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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 KHz

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#1,585
Hi Søren. I'm working on ideas for a stackable plug-in board for the DAC and I see the HiFiduino article includes a mechanical drawing of the board mounting, output socketry etc. Would it be possible to provide additional information to detail the positions of J1, J2 and J3?

Many thanks.

Ray
 
#1,586
Feinschmecker said:
Why not upsample thus avoiding any filter? Can that be done on the FPGA?
Click to expand...

Are you talking about non oversampling mode ? That can easily be done, t.ex. for 44.1:

Enter 8x 1.00000 as filter coefficients, 8 taps and gain set to 1.

The 8 is for 8 times oversampling, use 4 and 2 for other oversampling rates,
just like the 352/384 bypass filters using 1.

Again, I don't recommend non oversampling, and you then need the compensating filter for the 3db loss at 20 khz.
 
#1,588
I have posted an updated design of my amanero input board to the implementation thread, post #399.

emyeuoi said:
For my configuration with the Edel_NMR I need just the 3 U.FL. connectors and the external 3,3V that I already have.

So, I think that is not more sense for me to go ahead with the design of the board. I don't have any interest to run a GB if cannot help the community.
Click to expand...

I think your board serves a different purpose, it is smaller and simpler. Some people may prefer that, don't abandon it!
 
#1,590
spzzzzkt said:
I've attached a .skr with the 44.1 filter replaced with a minimum phase filter, linkwitz riley "shape" and 12dB filter slope and corner frequency of 159994.8Hz. My numbers are probably off but I'm setting the corner frequency at 0.4535*fs where the fs is 44100 * 8. (I re-read POS's post and corrected from 384 -> 352.8, oops)

I'm not sure why, but the rePhase filter is about 6dB quieter than the one Søren made, so

cheers
Paul
Click to expand...

A -3db at .4535 output sample rate is almost like no filtering. Any filtering work should be done relative to the input sample rate....

Don't know why the filter is off 6 db, maybe the design of rePhase need to be checked.... Anyway, you can add the needed gain in the 1021filt.txt file, using the "multiplier" parameter.

I'm very interested in hearing the result of experimenting with filters, but it should be real filters, like if using the L-R filter slopes it should be more like 192+ db/octave slopes....
 
#1,591
soekris said:
Are you talking about non oversampling mode ? That can easily be done, t.ex. for 44.1:

Enter 8x 1.00000 as filter coefficients, 8 taps and gain set to 1.

The 8 is for 8 times oversampling, use 4 and 2 for other oversampling rates,
just like the 352/384 bypass filters using 1.

Again, I don't recommend non oversampling, and you then need the compensating filter for the 3db loss at 20 khz.
Click to expand...

Is there a way to enable / disable filters by serial commands? Would something like that even make sense?

And while we are on the subject (of serial commands), are there any undocumented serial commands that we should know of? For example, is there a way to get feedback on the state of the FIFO (perhaps like % full or something?) or any of the inner workings of the uC / FPGA?
 
#1,592
Soren!

Do I need the 1Kohm resistor????
 

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#1,594
Dimdim said:
Is there a way to enable / disable filters by serial commands? Would something like that even make sense?

And while we are on the subject (of serial commands), are there any undocumented serial commands that we should know of? For example, is there a way to get feedback on the state of the FIFO (perhaps like % full or something?) or any of the inner workings of the uC / FPGA?
Click to expand...

Sorry, I will only document what needed for normal use....
 
#1,595
soekris said:
A -3db at .4535 output sample rate is almost like no filtering. Any filtering work should be done relative to the input sample rate....

Don't know why the filter is off 6 db, maybe the design of rePhase need to be checked.... Anyway, you can add the needed gain in the 1021filt.txt file, using the "multiplier" parameter.

I'm very interested in hearing the result of experimenting with filters, but it should be real filters, like if using the L-R filter slopes it should be more like 192+ db/octave slopes....
Click to expand...

So should I generate filters at 44100 rather than 352800 as POS suggested?
 
#1,597
soekris said:
When testing we do a FFT and measure distortion at -1db, we don't really see any difference between the different version as the initial precision is so good, even on less precise resistors.

But I expect long term the boards with more precise resistors will change less than the less precise resistors as temperature and long term drift are significant better with the more precise resistors....
Click to expand...

Thanks Søren.

Were you able to hear any difference in sound between the versions with 0.05% and 0.01% resistors?
 
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