DSP Xover project (part 2)

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#2,902
najda_i2s_out.png


I guess this would be right, i hope 😱
 
#2,904
Any update on if or when some new features will be added to Najda firmware?

It's over 2 years since I bought my Najda and I'm still waiting on the ability to get 8ch I2S out of it. I've been making do as I could run my speakers from 6ch but now I'm using 8ch and had to switch from my Buffalo DAC back to the internal Najda DAC. The Buffalo sounds quite noticeably better 🙁

I'm happy to perform any necessary hacks to make this work - if those other 2 channels are somewhere on the board I'll happily solder mods onto the board to get them. If there is a hacked firmware that enables those channels I'm happy to test. Now that I've compared the Buffalo to Najda DAC, I'm extra keen to use the Buffalo.
 
#2,906
MellowFellow said:
It's over 2 years since I bought my Najda and I'm still waiting on the ability to get 8ch I2S out of it. I've been making do as I could run my speakers from 6ch but now I'm using 8ch and had to switch from my Buffalo DAC back to the internal Najda DAC. The Buffalo sounds quite noticeably better 🙁
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Hi Mellow, do you use 8ch Buffalo or 4 in // ?. I have also a report from a friend stating that you can get much in transparency with outside DACs.
Question I have is should the clocks be synchronised, and if yes, how.
Also, as the Buffalo is not inexpensive, if you need 3 or 4 it is a no go, so I am looking for other very good I2S dac. If someone has an idea 😉

Jean-Louis
 
#2,907
JLOP said:
Hi Mellow, do you use 8ch Buffalo or 4 in // ?.
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Hi JLOP,

I use an 8ch Buffalo, so that's a single DAC board and four IVY-III boards. From memory, by the time you get the I/V boards and a power supply it's about $1000 to build an 8ch Buffalo.

If I built the Buffalo again I might look for another I/V stage. The output I get from the IVY-III really needs to go through a buffer and could use more gain before going to an amp - I'd be happier if I could run an amp direct from the Buffalo. And don't count on using the digital volume in the buffalo; the digital volume in Audirvana (Mac) is better than the Buffalo volume and an analog volume is better again. I've been running mine through a Bel Canto Pre6 to get extra gain and better volume control.

I'm not sure which clocks you are referring to but the answer is likely to be 'yes' regardless. Using a single 8ch Buffalo means I don't have to sync clocks between multiple DACs (eg, 4x stereo). I would certainly like to synchronise the Najda clock, Buffalo clock and my (external) ADC clock but I don't think the Najda supports a master clock input. I ordered a 24.576MHz TCXO clock to replace the crystal on the Najda a few nights ago and am waiting for that to arrive in the hope it improves the Najda.

...As you may be able to tell from that rant, I have invested much more than the Najda price in my DSP box which is why I'm very interested in firmware.
 
#2,913
dahlberg said:
Still interested in what happend with the addition of two more i2s outputs 😎
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I still really want chaparK to help us on this but in the mean time I have started looking for hacks and *might* have found something.

It looks like we can pick up 8ch I2S at the input to the AK4101AQV chip. These would be the same 8ch sent to digital outputs 1-4. I will need to use the soldering iron to install my TCXO clock when that arrives so will attempt to pull extra I2S output at that time. This mod (if successful) is not for the faint hearted - very tight surface mount work 🙁

I've nominated pins 3-6 as the interesting ones.... http://www.akm.com/akm/en/file/datasheet/AK4101AVQ.pdf

I'll bet the I2S signals are exposed at other places on the board but only chaparK has the schematic that would make this easier.
 
#2,914
dahlberg said:
😀

Still interested in what happend with the addition of two more i2s outputs 😎
Click to expand...

MellowFellow said:
I still really want chaparK to help us on this but in the mean time I have started looking for hacks and *might* have found something.
[...]
I'll bet the I2S signals are exposed at other places on the board but only chaparK has the schematic that would make this easier.
Click to expand...

Hi! 🙂

Alright, let's talk about I2S outputs.
There's one main bus conveying 8 channels. This bus is split between the DACs and the SPDIF transmitter AKM chip.
There's another bus going to Expansion Port 0 (3x outputs) and a third one going to Expansion 1 (6x inputs, only 1 used).

In order to increase the number of I2S outputs, the original idea was to route the clocks to the third bus and use here 2 transceivers for a total of 10 channels. I've looked at this as promised, and unfortunately there's no easy way to achieve that it seems.

I'd need to look at that again. The point is, if you check the data sheet of the DSP, you'll see that information about pin multiplexing and clock control is disseminated all over the place :fight:

The original aim of the Expansion Port is to allow system expansion 🙂rolleyes: oops!). So if you add the analogue expansion to your system, one I2S line conveys ch9/ch10 to the extra DAC, another I2S line is configured as a stereo input, and the third line is disabled.
Frankly, back at the time when I designed this board, I didn't expect that anyone would want to connect 8 DACs via I2S - I must have underestimated you guys 😉

We'll find a way.

MellowFellow said:
I will need to use the soldering iron to install my TCXO clock when that arrives
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I don't think that's a good idea. The proper way would be to connect that clock to the External Clock input on Expansion Port 1. This feature will be enabled with the next firmware release.
The crystal on the PCB is clocking the DSP, not the audio - at least not directly. The codec has an internal PLL that generates the audio clock - this chip also has an input for external clock, as discussed above.

DieterK said:
Will it be possible, as a future-project, to implement an loudness control?
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You mean a filtering profile that's changing with the volume setting? Or something more complex?
 
#2,915
chaparK said:
Alright, let's talk about I2S outputs.
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Thanks for your comments. My move from 6ch to 8ch crossover required a move from external to internal DAC and the sound quality is lower. I may still use the soldering iron to look for 8ch I2S while you look for an easier solution. My only other option is to move to another DSP platform 🙁

chaparK said:
This feature will be enabled with the next firmware release.
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I hope "the next firmware release" does happen one day but it has been promised so long that I'm now trying to work with what we have. This PLL is annoying because (now that you've pointed it out) I can't see a work-around without reprogramming the CS42428. And that's really hard for DIY as I don't think we have the existing code. I may have to give up the master clock idea (for now) and use the reclocking of the external DAC.
 
#2,917
Hello,Nick.
Thanks for your answer even if it wasn't as positive as i was hoping for.
For me personally it's not a big deal but for my friend building the 5-way system it sort of puts a dent in the planning. Lets hope that you figure it out somehow.

The wet dream would on the other hand be an all digital dsp using the highest available level of chipset / clock etc..... 😉

That said I still have to say that I really like my Najda setup 🙂
 
#2,919
Najda I2S outputs and clock.

How I2S outputs are clocked in Najda? Is output jitter free or how big jitter is?
Can external clock be used to reduce I2S output jitter.
Can external clock in general be feed to Najda DSP to make possible DSP synchronization from DAC clock?
 
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