DAC interference problems

[MWP]

Greetings all....

Ive just built up my DAC (PCM2902, DIR1703, PCM1730) and placed it in a nice 1U rackmount, etc.

Ive now got a very annoying problem with it.
Ive hooked up a led on the front panel to show the status of the DIR1703's UNLOCK pin (lit when recieving SPDIF data).

Every time there is some small disturbance in this rooms power supply (a light turning on, heater thermo turning on/off, turning the soldering iron on/off, etc), the UNLOCK led will go out for about 1sec (DAC stops working) and then continue like normal.

ATM im using the PCM2902 (USB "soundcard" IC) which then feeds the SPDIF signal directly to the DIR1703.

Anyone come across this problem before?

Thanks.

[A 8]

You need a power supply that is more effective in suppressing noise on the mains.

If you share how you've designed the supply to your dac my guess is that you'll get a lot of advice.

[MWP]

Ok...

12-0-12 torodial.

For the digital supply: torodial -> half bridge to produce 17-0V smoothed with 4*2200uF electros -> 78M33 reg for 3.3V -> a few 0.1uF caps.

Cant be much more simple.

[A 8]

I've not had the problem myself but it seems to be enough.

Pehaps you should also consider the cdp to have the problem and/or the interface between them.


You could try a film or ceramic in paralell with the 4 2200uF and or an inductor in series between the rectifier and the smoothing caps.

[Bricolo]

you could try with an ac filter

it's easy to try, you just have a ready to use filter to plug between the ac inlet and the trafo
and it only costs a couple of $

[MWP]

Ok, thanks ill try those things.

Could grounding be a problem?

At the moment the chassis is earthed.
But the DACs ground is isolated from the mains-earth/chasis.

I thought this might help to reduce ground loops... but might it be causing this problem?

[Bricolo]

Is the ground totally isolated from the earth? (floating)
If so, you could try connecting signal ground and earth with a resistor (10R, 5W) or 2 parallel diodes (but one in each polarity)

[Guido Tent]

Originally posted by MWP
Greetings all....

Ive just built up my DAC (PCM2902, DIR1703, PCM1730) and placed it in a nice 1U rackmount, etc.

Ive now got a very annoying problem with it.
Ive hooked up a led on the front panel to show the status of the DIR1703's UNLOCK pin (lit when recieving SPDIF data).

Every time there is some small disturbance in this rooms power supply (a light turning on, heater thermo turning on/off, turning the soldering iron on/off, etc), the UNLOCK led will go out for about 1sec (DAC stops working) and then continue like normal.

ATM im using the PCM2902 (USB "soundcard" IC) which then feeds the SPDIF signal directly to the DIR1703.

Anyone come across this problem before?

Thanks.

Hi

Did you use an input transformer for SPDIF ? If so, the ground of the RCA / BNC input (SPDIF) should be galvanically connected to the chassis you build the DAC on

It is very likely to be a Common Mode problem inducing noise currents in the SPDIF interconect

regards

[MWP]

Originally posted by Guido Tent

Did you use an input transformer for SPDIF ? If so, the ground of the RCA / BNC input (SPDIF) should be galvanically connected to the chassis you build the DAC on

It is very likely to be a Common Mode problem inducing noise currents in the SPDIF interconect

Hmmm, ok thanks, makes sense.
Im not using a input transformer... i have no idea where to get one from

Ive switched over to optical SPDIF between the PC and the DAC now anyway, so the problem is gone.

But ill fix it anyway since it has the USB and Coax SPDIF ports on the back of the DAC that can still be used.