Grubdac low voltage issue

Quote:

Originally Posted by NateYi 

Hello everyone.

 

I've noticed an weird issue with my Grubdac I built a while back.  Whenever my mini fridge kicks on or off, the sound in my dac cuts out.  Sometimes sound will just stop for a second and resume on its own, but usually it will just go silent altogether, at which point I unplug and replug the usb cable in.  I measured the voltage at the D- and D+ terminals on the board and I'm only reading 2.65 volts.  Could the fridge be causing a surge that's screwing with my dac, or maybe something faulty within the circuit/solder joints?

I'm sorry to say that this is a known problem.  However, in DIY parlance, it's really just a nuisance under normal circumstances.  Obviously, one of the primary design goals of the GrubDAC is all power from USB.  So, in order to ensure those sterling bass pulses, the current rating gets fairly close to where the USB protective circuits in a PC might cut out.  This is especially true if you have anything else connected.  As you have seen, the DAC restores itself quite readily once the PC is convinced that it has enough power.

Quite frankly, I've had amps and DACs plugged into the same panelboard circuit breaker run as a small refrigerator - I can't imagine anything worse.  The constant on and off motor run with high current cut-in and cut-off is worse than anything except perhaps a hair dryer, high-powered vacuum cleaner, or high-volume color laser printer.  It's simply asking for trouble.  If your amplifier or DAC doesn't pick up the motor noise or switching noise, then your PC's protective circuits and therefore the DAC, are going to be bopping on and off on a regular and quite irritating basis.
 

Quote:

Originally Posted by NateYi 

That makes sense.  I didn't know there was a protection circuit built into the usb guy.  I actually tried to solder in a little capacitor on the usb power side of Grubdac board to help with the voltage drop but it makes sense now why it didn't work.  Damn black magic.  

 

Do you think having a continuous UPS would solve the issue?  I would imagine that running the computer on a battery would essentially isolate my computer from my fridge. I'm thinking any change in voltage would be eliminated if the computer is getting a consistent flow of power from a battery, 

Well, I don't know that there's a protective circuit built into the GrubDAC.  I assumed it was the PC Bus.  This has been documented with other DACs/USB-powered amps.  When the current hits a certain limit, the USB Bus in the PCB will simply start dropping devices.*

Yes, a UPS should provide adequate isolation, but another circuit that was not supplying the fridge would be better all the way around, IMHO.
 

* EDIT: It may just be a voltage sag issue, too.  A sag in the wall voltage causes the USB on the PC to drop below 5V.  That might kick off the PCM2706/7 in the GrubDAC and other DACs, if they have a PCM2706/7.