Peter hi,

Unfortunately I don't think that the 24.xxx clocks will work, but I would be delighted if they could be made to. Its worth mentioning that the wave form I had from the 24.xxx clocks via decoupling transformers was not the best, quite some overshoot but well damped recovery. I don't think this is the cause of the failure of the 24.xxx clocks but its worth a mention. The clock waveform is on the list of stuff to be looked at on the 24mhz clocks as the waveform also overshoots but not quite so much.

I did have the thought that although the 24.xxx clocks don't work might the 22.xxx audio clocks work ?? I only have one of these to hand and had other testing planned for it so I was not planning to try the 22.xxx clock out here. Perhaps these would be worth a try at yours ?

Small performance variations in the 24mhz clocks being used here do appear to have an impact on sound quality. The state of charge of the battery powering the clocks can be heard for instance. I think this is good however because the the VCXO I'm using only has goodish phase performance which I hope means that further clock improvements could improve sound even more, that would be quit something. A friend of ours has a rather higher phase noise spec (but expensive) 24mhz TCXO to try out. It will be interesting to see what the results this produces compared relative to the VCXOs iv been playing about with.

Cheers,

Nick.

Peter hi,


This looked like a great given the excellent performance of the 24.xxx clocks so I bought a second 24.xxx clock last week and did some testing.

Results here were that I managed to get the PC USB pcie card to recognise a USB stick drive with the 24.xxx clock fitted. However the NOS USB interface with 24.000 mhz clock fitted would not connect to the PCIe card fitted with the 24.xxx clock.

Next I tried to fitted a 24.xxx clock to the NOS USB interface pcb and tried again to see of the 24.xxx clock at both ends of the link would help. Unfortunately I still could not get the NOS interface board to work (the usual green "USB" LED would not light up.

This is a real shame because the performance of the 24.xxx clocks is I another league to what seems to be available for 24.000 MHz clocks.

I did get in a bit of a fix with a battery which was not charged so it could still be that the 24.xxx clocks might work but I reasonably sure that the result is a sound one.

Did you fair any better with your tests on the 24.xxx MHz clocks Peter, has it worked with you ?

Cheers,

Nick.

Peter hi,

I understand that the settings are "preset" but I am very sure that something is happening to sound quality after refresh is pressed. It could of course be coincidental and be caused by something else other than time stability, but there is absolutely a difference to sound quality. Im wondering what the cause might be.

I leave the OS settings to XX these days (much better than sound than with "local" OS tweaks). My DAC is changed but I could hear this "refresh" effect before the last round of changes to the DAC and I suspect that these have increased resolution significantly to the point that the "refresh" click is much easier to hear now.

Paul is making a vist to my place this weekend, I will demonstrate the difference that clicking refresh makes and we can report back. Also it might be possible for Paul to try clicking refresh before playing in his system to see if a difference can be heard elsewhere.

Regards,

Nick.

Peter hi,

I have been finding that the effect / setting of the XTweaks Time Stability setting is not engaged when XX if first loaded. I think that the effect / setting the Time Stability setting can also be lost some times after music has been played and has stopped and is then restarted.

To cover how this is noticed. (my Time stability setting is set to Optimal).

If I start XX and then look at time stability in XX it will say use "refresh". When I play music before clicking the XTweaks refresh button I get music which sounds good but is not so coherent and had what sound like small resonances at some points in the spectrum. This will be the case each time I play until the refresh button is pressed in XTweaks, time stability then updated to “optimal” and when music is started it is noticeably more coherent and better presented.

I tend to press Xtweaks refresh just before music is started each time as quite often the non-coherent sound returns if I do not do this.

I seem to remember that this has come up before in another support post (although it was a side conversation to the main support question IIRC).

I was not too effected by difference in sounds but with the clarity that my system is giving these days it is now easy to pick out the effect of clicking the Xtweaks reset button.

Is this intended behaviour of the reset button ?

Kind regards,

Nick.

Anthony hi,

Sorry its taken a while to come back on this, I will PM you.

Cheers,

Nick.

Peter hi,

Time is a bit limited this afternoon, but there are a few points that I need to highlight to help get good results and I can see that thoughts are running on quickly in the post.

Regards the PC USB board.

I would go for a NEC chipset PCIe USB 3 board they are cheap and easy to replace the clock on. If it helps I will send a link to the one that I have modified later.

A key point to getting the best performance here is that both the NEC chipset and the 5v USB aux supply need to be powered by the PCs internal supply (this seems the wrong thing to do but sound is better). Just plug the board into the PC PCIe slot as usual to do this, it’s only the clock that need to have a “good supply”

Next is the new 24Mhz clock for the USB board. This needs to be transformer and capacitor decoupled on its signal output. Decoupling like this means that there is no problem with the USB Chipset (on the PC supply) and the clock using different power supplies. If the clock signal is not transformer decoupled the differential noise between clock supply and USB chipset (pc) supply effects sound quality. Even using a Battery to power the clock will not give best sound if the clock output is not transformer decoupled.

I can send you details of a suitable pulse transformer and capacitors to set up the clocks output.

You could use the PPAStudio USB board but if you do I would suggest using it with the PC supply connected to the molex (Paul and I have been corresponding on this there are other options for the clock but that means changing the board)

Regards the use of 24.xxx clocks

I did think of this as well but needed to place an order anyway as I only have one of the 24.xxx clocks, so I went for the 24.0Mhz VCXOs. The only reason I can think of that 24.xxxMhz clocks might not week is if there needs to be a  sync of some sort with the PCIe bus speed and 24.0 is needed for this. Worth a try though because the 24.xxxMhz clocks you use have top class phase performance.

For information I will send you the details of the VCXO I used although I have found a much better spec 24Mhz TCXO for Phase performance which I will also send.

About the NOS interface.

Here again its important that the new clock needs to be transformer / capacitor decoupled from the NOS board to separate the clocks power supply from the NOS USB PCB supply. Even using a battery to power the clock will not give the best results.

I am sure that you will be fine working out where to inject the clock signals onto both the PC USB board and NOS USB PCB  but if it helps I can PM you some pics.





I have not got time right now to expand on why some of points above appear to be important, but they have been subjectively tested and these points do make a BIG difference to the results.

I just wanted to nudge thoughts in the above direction if you are already working on this. Happy to discuss more this evening.

Best,
Nick.

Peter hi,

I only had time for a partial reply earlier so to expand a little...


Agreed, this is the 24Mhz USB 3 receiver clock on the NOS1 USB interface (not the audio 22Mhz and 24Mhz audio clocks on the NOS USB board already work great).


I’m not sure exactly here about the thought that two thing have changed, The only components replaced on the USB interface PCB are the standard 24Mhz clock crystal and the resonator capacitors for the clock crystal.  I think the (battery) power supply change is not very important but I will try powering the new 24Mhz clock from the 3.3v power supply used for the NOS USB interface PCB just to see.

The existing clock is a crystal driven by the USB chip not a active clock module a so it not possible to power the existing clock arrangement with an "external" supply (battery etc).


My thought is that this does come down to Jitter in the end but in the digital processing domain which must ultimately somehow result in jitter in the audio data stream. I think we are all resonably comfortable that you can influance jitter in the software domain from within XX so it did not seem a big step to assume that data hardware might be able to as well.

The thoughts below are very circumstantial but its possible to see how important the 24Mhz clock and derived frequencies are to the async USB link and moving data downstream into the FPGA.

My first reason for trying an upgraded clock is that as mentioned earlier in the thread I have re-clocked USB receivers on Audio interfaces in the past and had significant changes to sound quality. This would probably have been enough to try a new clock but the NOS USB PCB proberbly a very  expensive board and I did not want to commit to a possibly irreversible change without at least some research into what the 24Mhz clock drives and the areas that might be impacted by an improved clock.

This is what jumped out from data sheets.

• Looking at the NOS USB transceiver chip (I cannot get hold of the NEC USB Chipset datasheet), the USB transmitter multiplies the 24Mhz frequency by 20x to generate the 480Mhz USB 2 standard line transmission “clock”.  I guess that phase noise in the 24Mhz clock can really impact the X20 process and the stability of the 480Mhz derived transmission clock.
• The 24Mhz clocks at both end of the USB link (NOS and PCIe USB 3.0 card) will not be at exactly the same frequency (10s, 100s or 1000s of beats per min out, I have actually tried but failed to tweak my oscillators to match the crystal speeds  ). Could the receiver at both ends of the USB link be using somthing like a PPL to “clock in” received data. If this is the case the more stable data speed arriving the lower the chance of the PPL hunting or losing its lock ?
• To generate a 20x clock 480 Mhz transmission clock speed (or PPL lock if they are used), the phase accuracy of the 24Mhz source clock is going to very important. The standard clock is a simple sine wave oscillator with relatively poor phase performance. When compared to a low phase noise clock the standard crystals sine wave means accurate phase triggering must be hard for the USB chip and noise in the detection circuit of the USB chip can create a relatively large time shift in the detected clock edge.
• Final thought is looking down stream from the USB cards usb transceiver chip to the FPGA. I don’t know how the FPGA code is designed and therefore which source clock drives the data handling within the FPGA. I would guess that some of the FPGA could be slaved to frequencies derived by the 24Mhz USB Clock.

I could not really give hard arguments about the points above they are as likley to be wrong as right but it just felt like the 24Mhz clock was important enought to try an upgrade. Power supply and electrical noise might come into the overall equation but the change in sound is just too fundamental IMHO. It would be the biggest “noise” clean up tweak ever if it were just this alone. Whatever the cause,  the change in sound quality is defiantly for the better and IMHO is really, really large. I was rocked on my heals again this morning when I played a few more tracks.

I’m happy to send the implementation details off-line Peter if you would like them (its not too complex really but might help if you want to try it out), I don’t know if you have tried the capacitor modification to the USB board yet but the clock change is really is worth some time.

Best regards,

Nick.
Edit - language tidy up

Peter hi,

Yes definatly off topic, might it be a good idea to move the last 8 posts concering the clocked USB 3 card to this thread ?

http://www.phasure.com/index.php?topic=2749.msg28645#msg28645

Regards,

Nick.

Pater hi,

Jut a quick response for now, ill have to come back in more detail later today.

There is only one change to the NOS USB board, the extra components I mentioned that were removed are the resonator capacitors which are part of the clock circuit so I'm commenting on only one recent "change" which is the clock replacement.

I can try using the NOS USB interface 3.3v supply easily so I will give this a go. I am very sure that this is not about power however, so I'm not anticipating a significant change. I think this is a jitter improvment. Ill post back my thoughts about what is happening later.

Best,

Nick.

Hi Akremer,

I'm going to get a look at the card when Paul comes over to mine soon. As I mentioned above if the molex powers either the cards USB chip or is used for the 5v USB leads power supply then using a supply other than the pcs own internal supply proberbly won't sound best. My guess is that the PCIe bus signal / USB d+ d- signal suffers greater noise if the signal source and end points are not powered by the same supply. If this is right then it's better to use the pcs supply as this is used at both ends of the PCIe bus transmitting  / and receiving the data.

The exception is the USB boards clock power supply. If this is isolated from the power to the isb chip and the 5v usb lead supply then using a good supply is likley to improve the clock and since it is transformer decoupled at its output the smoothed supply to the clock doesn't cause the problem above. I think Paul's post is saying he found the clock supply to make a small difference.

I can not measure to pinpoint these ideas so could be something else happening.

Cheers Nick.

I mentioned above that the NOS1's USB interface 24mhz clock has been on the list of items for attention.

I bought a smd rework hot air station to help install a clock upgrade last week and got stuck in this weekend. I built and tested a 24mhz replacement clock from a VCXO with LiFePo4 battery power and transformer decoupled clock output yesterday. The standard NOS1 crystal clock and other components were removed and the new clock installed today. As expected the clock really dictates sound quality.

How does it sound ? With a few hours on it, its a HUGE change. I think the impact is proberbly magnified by the 6 modifications made to my NOS and PC's USB card but having said that this clock change has bigger positive effect on sound than ALL of the other changes put together and by a LARGE margin. Music has such a live quality, bass is so extended and tuneful there is such a sense of performance it's a massive step.

Today Iv been playing track after track of the harshest fastest most complex most difficult music I own. The stuff you put on to really test your system. In my case this stuff usually delivers a nugget of diapointment as the system falls apart here, there and everywhere. This afternoon has been very different. Nothing so far has tripped the system, playing this seat of your pants complex music is now simply riveting listening. And the clock is getting beter by the hour as it runs in. I knew that clock was going to be important but I'm shocked by the size of this change.

Next up is to decide how the final PC USB and NOS1 USB clocks are going to be setup. And turning the system again, the change is very large and I think PC Bios and XX Settings will need tuning to suit.

Paul is due to visit my place soon so it will be good to get his opinion.

A very happy Nick.

Anthony hi,

I'm really keen to take a look at it, also to listen to my modified card along side it. Im guessing Paul is focused on tweaking it so some of the details may out before we get together  . I'd be interested to put my scope on the clock. It wont tell anything about phase noise etc but will give a picture of signal amplitude and rise time. The key points from messing  about iv done here appear to be oscillator performance, quality of the decoupling (the transformer and matching) of the clock circuit and the clock's power supply. No surprises about these factors but as always implementation is so important so i'm really looking forward to seeing Pauls card.

Best,

Nick.

Paul hi

I don't know that card you have well so I'm making an assumption in the comments below that the card has both the USB chipset and or the USB 5v inline supply and the clock powered from the molex supply plug.

If this is the case then I'm not surprised that applying a "clean" supply to the chipset and or 5v inline supply does not sound so good. I think this may be a similar situation to what was happening here.

http://www.phasure.com/index.php?topic=2640.msg28369#msg28369

Again assuming that the usb chipset / 5v inline supply and clock are fed from the molex if you were to isolate the clock supply and put the battery or linear supply on that only but keep the molex connected to the SMPS then I think the result might be a good one. The only reason this seems to work is that the clock is transformer decoupled, so the good supply to the clock improves its performance but does not influence the USB chipset / 5v supply.

If the assumption about the molex powering both the USB card and or 5v inline USB supply and clock is wrong then please disregard these comments, time to think again

Looking forwards to hearing the card at mine when you come by.


Cheers,

Nick.

Very nice  could that be on a piggy back board or built into a lead  haha 

Nick.

Peter hi,

Yes I tried a variety of PSUs and a shorter 1m fibre cable but just could not get it to be as effective as direct USB. In the end though its been a useful part of the journey, adding to the understanding that reduction of jitter in the PC to DAC USB connection is more important to sound quality than galvanic isolation of the USB connection.

On another subject I spent half a day building a transformer isolated I2S lead last weekend to try in my NOS. I was not really expecting it to be successful given the link speeds but though it would be fun to try. At 16x up-sampling I managed to get reasonably good electrical wave forms across the lead but I think the rise times of the transformers put the data streams out of sync. I did get some music playing (which was very surprising  ) but under a massive layer of static.

I might spend a bit more time with it to see if I can pin down specifically what is happening. Also it might me fun to try at different upsampling rates just to see what happens.

Here's a couple pics of the "creation" 

Regards,

Nick.