USB dac issues AD712 buffer/LPF - diyAudio
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Old 5th January 2010, 08:23 AM   #1
diyAudio Member
Join Date: Jan 2010
Default USB dac issues AD712 buffer/LPF

Hi all ,
I am working on a output LPF of a PCM 2702.
Using AD712 as buffer.

The power supply is as shown :
Click the image to open in full size.

But there is hum noise from the buffer stage ,i can hear clearly although it is doing the LPF work and a buffered sound coming with the noise.
The connection is shown below...
Click the image to open in full size.

Help me with this one , could it be due to 2 different grounds?

i saw KECES dac schematic the are using a floating line from PCM2702.

Or , is it due to the cheap transformer i am using (for testing,later will add a toroidal).
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Old 5th January 2010, 10:24 AM   #2
Join Date: Dec 2001
Location: Schaffhausen Switzerland
More likely the opamp/buffer is oscillating at some high frequency, which always sounds like hum. Can you post a schematic for it?

Regards, Allen
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Old 5th January 2010, 12:18 PM   #3
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Join Date: Jan 2010
here is the LPF for one side:Allen Can you commentClick the image to open in full size.Click the image to open in full size.
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Old 6th January 2010, 12:19 PM   #4
diyAudio Member
Join Date: Jan 2010
yesterday i have checked Power supply with dropper of 4.7k in series from +15v ,

tried to drive a fiio e3 ,there is some problem,it cant drive!
normally supply shows voltage checked with LED.

is 9-0-9v, 500 miliamp secondary supply transformer too less?
Lets find the truth..inside!
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