USB Ground Lift

[rikhav]

Thanks @mansr and others 

I will do as advised and update on the thread 

 

[rikhav]

Cut the + 5v and DAC gets detected perfectly. No issues 

 

So now I at least know with my DAC I need the ground to be connected for the DAC to be detected by host PC

Thanks again for your help

 

[mansr]

13 minutes ago, rikhav said:

So now I at least know with my DAC I need the ground to be connected for the DAC to be detected by host PC

That's always the case with USB. Detection works by the device pulling one of the data lines high relative to ground, which it can't do if ground isn't connected.

[rikhav]

On 10/15/2018 at 5:46 PM, mansr said:

That's always the case with USB. Detection works by the device pulling one of the data lines high relative to ground, which it can't do if ground isn't connected.

 

Finally managed to make USB cable with no voltage + connection with the help of a close friend who is very good with making cables

 

For me it surely sounds better then before, can hear more into the music 

The difference again is not night and day but enough to hear a  difference

[Ralf11]

guess what I found...

 

 

 

 

[Ghoostknight]

sorry to revive this thread but im wondering if a simple isolation transformer could provide the necessary ground?

 

im not too experienced with electronics but if we connect V+ and GND from the input usb to the primary of the isolation transformer and just GND from the secondary going to the dac, would this work?

or does V+ need to be connected too on the secondary? maybe we could just use a high value resistor to tie V and GND on the secondory "together" to create the needed GND ?

 

is this too easy to function correctly?

 

i also had a cable once where i disconnected V/GND/Shield and it indeed sounded better but im wondering if we could make a cheap adapter with 3 usb connectors that are actually "to the spec" of usb while still isolating GND and V ?

 

i know usb isolators is the way to go but specially usb 3 ones are very expensive, so this could be a cheap reliable solution? and i kinda wonder if noise on the datalines gets rejected anyway by most chips

 

i actually do have topping hs01 isolator for my dac but im asking for my ssd connected over usb to my raspberry pie, i kinda would like to try to decouple both to some degree, while still being cheap

[JohnSwenson]

1 hour ago, Ghoostknight said:

sorry to revive this thread but im wondering if a simple isolation transformer could provide the necessary ground?

 

im not too experienced with electronics but if we connect V+ and GND from the input usb to the primary of the isolation transformer and just GND from the secondary going to the dac, would this work?

or does V+ need to be connected too on the secondary? maybe we could just use a high value resistor to tie V and GND on the secondory "together" to create the needed GND ?

 

is this too easy to function correctly?

 

i also had a cable once where i disconnected V/GND/Shield and it indeed sounded better but im wondering if we could make a cheap adapter with 3 usb connectors that are actually "to the spec" of usb while still isolating GND and V ?

 

i know usb isolators is the way to go but specially usb 3 ones are very expensive, so this could be a cheap reliable solution? and i kinda wonder if noise on the datalines gets rejected anyway by most chips

 

i actually do have topping hs01 isolator for my dac but im asking for my ssd connected over usb to my raspberry pie, i kinda would like to try to decouple both to some degree, while still being cheap

An isolation transformer is a very bad idea, there is a very good probability it will not work, and even if by some magic it does it would be a very poor connection.

 

Why? A transformer couples AC not DC, unfortunately there are parts of the USB signal (in particular what happens at the beginning of a connection) which looks much closer to DC than AC, these will be highly distorted by a transformer, most likely enough that connection will never happen. Transformers need to be designed for a specific frequency range, for example power transformers are designed for very low frequencies and Ethernet transformers are designed for very high frequencies. Again USB high speed has both very high and very low components, making it extremely difficult to make a transformer that would work. It would take a very special custom transformer which would be extremely expensive. AND it would be useless at isolating leakage currents which are low frequency AC NOT DC. And all of this is ignoring the fact that the actual electrical properties of the high speed signaling do not like transformers at all, again it would be highly distorted.

 

Just all in all an extremely bad thing to do.

 

John S.

[Ghoostknight]

1 hour ago, JohnSwenson said:

An isolation transformer is a very bad idea, there is a very good probability it will not work, and even if by some magic it does it would be a very poor connection.

 

Why? A transformer couples AC not DC, unfortunately there are parts of the USB signal (in particular what happens at the beginning of a connection) which looks much closer to DC than AC, these will be highly distorted by a transformer, most likely enough that connection will never happen. Transformers need to be designed for a specific frequency range, for example power transformers are designed for very low frequencies and Ethernet transformers are designed for very high frequencies. Again USB high speed has both very high and very low components, making it extremely difficult to make a transformer that would work. It would take a very special custom transformer which would be extremely expensive. AND it would be useless at isolating leakage currents which are low frequency AC NOT DC. And all of this is ignoring the fact that the actual electrical properties of the high speed signaling do not like transformers at all, again it would be highly distorted.

 

Just all in all an extremely bad thing to do.

 

John S.

 

thanks for the reply, but im just talking about GND and V+, not about the datalines you seem to refer too (i think)

 

i made a little picture in paint to illustrate

 

Is this actually possible or do we need to connect the plus-side at the secondary side of the transformer too? (maybe its possible to just connect the plus-side to the minus-side with for example a 100k Ohm Resistor to make the minus-side(GND) work?)

 

the transformer is just there to make the usb handshake work while still isolating GND (and to negate the possible 50V AC/DC offset between the 2 GND`s you were refering too on page 1 or 2 if GND is completely disconnected)

[JohnSwenson]

9 hours ago, Ghoostknight said:

 

thanks for the reply, but im just talking about GND and V+, not about the datalines you seem to refer too (i think)

 

i made a little picture in paint to illustrate

 

Is this actually possible or do we need to connect the plus-side at the secondary side of the transformer too? (maybe its possible to just connect the plus-side to the minus-side with for example a 100k Ohm Resistor to make the minus-side(GND) work?)

 

the transformer is just there to make the usb handshake work while still isolating GND (and to negate the possible 50V AC/DC offset between the 2 GND`s you were refering too on page 1 or 2 if GND is completely disconnected)

It still won't work. V+ and GND ARE DC, which is what a transformer blocks. The only way to use a transformer is to convert DC to AC, the transformer, then a diode bridge, capacitor and voltage regulator. You can actually buy these as modules, but you have to be very careful about using them if you don't want the switching happening in the module from contaminating the DC out.

 

We actually use such a module in the EtherRegen to power the B side. I spent a lot of time figuring out the best one to use and getting it to not muck up the B side power.

 

I think the best way to proceed is to carefully work out what exactly you are trying to eliminate before working out the hardware to get rid of it. When playing with grounds you also need to be very careful about what the ground is doing in the system. You can easily make the system non-functional or worse than you started.

 

John S.

[Ghoostknight]

6 hours ago, JohnSwenson said:

It still won't work. V+ and GND ARE DC, which is what a transformer blocks. The only way to use a transformer is to convert DC to AC, the transformer, then a diode bridge, capacitor and voltage regulator. You can actually buy these as modules, but you have to be very careful about using them if you don't want the switching happening in the module from contaminating the DC out.

 

We actually use such a module in the EtherRegen to power the B side. I spent a lot of time figuring out the best one to use and getting it to not muck up the B side power.

 

I think the best way to proceed is to carefully work out what exactly you are trying to eliminate before working out the hardware to get rid of it. When playing with grounds you also need to be very careful about what the ground is doing in the system. You can easily make the system non-functional or worse than you started.

 

John S.

 

Hmm maybe a switched things up but what module is used by those board? https://www.amazon.de/-/en/ADUM3160-Isolator-Coupling-Protection-AVR-JTAG/dp/B07YKQHB3J/ref=d_pd_sbs_sccl_3_4/260-7593681-1805002?pd_rd_w=Y5ka4&content-id=amzn1.sym.6023e427-25bb-42e7-aaa9-a6e0a8bdcb7b&pf_rd_p=6023e427-25bb-42e7-aaa9-a6e0a8bdcb7b&pf_rd_r=NRVP7JEWQJQGE48Q3VPG&pd_rd_wg=dCKAq&pd_rd_r=9235c35f-d3b9-4bdc-b77a-a71aee01aa3c&pd_rd_i=B07YKQHB3J&psc=1

 

is it actually not a transformer but a isolated DC-DC Converter? (are these the modules you are talking about where its all included?)

will the switching also contaminate the ground ? preferably i wont use V+ anyway

 

Well my main goal is getting rid of the ground connecting but still allowing the usb handshake to work (and avoiding the ac/dc offsets between grounds you talked before in this thread)

[Superdad]

5 hours ago, Ghoostknight said:

it actually not a transformer but a isolated DC-DC Converter? (are these the modules you are talking about where its all included?)

No, that is not the type of isolating converter we use in the EtherREGEN. 
 

And the USB isolator you linked to is just the old ADUM—limited to 12mbps, supporting only USB1.1 Full Speed.  Not useful for USB2.0. 

[Ghoostknight]

1 hour ago, Superdad said:

And the USB isolator you linked to is just the old ADUM—limited to 12mbps, supporting only USB1.1 Full Speed.  Not useful for USB2.0. 

im just talking about the black rectangluar thing, which is probably a isolated DC-DC converter

 

 

1 hour ago, Superdad said:

No, that is not the type of isolating converter we use in the EtherREGEN. 

would you mind sharing what you are actually using?

 

tho im also wondering if a isolated dc-dc converter is just enough since i just plan to use the ground and not actually V+

[Ghoostknight]

I found this link https://forum.allaboutcircuits.com/threads/isolating-usb-power-to-prevent-ground-loops.135912/ which suggests that JUST isolating V+ and GND and -NOT- datalines still has the potential risk of a huge potential difference between the two grounds and its adviced to join the two grounds with a resistor (not as good as isolating everything but probably better than hooking grounds straight to eachother)

 

Can you guys confirm?

 

then im wondering if i should just experiment with a resistor in place of the transformer in my drawing between grounds and check how large the resistor can be while still allowing usb handshaking

 

(btw i mainly want to somewhat isolate the peripherals of my raspberry pi from contaminating the ground and voltage rail of the raspberry pi itself, i have a upcoming project where i try to "mod" a raspberry pi with mainly new LT3045 Voltage regulators and new clocks and such a usb splitter device seems like a very cheap option to atleast "optimize" things without spending big bucks for a isolator (which needs to be usb 3.0 combatible for best speed of the attached SSD, and it gets worse if i count other peripherals in too with a usb 2.0 isolator like the Topping HS01))