USB powered DAC

[andy74]

Hi All,

Did anybody tried a DAC which uses the power from the usb port, not from its own power supply.

I have a cheap USB audio adapter which I use with XX on Vista engine 3 .

And I noticed that if it is connected to the usb hub with its power supply it sounds worse (different ) to me.
As opposed to when the power supply is disconnected from the hub.

Yes yes... Again a jitter affecting over power supply voodoo stuff

Andy

[SeVeReD]

You know I haven't tried it.  But that is interesting.  Usually people saying you want to stay away from the usbdac getting it's power from the computer.  But who knows, whatever sounds best for that component.  If it only need that little power try one of those rechargeble batteries?
http://www.bixnet.com/5v7libapa.html
like that, but ya, it's pricey too.  make one?

[andy74]

Yes but my point is that it is better to use power from usb (the same power supply where XX runs), than any other power even from the battery.

Because my theory is (as I mentioned before in other posts) that hte jitter magic treatment by XX is done mostly through PSU. So using different PSU for usb dac steals (removes) some of XX magic influence on SQ.

[PeterSt]

Again, interesting ...

But wouldn't it be hard to prove what you actually hear in this case ? I mean, a DAC running on batteries is generally appreciated as sounding better, although that too might not be because of the more clean battery power itself (if true already, but that's another thing).
I mean, when the DAC runs on batteries and is USB connected, it will always receive the power from the PC's PSU (I think). With Firewire it would be the same story. Now, what about the DAC not being fed by batteries but by its own PSU. Still the influence via the USB/Firewire cable would be there, but now it's mixed with the own PSU.
Btw, nothing tells me (for all of the DACs existing) that the DAC using an own PSU would use parts of the USB/Firewire power.

What to do with this ? well, I can imagine that I detach the power to my soundcard (Fireface this case), same with the DAC (TwinDAC+), and feed them by the PC's PSU. That would be new, right ? hahaha


All brings me to another serious question (for myself anyway), and that's about the kind of huge difference I perceive between SPDIF and USB towards the TwinDAC+. I talked about that earlier (maybe not on this forum), but this is about the both connections (which the TwinDAC+ swallows) being so different, while at the same time it is nearly impossible to choose one for being the absolute best. Here too I dedicate that to jitter, USB being better in the bass, SPDIF being better in the highs. But now, what about this :

The SPDIF connection goes through the Fireface (PC->SPDIF->Fireface->SPDIF->DAC) while USB goes directly to the DAC (PC->USB->DAC). So, I tend to say the difference comes from the rather different route. However, when it indeed would be so that the PC's PSU could pass on the signature of XX, it would do that via USB, and it would not do that via SPDIF. Or at least musch less, because there's no official power carrier in SPDIF.

At least for myself it is time to re-evaluate the USB connection, which I did some 4 months ago for the last time, when the performance of XX was quite different.


For those who jumped into this thread without background : Burning audio CD while XX playing.

[edward]

The SPDIF connection goes through the Fireface (PC->SPDIF->Fireface->SPDIF->DAC) while USB goes directly to the DAC (PC->USB->DAC). So, I tend to say the difference comes from the rather different route.

Peter, I don't agree with your description of the signal path. It implies that your are using the SPDIF from the motherboard to go into the Fireface. I'm pretty sure that's not what you are doing. And also USB DACs do not connect directly with the DAC chip. The USB connection goes into a receiver chip and then to a converter chip. AFAIK, there are only 2 outputs to convert to. Either SPDIF or I2S. Then that goes to the DAC. So here's how I would label the signal paths:

PC->Firewire->Fireface->SPDIF->DAC
and PC->USB->SPDIF->DAC
or PC->USB->I2S->DAC

So, all things being equal, a USB DAC that converts to SPDIF internally should sound the same whether it is connected by SPDIF or USB. The USB connection eliminates the need for an SPDIF cable, however, as you can guess, all USB cables do NOT sound the same either. And, of course, not all USB receiver chips are created equal, so . . . this explains why they DO sound different. And then there are those that do not like the USB->SPDIF converters so they prefer to convert to I2S (internally).

As for USB bus power. I believe it's difficult to compare, because a device that is truly NOT bus-powered, can ONLY be connected to it's wallwart (or battery), such as my M-Audio. The capability of bus-powering is removed from the connector pins, so I couldn't even bus-power my device if I wanted to. If, however, you have a device that CAN be bus-powered, even if you plug it into the wall (or battery) you still have the circuitry there for bus-power and still have potential for "dirtying" up the USB signal by drawing current over the USB cable (which is why most prefer to not have bus-power).

[andy74]

you are missing the point.
It is not "dirtying" by USB power but completely opposite: XX does something that affetcts USB power so in this case it is oposite to dirtying, or "dirtying in a good way" so the sounds improves.

[andy74]

as for your m-audio try powering it from PC PSU where XX runs

[PeterSt]

PC->Firewire->Fireface->SPDIF->DAC
and PC->USB->SPDIF->DAC
or PC->USB->I2S->DAC

You are completely correct Edward. In the heat of the battle I missed out on a few. But I tried to indicate the essential : one does not connect to the PSU of the PC, and the other does (or may do, depending how things are separated inside the DAC box; in the TwinDAC's case it's PC->USB->SPDIF->DAC).

My too fast writing (or better : your correction ) also reveiled another PC-PSU driven device : the Fireface.

[edward]

you are missing the point.
It is not "dirtying" by USB power but completely opposite:

as for your m-audio try powering it from PC PSU where XX runs

Thanks Andrey, I did not miss the point. I was trying to point out that up until now, MOST people have considered that USB power is "dirty", and I do indeed understand that you are illustrating the opposite. (Just playing "devil's advocate" as usual)

As for the M-Audio, perhaps you missed the point I made that I can't power it from the PC PSU even if I tried. And there are many devices like this. Which is why a direct comparison is difficult.

[edward]

My too fast writing (or better : your correction ) also reveiled another PC-PSU driven device : the Fireface.

Really? I thought you are using the Fireface 800. (See attached photo) Isn't this what the back looks like. That's a wall wart power plug on the left. It's not bus-powered. Is it possibly both?

[PeterSt]

No it is not. But depending on how things in there work / are connected, the Firewire power could be transferred into there.

[edward]

No it is not. But depending on how things in there work / are connected, the Firewire power could be transferred into there.

That's interesting. Have you tried different firewire cables to see if they sound different? (As I have found out with different USB cables on my USB DAC) I have currently settled on Kimber Kable's USB cable.