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

[Russ White]

Originally posted by glt
Russ,

Thanks for your listening impressions. I did order the opus upgrade thinking that with the '741, Wolfson is realizing all of their long experience in developing DACs. May I ask what filter did you use and what's the sampling rate (I'm assuming that you are using the Metronome)... thanks

Right now I am just running the DAC in a little test rig box I threw together (all from scrap). It's running in hardware mode (right now, not for long), so my filter options are limited to low,medium,high sample rates.

Later today I will be throwing in a controller with a VFD display to handle volume control and setup. The input will be IR(RC5) and rotary encoder.

I am using the Metronome at 96khz. So I have the filter set to medium sample rate.

I am also find that I really like the anti clipping filter!!! It makes some poorly recorded CDs (way too hot) sound much better. And it does not seem to negatively impact the good ones. Basically it just pads to the digital signal down 2db prior to the analog stage, at the digital filter.

The opus is under the IVY upside down so that all the I2S are short and straight. This is an excellent way to layout the modules.

Also note I am only using one PS. this was done for expediency more than anything, but I have proven it works very well.

Here is a picture, don't laugh too hard.

Cheers!
Russ

[glt]

Hi Russ,

I've seen that wooden box configuration many times before (maybe a different wooden box :-)). I thought the chip would support several filter modes at a specific sampling rate. From the data sheet p42, with pin 4 you can select the following filter responses: Pin4 (FSEL/DINR): Digital Filter Selection: for 32/44.1/48KHz: 0=Response1, 1=Response 4, Z=Response 5; for 88.2/96,176.4/192KHz: 0=Response3, 1=Response 1, Z=Response 2.

Thanks

[Russ White]

Hi glt,

Yes you very well may have seen this box before I have used it for other prototype work recently.

Ah yes, it is true you can choose between 3 filter modes. I just have not done so yet. I have been more busy getting the controller up and working. I don't plan on using hardware mode for much longer.

For now I have that switch open so I am using filter response 2.

I will probably play with it a bit later.

Cheers!
Russ

[glt]

Hi Russ,

Good to hear. I hope the OPUS "uber controller" will be available first (before the Buffalo uber controller :-)). VFDs are kind of expensive. I've purchased 2x16 OLEDs from ebay which are reasonably priced. I suppose you will support 2byX character displays. Thanks.

[Carl_Huff]

"VFDs are kind of expensive ..."

Yea, but nothing else looks as good and you only need to buy the one for your project.

[BrianDonegan]

The display we have selected is not that expensive (<$40 IIRC). The key to it is that it has an I2C interface rather than the quasi-standard serial/parallel interface. If you find another I2C based display, we can probably confirm that it will work.

And it does look really really good.

[fmak]

Originally posted by Russ White
OK I want to clear up a misconception.


The WM8741 is really well done. It hits all the right buttons. I have been listening to it for a while now, and I will not give it up. I have been A/B testing it with the buffalo and while they do both sound distinct, I would not say either has an advantage. Except in one area. The Opus is far less finicky.

Yes, I'd like to try the WM8741. Hoever, one issue I have is that the WM8804 front end won't handle 176.4k in hardware mode.

Have you now solved this? I listen to hirez a lot; upsampled or native.

Fred

[BrianDonegan]

Yes, I'd like to try the WM8741. Hoever, one issue I have is that the WM8804 front end won't handle 176.4k in hardware mode.

Have you now solved this? I listen to hirez a lot; upsampled or native.

We have a new receiver/MUX coming out based on the CS8416, which will natively support 176.4K without any special treatment. It will also sport 4 SP/DIF inputs (1 optionally balanced/AES). It will output S/PDIF and I2S. All S/PDIF ports are transformer coupled. Source selection is done via a four pin header, allowing either uC control or a simple switch.

[khundude]

Listening impressions vs the Buffalo please. Have you tried DSD with the Opus yet?

[Russ White]

Nearly done implementing the controller.

Again ignore the ugly box it just there to get the thing working.

I love the VFD. The picture actually does not do it justice. Blame the photographer.

The controller is just a modified old Joshua Tree controller.

All the hardware is setup now, I just need to write some firmware tomorrow.

Cheers!
Russ