USB dac issues AD712 buffer/LPF

[RamAUDIO]

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

The power supply is as shown :

An externally hosted image should be here but it was not working when we last tested it.

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...

An externally hosted image should be here but it was not working when we last tested it.

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]

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]

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

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[RamAUDIO]

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?