USB Isolators for Audio

This is the first time I evaluate USB2 high-speed isolators. I have evaluated USB2 Redriver and USB regen/reclocker cards. USB2 Redriver has little improvement to SQ. USB regen/reclocker PCIe cards have its own sound signature and the 5V DC supply really matters.

Most USB isolators were designed for rugged industrial use, but it works for audio as well. The isolation voltage ranges between 1kV to 5kV. Budget USB isolators like Topping HS01 only provide Ground isolation unlike the industrial ones which provide isolation for ground, power and signal lines.

The original Intona USB Isolator from Germany in crude plastic case was designed for industrial use. One person tried it with USB Audio signal path and discovered it indeed improves the sound significantly. The news spread quickly. Intona has the newer versions in metal case which can even improve Taiko Audio SGM Extreme USB Audio output.

Why the need to isolate USB

In industrial use, USB isolation was meant to protect computers from dangerous voltages in rugged environment, for example, PC-based oscilloscope used in automotive. In audio use, it’s to isolate the noisy DC ground of the computer power supply. Some high-end DACs already have USB Ground galvanic isolation inside the USB receiver. From my experience, using industrial-grade USB isolator can improve the sound further even when the DAC has USB Ground galvanic isolation.

The Need for USB2 High-Speed Isolators

High-res music in PCM and DSD requires USB2 to operate in 480Mbps high speed mode. Most of the earlier USB2 isolators provided by chip makers like Analog Devices only work in USB2 low speed (1.5Mbps) and full speed (12Mbps) modes, hence they are not suitable for USB audio use. One of the integrated circuit (IC) for USB2 Isolation with support for high speed and used in many USB Isolation products (including Uptone ISO REGEN) was Silanna ICE08USB which was introduced in 2015 but discontinued in 2019.

In 2021 Texas Instruments (TI) announced their ISOUSB211 product to be available in Q3 2022. Analog Devices recently has the ADUM4165/4166 USB2 high-speed isolators available.

USB2 High-Speed Isolators available for purchase

The list here is not comprehensive but includes the popular products. Most of the earlier products based on Silanna ICE08USB are no longer available for brand new purchase, which include:

  • Uptone ISO REGEN
  • iFi Nano iGalvanic3.0
  • Singxer UIP-1 USB Isolator

The following are the products we can buy as of March 2022:

  • Intona 7054-series USB2 and 7055-series USB2/USB3 Isolators
  • ALLDAQ ADQ-USB 3.0-ISO-PS / 3.0 Isolator incl. Power Supply
  • Virtins Technology VT USB-ISO-480 USB High Speed Isolator (>800 mA, comes as USB dongle)
  • Topping HS01 Ground Loop Isolator

Three of the companies listed above make industrial products. As mentioned earlier, Intona (Germany) makes USB2/3 Isolators for industrial use. ALLDAQ (Germany) and Virtins Technology (Singapore) are both PC-based measurement and instrumentation companies making products like oscilloscope.

Topping HS01

Topping HS01 USB2 Ground Isolator

The HS01 only provides USB ground isolation. It only supports 480Mbps high speed. I have done quick listening test with another friend. My recommendation – DO NOT waste your money and time with this product.


TI’s USB2 Isolator Evaluation Module

I bought two of these (only 1 unit allowed per order) since modifications need to be made. My first hand experience with the default settings – I was surprised by the improvement in layering, decays and details without being too digital. The sound is less congested. I prefer the sound when using TI’s ISOUSB211EVM compared to Core Audio USB P24 OCXO and JCAT USB XE cards.

EVM Modifications

Ideally the 5V from motherboard should not be used, but the default EVM configuration uses 5V from motherboard’s USB and isolated DC-DC converter to generate 5V to the DAC side. The default configuration also uses internal LDO to generate 3V3 from VBUS1 (input side) which is suboptimal. Changes made:

  • Disconnect 5V from USB A connector
  • Use external LDO to generate 3V3 on the input side
  • Disable 5V LDO (input voltage from DC-DC isolated converter) on the output side
  • Add terminal block for separate 5V inputs on input and output sides

2-rail 5V LPSU

I build my own 2-rail 5V LPSU so that each side of the board is powered independently. Here are some pictures. The encapsulated transformer is from Nuvotem Talema 80VA with dual 9VAC outputs.

Casing of 2-rail 5V LPSU
Back view of 5V LPSU
5V LPSU Inside View
Independent LPSU boards
5V LPSU placed above streamer
Modified EVM
Modified TI’s ISOUSB211 in use

The tests were done using evaluation board with makeshift setup like shown in the pictures above. Additional modifications were done by adding Vishay bypass capacitors at the 5V terminal blocks.

Bypass capacitors added to 5V terminal blocks
Vishay bypass capacitor attached to 5V terminal block

Another EVM board was purchased for comparison with the modified version. In its default configuration, the sound is totally different.

Intona 7055-C USB 3.0 SuperSpeed Isolator

Daniel Staemmler of Intona Technology could not confirm this will work my XMOS-based DAC, but he heard no complaints. Choosing 7055-B versus 7055-C was a tough decision since in What’s Best Forum, some Taiko Audio SGM Extreme owners prefer 7055-B (good for vocal) while 7055-C is said to be more suitable for orchestra and complex music. 7055-C has dual LT3045 regulators with lower noise measurements and supports up to 1A without using external power supply. 7055-B supports 0.5A only (single LT3045). There is Micro USB port if the connected USB device requires more current. In the end, I bought 7055-C and luckily it works well with my Marantz SA-10 used as USB DAC.

Intona 7055-C SuperSpeed Isolator
Intona placed near DAC
Intona placed near streamer

The Intona USB3 Isolator is indeed very small in size, easy to place behind DAC or music streamer. I prefer the sound when placed near the streamer. The USB2 port used is the one with separate 5V DC, called USB filter.

Analog Devices ADuM4166

A week after online order placed, I received Analog Devices EVAL-ADuM4166. Its operation requires 2 rails of 5V DC supplies, which I have already built. This board requires no modifications. The 5V DC terminal blocks are already on each side of the PCB. The jumpers were set to 5V at each side, with the 5V at peripheral side powering VBUS.

ADuM4166 Evaluation Board

ADuM4166 was selected instead of ADuM4165 as the external 24 MHz crystal is on the peripheral side, hence more suitable for USB Audio. The design makes it possible to use higher quality 24 MHz crystal or clock. The only surprising fact about ADuM4165/ADuM4166 family is that they are not USB2.0 certified, but per my tests it works with USB Audio.

Preliminary Listening Impression

With Intona 7055-C in my own system, the sound is very high resolution. Definitions and separations are very good. However, after long listening, it can be a bit fatiguing. The sound feels a bit unreal. With TI’s ISOUSB211, the sound is very musical but with slightly less resolution. Vocal sounds more realistic with TI’s ISOUSB211 and layering is really good. More details unheard before can now be heard, most likely due to lower noise floor. AD’s ADuM4166 surprisingly degrades the sound compared to using my own USB filter.

I also had the chance to test the USB isolators with Dr Azmel’s system in Taiping. DACs include Chord Hugo TT2 and M-Scaler combination plus Matrix Audio X-Sabre 3, mainly used for DSD. The Chords were tested with AA Streamer using USB input from JCAT USB XE but the sound was not impressive as reported by Dr Azmel. With TI’s ISOUSB211, the sound from the Chord components is good. When X-Sabre 3 is used, the sound is more musical, less fatiguing, and better layering. With Intona 7055-C, the sound is high resolution with good definitions and separations but lacks musical soul, consistent with what I heard with my own system. We also tested AA Streamer JCAT USB XE output into Denafrips GAIA then its I2S output into X-Sabre 3. We heard colored sound and we both do not like it.

Dr Mohd Azmel’s system in Taiping, Perak
Dr Azmel’s system with Intona 7055-C
Dr Azmel’s system with TI’s USB2 Isolator used in makeshift setup

Next Steps

The plan is to develop stand-alone USB2 Isolator based on TI’s ISOUSB211. It will include the required low-noise linear PSU to power each side of the USB2 Isolator and power the USB VBUS (DAC side) independently. Stay tuned.

Please leave comments here.

By Anwar

Dr. Anwar Ali is a consultant in the area of Operations Research / Decision Science. During his free time and as a side business, he builds high-performance and moderate-cost music streamer.