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

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#781
Russ White said:
We went ahead and ordered some ASRC boards they should be here any day. That board is called the "Metronome" If they work out alright then I will purchase stencils etc so we can offer them regularly. For now we may go ahead an offer a few to some people. But it is not easy to make these boards without a stencil, and we don't like to order stencils until a design is proven. 🙂
Click to expand...

Hi Russ, well I'm certainly interested in early testing when you get to that stage. I'm also interested in adding more DAC boards ..... how worthwhile do you think doing such would be? When will you get more boards in stock? Or maybe I should wait until your new designs are out ......?

Thanks,
Dan
 
#785
awpagan said:
Russ or Brian
What have you found as the best way of connecting via i2s

Any cable lenght limitations?
Use transmitter/receiver? ie
http://www.diyaudio.com/forums/showthread.php?s=&postid=1040349&highlight=#post1040349


allan
Click to expand...


There are a lot of variable factors at work here. Too much to explain here, but A couple notes:

1) Short lengths (<12") of normal hookup wire are just fine (nothing special required here. This is how I do my in case wiring. Though carefully twisting or braiding longer runs will probably help, with shorts runs you will probably just end up making the cable longer, so I just go straight if the length is short (< 5-6" or so).

2) For sample rates up to 192khz I have successfully used CAT5 up to 3' length. I just have not had any reason to try longer length. For long lengths > 3ft or so I would use SPDIF.

Also slower sample rates with slower clocks allow for more flexibility length wise then do fast ones.

If you want much more detail I would spend some time on google reading about bus termination, transmission lines, etc.

Cheers!
Russ
 
#786
Hi Russ,

Anything specific that you did to get 3' out of normal I2S? Did you have every data line twisted with a ground on the CAT5 cable?

I'm asking as I've had pretty bad luck with anything more than about 10". With my new DAC I'm thinking of using LVDS between the boards running I2S, but this gets expensive really quick when you are doing 5.1 . I would like to avoid this, as everything will still be in the same enclosure.

Any thoughts?

Thanks so much!!

Gert
 
#789
gbyleveldt said:
Hi Russ,

Anything specific that you did to get 3' out of normal I2S? Did you have every data line twisted with a ground on the CAT5 cable?

Any thoughts?

Thanks so much!!

Gert
Click to expand...

First what hardware where you using? Some ICs may be better at sending/receiving I2S than others.

Here is how I do CAT5 for I2S, but I am not sure its best. Each signal (MC,BC,WC,D) gets one side of a twisted pair, the other side of the pair is GND. The GNDs were all connected at one end (does not seem matter which) and a single GND line is connected to the other.

You could probably extend the length by using transmitter/receiver ICs.

The only reason I have done this was to test get I2S output from a SMC SMCWAA-G to directly feed an Opus from the SMC's uC. This worked very well, but requires very careful soldering. The SMCWAA-G has a module jack for Ethernet, I simply hacked it up for my own purposes. 🙂 Now I can connect it to an opus via SPDIF and I2S. It worked out nicely. I did this purely for fun as I already have a squeezbox, but I only paid < $50 for the SMC device so I felt very comfortable hacking it up.

Cheers!
Russ

Cheers!
Russ
 
#790
Hi Russ,

Thanks for the reply. Well, I wasn't taking any precautions when I was testing, but found the length of the cable to be very short for reliable results. I was driving it with a CS8414 though. I did not test using CAT5 and grounding one wire of each pair as I figured it'll still not be great, but your tests reveal otherwise so that will save me some effort😀

Thanks so much!!
 
#792
Hey guys, how's that DAC demo box coming along? It doesn't have to look pretty, just sound pretty!!

Burning Amp is around the corner!!
Click to expand...

Not look pretty... that's a good one.

Here are a couple pics. Boards are mounted (still waiting on ASRC and LCDPS boards to arrive/build). Wiring will start today. Front and Rear panels are being machined today. Artwork will be laser printed on the front panel.

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.
 
#794
Brian/Russ,
Do you guys have anything in the pipeline that does galvanic isolation of the DAC from the I2S source? I'm thinking of trying some TI ISO150's to isolate my I2S source (PC) which will have potentially noisy power. However, if you guys have something in the works, I may get lazy 🙂
 
#795
Are there two Ballsie's in that DAC, Brian?

Quick question: I just put together an LCPS and fired it up...I can adjust the voltage fine, but after bringing one of the rails up the two resistors on that side started smoking...voltage stayed steady though. I don't have time tonight, but I'll be looking at it tomorrow to see what mistake I may have made. I thought it would be a good idea to throw the question out in case anyone has an idea off the top of their head.
 
#799
dwk123 said:
Brian/Russ,
Do you guys have anything in the pipeline that does galvanic isolation of the DAC from the I2S source?
Click to expand...

Brian and I have talked this over several times in the past. We really only have one source that would really benefit (the USB source), so it has not been a high priority for us (lots of stuff going on right now). Still, we have given it some thought and if I were to design a PCB it would probably be around the Analog Devices ADUM2400 Quad-Channel Digital Isolator or something similar.

There are risks however, but none too major. One would need to be sure that the added propagation delay will not harm anything, it shouldn't as long as the pulses are not badly distorted, which they should also not be.

Nice thing about the quad part is that the propagation delay will be closely matched between channels (within 2ns). So it should work well. I am not sure I would try to use it to pass the master clock for a DAC working at 192khz (unless you went 128fs) as you would be pushing the limits on speed. But 44.1 - 96khz at 256fs should work nicely, at least on paper. I have yet to try it.

When I get some time I may give it a go.

Cheers!
Russ
 
#800
I just had a chance to look at the LCPS a bit more closely. First, I reflowed all the solder to ensure there were no cold joints. Next, I noticed that AC from one pair of secondaries was reading really low, so I took it from the LCPS to measure it again and got proper voltage. Hooking them back into the LCPS resulted in the low AC reading again. I've compared part orientation to my working LCPS and haven't noticed any differences. Anyone have any ideas?
 
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