I want to close out comments on the Anadco fibre USB extension system that I made here.

http://www.phasure.com/index.php?topic=2640.msg28094#msg28094

At the time of the post tweaks to the Anadco were improving its performance significantly. However, I now don't think that the Anadco can be made to equal or exceed the sound quality performance of a direct USB connection  (assuming there are no major electrical / noise problems with the direct USB connection). 

With an unmodified PC USB interface and NOS1 the Anadco could not be made to better the direct connections performance. With the clock upgrade to my PCs USB card and the upgrades made to my NOS1 the Anadco cannot get near the performance of the direct USB PC to DAC connection.

So the conclusion here is again the same that Paul and I reached when we tried the Anadco system in both of our systems a year and a half ago. I guess that the benefits of galvanic isolation of the USB link between the PC and DAC are outweighed by the complexity / jitter introduced in to the USB link by the Anadco.

Worth a try bit the Anadco system goes back on the shelf 

Nick.

There are a few members using the AirLink balanced transformers and more experiances in a thread on the forum.

I have ended up with couple of 3kva AirLink balanced transformers (as tested in the link above). They do make a really significant difference to sound quality and I generally agree with the tests findings on the AirLink. Paul and Mani also use them although I think Mani has 2X 5kva model IIRC. One thing that is worth bearing in mind and possibly not covered by the test is that the sound quality improvements are pretty much doubled (subjectively) if a dedicated audio system PE is setup with the AirLinks using an earth spike.

I also have some 2KVA single ended mains isolation transformers but compared to the AirLinks these are nowhere near so effective so I think a the balanced isolation transformer design is really worth the effort and cost.

The two 3kv AirLinks transformers power all of my audio system. PC, DAC and Gainclone amps are plugged into first AirLink and my active Subwoofers are plugged into the second AirLink. Placing the subs on their own AirLink makes a big difference. I agree with Berts view (below) that placing the "main amps" on the same isolation transformer as the rest of the audio system make a dull sound. This in the end was the reason for buying the second AirLink unit.

Its interesting that to obtain the best sound, I need to have my PC DAC and Gaincline amp plugged into the same AirLink unit. This seems to suggest that a common mains power reference point for these components is more important than the possible negative effects of hash being put back into the mains supply by the PC, DAC and Amps.

As you can tell I'm a big fan of the AirLinks  .

Cheers,

Anthony hi,

There is potentially a cheap way to see how much headroom the TCXO power supply has for improving sound quality.

I found the supplier of the piggy back board on your card online before I built my DIY clock and looked at the layout. I think its likely that the TCXO is run from a 3.3v supply derived from the 5 volt supply going to the piggy back board. It would be easy to check the pins on the TCXO with a volt meter to see if this is the case.

If it is a 3.3v supply then powering the TCXO with a 3.3v nominal voltage A123 brand LiFePo4 battery will give you an idea of what a really very good quality linear supply will do. I tried these batteries after reading about John Kenney's experiences using them to power clocks in his HiFace modified interfaces. There like nothing else I've come across.

It's important to get the A123 brand as the chemistry is different to other brands and this makes a difference. If you can find them 2100mah A123s are about £10 (uk). A good place to try is suppliers of radio controlled model cars and plane. With one of these batteries the chances are that you can leave the clock running for 2-4 days between charges so could even be used longer term but testing this way will really highlight if its worth investing more money on a good linear supply for the VCXO.

Cheers,

Nick.

I wanted to keep the information together in-context so i'v posted a couple of updates to the post on the 5v USB cable supply voltage.

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

and the post on building a replacement oscillator for a USB PCIe card.

http://www.phasure.com/index.php?topic=2640.msg28522#msg28522

The updates are in blue text.

Both have posertive effects on sound quality (well here at least  )

Cheers,

Nick.

Brian hi,

Not at all.
I am doing exactly as you say at the moment. Having worked on my PCIe card I'm using mobo usb3 as my standard setup at the moment. I find it beautifully smooth but lacking just a little presence. Very good for general listening though 

Regards,

Nick.

Anthony,

Thanks for posting the pics of the PPAstudio card. It's interesting to get your impressions of how it compares to other setups like the SOtM and Anadco.

Will post back an update when / if I get the oscillator setup bedded in.

Cheers,

Nick.

Coen hi,

I realised that also last night :-) The spec on the vcxo is not too bad as it is but I think I will set the frequency  adjust pin to a definite potential. Could be that the floating adjust is why the sound is not quite as expected !

Im considering using a specialist clock module as the final set up. The Dexa clock I use in my NOS1 has transformer coupled output which  to but is not available in 24mhz frequency so may have to work something out there.

Cheers,

Nick.

Hi,


I've been continuing to look at the digital side of my system as part of my PC / DAC program of upgrades. Today's fun has been with the oscillator crystal on my NEC chipset USB 3 card. The standard oscillator on the card is a crystal and two capacitor resonant circuit. It's about the lowest cost setup. An order was placed for some low phase noise VCXO oscillators some time ago, they arrived earlier in the week, much of today was spent working on the PC USB card.


Results of placing the VCXO into the USB card have been as follows.


Case 1) VCXO replacement of standard crystal, power from the PCIe 3.3v supply.


Sound quality overall not as good as the standard crystal. The highs have real sparkle and superb crispness but sound lacks richness and bass in particular has taken on more of the "one note" quality that has been fixed recently. Don't get me wrong it's absolutely not down side everywhere but overall it not as good as the standard crystal.


Case 2) VCXO replacement using a LiFePo4 battery.


The idea here is to see of the PC supply is spoiling the performance of the improved VCXO oscillator (theories here are linked to the USB cable related post above). The result is significantly better. Bass and general richness is improved on case 1), top end sparkle not quite so good. So why is the system not better than the standard oscillator ? My hunch is that there is still a different noise profile in the PC's 3.3v supply and the battery and the USB chipset sees this on its crystal input, with this in mind onto case 3.


Case 3) VCXO replacement with the LiFePo4 battery now with the output of the VCXO feeding the USB chip via a decoupling signal transformer.


Now we are really getting there. The positives are the sound has so little to do with the speakers :-). Bass is excellent (percussive in quality) the sense of "realness" and presence in the room has taken a big step forwards. But the top sparkle is not as smooth as I would like and although realness his improved there is now only a very slight loss of richness (like replacing a rare NOS valve with just a good modern production vale in an amp). Case 3 is wired as a "lash up" using stuff to hand at the moment, so things may improve with more hours on the new "clock" and a more sensible layout and running in the capacitors used. Also I don't want to be using the battery in the long term so it needs setting up to use the PC supply.


So conclusions so far.


- Firstly the oscillator in the USB host card REALLY matters.
- For an oscillator to work well it appears that galvanic isolation really helps.
- There is potential here for a very big step forwards, there are "problem points" in the sound that I have been living with for years that went way today. Sound is not as balanced overall as I want but I think that can be done.


Last thought is that in the past I upgraded the oscillator at the music interface's USB decoder chip (eg the DAC end of the USB link) and that is where the biggest gains were found. I have a second VCXO ready to use in the DAC if the PC card can be made to work (and I can work up the guts, it doesn't look easy to fit).


I'll post updates, for now a few pics.


Nick


UPDATE 25.10.13

The first clock circuit was built using components to hand but still pointed at significant improvements in sound. I've been placing better selected components over the last couple of weeks and the results are now really great.

First change was replacing the audio note SPDIF transformer (which was to hand)  on the oscillator output for a good signal spec transformer and choke combination, this gave a really big change and then finally there are now decoupling caps of the correct size ether side of the signal transformer. Together this has really elevated sound quality.

Sound quality is now best described as getting real. There are a lot of other changes besides the USB interface mods above in this post now implemented in my NOS1. These and now with the new clock on the USB card have sound to most enjoyable levels. Even my duo speakers are playing some of the most precusive and tuneful bass I have heard. The sound stage just makes me smile at times, from stereo speakers it can be like listening to a 5.1 multi channel system at times people and instruments all over the place  .

For now the batter power on the USB clock will stay the drain is so low one cell lasts for days between charges and no problems creating a clean supply within the PC. I don't think this is the final stopping off point on the USB card setup but for now whilst work continues elsewhere this will more than do 

I'll post any further updates here.

Nick.

Anthony hi,

Another consideration is the sequencing of the power rails during turning on. There mobo will expect a "power good" signal to be provided after the rails are sequenced on.

I had a look at options for building a linear supply a while ago but did not get further than reading arround what the supply would need to do.

Take a look here the "power good" information is half way down the page.

Cheers Nick.

http://www.tomshardware.com/reviews/power-supply-specifications-atx-reference,3061-2.html

Peter hi,

 I have read back my last post to myself and feel that it's not really appropriate for me to raise these points here, my apologies. This is Far better an off line discussion, I certainly don't intend to deflect attention from your achievements with the speakers.

I hope you will permit me to remove the post and we can discuss the topic elsewhere.

Kind regards,

Nick.

Paul hi,

Spot on ! This is exactly what I was hoping for. Most will not know but we both have very little desire to change the balance and presentation of the our systems right now.  This just seems to allow tuning of that small and persistant "sharp corner" in the highs. Its been remarkably difficult to tame without "filtering" using other methods to mask the problem but  in doing so sound is compromised elsewhere. This tweak seems to let the highs sparkle more but whilst not changing the sound elsewhere.

It's remarkable when you think that the cap you are using is just 20pf bypassing 100nf already in place. That's 1/5000 th of the main cap value. The devil as they say is in the detail.

I'm looking forwards to trying out some smaller caps in my system.

Cheers,

Nick.

Paul hi,

This may not appear so but could be very useful information. As we discussed I think the effectivness of the cap in this position is likely to be specific to the pc set up being used. Let us know if other sizes work / what characteristics of sound they give.

Cheers,

Nick.

Thanks Peter, I see what you mean. Im not sure about overall positive effects of the additional cap yet. I think some more listening and maybe changes to size are needed to decide.

Its interesting thought that at least in my system pc supply sounds better and that the attempts to "clean" the supply introduce such changes to the sound.

Im not sure it will lead to anywhere but fun to try out 

Cheers,

Nick.

Peter,

I really agree with you here, I dare not imagine how much time went in to tuning the DAC board ! Im looking at cap types but would not touch values its very obvious that there is design that's beyond me, so i'm not about to meddle haha.

The only change I did try  to a cap values on the board did not work (ref post above) !  .

Nick.

Edit - I selected the wrong post of Peters to "quote", it now reads as intended.

I wrote part 1 of this post a few days ago and was going to post in the USB Cables.... Again thread but decided against it. Then after sleeping on the thoughts below decided to try something else which may add weight to the ideas on the effect of USB power supply noise put forwards below. Part 2 of the post deals with observations today.

Part 1

 I had a play about with isolating the 5v pin of my USB cable last night. Its something I had a go at quite a while ago with a diy platted silver usb cable and got "good" results at the time.

http://www.phasure.com/index.php?topic=1977.msg20341#msg20341

I tried "cutting" the USB 5v supply (using PVC tape over the pin in the USB socket),  and following this then went on to try replacing the PC 5v supply with regulated 5v and 3.3v supplied derived from inside the NOS1.

I though I would post some observations on sound changes and ideas about possible factors contributing to the changes.

First sound quality.

1) With 5v PC USB connected.

Boarder sound stage, fuller but possibly slightly less damped bass richer sound and tone.

2) Without 5v PC USB connection (USB power pin taped over)

Sound stage shrinks slightly but is sharper in terms of pinpointing individual sounds. Sound is generally tighter but slightly thinner, tone is not so convincing. Bass is better damped but the room ambiance form low frequency is not there possibly giving the sense that the sound stage has reduced in size.

3) With 5v PC USB disconnected but NOS generated 5v or 3v supply provided to the USB power input.

Sound is smooth but loses high frequency information which results in sound stage shrinking and a loss of perceived presence. This is very similar to the presentation of the Anadco fibre interface or the X-sound PCIe capacitance card.



My preference overall was easily listening with the PCs 5v USB connection in place. This is not what I expected. 



Some thoughts on what may be happening.

What does the 5v supply do within the NOS ? two things (and similar for other interfaces):-

• First it is used to pull up a bus enable signal into the USB chip (this does not appear to be needed because the NOS works fine without any 5v supply).
• Second and possibly important here is that the 5v usb supply connects within the NOS (and may other usb interfaces) into an anti surge protection chip that protects the d+ d- data lines of the USB interface connection from surge conditions on the USB connection.
  

The surge protection chip is a diode network that connects the d+ d- to the +5v USB supply and signal ground of the NOS. What all of this might mean is that conditions on the +5v supply wherever it comes from could link noise to the d+ d- signal lines ???

What is interesting though is that sound seemed better with the PC USB 5v line connected. This is what lead to the test replacing PC USB 5v supply with the NOS's own Internal supply voltages to see if a "low noise" 5v supply would have less influence on the d+ d- lines and signal ground. As reported above the sound was smooth and similar to having the 5v USB connection cut completely but still my preference was for using the PC USB 5v connection.

This is a stab here, but an idea that might to explain why the PC usb 5v supply sounded better than either no 5v connection or a "low noise" 5v connection, could be as follows. The noise level on the 5v line, wherever it is taken from is probably going to influence conditions on the d+ d- lines at the anti surge device.  However it may actually be better from a jitter point of view to use this PC 5v USB. it might be that the d+ d- lines may be carrying similar noise spectrum to the PC 5v USB line which might present as common mode noise on all three USB lines and not impact the d+ d- data transmission so much as it reaches the usb decoder chip. Alternately when using low noise 5v supply (from the NOS internally) any noise carried on the regulated 5v supply will not have the same spectrum as noise on the data lines and as a result may have a greater impact on the d+ d- transmission to the USB decoder chip.

This is just an idea to provoke discussion, I'v probably has a bit too much to drink here last night when thinking about this but thought I would post the ideas. It would be good to get to the bottom of what causes the differences heard.

Part 2

So today I wondered what would happen if the 5v PC USB supply were bypassed (smoothed) with capacitors at the NOS end of the USB cable. The answer turned out to be quite a lot happens and some potentially good stuff at that.

I added a range of capacitance values between the 5v PC USB supply and the NOS USB card signal ground. Observations on sound are as follows (note the NOS already has 100nf in this location so the values stated are in addition to this).

2200uf
Sound is smooth loses presence base is controlled and strong but sound is unbalanced with highs rolled off. Just like the regulated 5v and 3.2v supplies, a pattern forming perhaps.

470uf
Overall balance improving but sill nowhere near not having a capacitor for presence etc.

10uf
Still losing the harshness of the unfiltered 5v USB PC supply but still also not well enough balanced or detailed enough.

400pf smother sparkling top end mids and lows sounding good but transients are just a little slower than an unfiltered connection

220pf now we are really getting there. Hash gone, presence intact, beguiling sparkling highs, transients intact !

I'll try a few more values round 220pf and listen more but this is sounding very nice. It's a tuning point rather than extremely large change of the USB pcb tweaks but very nice all the same. Seems to give the sense of transparency and focus of lifting the PC 5v supply whilst keeping the life scale and tone of having the PC 5v supply connected.

I will post more thoughts after some more listening.

My guess is that the value of cap that gives good results will vary from system to system because it may be linked to the noise spectrum coming from a particular PC.

Nick

UPDATE 25.10.13

Looking at a few PCIe USB 3 cards most seem to use a DC to DC converter to take the PCIe 3.3v bus voltage and convert this to the 5v rail that is carried by the USB lead. So the cards i have looked have a SMPS running at 300 to 450 kHz straight onto the diode clamp mentioned above that terminates the USB d+ d- signal lines most DACs. For most of us the supply will just sit idle (supplying no current) 'humming' away on the USB card. The tests above showed that bypassing this 5v supply with a clean supply was not great. But what happens of the USB's 5v rail has some resistive rater than capacitive load applied to it ?

I put a 1k potentiometer between the USB 5v rail and the signal ground on the NOS1 interface. Having the load really help sound here. Best sound for me is around 200 ohms of load so around 25ma of current. If you try this be carful not to go below about 75 ohms as you will start approaching the 500ma rating of your USB card or mobo usb port (by 10 ohms load) and may get a hot potentiometer.

Sound quality changes with the resistance but is better in my system with a resistance in place. At 200 ohms there is subtle but important change throughout the frequency spectrum. Sounds like a slight reduction in jitter.  Bass takes on a more tuneful deeper and percussive feel especially.

The resistor seems to work well for both pcie usb and mobo usb.

I was wondering of the effect might be about countering ground loop current between the PC and DAC. I know ATx supplies tend to elevate the pcs signal ground a few mv with respect to PE and in my case my amp signal ground is connected to PE which could be making a loop from PC to DAC to amp. Whatever the cause the resistor is defiantly staying in place for now 


Regards,

Nick.