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Battery Power - USB DAC (Dragonfly)
Battery Power - USB DAC (Dragonfly)
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Old 30th October 2012, 12:03 AM   #11
seawalker is offline seawalker  United States
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Originally Posted by abraxalito View Post
As far as I recall, the wires carrying 0V do double duty - as ground connections for power and as signal returns. That results in power supply noise appearing in series with signals.

There's another issue - common-mode noise from source - which in the case of a battery powered USB DAC - becomes the noise from the computer. A big loop is created between the computer's mains power supply and the toroidal transformer inside your active speaker. That this influences your sound can be easily verified - use a laptop running from internal battery. If the sound is clearer than when its running from its mains 'brick' then you have common-mode noise issues.

One way to attack these two issues is to have a star earth on the amp PCB and run each 0V connection back with its own wire. The one which will make the most difference is the screen connection of the input RCA - that's where the CM noise from your computer comes in. You'll need to be adept at cutting PCB tracks to isolate this and run its own dedicated wire back to the star earth. The way its designed the CM noise gets routed through the input PCB which is a no-no for SQ. After this the next biggest effect on SQ comes from cleaning up the grounding to the decoupling capacitors on the power rails. Again, give them their own 0V wire back to the star.

What do you mean by "screen connection of the rca input" ? Do you just mean where the rca connects on the other side of the sleeve to a hook up wire? I should ground that connection point?

Your help is much appreciated. Thanks for taking the time. I havnt popped the cabinet open to look at the amp in the speaker yet. so im not sure if Emotiva's version employs this poor grounding scheme. But id be VERY interested in finding out even if I cant fix it yet.

Im not to confident enough with knowing what im looking at yet - finding the right caps and their 0v connections. Perhaps i could post a pic?
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Old 30th October 2012, 12:15 AM   #12
abraxalito is offline abraxalito  United Kingdom
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I meant the outer conductor (screen) connection of the input socket. The best sound comes from having a dedicated ground wire to it.

Yes by all means post up pics, as large as possible, both sides of the PCB I feel pretty confident that Emotiva won't have changed QMS's grounding scheme.
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