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Old 5th June 2006, 06:25 PM   #1
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Default Only noise from TDA1541A based Sphinx Project 3 DAC

Hi DIY-people,
after following some threads, primarily about the CDM swingarm transports it's now time to post my first message because i have a problem with a Sphinx Project 3 D/A converter.

The DAC is based on a silver crown TDA1541A. I used the thing for quite some time and it did it's job in a wonderful way. A few weeks ago i needed to move some stuff and had to uncouple all my gear. I shut down my Teac transport, the Sphinx Dac and all other stuff. After reconnecting everything in the same way as it was before the only thing coming from the Sphinx is a lot of noise. You can hear the music in the background but the noise is really terrible.

Does anybody have any tips to get me started with this?

Thanks in advice for your help,

Lucas Unger
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Old 5th June 2006, 08:32 PM   #2
Sandor is offline Sandor  Italy
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Check the connection of the cap at pins 16 and 17 of the TDA1541A chip.

Paul
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Old 5th June 2006, 08:35 PM   #3
Sandor is offline Sandor  Italy
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Also check that the TDA1541 has correct supply voltages:
+5V at pin 28, -5V at pin 26, -15V at pin 15.

Paul
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Old 5th June 2006, 09:27 PM   #4
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Dear Paul,
first of all, thanks for your help! I checked the connections tot the small cap over pins 16 and 17 and these are fine. I resoldered them just in case, but it doesn't make a difference.

The results of the measurements on the other pins seem fine. I used pin 5 as the ground for these measurements which according to the spec sheet is the analog ground.

Pin 28: +4,89v
Pin 26: -4,99v
Pin 15: -15,07v

Any other suggestions? Anybody?

Greatings,

Lucas
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Old 5th June 2006, 09:47 PM   #5
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Here is a picture of the internals of the thing. The chip in the blue rectangle is the TDA1541A, the cap in the red circle seems to need to be replaced. The top isn't flat as it should be.

Greetings,

Lucas
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File Type: jpg sphinx_pj3_overviewsmall.jpg (56.7 KB, 373 views)
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Old 6th June 2006, 12:19 AM   #6
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The cap which connects pins 16 and 17 seems to be damaged a little. Just to be sure, i would like to replace it. Does anybody have any suggestions on what type and capacity to use?

Greetings,

Lucas
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Old 6th June 2006, 06:31 PM   #7
Sandor is offline Sandor  Italy
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Substitute that cap at pins 16 & 17 first. It should be 470 pF. Then substitute the other cap that looks damaged.
Paul
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Old 6th June 2006, 06:34 PM   #8
Sandor is offline Sandor  Italy
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For the 470 pF capacitor, a ceramic or mica type should fit.
Paul
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Old 9th June 2006, 06:21 PM   #9
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A few days ago i replaced the cap which connects pins 16 and 17 on the TDA chip. This didn't help unfortunately. Luckily i just received a fresh Panasonic FC to replace the cap with the bulb on top and that dit the job! Thanks for your help.

I'm thinking about replacing al the caps with Panasonic FC's. Is this a good idea or should i stick with the old caps?

Greetings,

Lucas
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Old 10th June 2006, 12:10 AM   #10
Sandor is offline Sandor  Italy
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Substituting all aged electrolytic capacitors with fresh ones should be worthwhile.

Paul
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