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Originally Posted by wackyterbacky /img/forum/go_quote.gif Wow, I had not checked this thread for a while since starting it. I'm glad to see there is still some interest. First off, I am driving a P-3A with the Juli@ I2S signals directly from the header on the digital board (picture). I am now driving 4 separate RG-174/U cables ( 50 ohm small flexible coax ) with the 4 signals. The shields are all tied together to ground on the Juli@ and are tied to the metal housing of the mini-DIN connector (which looks awful but works fine ). These cables are 15 feet (yes feet ) long to span from my desktop across my office to the P-3A. I can lock on with the P-3A up to 96kHz ( upsampling with foobar2000 and SRC ). The I2S signals have a lot of ringing on them. They are 3.3V signals but there is about 1.0V of ringing on the ground and VDD side. The MCLK signal looks more like a sine wave. But the P-3A is not smart enough to know that it should not work. I think the transceiver chip (DS26C32AT according to an email from Peter Madnick) is the secret. It is a differential receiver with sensitivity of 200mV. I have tried the Juli@ with an Audio Alchemy DTI Pro32 - it does not work. The DTI is looking for TTL input levels, and I think these signals have too much noise. I swapped out the P-3A opamps for LME49710 that I got as samples from Nat Semi. These are the single versions of the LM4562 quads that people were raving about. The sound is fantastic. The system consists of a modified Heathkit AA-151 and Klipsch Tangent 500 speakers with rebuilt crossovers and titanium diaphragms. I have musicians as neighbors who are amazed by this budget system. I am not proud of this "design" as very little design went into it, it was just a kluge to see if it would work, and it did. I would like to build a board with perhaps a 74LS244 quad driver or discrete transistor buffers, and to add some additional supply voltage filter caps. Question for audioengr - Any advice on what type of driver circuit to use? |
Originally Posted by nopietns /img/forum/go_quote.gif wackyterbacky, thanks for the pics. So the sound is just fantastic or is that a comparison to the SPDIF connection? audioengr, to connect the M192 to Juli@ Can I just connect the 4 different grounds to one of the VSS on the Juli@? |
Originally Posted by wackyterbacky /img/forum/go_quote.gif If I stayed with the Juli@ unbuffered outputs driving a cable, is there any advantage to changing cables to a CAT 6 or CAT 7 shielded twisted pairs? Would that be a less reactive load? |
Originally Posted by nopietns /img/forum/go_quote.gif Huh, when I emailed the North star design support on the layout of the RJ-45, the answer was: On the RJ45 connector there are 8 connection used in this way: 4 for the signals and 4 for digital ground. To connect the card to the DAC you need to have 4 signals SDATA Serial Data SCK Serial Clock LRCK Left/Right clock MCLK Master Clock Are You sure the other 4 pins are not just plain ground? |
Originally Posted by wackyterbacky /img/forum/go_quote.gif Steve Nugent gave some helpful tips which I finally had time to implement. I removed the I2S input resistors from the P-3A board. I have little experience with SMT components, but two soldering irons make it easy. The picture shows the metal shrouded PCB connector with the 4 sets of pads behind it. The resistors were in between those pads. I put a 10 ohm resistor in series with each coax cable at the connector on the Juli@. I changed the ground point for the shields to the screw hole just adjacent to the connector. The screw hole is surrounded by feedthrough holes which connect to the ground plane. I flowed a little solder into each hole. I soldered a small spade connector on my ground wire and screwed the spade tightly against the feedthrough holes. This may make no sense unless you have a Juli@. Also, I added a 220uF electrolytic bypassed by 0.1uF to the 3.3V VDD. I had to repair the Mini-Din connector so I reinforced it with several chunks of heavy shrink tube. The waveforms on the P-3A are much cleaner than before. There is still some ringing but it is attenuated from the prior set up. I am convinced that this helped the sound. I am noticing more separation between instruments and vocalists. I like Norah Jones "New York City" and use the title track to compare different tweaks. There is a harmony during the chorus, and I now hear the voices coming from different focal points. Perhaps there is less jitter. Or perhaps I am just imagining Norah Jones and her long lost twin sisiter in my lonely listening room? |