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Old 19th January 2010, 02:02 PM   #161
paulb is offline paulb  Canada
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Quote:
Originally Posted by TICUL38 View Post
Any progress with the a USB interface?...
What approach have you taken? Your input would be well appreciated.
Thank you,
Louis
I've drawn a schematic and have nearly finished laying out a PCB for a USB to S/PDIF converter board that includes a relay to switch between USB and S/PDIF inputs. I am holding off finishing it while I get my ezdac board built up and tested. I am still considering whether to change this to I2S output instead.
I'm using a PCM2704 for the conversion. The converter board will have an analog audio output as well.
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Old 19th January 2010, 05:54 PM   #162
TICUL38 is offline TICUL38  Canada
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Thumbs up USB interface

Quote:
Originally Posted by paulb View Post
I am still considering whether to change this to I2S output instead.
I'm using a PCM2704 for the conversion. The converter board will have an analog audio output as well.
Glad to use your continuing input on the USB interface... this option represents for me the principal reason for adopting the ezDAC... music stored on the iMAC.
PC music storage is the way to go for "whole house music" programming.

Your response above presents interesting info. What have been some of your pre-decision thoughts. My current thoughts are:

1. Should I break the power feed to the CS8416 when switching the USB/I2S feed to the PCM1794 module? this could be simpler than preventing USB/I2S back-feed to the CS.
2. Breaking into the PCM1794' I2S lines could be the tie breaker; I am getting into my "Monk's Zen" zone needed to tackle the SMD work, and feel adding to the task with cutting into the circuit may be ill-advised.
So, the USB/SPdif conversion may be the easier approach. I still question if added signal deterioration would occur with that extra ensuing SPdif/I2S step?
3. I would want a separate audio out for local headphone listening, but maintain a good RCA out for main system out. In your case, will the audio out plans integrated to the USB/SPdif board replace/add to the ezDAC audio out section?

Thanks for your inputs,
Louis
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Old 19th January 2010, 07:41 PM   #163
paulb is offline paulb  Canada
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I've gone back and forth on this (I2S vs SPDIF) a few times now. My last post here said I was switching to I2S, but I haven't done anything further on the PCB design yet.
If I2S, I would run it through the ASRC AD1896, so on the ezdac I would depopulate R19, 20, and 21 and attach flywires at those points.
Yes, USB/SPDIF would be simpler in regards to having to make mods on the ezdac.
The current design brings out the audio output to make the board more useful. The local PCB shop I would use (Alberta Printed Circuits) provides 2 boards minimum, so I was thinking I may use the second board in a portable application. The direct audio output would also be useful for testing or troubleshooting without an external DAC.
The current PCB size is 2.5" x 2.8" and includes a dual opamp for the audio output and a +5 to -5 voltage converter to give me a +/-5V supply. APC will charge me $45 for 2 of these boards, no soldermask or silkscreen. If I change it to I2S it would probably be about the same size.

Last edited by paulb; 19th January 2010 at 07:43 PM.
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Old 20th January 2010, 09:00 PM   #164
PJN is offline PJN  United States
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Hi All,

I'm just starting my build and will do the PSU first, after thats squared away I'll attempt the DAC. What transformer rating would you recommend, a 10 VA 15-0-15 and a 25 VA 15-0-15 are about the same price at Antek.

Thanks,

PJN
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Old 21st January 2010, 09:40 PM   #165
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ok, I looked at Read Research's Mains Op-amp PSU which is basically the same thing as the ezdual. They're using 10ohm 2W resistors for his R1/R2.

I've got 3x 33ohm 1/4w (in parallel) resistors that are frying. Not sure why the BOM specified 1/4w but I'll replace them with power resistors that can handle a few watts.

Maybe those are plenty enough for handling a walwart?
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Old 21st January 2010, 10:52 PM   #166
6h5c is offline 6h5c  Netherlands
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They shouldn't be frying, a single 33 ohm resistor can handle nearly 90mA before it dissipates 0.25W. That means a total current draw of 270mA max. for the three in parallel, and they are not even frying then. The fact that they are burning up means that there's something wrong, too much current is drawn somewhere, and a bigger resistor won't change that i'm afraid.

The ezDual is doing this on it's own, with no load? Also, the negative side seems o.k., isn't it? Post some pictures of the board if you can, maybe we can see what the problem is. See if something else gets hot, that current has to go somewhere. Are all caps' polarity in the right direction?

Regards,

Ray
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Old 21st January 2010, 10:54 PM   #167
6h5c is offline 6h5c  Netherlands
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PJN,

10VA is more than enough, plenty.

Ray
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Old 22nd January 2010, 02:12 PM   #168
PJN is offline PJN  United States
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Thanks Ray, I sure Ill have more dumb questions to follow.

Paul
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Old 22nd January 2010, 07:18 PM   #169
paulb is offline paulb  Canada
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Quote:
Originally Posted by 6h5c View Post
They shouldn't be frying, a single 33 ohm resistor can handle nearly 90mA before it dissipates 0.25W.
And it can handle a lot more than that before it actually fries. I think you have a direct short circuit somewhere. Try using an ohmmeter without any power applied.
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Old 24th January 2010, 12:10 AM   #170
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I found a short in the output cap. I replaced it and replaced the discolored resistors too.

My Ezdual is working now. I'm going to hook it up to my ezdac tomorrow.
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