SDTrans 384?

[jkeny]

was just wondering why the sd trans is supposed to be better than the other sd card wav players that are cheaper
were going to be modding the boards anyway?

http://www.ebay.com/itm/Improved-FPGA-L ... Sw8cNUO9KX
http://www.ebay.com/itm/111721479669?_t ... EBIDX%3AIT

I agree, Nige - it's a matter of implementation & if these ebay boards have decent ground design & good power can be separately supplied to individual, important elements of the board (such as clocks, I2S output chip), then there are probably only a few other issues to consider - FPGA chip & programming, ground bounce, etc.

[jkeny]

Doh! Deleted

[nige2000]

now thats isolation

mad shit :)

he who is without sin cast the first stone :)

[jkeny]

Yes, but this is clock speed you are talking about that has been derived from the one physical onboard clock on the Soekris board, PLLed within the FPGA chip & then output as the audio clock latching the shift registers in the ladder DAC output stage - it's not the raw, unprocessed output of physical clocks which can be used in a synchronous way to time both converter (SDTRANS) & DAC (SOekris) - this would be the optimal, lowest jitter clock configuration which also avoids the issues of multiple clock domains

<SNIP>

Yes, I would consider this a low priority experiment. A much more useful approach would be to find a suitable DAC which used 22.2792 & 24.576MHz clocks & use one pair of physical clocks as the synchronous clock signal for both SDTRANs & DAC

JKeny,

Actually the DAM clocking scheme is as follows:

"Clocking and FIFO
The DAC have a low jitter digital controlled oscillator (SiLabs si570), data is sent though a short FIFO and the FPGA and uC work together to measure incoming bitrate and adjust clock as needed, basically a digital PLL with very fast lock and very slow filtering. So the DAC itself only need serial data, word clock and bit clock, no master clock is needed, it will sync to whatever you feed it. "

So the clock frequency on the variable clock unit is varied slightly to make the FIFO work. AFAIK, it does not go through a PLL in the FPGA and I'd hesitate to call how it works a PLL, just a variable rate clock that keeps the FIFO from emptying (hopefully... there are some recent comments on the main DAM thread suggesting it may not work as expected in all cases, such as with an R-Pi I2S source which may not have a fully compliantly-clocked I2S signal).

Thanks for that. Yes, I seemed you have restored my memory about it's clocking which at the time I wasn't impressed by. In my experience (although I haven't used these Silabs clocks) - any clock which is variable is in theory a higher jitter than a fixed frequency crystal based clock. These Silabs clocks have a fixed frequency clock which is then processed through an internal DSPLL in order to achieve the clock speed determined by it's I2C signals coming from the FPGA. Any feedback loop (PLL) which is used in clock handling introduces jitter. On the plus side these clocks also have a differential output clk+ & clk- which is a good design.

Also, do you have any suggestions on that 'suitable DAC'? Of course, for anything run off the SDTrans using their MCLK signal, you will be running synchronous... that is one of my planned experiments, trying some EUVL & Curryman ES9022/23 & JL Sounds AK4490 DAC cards with the SDTrans. But that comes after I work the DAM mods.

Well, again, from experience the Sabre DACs sound best when operated synchronously (this turns off some input processes which are detrimental to sound) but any DAC which accepts Bit clock, LRCLK & data (& optionally MCLK) I suggest you try reclocking these signals just before they enter the DAC chip - you will find this improves the sound. I haven't heard the AK4490 but I like the sound of the PCM5102 or 5122 with low latency filter

Hmm, I always wonder about clocks like the Pulsar - I find improved PS to any clock goes a long way to improving the sound as most are sub-optimally powered anyway

I found Ian Canada's comments after trying a Pulsar in his FIFO most convincing. I think he does about as good of a job as anyone on powering them in his setup... and he might have used a LiPoFe4 on it.

Still, at the price for them, I won't be buying a set anytime soon, even after they become available again!

Later!

Greg in Mississippi

Yes, I seem to remember Ian recommending the LifePo4 & wonder if he tried this PS on his Silabs clocks how they then compare to the Pulsar? Yes the expense is prohibitive, I find, particularly when 2 are neded.

[jkeny]

now thats isolation

mad shit :)

he who is without sin cast the first stone :)

I can't see the logic in what is being done in this pic - can anybody?
If PS isolation from mains is what's needed then batteries would seem the way to do it, no?
I know people query the noise of batteries & I tell them that this is based on old battery chemistry SLA, alkaline, etc. not based on modern battery chemistries. Am I making the same mistake here in thinking the photovoltaic cells will be noisy - I really don't know?

[jkeny]

what hastens me is is we dont know what people consider to be a good digital audio reference and im dubious about these reference points more so than anything else

sure we jump through a lot of hoops but we have jumped through them
we do have good digital audio references that has to be among the best of them

so will probably have to wait on adolfo's impressions

I agree that when I read opinions about sound quality, I always wonder what their reference is.
Not boasting or being big-headed about it, but I sincerely believe that what we hear at our ad-hoc meetings is a digital sound of a very high quality. There may probably be even better sounding analogue or digital systems out there - we often say this - for instance when introducing the Intona, nobody thought it could improve what we were already hearing but it did - but I believe we are listening to kit that is in the top echelon of digital replay systems - even our devoted analogue members, who haven't heard the latest stuff, were saying a while back that the digital side was neck & neck with their TT systems (stop me if I am overstating this).

So, it's difficult to judge others impressions of SQ unless there are some common ground references to use.

[nige2000]

now thats isolation

mad shit :)

he who is without sin cast the first stone :)

I can't see the logic in what is being done in this pic - can anybody?
If PS isolation from mains is what's needed then batteries would seem the way to do it, no?
I know people query the noise of batteries & I tell them that this is based on old battery chemistry SLA, alkaline, etc. not based on modern battery chemistries. Am I making the same mistake here in thinking the photovoltaic cells will be noisy - I really don't know?

i cant see it been worth the hassle
and still need lots of capacitance
battery is the lazy mans super regulation and super capacitor only better
why make it more complicated

off topic
got a nice sq lift of an amanero with a regen clone on soekris although still prefer xmos version

jk is that qls 660 board coming out of its box?

[jkeny]

i cant see it been worth the hassle
and still need lots of capacitance
battery is the lazy mans super regulation and super capacitor only better
why make it more complicated

off topic
got a nice sq lift of an amanero with a regen clone on soekris although still prefer xmos version

jk is that qls 660 board coming out of its box?

Yep, I'll take some up-skirt pics for your ogling :)

[gstew]

I promised some pix of my SDTrans384 -> DAM DAC setup. Here are four... the overall setup, my digital test-bed power supplies, the u.fl connection from the SDT -> DAM, and a closeup of how I mounted the u.fl sockets on the SDT output connector. Note that I hard-soldered the u.fl leads to the DAM and because all of the other setups I plan to use it in only need 3" cables, I made up a set of 3" u.fl extenders.

I'm trying to get the best sound out of these setups that I can with AC power. The test bed has two separate sets of supplies, a 5v/3.3v set for sources and isolator input power, and a 2x 6.5v / 2x 13.5v / +-24v / 5v output mute (which is designed to drop-out fast when AC is removed). Connection for the main supply are good Hirose multipin, for the source/isolator whatever is needed for the source device. There are separate power cords for the source/isolator input supplies versus the main supplies... I run them through separate sets of filtering (heavily filtered & direct to the wall for the source/isolator supplies, lightly filtered & through a PS Audio P10 for the main).

Total power supply storage for all of the supplies is near 300,000uf, with most of that Jensen 4-poles. On this setup right now, I haven't modified the DAM, so only the 2x 13.5v supplies are currently used to power the main portion, with the SDT powered by the source 5v & the DAM isolators by the source 3.3v. The unused supplies all have bleed R's to minimize sparking mistakes when disconnecting/connecting.

And I did take a few minutes to listen to it last night. Without much warmup and with really no break in, it was pretty good and will be better once I start powering the sections separately and use the raw outputs.

Greg in Mississippi

[gstew]

Sorry for the slow pix, I had to do some re-sizing!

Greg in Mississippi