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what signals does a usb-dac need?

post #1 of 13
11/8/09 at 2:50pm
Thread Starter 
I asked myself, what signals does a usb-dac need?

I can imgine: - the 5v greeting signal
- some kind of signal where digital data is transferred
- ?
- ?
- ?

I was thinking about a digital out from my archos 605.

thank you
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post #2 of 13
11/8/09 at 3:02pm
power, ground, 2 data lines. same as any usb 4 wire connection.
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post #3 of 13
11/8/09 at 3:06pm
Thread Starter 
Is power necessary, because on some portable amps you can turn of usb charging.

Do the datalines use i2c signal?
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post #4 of 13
11/8/09 at 3:30pm
Yeah, do not think you need the bus power. At least my USB DAC provide its own on-board +5v power...
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post #5 of 13
11/8/09 at 3:55pm
Thread Starter 
If you see this problem from birdsview on all the DAPs available, there was a major step back, when PCDP stopped havin optical-out.

However, I followed the thread of to pull out a digital signal out of the ipod. It seems there is no result, so I thought maybe it is possible from my archos 605, because you can send out a spdif signal from a dock.

Maybe I can do something here.

At last I will try one of those chinese 1080p players with hdmi out. HDMI sends digital audio too...
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post #6 of 13
11/8/09 at 4:15pm
Thread Starter 
bumpppppp

anyone, knows what signal this is?
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post #7 of 13
11/8/09 at 8:48pm
You do not need power lines along with signal, for the most part, they are not related. You just need to power the USB receiver somehow.

USB protocol requires a data model contract to be established and where the host sends data in the correct format. This obviously depends on the receiver used.

Most of the common "USB DACs", a term I greatly dislike, follow USB Audio 1.1 protocol, for which most operating systems have drivers pre-packaged. Once the operating system establishes that the USB device connected follows this standard, it installs the drivers and uses them to communicate with the device.

USB is a Host-Client protocol, not a streaming one like S/PDIF. You can't just "send" it data and expect it to do something, you first need to "connect".
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post #8 of 13
11/9/09 at 7:04am
Thread Starter 
In my archos 605 there is the wolfson 8985 codec in it.

Maybe my furture usb amp/dac is the ibasso d10. The d10 has this usb to spdif converter chip: pcm2906

just made a pictur of what i want to do. What do you think is this possible?

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post #9 of 13
11/9/09 at 7:14pm
No. That won't work.
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post #10 of 13
11/9/09 at 8:46pm
Thread Starter 
****, do not know what to say.

Quote:
It is at times necessary to frighten the thinker who is on the wrong path, by the consequences, so that he may pay more attention to the principles by which he has been led off as in a dream.
from Dreams of a Spirit-Seer
by Immanuel Kant

However, is it possible to convert the signal to spdif on a other way? It is helpful that the needed signals can be reached at the dock pins.
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post #11 of 13
11/9/09 at 9:38pm
if you look at the datasheet for the pcm2906 you might see a pin you can tap.
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post #12 of 13
11/10/09 at 6:19am
Forget S/PDIF or USB if you're hacking an ipod or other similar DAP, those will be largely irrelevant. Inside the DAP, there will be an I2S bus going into the onboard DAC chip. This is typically a 4-wire + ground interface, you could tap the I2S and feed it into an external DAC chip. However, very few commercial DACs accept I2S input (even though many of them have I2S internally). There are a couple of DIY DACs that allow this option.

Before you rip anything open and do the surgery, you should thoroughly understand what you're doing. It's very easy to damage the DAP, and what you implement externally might not be any better than the DAP's onboard DAC.
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post #13 of 13
11/10/09 at 6:43am
Thread Starter 
you got me, I just, 2 hours before ripped of a cable from my 605. I soldered it back, but it does not work now.

I tried to follow the printed circuit, but cannot see where it is going.

I have to get this thing work again, if not I can just forget it. Then I will look at the I2C receiving DACs. Maybe I will buy me a dockingstation, torn it apart. Then I can maybe see how archos handels this signal.

Maybe I can manage to put something together that is much smaller then the dockingstation...

Thank you amb
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