One of the best opportunities for sound improvement of USB devices:
It's amazing, how much sound improvement you can get from a dedicated low-noise USB power supply for the USB chip of a DAC and other USB devices like: external harddrives, external CD-drive, Digital-to-Digital convertors, USB headphone amps and other USB-bus driven devices.

For your information: The USB DAC still needs its regular power supply if it not only powered by the USB-bus. Only the USB section is fed with the AQVOX low-noise power supply, because the most USB-DAC´s USB-chips gets its power from the computer via the USB cable.

The Problem:
The USB chips of most DACs or the whole DAC or devices are directly powered with the 5 V of the USB cable from the computer. This is called USB-bus powered.
Aside the regular 5 V between 30 mV to 200 mV ripple/noise are transmitted from the computer.
The more dirty the voltage is the more imperfect is the sound performance. Furthermore, most USB and DAC chips generate the digital clock from that 5 V voltage. However, the more the power supply voltage oszillates or contains noise, the more inexact the generated clock-signal is, resulting in jitter and other sound degrading problems. But clock generation is only one problem. Moreover, the performance of the whole circiutry and chips of the USB device is being affected, thereby downgrading the quality of the output signal significantly.

Another thing is that most USB-ports are limited to 500mV output and other USB-devices connected to the computer or USB-hub are affecting the power-quality. External USB-Harddisks without own powersupply are affecting the computers internal powersupply and all other USB-ports negative.

USB-cables - another sound degrading fact is that the noisy powerlines are affecting the two USB-datalines. Because non of the power- or datalines are shielded. It sounds better if the powerline is terminated and this is the case with the AQVOX USB Powersupply.

The Solution:
The powerful transformer (1-Ampere instead of the 0.5-Ampere from most USB-ports), stabilized AQVOX USB Low-Noise linear power supply has average under 1mV ( 0.001V) noise voltage. It is equipped with unique handmade USB adaptors, of which one side is being pluged to the USB socket of the DAC or device or computer and the back side takes the USB cable´s plug. Inside that adapter only the two USB data lines and not the powerline are routed through. The 5 V power supply line coming from the computer is terminated and replaced by the clean power of the AQVOX USB-Low-Noise power supply.

Galvanical isolation
The idea of galvanical isolation improves soundquality has lots of friends but has no real advantage. The only reason for a galvanical isolation of USB in audio-setups is, if a groundloop issue makes a loud humm. USB isolators make sense in industrial environments where voltage spikes of some hundred volts or hefty noise can damage the equipment or falsify the USB-signals. Any galvanical isolation, via electronic or via transformer under normal circumstances, brings no sound improvement but is mostly sound degrading. The "evil" computers noise is coming basically through the positive power-rail from the computer - and this is interupted in the AQVOX USB-PSU.

Also for use with M2Tech HiFace² with
USB connector type A

1. The USB-chip or USB-circuits in the DAC or whatsover USB-device are powered from AQVOX USB Power Supply. The supply of the USB chips comes not from the computer anymore.

2. The quality of the power supply for the USB chip in the DAC is drastically improved, resulting in a clearly discernible sound improvement. With most USB DACs the connected computer feeds the USB chip with 5 V voltage power. However, alongside with the regular 5 V voltage 30 mV up to 150 mV noise voltage are being transmitted.

3. Some USB devices lose their settings as soon as the comuter is being switched off. With the AQVOX USB Power Supply those devices keep their settings permanently.

4. The power of most USB-ports at computers is limited to max. 500mA. Attached external harddisk draw during operation lots of power and this affects the computers internal powersupply. AQVOX powersupply brings 1A.

AQVOX Low-Noise Linear (transformer) USB Power Supply with only average 1 mV noise and ripple voltage

Technical Specifications:

1. Power supply with conventional linear transformer (no switching power supply)
2. Stabilized and regulated with very low noise voltage stabilizers
3. filtered with approx. 4700 µF capacity for good power reserves backup
4. foil-capacitors for transient filtering
5. the powerline between computer and USB-device is disconnected
6. Output voltage: approx. 5 Volt and powerful 1 Ampere (only 0.5A comes from computer USB-ports)
7. Ripple & Noise: average under 1mV  (battery-notebooks or desktop-PCs have 30-150mV Noise in the USB power)
8. AC power input: USA, Canada, Japan and some other do need aditionally our small 110V to 220V transformer, price only Euro 5.-
9. IEC-AC power socket is compatible for AC power cables, we include a powercable for most countrys in Europe, USA, Japan
10. Short-circuit-proofed
11. USB Adapter: B-male to B-female, or A-male to A-female (other plugs available eg. for ONKYO ND S1 or Squeezebox just ask)
12. DC cable length 150 cm
13. AC Power cord: 180 cm for most countrys in Europe, USA, Japan
14. Weight: in total approx. 750 g
15. Suitable for many USB DACs, USB hard disk drives, USB Headphone Amps, USB to S/PDIF converters, USB micamps

AC Powercable - Schuko to IEC

100mHz digital scope, one vertical square are 10mV - this shows 50 - 60mV

2. Hard disks (internal + external): The actuators of the recording/reading heads produce interference voltage with each positioning or stop move.

3. Clock generators and chips like e.g. the CPU, northbridge, RAM or graphics adapter cause disturbances and noise.

4. Power supplies of notebooks and desktop PCs are not designed for lowest interference voltage and noise, since this is extra costs, not necessarily needed.

5. DC/DC converter producing up to 100mV ripple and noise.
and so on...

A typical picture of 5 Volt USB power from a desktop PC with running access of the hard disk.

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²HiFace is a trademark of the company M2TECH