[Kawai_man]

Hi I was just wondering If adding a resistor  in between a USB or Firewires ground wire would be a good way to reduce the rfi/emi noise? if so what the most resistance I could get away with? thanks

 

[t0wer]

http://www.radioshack.com/product/index.jsp?productId=3012599
 
Put them over the cord close to the device receiving input.
(usb mouse > computer, put close to usb end;  computer > usb dac, put close to dac)

 

[leeperry]

there's no escape: http://electronics-shop.dk/galvanically-usb_isolation
 
I'm using this cable, it has fixed noise issues compared to the cheapie that was shipped w/ the Xitel DG2: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250547392412

Gold Plated Connectors
Ferrite Core
Supports Hi-Speed, 480 Mbps
28AWG*1P+24AWG*2C

 

[Kawai_man]

 
Quote:

http://www.radioshack.com/product/index.jsp?productId=3012599
 
Put them over the cord close to the device receiving input.
(usb mouse > computer, put close to usb end;  computer > usb dac, put close to dac)

A ferrite core wont really do much and it will add impedance to the all the cables it covers this is not good for the digital signals, in order to get good noise reduction using a ferrite a wire actually need at least 5-10 turns on each end of a wire if it was possible to put it just on the ground wire it would be fine but since it covers all the cables inside the usb it will degrade that signal.
 
 
I dont have any noise issues by the way I just want to minimize the effects that the dirty ground from the computer has on a dac which affects the sound quality.

 
Quote:

there's no escape: http://electronics-shop.dk/galvanically-usb_isolation
 
I'm using this cable, it has fixed noise issues compared to the cheapie that was shipped w/ the Xitel DG2: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250547392412

 
The usb isloator looks like it might do the trick I know theres a few other in that price range too.  I want to know if my solution could work though I think it would but I want to know for sure , it will only cost me 1 dollar and the price of the cable

 

[ROBSCIX]

A good isolation circuit will allow you to feed in your own power supply.  This is what you want because that is where the degradation comes from in regards to audio, that and jitter.
There are many great USB isolation circuits out there.  Be careful though because if your devices is a high speed unit you might run into issue with isolation circuits.
 
I would also suggest buying a quality cable.  Not a super duper snake oil cable but just a quality cable. 

 

[esdk]

Hi All,
 
Here is some info to the ground looping problem heard as humming noise, bas distortion, etc.:
 
Quality USB/SPDIF cable.
A quality cable USB/SPDIF will not solve the degradation of sound when using an USB->DAC or an USB->SPDIF adaptor.
The problem is that a small difference in ground level will influence the audio signal. Prober grounding technique with a thick green/yellow ground wire will help the best - but the problem can still exist as the DACs deliver audiosignals with signal level of only 100mV (0.1V).
The so called quality USB and SPDIF cables are only good for a few purposes - extending the limit of cable length or/and if they have a huge chunk on it - remove EMC problems that would otherwise prohibit the device from being sold.
 
External powersupply is not a good solution either. 
The powersupply must be totally isolated (Class 3) to avoid making a new ground loop connection - most small DC power adaptors are Class 2, which have a cap to ground.
Don't worry about that noise from a correctly designed DCDC powersupply (USB2ISO has 50mv from 0-20MHz at 5V).
The powersupply noise on the 5V will not influence the audio signal. That is because most DACs for audio uses 3V which they get from at LDO inside the DAC module. Also remember that the noise is ontop of 5volt and easily cleaned by the caps used inside the DAC module. The noise on the USB port on PC can be 250mV - but will be reduced to 50mv through the isolated DCDC.
Also note that an external powersupply will not ensure correct initialization of the USB bus using the ADUM4160. Circuits at Home has some FAQ on this issue.
 
USB Jitter and DAC/SPDIF adatops
Jitter on USB does not influence the audio signal unless it is a bad designed DAC/SPDIF. The USB does not provide seperate clock - so a transmission from PC to USB device is captured at the local device clock source that will be PLL locked to the incoming packet. This means the clock will change when sending/not sending - Which is bad if used for the DAC/SPDIF and much worse than the jitter on signal rise times that can be introduced by having the ground looping problem. The USB isolator does not improve jitter - but it removes problems on the bidirectional USB signal that is introduced through the ground looping signal. 
 
NOTE:
When using TosLink (1mm Plastic cable) - no electrical connection exists. Also a lot of stereo amps has SPDIF isolated - they won't have any problems either.
The note about highspeed USB is correct - most isolation devices are Full Speed and a lot of USB->DAC/SPDIF also are full speed or capable of running full speed.
 
Here are the specs of the USB2ISO - USB 2.0 Isolator - http://electronics-shop.dk/usb-isolator
 
I have designed the USB2ISO device because nobody else did and I needed it for my stereo HD-DTS 7.1 along with FPGA ISP progammers for a PoE design. The device is sold at cost price with 2 year warranty according to danish law. First batch is almost sold out and next 1K batch is produced in mid August 2010 if Analog Devices deliver on time.
Other people making a USB isolators on the ADUM4160 are CircuitsAtHome (needs external PSU, No Case, Fun DIY possible), Olimex (No Case, needs external PSU sometimes), BB-elctronics (Expensive HUB), IFTools (expensive €198), MeilHaus Electronic (expensive €289)
 
Please do not remove this answer - it is meant to help others not just a commercial, thanx!
 
Best Regards,
 
Soren
Electronics-shop.dk

 

[cobaltmute]

Quote:

Don't worry about that noise from a correctly designed DCDC powersupply (USB2ISO has 50mv from 0-20MHz at 5V).

And you consider that good?

  Change the millivolts to microvolts and you're starting be be acceptable.

 

[esdk]

Hi Cobaltmute,
 
Actually that is good with 50mv noise on the USB power from 0-20MHz.
 
It all depends on where you measure - if that was the rail power for DAC it would have been terrible as you state. If you use 24bit and line signals of 100mv each bit is around 6nV (0.000000006V)
 
When you design a device for 240/110V you can easily get spikes, voltage dropouts of 40Volts - but before the voltage gets to your electronics in your design it has been designed to be stable. - Adding transformers,DCDC, Linear regulators, Coils, Bulk Caps and decoupling caps to allow for a firm and stable powersupply through out the entire frequency range of your design.
That is also what happens in off the shelf USB->DAC - sometimes they are too low cost and can be improved - but mostly it is just fun to see if there is a cap, they missed, that would mean the world - it seldom happens
 
Decoupling DACs info:
When adding caps to DACs to improve powersupply add bulk (10-470uF Low impedance) and 0603 caps with 100nF - these are good in the Sound Range but it is important that the wires to the DAC from 0603 caps are kept very short to avoid inductance.
Common mode Coils on cables will not help (The large chunks on USB cables) - these do not reduce the powersupply noise as they work in common mode (all wires go through the Coil).
 
 
Best Regards,
 
Soren
Electronics-shop.dk

 

[leeperry]

Hi esdk, I currently use your dongle on a S/PDIF transport, and the SQ is so much better when it's in the USB path
 
on this link, the USB 5V ripple was measured to be 20mV: http://www.head-fi.org/forum/thread/446375/usb-24-192khz-m2tech-hiface/120#post_6079626
 
my Corsair PSU was measured to have 7mV ripple on its 5V rail, but it's prolly higher after it goes through the mobo anyway.
 
is there any room for improved filtering in your dongle? it carries a 2y warranty so I don't even know what's in it as I didn't crack it open...got pics w/o the plastic case please? any improvement possible by using higher quality caps or so?

 

[esdk]

Hi LeePerry,
 
Thanx for your support, it is great to help other audio users with the same problem as I had - The ground looping noise.
 
I did not see the scope pictures before - great study and thanx for pointing me to that discussion.
 
As you can see the noise is 17mV when running on battery - So not much room for improvements compared to a death stable battery.
 
And as JayDee writes: "In practice this shouldn't be a big deal, as any linear regulator of even marginal quality would be able to track it. Even with these new anomalies, the laptop appears to be better than the PC I tested last night, and is still considerably better than the outboard supply that came with the other USB to SPDIF device."
 
If you want to play with the powernoise tolerance - you can place a 0603 100nF and 0603 1uF between the red&black wire in the USB connector just before your SPDIF module - I am pretty sure that you cannot hear the difference. People like JayDee and other that design SPDIF converters know how to remove that small amount of noise - Their biggest problem is the ground loop all the way to DAC - but isolating the USB bus removes this hassle so they can concentrate on cleaning the power
Please be aware that an external powersupply for the SPDIF module will/can create a new ground loop and introduce noise on the ground wire.
 
I have put a link to a small video off the production of a 1K batch in the SMD machines on the webpage - see http://electronics-shop.dk/?id=900
 
Best Regards,
 
Soren
Electronics-shop.dk

 

[leeperry]

hi Soren, indeed ADuM4160 is a fantastic chip...no question about that! It provides galvanic isolation and regenerates the USB clock, it makes USB a "frequentable guy" all over again
 
I've sent you a PM w/ internal shots of my S/PDIF transport, I don't really feel like soldering anything...but you tell me if you think additional filtering would help. Maybe an "audiophile" grade of your dongle would be in good order? Many ppl could use some additional filtering I'm sure. Some even used a battery on Oleg's unit: http://assets.head-fi.org/2/2c/2c792d89_4501432809_1454a77e6d.jpg
 
My USB S/PDIF transport runs on its own discrete linear regulated PSU: http://www.firestone-audio.eu/shop/products/allproductslisted/supplier220vac.php
 
so I believe the quality of the built-in PSU would only matter as far as the ADuM4160 filtering is concerned...I couldn't find any PSRR spec for it, so the big question is: will ADuM4160 provide "better" filtering on a less noisy PSU?

 

[esdk]

Hi Leeperry,
 
The ADUM4160 is just a low cost implementation of a USB isolator chip and does not regenerate USB clock or remove jitter on USB clock.
To control the direction of data on USB you need to look for a special state on which you change direction. To find the state you need to sample - to do that you need a clock - so the Adum4160 just finds the clock by edge detect and delay. This has nothing to do with regenerating clock which would require PLL.
 
There is no need for addition filtering on a digital USB.
As I told you PSRR is only used for analog signals - USB is digital. (PSRR= Power supply rejection rate).
 
Battery on Olegs unit is good - because you need a class 3 power adaptor to get isolation. Prober decoupling of SPDIF, DAC etc. is also good - but has nothing to do with ground loops.
 
The Electronics-shop.dk - USB2ISO has built in isolated powersupply which is class 3.
 
I am the designer and also seller of the USB2ISO module - but I only want the truth about our product - it only helps if you have ground loops from PC via USB (optionalver SPDIF) to the DAC.
 
I know that is fun to try to improve stuff, but believe me - it would be better if you actually try to help each other instead of confussing each other.
 
Also the so called quality USB cables are misunderstood - you CAN sometimes hear difference - but that is because of the grounding. Use a low cost Green/yellow wire and connect between devices and ground and the best quality USB cable can't compete.
 
The other way is to remove any ground reference between DAC and PC via the USB isolater - which a lot of people all over the world have done via the USB2ISO (As have you Leeperry)
 
Here is a FAQ and short video of the smd assembly of USB2ISO module - http://electronics-shop.dk/?id=900
 
 
If you read a "getting tired of answering the same questions" in the above - it might be true - sorry 
 
 
Best Regards,
 
Soren
Electronics-shop.dk

 

[leeperry]

sadly, they don't provide much details as they're prolly protected by a NDA..but here we go: http://www.analog.com/static/imported-files/data_sheets/ADuM4160.pdf
 
"the signal must be faithfully reconstructed on the output side of the coupler while retaining precise timing and not passing transient states such as invalid SE0 and SE1 states."
 
and Oleg told me: "ADuM4160 also has a nice side effect: it regenerates USB clock, which is used by many USB DACs; as a result, DAC works better off this clean clock.'
 
Quite frankly, ADuM4160 is a god send for USB Audio...many ppl have tried it and were blown away by the SQ improvement, like this guy: http://diyparadise.com/forum/index.php?topic=1063.msg11167#msg11167
 
"it is funny, all the sounds are there, some details too, it just doesn't  sound so realistic without the USB-isolator. Music Dies away. Some of the magic dies out, the room perspective, depth is not so clear.. It's not coming out of the speakers properly without the isolator... Funny!"
 
I fully agree w/ everything he said and I think this chip does a lot more for USB audio than you are willing to believe, and I still wonder whether it would provide a "higher SQ" from a better filtered PSU.
 
You don't seem to believe that a USB S/PDIF transport could sound better from a linear regulated PSU, but many ppl have experienced the improvement...and more and more of them come w/ a low ripple DPS for a reason.
 
I've rolled many USB cables, and my fav is 28/24AWG w/ a ferrite and gold plated plugs, paid $5 on ebay...I think many ppl have also noticed that USB cables changed the sound somehow, but you seem to be a hardcore skeptic...more power to you!

 

[esdk]

Seams to be more a mather of religion and conspiracy theories.
 
But great that you think the USB isolator does so much more - and if you believe it enough it's the true.
 
Unfortunately the first batch is almost sold out - maybe you (LeePerry) could wait claiming any more great things about the USB ground isolation device, until analog devices delivers the next 1K chips. 
 
Seams A/B/C/D tests could give you a hint maybe:
A. system with standard USB cable
B. system with golden cable
C. system with USB isolator and standard cable
D. system with USB isolator and golden cable
 
If you did that test objectively you would get better sound in scenario 2. Great sound in scenario 3 which would be equal to scenario 4.
Please note the prequisites: His system has ground loop from Mains to PC over USB->SPDIF to DAC to Mains.
 
The USB cable does not mather - a smaller AWG in USB cable will provide better grounding, that is why some people that does not have the USB isolator hear a difference. But as you also say the USB2ISO module is even greater. That is because you illiminate the current flow in the loop that could cause humming, bas distortion and loss of the highest frequencies.
 
The smaller the AWG - the thicker the cable - the less voltage difference in the ground loop - the less noise. Break the loop no voltage difference at all - Lovely Sound as it should be heard
 
Please try to write Analog Devices about the conspiracy - by-the-way the chip will be updated to a new version - maybe they will put more stuff in that they won't tell about!!!
- or maybe it is just to ensure better yield in manufaction process of the double isolation distance of 4K volt.
 
Please do not do the above ABCD test and write D is best - (I know you will
 
Buy your conspiracy USB isolator here: http://electronics-shop.dk/?id=1038 and read a FAQ here: http://electronics-shop.dk/?id=900
 
 
The new motto: "It is so much better than they tell!" 
 
 
 
Best Regards
 
Soren
Electronics-shop.dk

 

[leeperry]

well, the datasheet is clear about it...and many ppl have confirmed that the SQ was much better when it's in the USB path, we call it a real world experiment..you should try it sometime

 
my own field experience has been that:
 
-the best coax cable is the shortest, I currently use a 15cm 75Ω tinned copper RCA/RCA cable. Dan Lavry confirmed that the shorter the better:
http://www.lavryengineering.com/lavry_forum/viewtopic.php?f=1&t=144

SPDIF is fine, as long as the cable length are not very long (the shorter the better).

and many designers think that the impedance mismatch at the connectors is "academical": http://recforums.prosoundweb.com/index.php/m/381397/0/#msg_381397

At frequencies encountered in word clock and SDIF2/3 connections, the impedance mismatch problem at the connector is academical.

 
-the Firestone Bravo sounds much better on a proper linear regulated PSU: http://www.firestone-audio.eu/shop/products/allproductslisted/supplier220vac.php
 
You can see that the m2tech Evo also has a plug for an external PSU, and the Teralink X2 also sells w/ a DPS now: http://cgi.ebay.com/TeraLink-X2-Power-Supply-Unit-X2PSU-USB-SPDIF-/330455177982

It features EMI filter, CLC low ripple filtering and high accuracy reference voltage output.

 
Some even plug batteries on their m2tech hiface to bypass the high ripple USB power: http://images.blu-ray.com/htgallery/46945_full.jpg
 
A better PSU pays in cash SQ-wise, I used some JMLab reference records when comparing the wallwart adapter against the DPS on my Bravo, and the SQ was so much better on the DPS

 
-the Bravo has a galvanically isolated coax output, and -still- the SQ is so much clearer when the ADuM4160 is in the USB path...just like Oleg prophesied: http://www.circuitsathome.com/mcu/usb/usb-cable-of-my-dreams

USB isolation is good for you. Isolated DAC makes better sound, isolated oscilloscope produces cleaner trace

 
-I've also rolled quite a bit of USB cables, and each time the best ones have been the 28/24AWG w/ a ferrite and gold plated plugs..it's using a thicker wire for power and thinner for data, and I also prefer the SQ when the USB2ISO is at the back of my S/PDIF transport instead of the back of the computer...I like to believe that it cleans the cable interferences(my neighbors play the wifi-warfare game) and jitter(you prolly don't believe in cable jitter, though)
 
A link about cable jitter, that was different depending on the direction it was used: http://www.stereophile.com/features/368/index3.html
 
Keep in mind that my S/PDIF transport runs in adaptive mode, but some other ppl claimed to also hear differences between USB cables on async transports anyway.
 
Some ppl use the optional linear DPS on the Teralink-X2 together w/ your USB2ISO, you call it placebo and waste of money if you like...what matters is that ADuM4160 is fantastic for USB audio and your product is great: http://www.head-fi.org/forum/thread/468872/teradak-teralink-x2-released-19-1-10/300#post_6791263

 USB2ISO Usb Isolator + Teralink X2 + Teradak Linear PSU = Out of this world USB sound from Your PC with great price.

 
I'd suggest running some real world experiments, you might be surprised

 
and my question still stands: would ADuM4160 provide a higher SQ on a less noisy PSU? but you don't seem to be much of a PSU believer, and you're currently the only company selling self-powered affordable ADuM4160 dongles in a hard plastic case anyway