The S/PDIF output circuit is actually quite good, much better than what is in the SB3. The biggest bang for the buck there is to get rid of the RCA jack and put in a true 75ohm BNC. Thats going to be the biggest improvement. Not so easy to do, you have to keep the impedances to the board etc correct.
Now as for opening it up: It comes in two pieces, front and back plastic case, the front has the display attached and the back has the board attached. In between is the umbilical for the display, this is two flexible PC (FPC) assemblies, one one small (for power) and one wider (for signals). These are permanently attached to the display and go into connectors on the board attached to the back. There is very little slack on these FPCs, this is the main problem with taking it apart and getting it back together. You have two approaches here: take the cables out of the connectors and separate the two pieces OR leave the umbilical in place unscrew the board from the back case. Taking the FPCs out of their connectors is quite easy, but it is a royal pain getting them back in correctly without damaging anything when putting it back together. In the other approach you keep the umbilical in place and "clamshell" the two halves, opening up a small space between them and getting a small screwdriver in to take out the screws holding the board to the back case. You do this for all four sides. All the screws are around the periphery of the board so this can be done. Be careful not to exert too much tension on the FPCs, you don't want to rip anything or cause them to come out of the connectors (the connectors are latching, the FPCs are held quite well in their grasp). Its hard to say which is the best approach, I've done it both ways and its about equal amount of swearing either way. Even if you go for the disconnect the FPCs route you still have to unscrew the board from the back, all the interesting stuff is on the side of the board between the board and back. Currently you have taken off the silver "foot" and the two screws that hold the front and back together. At this point the only thing holding them together is friction, there are no more fasteners or latches or any such. You just have to pull them apart. A thin blade such as a putty knife might be helpful in trying to pry them apart. Once they DO come apart make sure you don't put much tension on the FPC. You DON'T want to grab the front and back and put huge force on them, and then have them "explosively" separate and rip the FPCs out. Gentle persuasion works better. In addition to the above there are two twisted pair going between the front assembly and the board (the microphone and the speaker). These have connectors and are easy to remove, just make sure you draw a picture noting the orientation of the colored wires so you can put it back together the right way. After you have the board unscrewed from the back you have to get the board out of the back. This isn't easy. The board fits under a "lip" molded into the case, the fit is VERY tight. I found the best way to get it out is to hold the back in your fingers and use your thumbs to apply pressure to the connectors on the back, pushing them back in, this will force the board out of the back case. Now on to what to do once you HAVE it apart. The first thing is to bypass the caps on the analog outs, they are not needed, getting rid of them makes a big improvement in sound. Next I would work on the power supplies. There are two switching DC-DC converters inside, they supply the 1.2 and 1.4 volts for the processor. One of these also supplies 10V to a 5V regulator which drives the DAC chip. So even though the DAC chip is 5V it is NOT run off the main 5V supply, they did try and isolate it from what is going on inside the box. I would build an external supply that had two 5V supplies, one for the main input, and one very good one for the DAC chip. In addition it will provide the 1.2 and 1.4V for the CPU. You can't just replace the DC-DC converters with linear regs in the box, they would dissipate too much heat. There are no ventilation holes and its a plastic case, the heat from these regs would fry the insides. Next would be the oscillators. They are just regular logic gate and crystals, same as used in the SB3. The power rails in the Touch are cleaner so you DO get lower jitter, but its possible to get even better. I would build a tiny board with two low jitter SMD oscillators and a really low noise regulator and install that over the main board (there is a LITTLE room between the board and case) with very short pigtails going down to the main board to replace the crystals. Thats what I would do for first level mods. There is a lot of work that could be done on the headphone amp, but anybody REALLY into headphone listening is probably already using an external headphone amp connected to the analog outs or to an external DAC. That should keep you busy for awhile! John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=78244 _______________________________________________ Touch mailing list Touch@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/touch
