USB dac issues AD712 buffer/LPF

RamAUDIO · 5th January 2010, 08:23 AM

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

The power supply is as shown :

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...

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).

Allen Wright · 5th January 2010, 10:24 AM

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

RamAUDIO · 5th January 2010, 12:18 PM

here is the LPF for one side:Allen Can you comment

RamAUDIO · 6th January 2010, 12:19 PM

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?

5th January 2010, 08:23 AM	#1
RamAUDIO diyAudio Member Join Date: Jan 2010	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 : 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... 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).

6th January 2010, 12:19 PM	#4
RamAUDIO 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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5th January 2010, 10:24 AM	#2
Allen Wright R.I.P. 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

5th January 2010, 12:18 PM	#3
RamAUDIO diyAudio Member Join Date: Jan 2010	here is the LPF for one side:Allen Can you comment