Question 1

What is the advantage or disadvantage of using a power supply voltage higher than the 5v you get through the usb to dc cable?

Accepted Answer

The USB power plug included, when plugged into the PC directly just have an overwhelming hiss.  The hiss left when I used a 1A 5V USB charger, but the best sound came when I found an old large "wall-wart" 12V 1A with the same plug.  The jump from 5V to 12V added a lot of warmth and detail.  Get the linear supply wall-worts, not the switching kind (generally smaller in form-factor).  I also used ferrite snap-on cores on the audio from the pc, high quality shielded audio cables.  I'm most pleased with this unit when it's properly powered.

Question 2

Is this a decent headphone amp for a turntable that has a built in pre amp?

Accepted Answer

Signal source is irrelevant as long as it is a low impedance line level.

Question 3

Can someone post a link to a good DC power adapter for this sold on Amazon?

Accepted Answer

When I purchased this item recently from Amazon, I had a similar concern about the power supply, because I live in a 220V 50Hz electric supply zone. In my case, I received the amplifier with a charging cable having a standard (I think) plug on one end and a USB A plug on the other end. This end can be plugged into any phone charger with a USB A port. I found the amplifier works very well if this is also plugged in the USB port on the computer.

Question 4

How do I pick another power supply for this? I’d like to replace it but don’t know how to figure out if something will work with this.

Accepted Answer

I’m using a Radio Shack 12volt 1000ma power adapter. It comes with different tip sizes so I used one that fit and that had a positive center like shown printed on the back (near the receptacle) of the amp. The range required of the Douk is 5 volts to 20 volts so mine being 12 volts is good. In the reviews someone  commented that they had issues with using 5 volt chargers. That’s why I went with a little more power. 
Check your manual in case they made changes to this unit since the time bought it( earlier this year)

ASIN	B08C2MKBGN
Best Sellers Rank	#16,935 in Electronics ( See Top 100 in Electronics ) #28 in Headphone Amps
Brand Name	Douk Audio
Customer Reviews	4.4 4.4 out of 5 stars (850)
Item Weight	5.92 ounces
Manufacturer	Douk Audio
Maximum Supply Voltage	20 Volts (DC)
Minimum Supply Voltage	5 Volts (DC)
Model	XZ-U3
Mounting Type	Freestanding
Number of Channels	2
Output Power	1300 Milliwatts
Part Number	XZ-U3
Specification Met	FCC

Douk Audio U3 Headphone Amps, Mini Hi-Fi Amplifier for Home Desktop PC 6.35mm / 3.5mm Headsets, Class A, RCA Input, DC 5V

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