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rossl 22nd December 2009 12:39 AM

HDX1000 Networked Media Tank as a FLAC decoder for a DAC
Here is my most recent project. The HDX1000 uses a Sigma Designs SMP8635 processor and connects to my wired ethernet router. It will play FLACs on it's own hard drive, and play FLACs from a hard drive on my PC that I have set up as a share behind my firewall. Of course it will also play videos. I still have an older Popcorn hour A100 that I have for video use.

I bought the HDX1000 online and it was shipped by FedEx from Texas.

rossl 22nd December 2009 12:40 AM

Now the HDX needs a hard drive and a minor modification.

I bought a SATA 128 gigabyte solid state flash hard drive from Micro Center in Columbus. I just checked again today and they are not on the web site any more, I don't know if you can still get the same model.

You can ignore the online reviews of this hard drive that complain the Kingston model is slow. It may be slow as a laptop hard drive, but it is plenty fast enough to be a media server. The faster 128gb SSD costs about 180 US dollars more. Don't pay the extra money.

My main requirements were that it have no moving parts, so it is silent and won't crash. It doesn't seem to heat up the unit, either.

I also had to scrounge through my parts bin for some small metric screws, the included ones didn't fit.

rossl 22nd December 2009 12:42 AM

I turned it on for some listening tests. The coaxial output sounds OK. The TOSLINK does sound harsh, as reported in some HDX1000 reviews on some other web sites.

rossl 22nd December 2009 12:43 AM

OK now we get down to business. Time to trace out the wires. This picture is the bottom corner of the board. The TOSLINK transmitter has plastic pins inserted near the label M9 and output goes to the left. TOSLINK has 3 soldered pins just to the right of that, and the bottom pin is the signal.

I determine the TOSLINK is a 5V part and there is no bypass cap within an inch of the transmitter, so I solder a ceramic cap directly to the 5V and GND pins. Later listening tests reveal the cap helped, but it's still not as good as the coax. I can see no marking on the TOSLINK. If I had a 5V Toshiba TOTX part, I would replace the transmitter and see if that helped. I don't have any on hand and Digikey is out of stock. Since I'm not going to use the optical, I'm not going to pursue improvments to it. If I had one of the units like the Popcorn A110 that only have optical out, I would definitely try to improve that.

ceramic capacitor is a 10uF 10V 1206 size X7R - digikey number 587-1333-1-ND

I trace the SPDIF signal from TOSLINK pin back to C158. That PCB then traces directly back to a place where it goes under the BGA CPU Sigma processor. I see no evidence of a series termination near the Sigma CPU. C158, unknown value, couples the signal to R105, 220R and then R106, 120R. The divided voltage SPDIF Signal goes from the left side of R106 to the large coax pin that is inbetween the labels L18 and L20. The coax ground is the pin above L20.

The divided voltage SPDIF is close to 75R impedance but not perfect. If R106 was a little lower in value it would be closer to 75R. 110R would be a good starting point to try, just guesstimating on the output impedance of the BGA driver. I'm going to leave it as-is for now. Later I may solder a 1K3 resistor across the coax pins to lower that impedance a few ohms.

rossl 22nd December 2009 12:44 AM

time to rip out that RCA coax

I coudn't unsolder the RCA coax ground because the pad is too well connected to the ground planes. I had to snip the RCA leads and snap off the jack that is piggy-back on the TOSLINK. No going back now, I destroyed the leads to the RCA.

I prepared a small piece of RG-187 75-ohm coax. The center conductor is very fragile. I stripped the insulation from the shield and soldered a wire around the shield and then attached it to coax ground, so that the force of bending the wire would transfer stress to the shield and not the center conductor. Then I soldered the center conductor and put on a glob of hot melt glue for good measure.

rossl 22nd December 2009 12:45 AM

The 75R BNC bulkhead connector is digikey number 501-1151-ND

it is isolated, the cable shield does not contact the case ground.

rossl 22nd December 2009 12:47 AM

The hole for the RCA jack is a little too small for the BNC. I buzz out the hole with the Dremel tool rotary sander. It cuts through that soft aluminum pretty fast. I enlarged the hole in the direction away from the optical and analog RCA jacks to give it a little extra room.

rossl 22nd December 2009 12:48 AM

Tighten down the nut on the inside with a 5/8 inch socket

rossl 22nd December 2009 12:49 AM

Put the circuit board back in and solder up the 75R transmission line. again, I soldered the shield first to absorb the stress of bending the coax. then the center was soldered in.

Before I re-installed the circuit board, I decided to solder an RC termination on the bottom side directly across where the RCA coax leads were formerly soldered. 5pF and 332 ohm in series across the SPDIF output signal. That will lower the impedance at high RF frequencies and reflections.

I may later try a RC termination on the bottom pin of the Toslink to ground to see if that improves anything. (on the 3V3 SPDIF out of the processor.)

rossl 22nd December 2009 12:51 AM

re-attach the hard drive and put the case back together

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