If you are going to perform surgery on the Touch you are much better off getting rid of or bypassing the output caps all together. The DAC chip already has a circuit which provides a signal that has no DC bias, there is no need for a cap on the output. I really have no idea why there is one in the first place. The only thing I can think of is that the engineer that added the caps thought the DAC had a DC bias on its output since it just uses a single 5V supply. (BTW the DAC chip has a switching DC-DC converter inside to make the negative voltage)
Because the cap has its + terminal connected to the DAC chip you want to apply a negative voltage to the other side to properly bias it. 6V should be about right. An easy way to do this is a 6V alkaline lantern battery. Connect the + lead of the battery to GND of the interconnect, then run a resistor from the - terminal to each signal wire. (that's two resistors, one for each channel, the other ends connected to the negative 6V) IF the amp has a film cap (or bipolar electrolytic) on its input, that's all you need. IF the AMP is DC coupled you will need to add a film cap to each signal channel. If you don't know what is on the input of the amp the safest bet is to use the caps as well as the resistors, but if you know the amp already has one, there is no reason to add another. You can play around with the resistor value. I'm going to say somewhere between 10K and 50K. The higher the value the less current will flow through the battery, which means a longer battery life. Higher values have a little more noise so there is a tradeoff here. You can use inexpensive resistors or expensive resistors, that's up to you. If you need the cap, that starts getting a bit more complicated. The bottom end of the range is probably .5uf but you could also go up to several uf depending on the amp input impedance etc. There is also a huge range in price for different caps, from 20 cents to several hundred dollars. Again I am not going to make ANY recommendation on that. Just remember that there is already a cheap electrolytic coupling cap in the chain. I was specifically looking at an article that was analyzing what happens with an unbiased polarized electrolytic while varying the input voltage from .1V RMS to 2V RMS. I don't remember exactly where it is, I can't find it right now. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=93875 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
