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A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)
A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)
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Old 17th August 2014, 03:14 PM   #2481
nige2000 is offline nige2000  Ireland
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Originally Posted by Almeg69 View Post
I have been altering the value of the output filter capacitors, What is the largest value allowed ? The recommended value of 5 - 10 nf per stack, can this be increased to 20 or 30nf per stack ?

Thanks, Alex.
Been doing lots of reading on that hf cap
Haven't done any experiments yet
But from what I read it really is subject to testing
But would have thought up to 30 pf would be in range for testing
Many values will need to be tested as most of them will have a neg to no effect for sq due to a small window
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Old 17th August 2014, 04:47 PM   #2482
stijn001 is offline stijn001  Netherlands
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Alex, 4.7-10nf per "board"..., i.e. a stack implies multiple boards. In my case I have four boards and used 22nf, which is pretty conservative.
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Old 17th August 2014, 04:58 PM   #2483
Almeg69 is offline Almeg69  United Kingdom
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I am using Vishay 1822 100v 100nf with 11 dac boards.

I want to try extra capacitance as increasing the value helps with resolution, ambience and purer treble. I do not want to damage anything by going too high a value ....
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Old 17th August 2014, 05:18 PM   #2484
stijn001 is offline stijn001  Netherlands
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You effectively creating a low pass filter, the only thing you’ll eventually damage is the high frequencies when you get into the audible range..
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Old 17th August 2014, 05:29 PM   #2485
Almeg69 is offline Almeg69  United Kingdom
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Originally Posted by stijn001 View Post
You effectively creating a low pass filter, the only thing you’ll eventually damage is the high frequencies when you get into the audible range..
Good news, I think the roll off is 100khz for 5nf and 50khz for 10nf so if I go too far I will limit the HF response only but not damage the dac boards :-)
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Old 17th August 2014, 06:02 PM   #2486
dddac is offline dddac  Germany
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The larger they get, the lower the HF cut off.... It is a simple 6dB/Octave low pas filter with the Rload.... so easy to calculate.... my recommendation causes a 3dB Point between 50 and 100kHz... It is very arbitrary and just pick what you like best
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Old 17th August 2014, 06:17 PM   #2487
Almeg69 is offline Almeg69  United Kingdom
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Originally Posted by dddac View Post
The larger they get, the lower the HF cut off.... It is a simple 6dB/Octave low pas filter with the Rload.... so easy to calculate.... my recommendation causes a 3dB Point between 50 and 100kHz... It is very arbitrary and just pick what you like best
Thanks Doede,

I will keep it below 600 nf. Cut off 22khz ....
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Old 18th August 2014, 12:25 AM   #2488
nige2000 is offline nige2000  Ireland
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This might be of interest for the pos neg cap
http://www.diyaudio.com/forums/loung...technique.html
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Old 18th August 2014, 05:31 AM   #2489
dddac is offline dddac  Germany
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Hi Nige2000,

Can you elaborate a bit more what you are trying to do with the split resistors on the Outputs? The Rload value was determined to be 133 Ohm, you seem to be far off with that which will increase THD (when larger) or reduce the Output voltage at 0dBFS when lower

What are the improvements you indicated? Did you measure anything you can share?

Thanks!
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Old 18th August 2014, 05:31 AM   #2490
dddac is offline dddac  Germany
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Originally Posted by Almeg69 View Post
Thanks Doede,

I will keep it below 600 nf. Cut off 22khz ....
not per Deck of course
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