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Post by themystical on Jan 21, 2013 16:23:46 GMT
Hi Guys I have been investigating a usb isolation/low noise power solution for my Amanero I2S interface. There appears to be no reasonable commercial device that will handle High Speed USB and in any case my interest is in DIY. Having read all the good work done on this forum by SandyK and others vis a vis JLH and splicing into USB cables etc., I have been wondering how to get isolation for the earth connection as well. In my view, this is a prioriy second only to a clean, low noise 5V supply; data connections being much lower priority. Anyway, I came across this recently release commercial product apparently designed by AMR and build by iFi - audio iUSB isolator, see link below: www.ifi-audio.com/en/iUSB.htmlThis device has a switch which allows the user to choose whether the earth connection should be on an isolated basis or not - Brilliant! What I have been struggling with is to understand how it actually works. It doesnt seem like "galvanic" isolation is a valid option because I don't think the USB connection will work if there is no earth connection between the two interconnecting devices. Below is a photo of the circuit board. fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-prn1/457390_490388604330220_623625141_o.jpgIt is clear from the photo that the data lines are just routed "through" and +5V is derived seperately. Anybody have any insight as to how they might be dealing with the earth isolation? It would provide a good improvement to the current designs we have on the table.
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Post by Deleted on Jan 21, 2013 19:50:30 GMT
You could pop your question onto the end of the Computer Audiophile thread which has been looking at this for roughly a year. I only skimmed through but didn't see any direct explanation as to exactly how the earth circuit is handled.
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Post by Deleted on Jan 21, 2013 20:38:05 GMT
I have been wondering the same, as well as the accuracy of their claimed figures for PSU noise.( .1uV, yeah,right!) It annoyed me that the guy who posted all this stuff in C.A. was waxing lyrical about it without even having used the one he has, at least at the time. Alex
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Post by themystical on Jan 21, 2013 20:38:33 GMT
You could pop your question onto the end of the Computer Audiophile thread which has been looking at this for roughly a year. I only skimmed through but didn't see any direct explanation as to exactly how the earth circuit is handled. Yes I had a look at that thread as well. I think the manufacturer has also posted on that thread and is obviously protecting his commercial interest being quite cagy so I don't think there is any possibility of an answer there. I am afraid the only way is to work it out from first principles with the help of the picture of board that I have also linked to.
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Post by themystical on Jan 21, 2013 20:56:59 GMT
I have been wondering the same, as well as the accuracy of their claimed figures for PSU noise.( .1uV, yeah,right!) It annoyed me that the guy who posted all this stuff in C.A. was waxing lyrical about it without even having used the one he has, at least at the time. Alex You can see from the board that there power section is mult-staged and quite extensive so I am sure it is pretty good although I am not sure that .1uV is practical. In fact I am pretty certain that it isn't. However, on the power side there are a number of options that you have as a DIYer including the JLH, Salas, TPR etc. so although I would like to understand what they are doing, I am not too desperate to do so. I dont have an alternative for the earth isolation though so need to find a solution. When you look at the ground management section of the photo, you see a 6 terminal switch, capacitor C2 and Resistor R3 and 2 Diodes (D5 and D6). One pole of the switch is obviously bringing on an LED and another switches the earthing circuit. I think they have freely admitted that it is not galvanic isolation so the earth connection is obviously an electronic circuit? Am I right in saying that you can't have any diodes in the actual earth path itself because where is the diode conduction voltage going to come from? What I wondered was whether an in-line resistor would attenuate noise and still register as an earth connection ( an earth lift resistor effectively) and whether the switch was shortcircuiting this? Any ideas anyone?
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Post by themystical on Jan 21, 2013 22:58:37 GMT
Ahaa....maybe a clue here? A loop breaker circuit? See Fig 4 and explanatory text in this link. sound.westhost.com/earthing.htmOkay it is not exactly the same, back to back diodes - not a bridge but sure looks like the thing. Question is a USB earth connection work if it had a say 10 Ohm resistor it? and surely the parallel capacitor would let HF noise through which is what we are trying to avoid?
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Post by Deleted on Jan 21, 2013 23:03:23 GMT
Ahaa....maybe a clue here? A loop breaker circuit? See Fig 4 and explanatory text in this link. sound.westhost.com/earthing.htmOkay it is not exactly the same, back to back diodes - not a bridge but sure looks like the thing. Question is a USB earth connection work if it had a say 10 Ohm resistor it? and surely the parallel capacitor would let HF noise through which is what we are trying to avoid? That is my thinking exactly . In this case, it doesn't sound like a good idea to have a parallel ceramic capacitor. Regards Alex P.S. For R.G. members, there should be 100 of Greg Erskine's latest dual JLH PCBs departing for the U.K. around Friday this week. Jon Clancy will be announcing details after he returns from Sydney. I don't know about the costing at the moment, but it will be very modest , due perhaps to a donation to charity component? That will be Jon's call. There is NO profit involved with the JLH PCBs, as is always the case. Greg Erskine is owed a great deal of thanks for the time and effort, as well as money he has put into various versions of these PCBs to get them available to RG members , as well as a few members from other forums.
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Post by themystical on Jan 21, 2013 23:33:40 GMT
That is my thinking exactly . In this case, it doesn't sound like a good idea to have a parallel ceramic capacitor. Regards Alex[/quote] Yes I think you are right. The larger you make that resistor, the more it will attenuate any noise in the earth connection. I understand typical values in ground lift applications are between 10 and 100 Ohms. So I guess the million dollar question is will a USB connection operate correctly at high speed with a 10 to 100 ohm resistor in series? Anybody have a chopped USB cable lying around that they can experiment with or is there anything in the USB cable standard that will answer this?
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Post by themystical on Jan 21, 2013 23:53:18 GMT
Perhaps the capacitor is a directional type - an electrolytic say - which conducts HF noise from the attenuated side to the non attenuated side? Thanks for the JLH Board info Sandy....I certainly would like some. Hopefully Jon will post availability on this forum upon his return.
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Post by Deleted on Jan 22, 2013 0:18:28 GMT
I just tried a modified USB Power Injector as a guinea pig, by cutting the small copper land between pin 4 on the incoming USB socket and inserting a 10 ohm resistor. (far left, and centre of PCB)Yes, it does work still, but I can't really evaluate the SQ as although this modified USB Power Injector gives a definite SQ improvement normally, it isn't quite up to the standard of the normal +5V JLH supply when using a USB memory stick.This doesn't necessarily mean that it will still work with other USB devices.
Alex
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Post by themystical on Jan 22, 2013 0:29:08 GMT
I just tried a modified USB Power Injector as a guinea pig, by cutting the small copper land between pin 4 on the incoming USB socket and inserting a 10 ohm resistor. (far left, and centre of PCB)Yes, it does work still, but I can't really evaluate the SQ as although this modified USB Power Injector gives a definite SQ improvement normally, it isn't quite up to the standard of the normal +5V JLH supply when using a USB memory stick.This doesn't necessarily mean that it will still work with other USB devices. Alex Wow that was quick and a very good start. Have you got a 100 Ohm resistor you could pop in and see whether it still works? I guess the acid test is with a high speed USB device but I am beginning to get confident that this is a very workable solution and is indeed the solution used by AMR. I am off to bed now Alex but many thanks for your help and have a good day!
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Post by Deleted on Jan 22, 2013 0:54:31 GMT
Yes. This USB memory stick still plays "Rhiannon" from Fleetwood Mac in 24/96 without any noticeable problems. Regards Alex UPDATE. I have now done the same to my +5V JLH USB PSU, and a couple of new rips from Jheena Lodwick made in Windows Safe Mode, sound noticeably better than my previous best.They simply sound a little cleaner, with more "blackness" around things. As most of you guys are asleep at present , I have invited a C.A. member from the U.S.A. with a JLH PSU to try this too. Jim's reports are also quite positive, although even with 100 ohms he had a couple of failures after 8 minutes of play with his USB DAC. My USB memory stick continued to play for 90 minutes with 100 ohms, before I ended the test. P.S. Yes, the checksums of the rips remained unchanged.
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Post by themystical on Jan 22, 2013 10:54:58 GMT
Yes. This USB memory stick still plays "Rhiannon" from Fleetwood Mac in 24/96 without any noticeable problems. Regards Alex UPDATE. I have now done the same to my +5V JLH USB PSU, and a couple of new rips from Jheena Lodwick made in Windows Safe Mode, sound noticeably better than my previous best.They simply sound a little cleaner, with more "blackness" around things. As most of you guys are asleep at present , I have invited a C.A. member from the U.S.A. with a JLH PSU to try this too. Jim's reports are also quite positive, although even with 100 ohms he had a couple of failures after 8 minutes of play with his USB DAC. My USB memory stick continued to play for 90 minutes with 100 ohms, before I ended the test. P.S. Yes, the checksums of the rips remained unchanged. Thats great news Alex. Perhaps an electrolytic at say 0.1uF in parallel connected the right way around might improve it even further? I think a switch to short circuit this arrangement is a good idea as it covers the types of failures that Jim experienced?
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Post by Deleted on Jan 22, 2013 11:10:22 GMT
Hi We will need to try that with and without. You don't normally see earthlift resistors in power amplifiers bypassed, do you ? I can say though that fresh rips in Safe Mode sound even better now ,despite what the check sums say! I have just uploaded freshly ripped versions of a couple of tracks for confirmation by a European RG member and others who have already heard the previous recent rips linked to in Saucerful.(Staff area) Regards Alex P.S. I couldn't measure any steady voltage across the 100 ohms,not even a few mV.
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Post by themystical on Jan 22, 2013 11:26:10 GMT
Hi We will need to try that with and without. You don't normally see earthlift resistors in power amplifiers bypassed, do you ? I can say though that fresh rips in Safe Mode sound even better now ,despite what the check sums say! I have just uploaded freshly ripped versions of a couple of tracks for confirmation by a European RG member and others who have already heard the previous recent rips linked to in Saucerful.(Staff area) Regards Alex P.S. I couldn't measure any steady voltage across the 100 ohms,not even a few mV. Exvellent - Guess it is almost bedtime for you but looking forward to your report on the capacitor addition at some stage. No you don't normally have switches in parallel with the earth lift in power amps but than again, this is less sensitive in a power amp analogue context - in the USB circuit it is catastrophic in the sense that it either works or doesn't? In case it doesn't it would be simple to flick a switch? Are you using a scope for the measurent? I don't think the noise will be steady state and will vary depending upon the quality of the host switched mode supply and what the internal electronics in the host PC/Laptop are doing at that precise moment.
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Post by Deleted on Jan 22, 2013 11:45:10 GMT
Not at this point. It was quite awkward getting even a DMM across the resistor while the PSU was in use. I was more looking for evidence of some kind of small curent used to tell if the lead was connected or not.It could of course be probing at specified intervals. Jim has already played around with diodes in that area, so he may continue on while I am asleep. Regards Alex
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Post by themystical on Jan 22, 2013 12:19:22 GMT
Not at this point. It was quite awkward getting even a DMM across the resistor while the PSU was in use. I was more looking for evidence of some kind of small curent used to tell if the lead was connected or not.It could of course be probing at specified intervals. Jim has already played around with diodes in that area, so he may continue on while I am asleep. Regards Alex I think we are playing around in the microvolt area and transient phenomena so it would be impossible to analyse without a scope. The diodes are a bit of a red herring here as they don't come into play unless there is a real short circuit and ground potential is raised at either end with respect to the other to allow them to conduct. They just fail in the right way and short circuit the added resistor in a real fault situation - no impact on attenuating noise. Does Jim post on this forum?
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Post by Deleted on Jan 22, 2013 12:33:54 GMT
That's why I didn't worry about trying diodes. Jim mainly posts in C.A. as sjoc2000, and occasionally in DIYAudio.He was going to continue on from the 100 ohms after a sleep.Which is what I am about to do. Alex
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Post by themystical on Jan 22, 2013 16:43:41 GMT
Alex I have not made much progress with this in your absence but one thought that has occured to me is about the sizing of the resistor. In typical power amp situations, 10 ohms would kill hum which is at 50Hz. However, impedance rises in proportion to the frequency so will probably be less effective at higher frequencies. How high can we go before you think the USB link will stop functioning? Obviously the higher you go with this value, the closer it is to galvanic isolation so if for example 1k or 10k is doable (is this a word?) so much the better.
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Post by Deleted on Jan 22, 2013 18:29:26 GMT
Yo, Well I can confirm that firstly, there is no problem with pen drives being recognised and read (running for several hours now) and there is an improvement with the earth lift rip. Mainly in solidity and nuances such as resonances becoming more evident with more discernible decay. Out of curiosity I popped in the 10ohm earth lift into my jaycar injector, as described above by Alex. I then re-extracted the newest files again and bugger me, not the same amount of improvement but still apparent over the original extraction. Definitely onto something here
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Post by themystical on Jan 22, 2013 20:10:26 GMT
Yo, Well I can confirm that firstly, there is no problem with pen drives being recognised and read (running for several hours now) and there is an improvement with the earth lift rip. Mainly in solidity and nuances such as resonances becoming more evident with more discernible decay. Out of curiosity I popped in the 10ohm earth lift into my jaycar injector, as described above by Alex. I then re-extracted the newest files again and bugger me, not the same amount of improvement but still apparent over the original extraction. Definitely onto something here Hi cj Definitely sounds like we are heading in the right direction with this and the improvement will depend upon "how bad" your laptop/PC is to begin with. If we can get a handle on the maximum size of resistor that the USB link will tolerate, that would be good as the higher the resistance value the better the isolation.
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Post by Deleted on Jan 22, 2013 20:48:35 GMT
This is the thread that my friend Jim from Iowa has started about experiments with a JLH and USB PSU improvements. www.computeraudiophile.com/f6-dac-digital-analog-conversion/continuing-pursuit-power-supply-improvements-and-improved-dac-performance-14165/ Jim is presently using 10 ohms again, and will try increasing up to 100 ohms where he struck problems. However, we shouldn't normally need to go much higher than that as the earth lift resistor in most amplifiers is around 10 ohms, or in a recent Silicon Chip magaxine design 22 ohms, because they obtained slightly better measurements due to the proximity of a toroidal transformer. The reason being that with a typical PC as distinct from a laptop, we are seeing a good old fashioned earth loop with devices such as USB memory sticks for example.The -VE supply from the PC is internally connected to the shield in USB memory sticks. You can easily verify this by measuring between the black wire ( 0 volts line) and the screen with the device plugged in.You will see a short circuit. Unplug the USB memory stick and the s/c will disappear. I was previously aware of this. Regards Alex
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Post by themystical on Jan 22, 2013 21:44:05 GMT
Taking a look at Jim's posts on CA, it looks like he managed to get the USB link working with a diode in line, albeit only for short periods. That is in effect a series resistance of many Megohms. I think it would be worthwhile sticking in a resistance of say 1kohm at some stage and seeing whether the link still works. I see the solution as a user switchable earth isolation switch e.g. Position 1 - No isolation - resistors shortcircuited Position 2 - Earth isolation - 10 Ohm resistor engaged Position 3 - Max isolation - 100 Ohm resistor (or higher value) engaged Thats pretty easy to implement and would cater for the vagaries of different USB devices In a DIY context, there would be no need to do anything special. I mean how hard is it to desolder and solder a different resistance value?
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Post by Deleted on Jan 22, 2013 21:55:54 GMT
Jim told me a few minutes ago that he noticed a small improvement at HF, by putting a 100uH choke in series with the 10 ohms. I would be wary when going there though, as even inserting a 5A 100uH choke in series with an internal writer's supply tended to exaggerate HF detail, despite a bypass capacitor after it. Alex
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Post by themystical on Jan 22, 2013 22:59:14 GMT
Jim told me a few minutes ago that he noticed a small improvement at HF, by putting a 100uH choke in series with the 10 ohms. I would be wary when going there though, as even inserting a 5A 100uH choke in series with an internal writer's supply tended to exaggerate HF detail, despite a bypass capacitor after it. Alex Alex From a first principles point of view, a choke in series with say a 10 Ohm resistor sounds like a good idea - provided the USB circuit will function. This is because the impedance of the connection will go up as the frequency increases (z=2(Pi)fL). This means that the higher the frequency, the more effective the isolation. The ideal theoretical solution is the resistor in series with the choke with a directional capacitor in parallel to both - filtering hf from the protected size. Not sure about the sizing but if the USB connection works with it in place thats good. I suspect your caution is coming from a different application of the choke? Avinash
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