This is a question from the OPA1688 Super CMOY, 2x 9V with real ground and headphone relay - PCBs thread post #357
I am looking to add an optical input to my headphone amp and as I have plenty of room inside the case I could DIY and wire-in a portable optical DAC.
Would there be any reason why I could/should not power the following HIFIME USB-Powered SPDIF Optical ES9018K2M DAC right off the same USB 2.0 power cable going into my amp, which is feeding power to my RECOM RW-0509D DC-DC Converter?
The RECOM DC-DC converter at max is using under 1W (<300mA @ <5V and the proposed DAC unit above is well under 0.5W (<80mA @ <5V). The maximum allowable for USB 2.0 is 2.5W (500 mA @ <5V) so well within those parameters.
I would wire in the DAC's USB power cable right at the 5V power +/- input points (2|3 and 22|23) on the RECOM Power Supply Module Board that I built like so:
Or should I simply keep the power supply separate and run a second USB 2.0 power-only cable?
I am looking to add an optical input to my headphone amp and as I have plenty of room inside the case I could DIY and wire-in a portable optical DAC.
Would there be any reason why I could/should not power the following HIFIME USB-Powered SPDIF Optical ES9018K2M DAC right off the same USB 2.0 power cable going into my amp, which is feeding power to my RECOM RW-0509D DC-DC Converter?
The RECOM DC-DC converter at max is using under 1W (<300mA @ <5V and the proposed DAC unit above is well under 0.5W (<80mA @ <5V). The maximum allowable for USB 2.0 is 2.5W (500 mA @ <5V) so well within those parameters.
I would wire in the DAC's USB power cable right at the 5V power +/- input points (2|3 and 22|23) on the RECOM Power Supply Module Board that I built like so:
An externally hosted image should be here but it was not working when we last tested it.
Or should I simply keep the power supply separate and run a second USB 2.0 power-only cable?
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Lavalier kindly responded to my question in the original thread.
From my own experiments, what you want to do will definitely work.
So long as you’re not using a USB 1.0 port or a buss powered USB hub that will only deliver 100mA. Most typical computer’s 2.0 ports or powered hubs deliver the full 500mA which is more than enough for the Super Cmoy and that particular DAC. Plus, since the Recom converter is transformer isolated the two devices shouldn't (?) adversely affect each other.
I tried out some other low power usb devices in parallel with the Super Cmoy and they all still worked on my computer without issue.
As a safety precaution though, I would first power it off a phone wall charger so if something is wired incorrectly you don’t risk damaging your computer
Something that I haven't experimented with (but have been reading about) is what to do with the unused D+ and D- USB data lines. I left them floating in my experiments and it worked fine on my Apple wall chargers and my Macbook Pro. But I've read sometimes they should be shorted together, other times they should have resistors added in a certain configuration...
One more thing I noticed that I'm trying to figure out and if it's related to the data pins configuration is on all my Apple phone chargers and Macbook Pro, it only drew the appropriate current it needed, but on cheap generic brand chargers it pulled WAY more current (amps vs mA) than required and the Recom converter obviously got a lot warmer. I don't have the exact current/temperature measurements on hand but I'd love to get some thoughts on this from others
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