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Old 12th August 2009, 05:27 AM   #21
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Kurt - thnx for the reply

o.k. i can cut down the frequenca range (down to 20 or 30kHz) using LPF but i would not like to have one opamp more.. it is enough that i have one in I/V conversion inside the chip...
heheheh
o.k.... do You think LPF on the output of the dac (before the tube stage) should be o.k.???
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Old 12th August 2009, 05:27 AM   #22
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(double posting - sorry guys)....
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Old 12th August 2009, 05:27 AM   #23
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(double posting - sorry guys)....could not delete the posts.. don't know why....
sorry again...
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Old 12th August 2009, 06:02 AM   #24
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schematic of the tube stage.....
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File Type: jpg dac_tube stage rev01.jpg (45.7 KB, 373 views)
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Old 12th August 2009, 06:11 AM   #25
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Quote:
Originally posted by sparkle
Kurt - thnx for the reply

o.k. i can cut down the frequenca range (down to 20 or 30kHz) using LPF but i would not like to have one opamp more.. it is enough that i have one in I/V conversion inside the chip...
heheheh
o.k.... do You think LPF on the output of the dac (before the tube stage) should be o.k.???
The DAC chip does not necessarely include an op-amp just bcause it is a U out DAC chip.
I think the WM8740 might feature a switched capacitor anti aliasing filter, which natviely makes it a U out chip. So you can find u out chips both with internal I/V conversion devices, and i.e CS4398 which is a u out chip without any I/V conversion.
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Old 12th August 2009, 07:55 AM   #26
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o.k. - but basically the tube stage schematic should work like posted ... right??
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Old 20th August 2009, 05:19 AM   #27
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??.....

i had a report from a friend of mine that tube stage might not work together with the dac... i asked the guy who tested the tube stage and he confirmed that the circuit together with the dac should work fine.... any further opinions...?
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Old 26th March 2012, 10:15 PM   #28
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Default WM8740 not need any LPF

Quote:
Originally Posted by Kurt von Kubik View Post
You definately need to post filter the output from the WM8740.
It is a very noisy DAC, and on top of that, it performs better with post filtering. Wolfson Micro recommends a lowish 20 KHz LPF for the device, to meet their standards.
Maybe, but I had to remove all the filtering capacitors from LPF at the output of WM8740 to get a proper sound.
OPA2132 works very very fine without LPF capacitors, creating unbalanced signal to discrete headphone amp which also hasn't got any LPF filter.
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Old 28th March 2012, 01:10 PM   #29
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Quote:
Originally Posted by Kurt von Kubik View Post
BBs chips, as they only need smoothing of the analog signal. Most other chips are musch more noisy, as it is the working frequency of the DAC or antialiasing filter, that has to be filtered.
Have you any experience with AKM dacs such AK4396? If you include Vout dacs to your statement above, of course.

Last edited by terranigma; 28th March 2012 at 01:13 PM.
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