bliss. Enjoy.

[audio-heaven]

If all you golden ears think the Prometheus DAC is the best you have every heard. What can I say? Ignorance is bliss. Enjoy.

Awww but it's mommy still loves it no matter what you say 

[audioferret]

And you have heard this DAC?  What did you compare it to?  What do you have in your system?  Have you designed DACs?  Which commercial DAC is out there that you designed and built?  How does it sound?  Is anyone buying what you have to offer?

[holderlin]

I've been listening to the promitheus dac for about a week now.  It probably has between 50-60 hours on it.  I bought it to compare it to a modded DAC-AH which I unchasissed and screwed to a wood base.  I've liked the sound of it but couldn't resist Nicholas's new creation.  Preliminary impressions are that the  promi has a wider and deeper soundstage, better detail, resolution and dynamics than the DAC-AH.  It retains the tonal character of the AH but gives everything more presence. 

I've been waiting to break in the promi before doing a side-by-side comparison of the two.  I'll report in more detail when I've done the comparison.

Bob

[H2K]

Bob,

I've got one on order - how long did it take to receive yours?

[tanchiro58]

Preliminary impressions are that the  promi has a wider and deeper soundstage, better detail, resolution and dynamics than the DAC-AH.  It retains the tonal character of the AH but gives everything more presence.

I agree with holderlin at this point. After 400 hours (about 2 weeks roughly) you will hear more details and defined music especially the guitar strokes (to my ears) until you bypass the two output capacitors (nichicon muse gold 22uF/100V) with either Mundorf silver oil caps or NOS Vit.Q PIO caps you will like the DAC more (more body).

 

[holderlin]

It took about 7 weeks to get mine.  However, I ordered a usb version and Nicholas wasn't happy with the way it was working so had to re-think how he would deal with the USB version.  This was the primary reason for the delay.  He's decided, at least for now, to build a separate usb module.  I'm awaiting the module.

Bob

[jb]

 

And you have heard this DAC?

I don’t have to listen to the Prometheus DAC to know it’s based on a flawed concept and the circuit design and PCB layout was done by someone who knows nothing about digital logic.

What did you compare it to?

I don’t have to compare the Prometheus DAC to anything to know there are better DAC chips than the TDA1545 and better S/PDIF receivers then the CS8414.

What do you have in your system?

What does my system have to do with the Prometheus DAC?

Have you designed DACs?

Yes. Eight at last count, with one more in development.

Is anyone buying what you have to offer?

No. I don’t offer my designs for sale to the public. Studying, designing, and testing DACs is a hobby and dealing with customers, especially wannabe audiophiles, would take all the fun out of it.

[gooberdude]

Thanks for the info jb.     If you've been following the Promitheus growth this last year or so you've noticed just how many new products they've released...and they've all been well received from what i can tell.  AFAIK the DAC is Promi's only digital offering.


I think its great to post ideas about this or any other product of Nicks...he reads these posts and if you're ideas make sense, he may incorporate them.    It doesn't make sense to take a negative tone though, you don't even own the gear dude.  i bet you haven't heard a single piece of Promi gear   

Noone should get upset about jb's comments, we're talking about a $400 DAC here, not some $10,000   Class A piece of gear.      i'm sure if guys (jb included) wanted to blast the other budget DAC's internals avail it could be done.    In this price range i've read many posts of DAC's with hiss, tipped up treble and a strident digi sound.     so far the Promi DAC hasn't been grouped in with that bunch, and i think that was Nick's goal.     provide something that works for a low, low price. 


matt

[tanchiro58]

I don’t have to compare the Prometheus DAC to anything to know there are better DAC chips than the TDA1545 and better S/PDIF receivers then the CS8414.

jb,

I do not know what are you talking about here. But what I know in the digital world there is a new chip TDA1547 and CS8417 which has been developed and tested. There is a japanese DAC product using these new chip and S/PDIF receiver (to my knowledge).

[jb]

I do not know what are you talking about here. But what I know in the digital world there is a new chip TDA1547 and CS8417 which has been developed and tested. There is a japanese DAC product using these new chip and S/PDIF receiver (to my knowledge).

The TDA1547 is a sigma-delta hybrid and not of any use for a NOS DAC. Besides, it is obsolete and discontinued. If you like sigma-delta, there are many better choices that are still in production.

I can’t find any mention of a CS8417.

Fifteen years ago S/PDIF receivers, such as the CS8412, phase-locked the VCO to the bi-phase data stream. Unfortunately, the resulting clock was modulated by the data content. But, that was OK because, back then, parallel DAC chips used FSYNC to trigger the D/A conversion and FSYNC was spectrally pure. All the bit clock had to do was strobe the data bits out of the receiver and into a latch. Later, serial DACs appeared and used the bit clock to trigger the conversion and the spectral contamination in the recovered clock created jitter. Asynchronous reclocking was proposed as a way to decouple the recovered bit clock from the S/PDIF data stream. The idea was that random jitter was preferable to data-correlated jitter. In reality, asynchronous reclocking produces way too much jitter and it is not random but is very predictable resulting in a systematic modulation of the reconstructed audio signal.

[/quote]

Noone should get upset about jb's comments, we're talking about a $400 DAC here, not some $10,000   Class A piece of gear.      i'm sure if guys (jb included) wanted to blast the other budget DAC's internals avail it could be done.    In this price range i've read many posts of DAC's with hiss, tipped up treble and a strident digi sound.     so far the Promi DAC hasn't been grouped in with that bunch, and i think that was Nick's goal.     provide something that works for a low, low price.

Why does low price always have to mean low quality? Why go to the expense and bother of asynchronous reclocking when you can solve the problem reclocking was supposed to fix by just using a more up-to-date S/PDIF receiver? Modern receivers, such as the CS8415A/16, phase lock on the biphase preambles and the recovered clock is not coupled to the incoming data. I don’t like the CS8416 because is requires dual supplies and includes a digital low-pass filter. The CS8415A uses a single 5v supply and outperforms the CS8414 in every way.

Replacing the CS1814, 100MHz oscillator, and 74AC374 with a CS8415A will reduce cost and improve performance…unless you are in love with the ‘analog-like’ sound produced by asynchronous reclocking. For me the goal is to reproduce the sound of real, live, acoustic music and not the nostalgic duplication of a bygone technology.

[gooberdude]

Your knowledge of this subject is just awesome jb, please tell us more...


I made the analog sound comment 'cuz it seems that often DAC reviews mention that quality, or a lack thereof, as some sort of basis.    i don't own a DAC but plan to get a pc based ssytem going at some point...so i'm interested.   

I for one welcome a strong digi sound as long as its not harsh. being a bass head its tough not to dig it.  the HF's of digi have always been a detractor to these young ears though.

budget gear is often lacking, sins of commission rather than omission.   its just a fact in this hobby seems like, pitty too.   gotta work to find nice gear at low prices.


make us some dope DAC's for $300 bro!!!


 

[audioferret]

Noone should get upset about jb's comments, we're talking about a $400 DAC here, not some $10,000   Class A piece of gear.      i'm sure if guys (jb included) wanted to blast the other budget DAC's internals avail it could be done.   

I am not so much concerned about the cost of the product reviewed as much as the overall tone of this thread.  JB has a lot to offer - clearly he knows quite a bit about how to put together a decent DAC.  I wish I had a strong working knowledge of chips so I could evaluate a product based on its internal components, much less build my own.  Goodness knows how many times I have scratched my head when trying to keep up with the many reviewers (professional as well as enthusiest) who identify them in their discissions. 

The approach of JB, as well as all of us, could use a little tact.  The unilateral condemnation of a person's idea, project, or product is just not very helpful to moving the discussion forward.  My questions were aimed at driving that point, to which JB gave adequate responses to.  Further, decrying the general populace of this board as "wannabe audiophiles" is especially arrogant.  To my perspective, audiophile is merely one who has a passion for reproduced sound - noone here is claiming to be an electrical engineer or sound engineer - we just like music.  Just like our tastes in women (and for some, men) everyone knows what they like.  We don't all agree, and sometimes we can't explain why we prefer what we prefer.  You like a precise, perfectly reproduced sound - don't be so harsh if someone likes theirs a little rough around the edges.  I do appreciate how well you have explained the differences in chip hardware.  I am only capable of evaluating the difference in how it sounds.

What would be really useful is demonstrating how much better the DAC could be by swapping out the receiver chip and DAC chip in this topology.  I think everyone here, (including Nick) would be willing to spend a few bucks more to do this if it really produced a dramatic differnece.  I think Nick's approach is based on the "whole" rather than one or two strong parts.  His use of transformers appears on the surface to be a very strong foundation for any implementation.  I would be very interested why the given chips were selected if other, allegedly superior, chips are readily available. 

 

[gooberdude]

After i posted last here i began reading the Altmann DAC thread just a few down from this...seems jb was talkin' trash there too, and blasted the Promi DAC also.

often approach's like jb's are met with friction here     



I'm kinda interested to know if Promi DAC users are gonna try coupling feet and/or isolated tonewood platforms.    And, also what power cords you guys are using.

[audioferret]

After i posted last here i began reading the Altmann DAC thread just a few down from this...seems jb was talkin' trash there too, and blasted the Promi DAC also.

often approach's like jb's are met with friction here     

I also had researched his other threads before posting my opinion.  Again, I don't care one way or the other about the DAC itself.  I had to cancel my order as I am getting deployed to Iraq in a few and won't be able to bring it with me.  Maybe when I return. 

The attack came across as if it was aimed personally at Nick and the rest of our community.  I feel that kind of behavior is unwarranted and should be put in check.

[gooberdude]

I agree completely, the guy has it out for Nick.


Kick some ass over there, watch your back, come back & tell us stories.    The Statement DAC will be out by then anyway.


all kidding aside, best of luck.

[tanchiro58]

I'm kinda interested to know if Promi DAC users are gonna try coupling feet and/or isolated tonewood platforms.    And, also what power cords you guys are using.

With my Promitheus DAC I use what Nick included the footers in the package under my Delrin Acetale plateform in between with a 3 inches maple platform. I also use DH cones and Shun Mook discs and footers to try which one is the best match for the DAC and my taste. I have ordered from Nick the power cord that he built only for the DAC (he said AC cord improves the sound of DAC too!).

[gooberdude]

very cool Tan, keep us posted on your impressions...

[Whitese]

Audioferret...good luck and stay alert, and dont daydream about gear ya hear?

Stay Safe!!!


jack