Audio-Gd Master 7 - Discrete Fully Balanced DAC (PCM1704)

[drez]

  Al, many thanks for the info! I will check the link.
 
The Offramp 5 is still tempting me but I am not sure about the investment. The latest 2014V2 M7 firmware is good and I have almost decided to leave the Offramp 5 path. But I have some computer/USB noise related problem and I hope that one of these "USB conditioners" could help: I hear a high frequency noise if my M7 is connected directly to the computer via USB. The noise disappears if the M7 is connected via the DI-V3 coax (the DI-V3 is connected to the comp in this case). The problem is not really annoying because the noise is not present at the normal volume levels used for listening. But it is evident that something unwelcome is entering the M7 via the USB input.

 
If noise is the problem I would say that it could be on the D+/D- or the +5V of the connection.  Taping the +5v pin might help, but my guess is it won't help much if USB32 lifts the +5V anyway.  Similarly, the iFi might only help by providing  cleaner ground, I think the ShortBlock similarly addresses ground related problems.  In my system I find it better to leave the ground connected between computer and DAC/DDC, not saying that any of the ground tweaks wouldn't be helpful as I haven't tried them all.  The Aubisque might work, but I would say it might be better to address the underlying problem.
 
Are you using the same wall power outlet for computer and DAC?  Is this a laptop or PC?
 
Most of the USB transports will offer galvanic isolation from the computer, and might ultimately offer better performance than the USB32 depending how much you are willing to invest.  I guess if some of the tweaks work well with the offramp then they can be carried over if you chose to use an external USB transport in the future.
 
Anyway I hope you get your noise problem sorted.

 

[Sapientiam]

   I hear a high frequency noise if my M7 is connected directly to the computer via USB. The noise disappears if the M7 is connected via the DI-V3 coax (the DI-V3 is connected to the comp in this case). The problem is not really annoying because the noise is not present at the normal volume levels used for listening. But it is evident that something unwelcome is entering the M7 via the USB input.

 
Sounds to me as if you have a common-mode noise problem. The way to verify if its that is use a laptop on battery power as the USB source. If there's no whining then, then that's your problem.
 
Even though you can't hear the noise at normal listening levels it will still be degrading your SQ- the noise is high frequencies and this intermodulates with the audio to grey out (or remove warmth from, if you prefer) the sound.
 
The noise couples into the audio via common ground impedance coupling. The grounding to the USB input should be a dedicated wire directly back to the transformer secondary but I rather suspect Kingwa has not done this (I've examined photos of internals of his designs).
 
One solution is to add a common-mode choke. A 'Short Block' (from Empirical) is one such but you don't need to get one from Steve N. Lots of ferrite clamps (and I do mean lots, one isn't enough to make much of a dent) around your USB cable will help somewhat. A dozen or so ferrite clamps are still much cheaper than anything 'audiophile'.

This is really just a band-aid though, the best solution is correcting the internal ground wiring of your DAC so that the noise from the computer is kept more separate from the audio.

 

[drez]

   
Sounds to me as if you have a common-mode noise problem. The way to verify if its that is use a laptop on battery power as the USB source. If there's no whining then, then that's your problem.
 
Even though you can't hear the noise at normal listening levels it will still be degrading your SQ- the noise is high frequencies and this intermodulates with the audio to grey out (or remove warmth from, if you prefer) the sound.
 
The noise couples into the audio via common ground impedance coupling. The grounding to the USB input should be a dedicated wire directly back to the transformer secondary but I rather suspect Kingwa has not done this (I've examined photos of internals of his designs).
 
One solution is to add a common-mode choke. A 'Short Block' (from Empirical) is one such but you don't need to get one from Steve N. Lots of ferrite clamps (and I do mean lots, one isn't enough to make much of a dent) around your USB cable will help somewhat. A dozen or so ferrite clamps are still much cheaper than anything 'audiophile'.

This is really just a band-aid though, the best solution is correcting the internal ground wiring of your DAC so that the noise from the computer is kept more separate from the audio.

 
Thanks for the in depth explanation.  I wonder if this is why Emprical do the filtering in the cable, and other converters like Berkely BADA USB use computer power/ground for the USB receiver and keep this separate from the internal power?  If this could be done in the USB controller card, all things being equal could this be better still?

 

[Sapientiam]

Here I'm speculating a bit but seems to me that the guys over at BADA have been up to speed with common-mode noise issues for a longer time than Steve N at Empirical has.This is based on some interaction I had with Steve on another board over a year ago. My impression then was it was a bit new to him. Hence I guess when he learned about it he devised an add-on solution to fix it.
 
OTOH Ayre have implemented USB isolation for quite some time - the original QB9 had it - but if you talk to Charles Hansen he'll say this doesn't 100% fix problems in that he mentioned still some SQ differences from changing USB cables. So yes - full isolation of the USB (not just the +5V wire) is a long way to fixing it - trouble is nobody's got a cheap solution for high speed USB. Full speed USB (allowing you to go up to 96k/24bit only) solutions are two a penny though nowadays.

 

[ManAtWork]

Al, many thanks for the info! I will check the link.

The Offramp 5 is still tempting me but I am not sure about the investment. The latest 2014V2 M7 firmware is good and I have almost decided to leave the Offramp 5 path. But I have some computer/USB noise related problem and I hope that one of these "USB conditioners" could help: I hear a high frequency noise if my M7 is connected directly to the computer via USB. The noise disappears if the M7 is connected via the DI-V3 coax (the DI-V3 is connected to the comp in this case). The problem is not really annoying because the noise is not present at the normal volume levels used for listening. But it is evident that something unwelcome is entering the M7 via the USB input.

Would it related to the cable or your motherboard?
You can contact Kingwa for assistance.

 

[ALRAINBOW]

I would email kingwa as he should have some ideas
Regarding this.
I would also put a post up on computer audiophile
And computer circle.
Some one there will have some answers as well
The first one has some really smart people
And gets a fair amount of traffic
Al

 

[ManAtWork]

I would email kingwa as he should have some ideas
Regarding this.
I would also put a post up on computer audiophile
And computer circle.
Some one there will have some answers as well
The first one has some really smart people
And gets a fair amount of traffic
Al

Very easy to do some trouble shooting yourself.
Swap another USB cable to see if the problem still exists - cable related issue
Swap another USB port of your computer to see if related to a fault port
Swap another computer (or laptop) to see if the motherboard issue

 

[ALRAINBOW]

I asked that already and I believe it was all done
Except the CPU. The fact that the dvi3 works makes me think
It is inside the M7 USB board
Al

 

[seaice]

Thanks to all! I have tried everything mentioned in this thread. Summary:
 
Notebook: OK, no noise.
 
Desktop PC: high frequency noise. It is not the typical "ground" hum related to the audio equipment. The frequency is very high and it is changing very quickly...
- Unsuccessful attempts so far: Different USB cables, different USB ports, pure USB data connection (power USB line disconnected). And of course, power cables - everything is in the same power strip and grounded properly... Nothing helped. Result: The noise is related to the USB in my desktop PC.
I tried the ferrite cores today (found 2 at home) and this was interesting - there was a partial success in suppressing the noise. The noise has changed but it is still there.... I will try more of them.

 

[ManAtWork]

Thanks to all! I have tried everything mentioned in this thread. Summary:

Notebook: OK, no noise.

Desktop PC: high frequency noise. It is not the typical "ground" hum related to the audio equipment. The frequency is very high and it is changing very quickly...
- Unsuccessful attempts so far: Different USB cables, different USB ports, pure USB data connection (power USB line disconnected). And of course, power cables - everything is in the same power strip and grounded properly... Nothing helped. Result: The noise is related to the USB in my desktop PC.
I tried the ferrite cores today (found 2 at home) and this was interesting - there was a partial success in suppressing the noise. The noise has changed but it is still there.... I will try more of them.

Looks clear that related to your PC, may be something wrong inside.
If so, nobody can help until you fix the fault, or get a replacement.
Sorry about this, pal.

 

[ALRAINBOW]

If you have a PC power supply I would change it
As that being the number one cause if noise
Al

 

[seaice]

OK, thanks again. The fact is that this my primary work PC less than 1 year old and I have no problems with it. I will consider the power supply but it takes a longer time.
 
Just FYI: My PC power supply is Seasonic X-750
And the motherboard was also mentioned earlier: ASUS P8Z77-V DELUXE

 

[ciphercomplete]

I have never had any noise issues with my M7 while using the usb input, but my computer (music server) is fanless, has only a 64 gig solid state hard drive and uses a pico power supply.  Fact of the matter is that any large PC power supply is going to be noisy.  What you want is a low power consumption cpu and a power supply just large enough to get the job done, all of which are somewhat incompatible with a computer a person would want to use for day to day tasks.

 

[Sapientiam]

  I tried the ferrite cores today (found 2 at home) and this was interesting - there was a partial success in suppressing the noise. The noise has changed but it is still there.... I will try more of them.

 
I've suggested this as a fix on at least one other forum - you are the first person to take the time to do this and report back. WTG!
 
Another solution is power line filtering to the PC to suppress the noise. The mains wiring is part of the noise loop, so if you can raise the impedance either at the PC end or the DAC end or both you'll reduce the noise. What's needed is a mains rated common-mode choke. They're available from the usual electronics catalog suppliers (Farnell, Mouser etc.). You just need to choose the appropriate current rating - a PC might take 1-3A depending on how its kitted out with graphics cards. The DAC will be under 1A.

 

[ALRAINBOW]

Great reply. , if I may ask you a question. . If the ground potential is equil in both devices why is the gnd the problem. . Next even if he bought a ISO transformer the gnd is common on both from input to out put . And last why changing the already noisey switching power supply not be a viable option. Please do not take my interpitation as doubting your ideas . I just do have some understanding in this and want to learn.

Thanks
Al