Here's a schematic I drew up for someone else doing exactly the same thing. Note I have not actually implemented exactly this schematic, in my DAC I'm using an FPGA to do the converting etc, but this SHOULD work, I've simulated this and it does the right thing.
Note the circuit for shfting the data from left justified to I2S is a little complicated, this is to make sure that you don't have a race condition at the input to the DAC. The basic concept is the data gets clocked by the bclk which shifts it over by one so its I2S spec. What this does is clock data by the reclocked bclk, then clock it again by a reclocked inverted bclk, then the output is reclocked again. The net result is that the delayed data has exactly the same timing in relation to the other signals as the original data has, thus almost guranteeing you won't have a timing problem. The voltage conversion is done with HC logic run off 3.3V, since its 5V tolerent it works fine with this. In this cicuit I've specified the Tent 5V shunt regulator to run everything except the inverters driving the SB3. You certainly can use another regulator, but using the Tent makes this really easy, its hard to design your own regulator that will work as well as this and cost significantly less. Note I'm using a 174 to do the actual reclocking, this flies in the face all the conventional wisdom, there IS a reason for that. It depends on how you are building this. If you are using a PC board with SMD parts the best way is the "pico gate" single gate chips, these work wonderfully well for this. If you are using through hole parts and hand soldering things up I personally think the 174 is a better compromise. Because the DIP chips are so much larger they have much more capacitance and inductance on their package pins, using 4 or five of these will degrade the clock driving all of them worse than the jitter inside the one chip. Using 74s with both flops used is also not bad, thats kind of a wash with the 174. I definately would not use DIP 74s and only one flop per package, that sounds worse than a 174. I hope this helps. I definately think its worth the effort to get this up and running. John S. +-------------------------------------------------------------------+ |Filename: SB12S.jpg | |Download: http://forums.slimdevices.com/attachment.php?attachmentid=2612| +-------------------------------------------------------------------+ -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=32761 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
