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PC to DAC. Is the 5v & Ground necessary?

Mayank Shah

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While connecting a PC to a DAC with an USB cable, is the 5 volts really required on the DAC end? If so, why does the DAC need 5 volts from the USB cable? Some cable manufacturers mention that to avoid unwanted noise, the ground lead of the USB is isolated from the DAC.
 
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Nikhil

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This depends on the USB chip used.
Some need it while some don't - depends on your DAC.

The 5V is needed for the initial handshake that establishes the connection.

Regards


.
 

Kannan

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There are cables available with twin output on the other side, one only outputs data and the other power. You can try it and see if the DAC gets detected.

Similarly most good DACs with inbuilt trafo are not affected by PC noise. Inside these DACs , the USB-chips are powered from the DAC´s internal power supply. The power(5V) from the computer USB port is not served to the DAC through the cable, so no noise can enter the DAC and have an adverse effect on the data line.
 
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jls001

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Whether 5V is necessary or not is dependent on the implementation of the USB receiver in the DAC.

As Nikhil said, some receivers need the 5V for initial handshake between USB DAC and host despite the DAC being independently powered by its own power supply, and once handshake has been established the 5V line can be disconnected (using some jumper arrangement).

Some other DACs need the 5V to power the USB receiver portion of the DAC. In this case 5V can't be cut off even after handshake.

On a DAC that doesn't need the 5V line, cutting off the 5V makes the sound substantially cleaner.
 

Mayank Shah

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Thanks. Other than asking the DAC manufacturer, about the requirement for the 5v, is there anyway to know this from the general specifications provided? What about the ground wire on the USB cable from pc to dac?
 

jls001

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Thanks. Other than asking the DAC manufacturer, about the requirement for the 5v, is there anyway to know this from the general specifications provided?
Don't know about this. I don't think DAC manufacturers will go about publishing such minute details on their spec sheet. Others who own the same DAC might be able to help answer especially if he/she happens to have tried different cables.

What about the ground wire on the USB cable from pc to dac?
Ground wire is essential. As are Data+ and Data- lines.
 

Mayank Shah

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I guess, unless the dac manufacturers specify this explicitly that the 5v is NOT required, it would be safe to assume that it does.
 

spirovious

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While connecting a PC to a DAC with an USB cable, is the 5 volts really required on the DAC end? If so, why does the DAC need 5 volts from the USB cable? Some cable manufacturers mention that to avoid unwanted noise, the ground lead of the USB is isolated from the DAC.
Which specific dac? Some DACs are usb powered only.Then 5v is needed.
 

Mayank Shah

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My thought was the other way around, if a dac ran on external power then why the 5v from usb. Cheers.
 

superczar

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My thought was the other way around, if a dac ran on external power then why the 5v from usb. Cheers.
The explanation is slightly technical but let me try nonetheless
The two data wires are differential data lines (D+ and D-) i,e use differential signalling (i.e. opposed to each other) so that the receiver can subtract the two to get the actual 1/0 bits while filtering out any noise that both would have picked up on the path.
These 1-0 bits however need to be referenced against something and that's why you have the Vbus (+5V) and Gnd (0V)
Without said reference voltages, the actual signal would be meaningless.

Here is a more detailed explanation

Keep in mind that most newer USB host chips will be able to self adjust and apply a pull-up on the Data line in absence of Vbus but it isn't recommended.

There also seems to be some mixing up of this element with ground isolation/ground loop prevention - That's an entirely separate topic
 
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amit_s

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You can try with a cheap usb or printer cable. Just cut off 5v wire(only) at the source end. I did it with my audio-gd dac and its working perfectly since last 3 years. To my perception, cutting off 5 volt line increased the clarity and air around instruments. You can find usb connection digram on internet.
 

Mayank Shah

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Finally, got a reply from the DAC Manufacturer, they said use a normal cable, no need to isolate anything. But have certainly learnt a thing or 2 from this. Thanks to all.
 

rikhav

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Many dacs either disconnect the 5v internally or have a switch also to switch it on or off
But most don't mention it as a feature or feel it's important to mention
 
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