EE question regarding wadia 170i
May 29, 2009 at 10:29 PM Thread Starter Post #1 of 3


100+ Head-Fier
Jun 24, 2007
Before I ask this I want to preface it by stating that I most likely fall into the catagory of knowing just enough to be dangerous. So be gentle.

Okay. I've been checking out my iTransport. There are a few things left undone inside which got me thinking about fiddling with it.
The iPod feeds this thing via it's own pins 25 and 27 which, as we know, are the USB +/- on the iPod. This translates to pins 3 and 4 inside the iTransport. From here each leg first goes through a 27ohm resistor and then accesses the bottom square chip on the right where the yellow circle indicates in the picture. Both legs are also attached to the ground plane via 15k resistors prior to this.
Anyway, they exit the processing on the right where the purple cirlcle is indicated and then travel over to the TI PCM270X chip at the top of the picture as indicated by the small green circle. Here they access the PCM270X via pins 8 and 9 where they are converted to SPDIF and exit via pin 5 with a nifty difty little digital signal.

Okay, thats how the Wadia works.
What has got me curious is the spots at the bottom right indicated with the large red dot and blue dot.
Both of these are spots for USB connectors. The one with the red dot feeds directly from pins 3 and 4 inside the transport to their respective USB +/- without anything inbetween. The one with the blue dot leads directly over to the PCM270X chip where it passes through a pair of resistors before connecting to pins 8 and 9.
Logically, these spots were for future USB output (red) as well as USB input (blue).
Okay, so I hook up an external USB DAC to the output (red). I get my +5V where it supposed to be plus some sort of signal on the line. I know this only because I tested for a frequency with my digital multimeter. But I get no actual communication with the DAC. I know the iPod is outputting info because I am still getting a digital signal out of the PCM270X chip. But nothing out of the USB side.

So I take my computer and hook it up to the USB input (blue) which, as I said, directly feeds the digital conversion chip. The USB +5V from the computer powers up the chip even with the Wadia unplugged and my DAC locks to the chip but nada. No music.

Anyone know why these arent working? I know its probably something simple about USB protocol that I am unaware of. So I ask you guys.................

May 30, 2009 at 8:53 PM Post #2 of 3
The connection to the PCM270X is likely a USB input. If jumpered correctly, it can probably be used for USB to S/PDIF converter. Wont be great, but will work.

The other one, I dont know. To get USB output and audio streaming compatible is a big deal. Only computers have this to my knowledgge.

Steve N.
May 31, 2009 at 4:22 AM Post #3 of 3

Originally Posted by audioengr /img/forum/go_quote.gif
The connection to the PCM270X is likely a USB input. If jumpered correctly, it can probably be used for USB to S/PDIF converter.

Yes, according to the datasheet they are connected to the USB input of the PCM270X.
I'm not sure what it would take as far as jumpers go.
That was pretty much my question though.
Appearently there is more involved than just connecting "USB output" to a "USB input".
I tried that and it doesnt work.

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