Soekris Dam Dac

[gstew]

<SNIP>
Thanks for the reply, but the next pin is labeled as FPGA MCLK OUT.

Just wondered if anyone had confirmed that it did not work?

Val

I haven't, but I have not seen anywhere where he said you could feed a clock to the FPGA.
Everything I've seen is that you can't feed an external clock into this DAC.

id imagine theres a clock switch option to be implemented yet in future fpga firmware

What I have read in the main thread is that the I2S MCLK OUT is designed to work in conjunction with I2S FSEL IN with sources that can accept a master clock input such as the Amenaro or BeagleBone Black running the right driver. Then the source device sends the clock frequency family to the DAM via the I2S FSEL IN and receives the clock via the I2S MCLK OUT. While the I2S MCLK OUT (n FPGA MCLK OUT) do appear to be working, AFAIK the I2S FSEL IN is not activated as of the current firmware revision. Due to the clock signal output working, some have reported some success in using that to sync their source device, but of course they can't have an automatically controlled source sampling rate clock family change... I suspect it works ok for some setups, but with some glitching noises at the changeover.

I have not seen any explanation for the FPGA MCLK OUT, I suspect it was initially designed to use in syncing multiple boards together when run in Dual Mono or Crossover modes, but Soren has indicated that they will work in that mode without clock syncing.

I have not seen anything about feeding the clock into the DAM in the main thread, except on people's wish lists.

Greg in Mississippi

[nige2000]

not getting much of a run of time at this clock thing i had a myriad of fixed clock grounding issues that continue to mystify me
and remind me too much of the feckin mobo clk mods
anyway ive a 45mhz clk on it now im fairly sure its better than the adjustable as its just been awhile since i heard the adjustable clk
ive a gut feeling it will accept a 22/24 either
achieving synchronicity will be more difficult probably involving some lcs to try and keep the signal integrity intact
and that brings us to thinking which is the lesser evil more chips in sync or less chips and async clocks

maybe a clock board to manage it all needs to be made

[nige2000]

anyone still interested in dam mods?

ok 22mhz test


more detail and better definition
but if i try to add wire to bring the clock signal back to the reclocker i lose lock on the soekris
if i use the fpga clk output to run the reclocker definition decreases but decay and reverb improves and by comparison has less digital edge to the sound which is most of what i hope to achieve with synchronicity
now as that 22/24 freq is acceptable i wonder if i use some coax to send the signal back to the sd card player would/could i avoid having to use integrated chips to achieve synchronicity

[alecm]

nige2000, many thanks for brave steps, i waiting for clock changes long time. for sure i will try the same. I like this thread. Here is lots of interesting researches. Thanks for sharing your experience.

5 different Soren DACs were researched and heavily moded(almost all mods described here and even more) by me, and I clearly noticed, that all dacs has different measurements more than normal spreading in comparison with another dacs. All has a different level of harmonics. Sometimes 20-30db of difference(The measurements were made using a Lynx Aurora ADC predominantly at a frequency of 96K 24-bit)

My idea, that the answer is a difference(spreading) of resistors and their mutual ratio. And this is the one of significant factor that influence on measurements, harmonics and sound quality in the final. Even more, I have changed resistors and received a clear change in harmonics level.
Look at this.



i see that the r2r soekris schema is


There is 1021 .01 version dac from the first delivery. Having re-measured of each resistor there. And have received the following results:

Yellow marked real accuracy percentage that are outside of the specified accuracy - 0.01.

so my conclusions:
- It was stated that the precision resistor is 0.01, but in reality there are resistors with an accuracy of less than stated
- By itself, the accuracy is not so important, more important it is 2R and R mutual ratio (should be 2), and the same resistors in series (bits).
- Since the resistors in the matrix has a significant variation (over 0.01), which means that the result of these relations and also provide spread.

I want to ask an advice here on r2r matrix construction. For me it remains full unclear until the end the sense resistor in bit from 0 till 2 rows. Soren calls it like “thermometer”. What is the practical sense of 0,1,2 rows? Any thoughts?

[rickmcinnis]

alecm,

I have nothing to add to your post since, as usual, you are out there in the vanguard.

BUT I am glad to see you here where you belong!

[nige2000]

welcome alecm
think your a mile ahead of us there
willing to get up to speed and help out with your ideas though
ultimately i think we need a simpler discrete r2r dac to work on and we will run out of road eventually with this build template
if theres any mods we haven't done let us know please

on the clock thing jk suggested using less wire on the clk inputs before breaking into the coax cables so i shortened and replaced with some finer wire and got the reclocker working good
it seems pretty obvious that async is putting an edgy metallic edge to the sound by comparison and loss of micro detail, decay, reverb and maybe even a slight bit brash by times (of course by comparison to sync)

did try to get use the same clk signal on the sd player but was unsuccessful and dam will not lock
as far as im concerned synchronous is just the way to do it and have all moving to the one drum beat as much as possible

[nige2000]

I want to ask an advice here on r2r matrix construction. For me it remains full unclear until the end the sense resistor in bit from 0 till 2 rows. Soren calls it like “thermometer”. What is the practical sense of 0,1,2 rows? Any thoughts?

wonder if therses any point asking soren?
At worse case there will be no reply or a political type non disclosing reply

Listened for an hour with fixed 22 clk feeding fpga and the pre fpga reclocker
Im positive the adjustable clock shoud be removed and replaced with fixed clk and i2s prealigned
Resolution is immense with darker background and a level of coherance ive not experienced before
The biggest improvement since vref ;)

[gstew]

Nige,

Great work!

Do you have any u.fl cables you can use? I've been cutting one end off and hard-wiring it in, in your setup you might just want to use the coax and HW both ends.

Greg in Mississippi

[nige2000]

Nige,

Great work!

Do you have any u.fl cables you can use? I've been cutting one end off and hard-wiring it in, in your setup you might just want to use the coax and HW both ends.

Greg in Mississippi

i have cables but wheres a cheap place to get plugs/sockets?

[rickmcinnis]

I have got them from MOUSER but they are generally available.

The sockets are impossible to place on the SOEKRIS without adding some wire so then what is the point?

You will have to use a piece of solid core wire to bundle the ground mesh.

I am soldering direct the isolater outputs but relented and soldered to the connector for the SDTrans since I know I will have to take it away to do the battery and clock mods, but I would be much more at ease with a soldered connection.

Obviously, one should buy the longest cable for just the cable. It certainly does not look special but I figure they know what they are doing. I have always used this so I have nothing to compare it to.