Are you into high quality PC audio? Do you have one of these nice USB DAC’s that pull all the good musical stuff out of your computer? Then you might need to check this article out. You can vary well improve your USB DAC performance by isolating it from all the garbage coming from the noisy(electronically) PC.
What I’m about to show in this article is a way to build you own USB isolator and improve your USB audio. The isolator itsel is build around the ADUM4160 chip from Analog Devices. The complete datasheet is here:
Since the schematic for this project is rather simple, a single layer printed circuit board can be made. Of course a double layer is always better option.
This is how the whole thing looks:
The project also makes use of one high quality LDO regulator. In this case I’m using Linear Technology’s LT1763 fixed voltage (5V). I’ve used this one before in some other projects and I’m quite happy with it. The datasheet is available here:
The board allows you to use external regulated PSU just in case you don’t trust the LT’s chip. This is the complete schematic for this project:
The circuit is pretty straightforward but here is some explanation. JP1 switches the speed – open=low speed(1.5Mbps), close=full speed(12Mbps).
JP2 function is explained here:
The ADuM4160 has an option to delay application of the upstream pull-up under control of the peripheral. This function is controlled by the PIN input. In this application, the PIN input is jumpered high so that the upstream pull-up is applied as soon as peripheral power is applied. In other applications, it can be connected to a GPIO pin of a controller, a fixed delay circuit can be applied, or it can be connected as shown in this circuit. It is the designer’s choice how to use this functionality.
I personally use id closed. JP3 allows you to switch between the power supplies of the second half of the isolator. I recommend using the build in regulator. In this case the board need 10-15VDC. A simple DC adapter will do the job.
The PCB artwork in 1:1 scale pdf file and component placement is available for download HERE.
The PCB can be easily made using a laser printer and an iron. I encourage you to try this simple upgrade, as you won’t be disappointed.
where’s the parts list?
use the attached schematic.
Oh wow, I need to try this. I assume that this provides galvanic isolation to prevent hum from entering your USB connected DAC. Many DACs do not offer USB isolation 🙁 It seems like such a simple thing to add, so why do manufacturers not include this feature already built-in?
well it might seem as an easy to implement stage. However most of the manufacturers are tightly limited by the BOM and costs. Also, consumer grade audio electronics are not considered to require this type of isolation IMO. Also there are many manufacturers who are trying to strip the production costs to a fraction of a cent, so these additional components just don’t fit the bill. Sadly…
I’m new to EAGLE and got some problems to create new parts, so this is why I would like to ask, where I can find the EAGLE-library data files for the ADuM4160 and the ACM4532.