Tír Na HiFi

Here's my experience with isolation

When I was developing the Ciunas a couple of years ago, I did a number of prototypes

I did a prototype which was fully decked out in isolation. USB 2.0 high speed isolators weren't available then so I isolated the I2S signals coming from the Amanero board to the downstream chips (Dac or SPDIF transmitter chip). I reclocked the I2S signals just before the input to these chips. I used the GMR isolators as my research also determined they were the lowest jitter isolators available. I powered each side of the isolators by an individual battery, no other power. The idea of using the isolators was about checking the audible effect of isolating noise on the ground lines on the USB cables, not about noise on the power lines.

So the audio clocks were on the "downstream" side of the isolators & fed back through the isolators to the Amanero chips. This is synchronous clocking. So this is the best configuration that can be used - clocks on the "clean" side & sent back to the "dirty" side, reclocking of I2S signals after the isolator (because even the GMR ones add some jitter). This is the configuration used by the best designs (they term it "galvanic isolation") except they don't use isolated battery power on each side of the isolator

Now when I compared this with the exact same configuration but without the isolators, there was no audible difference. I believe the use of batteries probably is the underlying reason why there was no audible effect

Now, here's the interesting part -now that USB 2.0 high speed isolators are available, using one in front of the Ciunas makes an audible difference as it does with all DACs tried.

So the isolation of the USB digital signals themselves is the important factor - it appears that is what the noise is riding on, not the USB ground line. And the USB signals coming out of the isolator are improved by regenerating using a USB hub chip.

Now another factor - if the "dirty" side of the USB isolator is powered by VBUS it is audibly noticeable. If the "dirty" side of the isolator is powered by a linear supply it sounds better but better again if it is powered by battery

i ordered a second unit from aliexpress so i can examine it a bit easier and try figure out what exactly the ak4118 chip does or is it there for spdif?
there is also a simpler unit with i2s only with no ak4118 but it has no audio freq clocks on it which kinda has alarm bells ringing a bit
curiosity killed the cat and ordered one of them aswell

Curiosity got the better of me and I wondered if either or both boards have arrived? Or are they on the slow boat from China still?

jrling wrote:

i ordered a second unit from aliexpress so i can examine it a bit easier and try figure out what exactly the ak4118 chip does or is it there for spdif?
there is also a simpler unit with i2s only with no ak4118 but it has no audio freq clocks on it which kinda has alarm bells ringing a bit
curiosity killed the cat and ordered one of them aswell

Curiosity got the better of me and I wondered if either or both boards have arrived? Or are they on the slow boat from China still?

Yea they have arrived
The amp build has been a distraction from this and the soekris dac modding

However i have taken the ak4118 chip off and it doesnt work without it so i put it back on

Ive done nothing with the other sdcard player only switched it on
it is a smaller board
If i were to guess id imagine this simple board reclocked to audio frequencies via flip flop will be good also

I see youve changed dacs hows that going

K.I.S.S. is very much my maxim too. Look forward to a report in due course.

I still have my Chord DAC 64 MkII, but haven't used it for a while.

Lars Moltke in Denmark, the original designer of the Bow Technologies gear is operating on his own account now and he offered a USB input conversion via a M2Tech Hiface EVO converter to an upgraded internal DAC using dual PCM1704 chips, for existing owners of their ZZ-Eight CD players. Can at the flip of a switch also operate as a stand alone CD player. It really is NOS as he removed the DF 1704 filter. There are numerous PSUs for different circuits inside too.

Definitely not a cheap option, but beautifully and thoughtfully executed and the end result is magnificent.

So not computer audio reborn, but a ZZ-Eight CD player reborn certainly.

Actually, an even bigger advance in SQ has been WTFPlayer where I have been beta testing and may be you have too? Quite extraordinary how much more WTF has extracted from 16/44.1 discs. Not up to SD card player standard perhaps, but for us Intel mobo crowd a good shot at what you and Rick/Greg are hearing.

Jonathan

If i were to guess id imagine this simple board reclocked to audio frequencies via flip flop will be good also

Have you been enjoying our fantastic summer or trying out the above project?!

jrling wrote:

If i were to guess id imagine this simple board reclocked to audio frequencies via flip flop will be good also

Have you been enjoying our fantastic summer or trying out the above project?!

This is my busy time of year though things should ease shortly
The new amp project and gb will be first priority
Hopefully get back to dac and sd card stuff next

Is this player limited to just 32GB?

wushuliu wrote:Is this player limited to just 32GB?

dont know

nige2000 wrote:

wushuliu wrote:Is this player limited to just 32GB?

dont know

Well I've got it up and running: Fox Xpresso clocks (though I didn't realize they come unmarked so I had to figure out place with trial and error once they were out the package); NDK 32khz clock and half-assed Xpresso 8mhz soldered as it was smaller than I expected. I2S out the pins - works out to be closer to my soekris position wise. TPS74A700 power supplies.

Some stuttering with 192k tracks but other wise seems to be playing okay. Low noise floor and grain-free sound. Going to give it some time to settle in.

I tried the reclock but the soekris didn't lock on. Probably didn't do it right, oh well.

pics please
Are u using a 574 or the potato 7474

Mucking about with i2s gnding might get 192 working
Lifepo4?