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Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
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Old 11th September 2019, 07:41 PM   #281
MarcelvdG is offline MarcelvdG  Netherlands
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Don't forget to give the valve DAC main board a termination of about 750 ohm. Without it, the signal level gets quite large (though not large enough to blow up the buffer - unlike what I wrote originally) and the DAC's noise modulation gets much worse.

Assuming 15 nF for C28 and C50 on the main board, and assuming that the negative output pins of the main board are grounded and the positive pins are connected to 750 ohm to ground in parallel with one of these filter boards, the whole response will be roughly a cascade of a first-order filter at 16042 Hz and a second-order Butterworth filter at 118627 Hz - not very good, but good enough to test if it works. With C28 and C50 reduced to 2.2 nF, it gets close to third-order Bessel at 80 kHz or so, which may work well for the higher DSD rates.

Last edited by MarcelvdG; 11th September 2019 at 08:04 PM.
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Old 11th September 2019, 09:34 PM   #282
nautibuoy is offline nautibuoy  United Kingdom
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Thanks Marcel. I'm certain I have one of the buffer boards leftover from a previous project but I can't put my hands on it at the moment - may not be quite so cheap if I can't find it!
I will try and configure it with an approximation of the filter you have suggested.
On other matters, today the smd parts that were out of stock arrrived so it shouldn't be too long before the digital sections of the Valve DAC board get soldered up.

Ray
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Old 11th September 2019, 09:43 PM   #283
MarcelvdG is offline MarcelvdG  Netherlands
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Good luck with soldering the small parts!
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Old 12th September 2019, 06:03 AM   #284
nautibuoy is offline nautibuoy  United Kingdom
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Quote:
Originally Posted by MarcelvdG View Post
Good luck with soldering the small parts!
Thanks, however, I'm cheating as I have an experienced friend who is taking care of it for me.
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