[tanchiro58]

Hi, first post here.

I’ve been following this thread for a while and received a Promitheus DAC earlier this week (used from original owner).

As several others have reported, mine also has a significant amount of hum/noise. 

Has anyone with the hum/noise heard back from Promitheus on this, or resolved the issue in some other way? 

Given that several folks are experiencing this, does this appear to be a design/quality issue with some units, or perhaps a part that gets easily damaged in shipping (mine was double-boxed and packed very well by the original owner, and I do not see any obvious internal damage)?

Here are my specific observations and things I tested:

The noise/hum is audible from my seat (3 meters from the speakers) when I pause my transport and when no track is playing, with the preamp’s volume at a moderate setting of around 9 o’clock.  The noise/hum tracks with my preamp’s volume level.

The noise/hum is present when no digital cables are connected, as well as when a coax digital cable is connected.  Interestingly, when no digital cables are connected there is a low hum and high whine from both the coax and BNC inputs.  However, when a digital cable is connected to the coax input, the coax produces only the hum (no whine), but the BNC still produces the hum and whine.

In troubleshooting this, I tried all of the usual suspects – tried 2 different power cords, 2 different analog cables, 2 different AC circuits, moved the DAC to different locations, tried a cheater plug to lift the ground.  Nothing had an impact on the noise/hum.

I also tried the various output voltage jumper positions.  The noise/hum is present in all positions, but varies in relation to where the noise/hum becomes audible vs. preamp volume setting.  The other thing I noticed is that the output voltage from my jumper settings does not appear to match what is in the manual.  For example, the middle jumpers are the loudest on my unit, but according to the manual, the middle jumpers should be the middle (2v) output.  Does this mean there is something wrong with my unit?

The one last thing I can think of to try is to get a RCA-BNC adapter and connect digital cables/sources to both digital inputs simultaneously.  The thought here is to see if perhaps noise is entering the unused BNC input.  I know this is a long shot.

I know that Nicholas from Promitheus posts on this thread, so I hope he (and others) will comment on this issue and how to resolve it.

I will also send Nicholas an email on this.

Thanks,

Adam

Adam,

I do not have problems of hum/noise in my DAC. The only one problem is I can use (have signal) this DAC in my system but it does not have signal in other system (like I stated before in this thread).

You might use a truly 75 Ohm digital cable to avoid those problems IMO. I got the Silver digital cable (well grounded hand made).

Good luck,
Tan

[PromitheusAudio]

Adam
Drop me an email with pics of the board. Then from there i can advise you better

thanks
Nicholas

[adam2434]

Tan, thanks for the reply.

I have the noise even when no digital cables are connected.

I did get a RCA-BNC adapter today, so I'm going to connect transports to both digital inputs to see if that has any effect.

Nicholas, I emailed you a link with pictures from the original owner.  Let me know if they are adequate.

Thanks,

Adam

[adam2434]

Well, I ran the experiment with both digital inputs connected to transports.  This did not eliminate the hum/noise.  I figured this was low probability.

I also connected the DAC's analog outputs to my home theater receiver for an experiment, and the hum/noise was present there also.

I hope there is a solution, because I really think I would enjoy the sound of this DAC if the hum/noise were not present.  The hum/noise is distracting during track changes and simply should not be present.

[Milenko27]

I also have a hum in my dac, i dont notice it when i am playing music but it is a bit annoying when changin cds skipping tracks......
The hum has always been there, i recently changed the op-amps to the opa-moons, got a bit sweeter sound.
When that is said, i must say that i really love the sound of this dac, it is stunningly good, a bit annoyed by the hum issue though, but in every other instances it is perfect and a great product....

Any one know how to solve the hum issue?

[PromitheusAudio]

Adam
If you can send me the board back, i can get it fix and send it back to you
i just need the board only to fix it

thanks
Nicholas

[adam2434]

Adam
If you can send me the board back, i can get it fix and send it back to you
i just need the board only to fix it

thanks
Nicholas

Nicholas,

Could you see something “wrong” with the board from the pics in the link I emailed you last week?

Thanks for the offer to look at the board.  However, desoldering, shipping, and resoldering the board are not an option for me, as I do not have soldering experience/tools.

The original owner has agreed to provide a refund, so I will be shipping it back to him.

[tanchiro58]

Adam
If you can send me the board back, i can get it fix and send it back to you
i just need the board only to fix it

thanks
Nicholas

Nicholas,

Could you see something “wrong” with the board from the pics in the link I emailed you last week?

Thanks for the offer to look at the board.  However, desoldering, shipping, and resoldering the board are not an option for me, as I do not have soldering experience/tools.

The original owner has agreed to provide a refund, so I will be shipping it back to him.

Adam,

My opinion is you just save some more cash to get a brand new DAC from Nick. It is worth the money and is a fraction of the price compared to >1K DAC sonically. I used to buy so many kind of DACs but end up to keep this one. 

I got a problem with the previous board of my DAC too and Nick sent me a brand new one to replace it. At that time I was wobbling to desolder and solder the boards but I got a good result. 

Good luck,
Tan

[Audionut1]

Hey Mart and Tan,

Thanks for the advice regarding the GD discrete modules.  I'd gotten the correct units (singles) and the extensions so I could hook them up without having to mess with anything on the main board, but I was assuming the chassis was an ideal place to attach the white "ground" wires.  Oops!  Those need to be attached to the signal grounds coming off the board to (and then from) the transformers on the right side of the DAC.  Once I got the grounds connected correctly the units work like a champ... and I agree with the others who have tried them... they are a very worthwhile upgrade.  And they work wonderfully at the +12 and - 12 volts the DACs are preset to, so I didn't have to adjust the voltage to them (whew!).

Neil

Walkern,

Glad to hear the upgrade was worthwhile.  Would you mind sharing with us how the GD discrete modules improved on the already great sounding DAC?

Thanks,
Craig

[walkern]

Hi Craig,

I e-mailed the folks at GD Audio and basically said my DAC now sounds more like good vinyl.  Marginal discs are less offensive sounding and well recorded discs sound spectacular.  Instruments seem to have more body and more accurate tonal characteristics, and in some cases more weight (double bass for example).  Singers seem more present (3D) or in the room with me (or me with them), and female vocals that previously could sound a bit shrill are more relaxed and smoother sounding.  The extreme top end seems to have a bit more clarity and shimmer (can hear more of the harmonics of instruments like cymbals or triangles or bells), and seems a bit more extended as well.  The DAC seems to be capturing and revealing more information (lyrics seem more intelligible), yet simultaneously it sounds more organic or musically natural.  I was at a local symphony concert last weekend and came home and fired up recordings of what had been played and was pleasantly surprised with how close my system matched the general character of the orchestra.  Previous trips to the symphony have lead me down the upgrade path more often than not.  The dynamics seem a smidge more ... uh... dynamic, both micro and macro.  The bottom line is, I find myself listening to more music, and re-discovering all sorts of discs, and I am watching TV and reading less.   Always a good sign.

Neil

[Audionut1]

Hi Craig,

I e-mailed the folks at GD Audio and basically said my DAC now sounds more like good vinyl.  Marginal discs are less offensive sounding and well recorded discs sound spectacular.  Instruments seem to have more body and more accurate tonal characteristics, and in some cases more weight (double bass for example).  Singers seem more present (3D) or in the room with me (or me with them), and female vocals that previously could sound a bit shrill are more relaxed and smoother sounding.  The extreme top end seems to have a bit more clarity and shimmer (can hear more of the harmonics of instruments like cymbals or triangles or bells), and seems a bit more extended as well.  The DAC seems to be capturing and revealing more information (lyrics seem more intelligible), yet simultaneously it sounds more organic or musically natural.  I was at a local symphony concert last weekend and came home and fired up recordings of what had been played and was pleasantly surprised with how close my system matched the general character of the orchestra.  Previous trips to the symphony have lead me down the upgrade path more often than not.  The dynamics seem a smidge more ... uh... dynamic, both micro and macro.  The bottom line is, I find myself listening to more music, and re-discovering all sorts of discs, and I am watching TV and reading less.   Always a good sign.

Neil

Neil,

If I could acheive the types of improvements you describe, the DAC may be just about perfect in my system.  It already sounds great, but there's always room for improvement, if you know what I mean.  Thanks so much for the detailed description.

Craig

[PromitheusAudio]

Good to hear you like the GD audio stuff.
We are now focusing more with the Burson audio. Now i am keeping them in stock for use with our DAC.
I prefered the Burson over the GD audio when i compared them

Will do a special "burson edition" dac shortly

[tanchiro58]

Good to hear you like the GD audio stuff.
We are now focusing more with the Burson audio. Now i am keeping them in stock for use with our DAC.
I prefered the Burson over the GD audio when i compared them

Will do a special "burson edition" dac shortly

I agree with Nick. I have had the DAC with Burson opamps installed and never look back to all DACs (same league with NOS DAC) I own before included Altmann Attraction DAC. At least you need to have a reference DAC to compare with.

[pault6769]

Can someone  please post a picture of the Moon OPA's installed in the DAC, I want to see where the ground wires are soldered exactly. 

[Milenko27]

I soldered mine to the ground out on the output transformers

[tanchiro58]

Can someone  please post a picture of the Moon OPA's installed in the DAC, I want to see where the ground wires are soldered exactly. 

You can solder to the ground found at the power supply tranny which is closer to the pcb dac. I am sure they have same grounds like Burson.

[efm2]

Hi,

Any review of the C-cored DAC? Very interested in this one. Also, with the hum problem, do you think  the separate power supply will improve if not totally eliminate it?

thanks

[art]

I hope that Nicholas will not mind me butting in on his circle, especially with all that is going on today, but I have a question for the person who made the following post.

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?

Why do people such as yourself throw around buzz words like this, without even specifying what the hell they are talking about?

Are you talking about word clock jitter? Bit clock jitter? The same amount of phase noise gives much different jitter numbers. On top of that, whether or not the jitter is data-correlated is also important. But you make no mention of that, just regurgitate the same ol' "jitter below a certain level is inaudible"  assertion.

I agree with JohnR and Chair Guy that this sort of discussion belongs in the Lab section. Where people who know what they are talking about can 'splain it to you without making a muck of someone's Circle.

For the record, I do not know who Nicholas is, what his company is, what they make and whether or not it is any good. BS is just BS, and needs to be confronted wherever it pops up.

Please forgive my butting in, and let's hope this place is still here on Monday morning.

Pat

[OvS]

Hi,

Someone have any updates about the promitheus dac ?