Mr White's "Opus", designing a simple balanced DAC

[Russ White]

Schematic

[Russ White]

The DAC will need two power supply voltages.

One 5V and one 3.3V. I am working on a PCB for that too. But just about any power supply at those voltages will be fine.

[pinkmouse]

Your silkscreen notations for the jumper settings will end up as indecipherable blobs, they are way too small and too fine.

Does that qualify me as a beta tester?

[Russ White]

Originally posted by pinkmouse
Your silkscreen notations for the jumper settings will end up as indecipherable blobs, they are way too small and too fine.

Does that qualify me as a beta tester?

Good point.

The PCB Fab says they are within spec, but we will leave the documentation for jumper settings here and on our site so if people get blobs we won't be out of luck.

If you want in on the test then your in.

Cheers!
Russ

[pinkmouse]

Ta!

I'm actually supposed to be working at the moment, so I didn't have more than a quick glance. I'll have a better look when I get home.

[BrianDonegan]

I'm actually supposed to be working at the moment

Well, that's no excuse... so are we!!

[pinkmouse]

It's ok, I just printed everything out on the works printer for later perusal!

Oh, and anther quick point, can you move the component designators out from under the footprints? It makes fault finding so much easier. Not a great problem with the number of components on this board, but a good habit to get into.

[jean-paul]

I know I am late The input stage could use some refinement IMHO. I would load the primary side after the cap with 150 Ohm and I would load the secondary side with 150 Ohm too. Definitely keep the input cap, it protects the pulse transformer from DC. A 10 kOhm from the SPDIF-2 to GND wouldn't hurt, it will keep the primary side at low potential when switching cables with the DAC powered on. I used this circuit a lot ( also for inspiration ) but please note that it uses a 1:4 transformer:

http://members.brabant.chello.nl/~m....ml/dig_r2a.pdf

*It is adviseable to use a 75 Ohm BNC chassis connector directly on the PCB for optimal results as standard PCB connectors really aren't suitable 75 Ohm devices. Please see the DAC Peter Daniel designed to see what I mean. The circuit with SN75179 also works well but IMO the guideline with semiconductors is that "less is more"....

When I was searching for the right thread I stumbled upon this one that I did not try ( to me both the caps and the 10 Ohm resistors at the secondary side seem useless but I may be wrong ) but you'll get the idea:

[jean-paul]

BTW did I mention I'd like to be beta tester as well ? If you appreciate further comment please let me know. I have some other suggestions.

[Russ White]

Originally posted by jean-paul
BTW did I mention I'd like to be beta tester as well ? If you appreciate further comment please let me know. I have some other suggestions.

Your in,

Let, me see what I can do about your suggestions.

Keep in mind I did not anticipate the PCB being directly mounted to a chassis, so I have not provided for PCB mounted BNC or RCA. Instead I was going to allow for chassis mounted connectors which would be wired to the PCB via the terminals. This may not be optimal, but it is very practical...

Cheers!
Russ