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Does computer power source (switching vs. battery) matter for a USB bus - powered device (e.g. ADC or DAC) ?

benanders

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I use a USB bus-powered ADC / DAC:
Should it perform differently if connected to a typical switching PSU-powered computer, vs. a battery-powered laptop?

The unit is a KORG DS-DAC-10R for digitizing records (or specific masters) not already [easily] available in 1’s and 0’s. I know - the KORG proprietary software isn’t ideal and there’s no need to run further circles on why some of ya’s think vinyl is below par in this thread, so let’s please stay focused on the PSU-to-USB bus-power question. ;)
 

staticV3

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I use a USB bus-powered ADC / DAC:
Should it perform differently if connected to a typical switching PSU-powered computer, vs. a battery-powered laptop?
No.

Generally, USB-powered devices have power filters inside so that the type and quality of power supply does not matter.

That being said, there are definitely poorly designed ones that will be affected by a noisy power supply.

I don't know what category the Korg belongs to.
 

Doodski

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I use a USB bus-powered ADC / DAC:
Should it perform differently if connected to a typical switching PSU-powered computer, vs. a battery-powered laptop?
No, it should not perform differently if the gear is in spec. Volts are volts and current properly smoothed is current. The laptop is likely to have a PWM power supply in it anyway.
 

DVDdoug

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USB power is notoriously noisy and that noise can sometimes get into to analog side of an ADC or DAC. If you get that problem it's usually a high-pitched whine from the switching supply/regulator in a computer or from the digital switching inside the computer.

Battery powered laptops are not immune but you are less likely to get ground loop noise with a laptop. Even when plugged-in, most laptops don't have a connection to the power line ground.

It's more commonly a problem with ADC preamps (phono or microphone) where the high gain amplifies any noise. With DACs and line-level ADCs it's more rare.
 

Doodski

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USB power is notoriously noisy and that noise can sometimes get into to analog side of an ADC or DAC. If you get that problem it's usually a high-pitched whine from the switching supply/regulator in a computer or from the digital switching inside the computer.
The digital ICs that feedback noise into the B+ power supply are controlled with inductors @ the B+ power line. It works if not cheap about stuff. Meaning use it and most of the issue is controlled and all is well.
 

AnalogSteph

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I use a USB bus-powered ADC / DAC:
Should it perform differently if connected to a typical switching PSU-powered computer, vs. a battery-powered laptop?
Not generally per se, but should your setup ever happen to include a ground loop, all bets are off. Most phonopres and turntables tend to be floating affairs though, so you are likely to be fine in that respect.

Should the computer power supply have a tendency to make its output ground float considerably removed from earth potential (as can happen with laptop supplies sporting a 2-prong mains connection), you may want be using the Korg's ground terminal to hook up a good ground. While in theory it should not make a difference if the entire signal path from the cartridge is well-shielded, there still is the cartridge itself as a potential weak spot.
 

Sokel

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I would say that it's pure lack:


(I will not link the gazillion threads about PC - laptop noises)

I have seen monsters measuring otherwise well measuring DAC'c.
The thoughtful thing to do any manufacturer is to have an isolator after the PC.

(an example of an isolator which sadly didn't work but you can see the difference even if it doesn't)


Otherwise is a shot in the dark.
 
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benanders

benanders

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I was wondering about the root of the query as to why it would be different....

Aha - this question is more comprehensibly phrased! ;)

The root of my query boils down to a wording difference between us, nothing more than that - there could be a difference between any two (or more) variables that (1) a person might observe but (2) does not sufficiently understand to meaningfully predict whether or not the two (or more) variables should (or do) differ. Hence my carefully-chosen wordings.

I do not know enough about USB bus-power to suspect the upstream power supply would have an audible / more-than-negligible effect in the audio being digitized from said ADC’s process.
In short, I did not suspect a difference should exist any more than I suspected I difference should not exist: I’m generally not one to discount possibilities based on my own ignorance. :D

I’m surprised I couldn’t find much on upstream device power supplies vs. USB bus-powered kit in other threads before this one. Perhaps poorly chosen keyword searches on my part. The input has been very helpful, guys!
 

Doodski

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I do not know enough about USB bus-power to suspect the upstream power supply would have an audible / more-than-negligible effect in the audio being digitized from said ADC’s process.
In short, I did not suspect a difference should exist any more than I suspected I difference should not exist: I’m generally not one to discount possibilities based on my own ignorance. :D
All of the digital ICs feedback square edged high fundamental frequency digital noise back into the power supply and that affects the operation of all the ICs which then create more noise and so it goes on. The smoothing capacitors in the power supply feeding the digital circuitry can smooth most of the bad stuff but the digital feedback noise waveform is square edged and is a challenge to get rid of entirely. So somewhere it has to be smoothed. That is done at the power input at the ICs in the form of that inductor that I mentioned. Any effect on the output of these digital ICs is not affected by the noise in the power supply unless the noise is very very obviously present and stops the detection voltage trigger points in the digital ICs from being triggered properly. These detection voltage points are supposed to eliminate what is called indecisiveness which is when the IC cannot determine if there is a square wave or not and then the IC glitches due to not being able to determine if there is a zero or a one present. So this stuff can get pretty complicated and convoluted to trouble shoot. It does happen.
 
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