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Removing 100Mhz signal from ES9018 analog outputs - Russ White
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diyaudionut  
#1 Posted : Tuesday, July 24, 2012 7:50:24 AM(UTC)
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Hi there, after completing my B3 and confirming that it worked properly, I noticed on my oscilloscope that there is a 100Mhz signal on the left and right DAC outputs (running in stereo mode). I'm guessing it's from the clock.

Is there any way to remove it that doesn't involve a resistor-cap-resistor setup in the signal path?

Thanks.
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avr300  
#2 Posted : Tuesday, July 24, 2012 4:30:07 PM(UTC)
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Pure curiosity - what magnitude are you seeing ?
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diyaudionut  
#3 Posted : Tuesday, July 24, 2012 9:07:38 PM(UTC)
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Originally Posted by: avr300 Go to Quoted Post
Pure curiosity - what magnitude are you seeing ?


It was a few days ago, but I think I remember it being about 200 millivolts

I'll remeasure it when I have time.
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Russ White  
#4 Posted : Wednesday, July 25, 2012 12:46:20 AM(UTC)
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That is normal, its a product of the way the DAC itself works, you will need to filter it.

I noticed the same thing when I first played with the ESS demo board. :)

Edited by user Wednesday, July 25, 2012 12:46:50 AM(UTC)  | Reason: Not specified
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Russ White  
#5 Posted : Wednesday, July 25, 2012 12:48:04 AM(UTC)
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BTW, that is why our outputs stages have filtering built in. ;)
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diyaudionut  
#6 Posted : Wednesday, July 25, 2012 5:46:27 PM(UTC)
diyaudionut

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Originally Posted by: Russ White Go to Quoted Post
That is normal, its a product of the way the DAC itself works, you will need to filter it.

I noticed the same thing when I first played with the ESS demo board. :)


Originally Posted by: Russ White Go to Quoted Post
BTW, that is why our outputs stages have filtering built in. ;)


Haha, yeah I looked at your output stage schematics and figured as much.

I'll be using transformers for I/V and Balanced-to-single-ended conversion, and then a 6SN7 for voltage gain. After that, I'll be using a Tripath TK2050 amp, which has an 80khz output filter.

Since this setup will have a 80khz filter at the end, can that be the only filter?
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Brian Donegan  
#7 Posted : Wednesday, July 25, 2012 6:08:52 PM(UTC)
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I think your transformers will double as a LP filter...
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Russ White  
#8 Posted : Thursday, July 26, 2012 12:57:52 AM(UTC)
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Yes, like Brian said, a transformer is itself a low pass filter. :) Also the noise signal almost completely common mode. Thus a good fully differential I/V will cancel it out. :) This why differential DACs are the norm these days.
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