Modding USB cable to power DAC with external PSU

[rodelius]

Hello.

My DAC sounds fantastic through its SPDIF input but when driven through USB the sound quality strongly depends on the computer.

I know it should not happen with async USB but the difference is clearly audible.

With my laptop (battery powered) it sounds great, with one of my Mac Minis it sounds acceptable and with my newer Mac Mini with integrated SMPS it sounds awful.

 

As my DAC's USB receiver is powered by the computer and my HiFace EVO SQ clearly improved when I replaced the cheap PSU for a nice regulated supply I began to investigate the ways to power the USB receiver chip externally. I tested the DAC with a Placid supply and usb power injector cable but it did not work with any of the Macs. The DAC USB led always lights up but the computer does not recognize it.

I then modified an USB Female B to Male B adapter and isolated the +5v coming from the computer and soldered the Placid cables to the USB male end (leaving the minus cable conected to both ends) and it did not work either. Would it be possible that the computer +5v needs to be terminated in a certain way or cannot be simply cut because it is used to negotiate with the USB device? Or should the external PSU be connected to pin 1 and ground instead?

I searched all over the forums and it seems that there is no consensus on the right way to do this.

 

Before going for a commercial solution e.g. AQVOX USB Supply or purchasing a High End USB Hub I would like to have a clue of what is really needed to power an USB DAC externally in a manner that the DAC is recognized by the Mac.

 

Any help will be greatly appreciated.

 

Rod

[sandyk]

Hi Rod

Check out this thread

http://www.computeraudiophile.com/f6-dac-digital-analog-conversion/continuing-pursuit-power-supply-improvements-and-improved-dac-performance-14165/

 

I posted a diagram of a few things that you can try too.

Regards

Alex

[rodelius]

I posted a diagram of a few things that you can try too.

Regards

Alex

 

 

Thanks Alex, will try both options and post the results.

[sandyk]

Rod

When you are using the external linear PSU with Vbus (+5V) disconnected at the USB-A plug, (PC end) it may also be worthwhile trying the 1/2W 220 ohm resistor across + and - of the plug. This may fool the PC into believing there is a connection, as it does with the USB memory stick with only D+ and D- connected .

 

Regards

Alex

[sjoc2000]

Thanks Alex, will try both options and post the results.

 

 

Hello Rod;

 

It may be that the 220 ohm trick will work that Alex referred to will work. If not, it is not the + of the dac the pc is looking for, but data on the ground. Assuming a pc with windows 7, check to make sure there is no voltage between the dac ground, and the pc side of the cut ground in the usb cable to play it safe.

 

If not, then tie the dac ground to the "pc ground" side ground via the usb cable. Don't be concerned with the + of the usb. Make sure that the data line shield has not been compromised or is in any way in contact with power lines. That should work.

 

You can then inject +/- from your improved ps into +/- of the dac side via usb cable

 

Try that, and then listen to your system and see what has been gained, and let us know. There is a nifty way to attenuate any little residual noise nastiness that continues to reside on the pc ground.

 

Of course you do all of this at your own risk :0)

 

Get stuck or have a question just ask...

 

Sincerely,

 

Jim

[rodelius]

Alex, Jim, thanks for your help.

I built a small adapter on a PCB taking care that the data cables did not exceed 1 inch.

Tried option 1 and 2 of the following drawing and they did not work. (Option 2 and per Alex suggestion, will try Option 3 next time)

Will do the same by stripping a cable to keep everything closer and better shielded as soon as I have a minute.

 

If you have any other ideas, I will try them.

Thanks!

[rodelius]

Alex, do you think that the Alltronics USB isolator would work? I mean... Will it isolate a good portion of the psu noise while leaving the data untouched?

[Jud]

Hello.

My DAC sounds fantastic through its SPDIF input but when driven through USB the sound quality strongly depends on the computer.

I know it should not happen with async USB but the difference is clearly audible.

With my laptop (battery powered) it sounds great, with one of my Mac Minis it sounds acceptable and with my newer Mac Mini with integrated SMPS it sounds awful.

 

Rod

 

Hi, Rod, I wanted to comment just on this part of your original message. People tend to be too general and sweeping with statements like "hi res always sounds better" or "async USB eliminates all differences prior to the DAC input." What async USB eliminates is jitter caused by locking on to a jittery source. That's it. A USB cable is an electrical cable like any other, so it has no special immunity to any problems caused by noise in power or ground.

[sandyk]

Hi Rod

What I meant with my previous post was to try disconnecting ONLY the red wire (VBus) and fit a 220 ohm resistor between + and - with the black wire still connected.

I have only tried the Altronics Isolator with USB memory sticks , but it caused CDs ripped to that memory stick to have an exaggerated and fatiguing sounding HF response due to their choice of capacitor types and values.. It sounded much better with a 1,000uF 16 volt electrolytic capacitor at the input to the 7805 voltage regulator instead of the 10uF . The capacitor at the output of the 7805 could be a normal 470nF film type capacitor , or even a higher value electrolytic. Where are you located,as there may be a minimum order value from Altronics.

 

Regards

Alex

[rdsu]

[rodelius]

Hi, Rod, I wanted to comment just on this part of your original message. People tend to be too general and sweeping with statements like "hi res always sounds better" or "async USB eliminates all differences prior to the DAC input." What async USB eliminates is jitter caused by locking on to a jittery source. That's it. A USB cable is an electrical cable like any other, so it has no special immunity to any problems caused by noise in power or ground.

 

Understand and agree.

According to the manufacturer, however, the DAC should be immune:

 

Your descriptions of sonic differences in the USB system are surprising.* We have tested the DAC2 with a variety of USB cable lengths and all measurements are identical.* No jitter-induced sidebands or jitter-induced distortion is detectable with any cable tested.* In addition, no spurious tones related to the USB subsystem are detectable.* Measurements of the USB and S/PDIF inputs are also identical. The DAC2 uses Asynchronous data transfer and does not rely on clocks generated in the computer.* The DAC2 conversion system uses a fixed-frequency oscillator to pull data from the USB subsystem.* The conversion system, and conversion clock are well isolated from the USB subsystem.* If you are experiencing sonic differences, I would suspect one of two things:

1) The computer playback path is not bit-transparent

2) A ground-loop exists between the computer and your power amplifier

 

But not only I find differences between computers.

Different USB cables (Audioquest Forest and Carbon, WW Starlight, Kimber copper, Belkin etc) sound different. And the difference between any of them and an el-cheapo 6 inch cable is very noticeable. The short little cable sounds noticeable better than any of the highenders.

I carefully looked for ground loops and possible sources of EMI and RFI but I have been using the very same kit for some time and am pretty sure that everything is fine.

 

A few minutes ago I ordered an iFi USB supply from iFi-Audio France. Hopefully I will have next week.

 

Thanks for writing.

®

[rodelius]

Hi Rod

What I meant with my previous post was to try disconnecting ONLY the red wire (VBus) and fit a 220 ohm resistor between + and - with the black wire still connected.

 

I also tried that, Alex

I actually did that first and then cut the cable to fit option 1 of the diagram you pointed me to yesterday:

[rodelius]

 

Muito obrigado.

Unfortunately, the USB chip of my DAC is powered by the computer.

[sjoc2000]

Alex, Jim, thanks for your help.

I built a small adapter on a PCB taking care that the data cables did not exceed 1 inch.

Tried option 1 and 2 of the following drawing and they did not work. (Option 2 and per Alex suggestion, will try Option 3 next time)

[ATTACH=CONFIG]5123[/ATTACH]

Will do the same by stripping a cable to keep everything closer and better shielded as soon as I have a minute.

 

If you have any other ideas, I will try them.

Thanks!

 

 

 

Rod;

 

First time I've had to get back to this.

 

Hmmmm, Rod, the first option should work as described by Alex's nicely done little schem.. At least it did for a Peachtree Dacit/pc/win 7.

 

I don't want to wear you out on this, but are you taking time to check and setup windows playback devices, disabling where needed, and setting as default the appropriate device? Also volume control opt. and vol mix opt.?

 

I just use a pc and win 7, are you using a pc or apple here for implementation?

 

My point is with option #1, you may have accomplished the task at hand, but didn't know it because of settings not being correct for the os.

 

Just some thoughts,

 

Jim

[rodelius]

Jim, I tried Alex' first option, both with a led in series to the resistor and without.

The adapter's led lights up and the DACs USB led shows that the USB is active, but none of my Macs shows the DAC listed.

 

Just to clarify: Alex' schematic is the one with a white background. The one with beige background and 3 options is the one I drawn yesterday to show the options I tried (1 and 2) and the one I intend to try tonight.

 

By the way, I tried them all both with my laptop and with my Mac Mini and with 2 DACs with USB input and carefully measured and cheched everything out before connecting.

 

As both leds were lit I guess there could be something impeding that the computer negotiates with the dac properly.

 

TTYL

[sjoc2000]

Jim, I tried Alex' first option, both with a led in series to the resistor and without.

The adapter's led lights up and the DACs USB led shows that the USB is active, but none of my Macs shows the DAC listed.

 

Just to clarify: Alex' schematic is the one with a white background. The one with beige background and 3 options is the one I drawn yesterday to show the options I tried (1 and 2) and the one I intend to try tonight.

 

By the way, I tried them all both with my laptop and with my Mac Mini and with 2 DACs with USB input and carefully measured and cheched everything out before connecting.

 

As both leds were lit I guess there could be something impeding that the computer negotiates with the dac properly.

 

TTYL

 

Your methods imply that you are very clear about what your doing. :0)

 

This may have something to do with apple usb dynamics vs pc. Being I'm a pc guy, I will retire and watch. I look forward to your finding a resolution, and a further understanding for members here of how to better implement usb, DIY style. :0)

 

Jim

[rodelius]

It works!

While assembling option 3, realized that one pin of the A to B adapter I was using to keep everything as short as possible was a bit loose.

So I grabbed a short cable, cut the connection to the led and voilá! Option 1 worked as Jim and Alex suggested.

 

A few pics of the experiment:

Sound panel showing the DAC available – and playing some music!

 

Close view – Led and resistor not necessary!

 

The whole thing close to the Placid PSU ready to be connected to the Mac Mini

 

Thanks everyone for the help and support.

Rod

[sjoc2000]

Congratulations Rod;

 

Now when you have the time and inclination try this. Connect the grounds of the new ps and the dac side of the usb cable together. Jerry-rig a 47 ohm resistor in series with a 2 uH inductor (Radio Shack (choke)- $6.00). Use this to now connect the previously described grounds to the pc side of the usb ground.

 

You should notice a nice little bump in sq as a result of further attenuation of residual noise on the pc ground. That's my American style attenuator :0) , Alex likes his Aussie style, don't tell him I said this but the American style is better. hehe :0)

 

 

Jim

[sandyk]

Hi Rod

Great news. It is becoming clear that Async USB isn't the ultimate solution on it's own, no matter what the manufacturers may claim. Jim's solution may be necessary for some gear, but the ultimate SQ is obtained with just D+ and D- connected in the cable, and the resistor across the + and - of the USB-A plug and a far better than average external +5V Linear PSU.

BTW, to my surprise, a WD Elements 695GB portable HDD worked VERY well with music playback using this method.

CDs ripped to a Corsair Voyager USB memory stick also sound better when using this method despite having identical check sums to the same material saved elsewhere.

Problem when hocus-pocus works? - Page 5 - General HIFI Discussion - HIFICRITIC FORUM - HIFICRITIC FORUM : hi fi audio systems forum

See the last 2 posts by Martin Colloms.

Regards

Alex

 

 

 

 

 

"If you can't hear the difference between an original CD and a copy of your CD, you might as well give up your career as a tester. The difference between a reconstituted FLAC and full size WAV is much less than that, but it does exist."-Cookie Marenco. cookiemarenco.com/

[sandyk]

Rod

Make sure that what you have done continues to work over a longer period of time.

Funny things can happen with USB, even with external HDD cases, and you may sometimes lose the connection for no apparent reason.

Regards

Alex

[jamesg11]

 

Anyone got the matching FireWire image?

[rodelius]

It is becoming clear that Async USB isn't the ultimate solution on it's own, no matter what the manufacturers may claim.

 

100% agree.

I was really hoping to get rid of the EVO and its PSU (I love the sound) and simply use an USB cable to link my MacMini with the DAC.

Unfortunately this did not work for me.

 

I tried many DACs with async USB. To my ears, none of them could match the SQ of my Buffalo II driven by the EVO when powered by LiFePo4s.

 

As always, good PSUs and good electronic practices are mandatory for good audio quality.

[rodelius]

Make sure that what you have done continues to work over a longer period of time.

Funny things can happen with USB, even with external HDD cases, and you may sometimes lose the connection for no apparent reason.

 

Sure. As I ordered an iFi unit, won't be probably using this DIY adapter for a long time, but, until the iFi arrives, will be having some fun powering the dac with different PSUs and batteries. :-)

Just made this experiment to see if the async USB option of my DAC could be used to get a nice SQ.

I am really happy with the HiFace EVO, but wanted to use the DSD over PCM feature of my DAC. As it only works with USB, I needed something to make the connection as clean as possible.

 

Cables are not a solution. Some of them are better to my ears, but, in my case, the best sounding are the shortest ones.

[sandyk]

Cables are not a solution. Some of them are better to my ears, but, in my case, the best sounding are the shortest ones.

Hi Rod

The members of another forum bought a couple of long up market cables, then cut them into shorter lengths, fitted new plugs and distributed them among themselves. Quite a few also use JLH PSU add-ons in external +5V Linear PSUs, as well as modified cables.In John Kenny's forum some don't even use cables, they use right angle adaptors. My own USB cables are cut as short as possible and modified as per previously and the plugs heatshrinked.

Regards

Alex

[rodelius]

In John Kenny's forum some don't even use cables, they use right angle adaptors.

That is exactly what I intend to do this weekend. I plan to build an A to B male adapter with a socket for an outboard PSU:

I will have to sort some cable cluttering out at the back panel of my DAC as it is pretty crowded back there, though :-)