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COD DAC Project Questions (Module placement, fanout, etc.)
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Joined: 3/2/2008(UTC)
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I recently ordered a couple of the COD pcb, an IVY pcb and an assembled spdif receiver. I am planning on stacking the two cod modules one atop the other, and placing the IVY very close to the stack, but what I was wondering was how far apart can I place the spdif receiver from the cod modules before this creates potential issues with the quality of the I2S signals to the dac chip?
One other question relates to fan out on the spdif receiver, how many modules can I drive before I need to consider buffering the I2S?
Eventual plans are for a pmd100 based digital filter board, and metronome asrc which would be switch selectable from the front panel.
Anyone ever used ISO150 with these modules?
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Hi Kevin,
Good questions.
Try to keep the I2S run shorter than about 8" and you should be just fine. Just be sure not to route analog or power supply wires close to the I2S lines, if you need to cross them do so at 90 degrees.
You can very easily drive at least 2 DACs from a single receiver (I have not tried more). More would probably be worth at least considering a buffer of some sort.
I have not used the ISO150 yet, but I have looked at it. It would be fun to try it. If you do please let me know how you liked it.
Cheers!
Russ
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Rank: Member
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Hi Russ,
Thanks for the quick response, I should be able to keep the I2S well under 8.0" I am planning to build some ISO150 based isolators at some point to go between the dac boards and the receiver. I'll let you know what I think once I do it.
Kevin
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Rank: Member
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Joined: 3/2/2008(UTC)
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One other thing that would be really helpful would be bills of material for the pcbs, it would make ordering all of the bits and pieces a lot easier. I'd like to get a one up on the arrival of my blank pcbs.
Kevin
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Rank: Member
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I've got all of the modules built up, still wrestling with what power supplies I am going to use. I have purchased AN TEK toroids AN-0209 (2 x 9V/20VA) and AN-0220 (2 x 18V/20VA) for whatever psus I decide to use. Right now I'll probably go with a pair of LM-317 for the digital supplies, and something very loosely based on the Jung Super Regulator designs with pre-regulators. For now I need to find all of my old bench supplies to test the modules. LOL Edited by user Thursday, March 13, 2008 9:40:11 AM(UTC)
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I didn't have exactly the same setup, but when I attached a third opus board to my dac stack I had noise issues instantly from power up. I didn't do much more testing aside from making sure the spdif and third opus board were good (they were), so it leads me to believe that two boards is about as much as it can take without a buffer.
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I have had four DAC modules attached to my metronome without issue. Typically we find such noise problems to be related I2S wiring and PS wiring issues.
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Rank: Advanced Member
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Brian Donegan wrote:I have had four DAC modules attached to my metronome without issue. Typically we find such noise problems to be related I2S wiring and PS wiring issues. I guess that was probably the issue then, I was putting them into a pretty small case, so the wires were somewhat close to each other.
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Rank: Member
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Finally decided on power supply design, ended up designing and building my own. The low voltage digital supplies are based on the Rohm BA17807 7V regulators in TO-220 FP packages.
The +/-15V supplies are somewhat similar to the Jung super regulator topology, but an op-amp (LME49710) op-amp configured as a high speed integrator. Pre-regulators are Rohm 5V LDO types with their ground pin floating on the outputs. Reference is a TL-431 and is bootstrapped to the pre-regulator to assure the regulator starts under load.
I am using two COD boards I built up with PCM1798 dacs in mono into an IVY - the IVY balanced outputs drive a pair of UTC A-21 line transformers and convert the output to unbalanced.
Sounds really good.. More details to follow.
All I can say is keep I2S leads very short!!
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Twisted Pear Audio Support
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Product Support
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COD DAC Module
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COD DAC Project Questions (Module placement, fanout, etc.)
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