Usb audio interfaces _ one quick advice.

Hi Guys !
i need just one very basic advice.
If i have a usb interface with external power supply (i.e. not usb powered) how much will i gain
in terms of lower noise and/or lower THD by replacing the very cheap stock smps with another one with better specifications ?
Just this.
Thanks a lot to everyone.
Regards, gino
 
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If i have a usb interface with external power supply (i.e. not usb powered) how much will i gain replacing the very cheap stock smps
with another one with better specifications ?
will i be able to get lower noise and/or lower THD ?

Hi Gino,

the smps power supply feeds the USB interface, or you're referring to PC's power supply?

In case of the first option a linear supply could make some difference but withouth knowing something more it's difficult even to guess...

This USB interface is a soundcard? It outputs SPDIF? I2S? It's isolated?
 
Hi Gino,
the smps power supply feeds the USB interface, or you're referring to PC's power supply ?

Hi and thanks a lot for the very kind and helpful reply.
This is the interface in question

Phonic FIREFLY 302 USB Portable 5X6 USB Interface | Musician's Friend

it comes with a ridiculous ac wall adapter smps.
To be honest i should receive in the next days. I asked the guy selling it and he confirmed that the external power supply is very cheap looking.
As soon as i will receive it i will post its noise graph.
But this is a very general question.
Usb audio interfaces is my only real present interest.
My final goal is to get the lowest noise and THD one i could afford (with XLR line level input).

In case of the first option a linear supply could make some difference but withouth knowing something more it's difficult even to guess...
This USB interface is a soundcard? It outputs SPDIF? I2S? It's isolated?

Yes it is a soundcard. Yes it has spdif in/out.

B_PHONIC_firefly302usb.jpg


However i do not know what isolated means :confused:

Actually i will be able to run some measurements with other power supplies i have at hand
but the problem is that they are all very cheap and low quality smps.
I am pretty sure they have ripple in the order of hundreds of mV :rolleyes:
I am very willing to try some kit with the ripple in the order of the uV ;)
unless this will not provide any improvement.
This is the reason of my question.
I am sure that kits of uV power supplies will be very very expensive.
And this could also be a method to evaluate indirectly the quality of the power supply ?
Thanks a lot indeed again.
Kind regards, gino
 
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From the labeling and max output specs, I would be guessing that there's an LDO inside (or maybe even a plain 78xx/LM317) to bring analog supply voltage to about +7..7.5 V. Where the DC/DC for phantom power supply would be connecting is anyone's guess.

What makes you think that ripple is a problem? Of course a really cheap and nasty SMPS may have excess ripple, but IMHO the main reason for SMPS nastiness is common-mode noise. Most of that should be drained over the USB shield here, so unless you've got a ground loop running over that (i.e. unbalanced connections) you'll probably be fine. Otherwise you could still try a plug-pack type supply of decent quality, but nobody will guarantee you that this quietens down the ground sufficiently.
 
From the labeling and max output specs, I would be guessing that there's an LDO inside (or maybe even a plain 78xx/LM317) to bring analog supply voltage to about +7..7.5 V.
Where the DC/DC for phantom power supply would be connecting is anyone's guess. What makes you think that ripple is a problem?

Hi thanks a lot indeed for your both very kind and helpful reply.
Let me make an introduction.
My main and almost only interest are usb audio interfaces.
For me low distortion and low noise are everything.
I am also a little annoyed by some many listening opinions i have read.
So i decided to try to finally measure something myself with my pc.
I have found this Arta software that i understand it is good quality.
The only measurement that i have been able to perform until now is the noise measurement.
So i am measuring everything i have at hand.
Another aspect that i do not like are usb powered interfaces.
So i bought one with external dc adapter. i should receive it very soon.
I will test it with the stock power supply, a cheap smps.
I do not know how much the noise will be.
So my idea to test it with a better power supply, linear or smps.
For sure i will test it with anything i have already at home just to see for any benefits in terms of lower noise.

Of course a really cheap and nasty SMPS may have excess ripple, but IMHO the main reason for SMPS nastiness is common-mode noise.
Most of that should be drained over the USB shield here, so unless you've got a ground loop running over that (i.e. unbalanced connections) you'll probably be fine.
Otherwise you could still try a plug-pack type supply of decent quality, but nobody will guarantee you that this quietens down the ground sufficiently

Thanks a lot indeed for the very interesting advice.
I guess the only way to check these possible issues is with measurements.
I will measure in every possible way to find the solution that with the same interface will give me the lowest noise.
From what i have read galvanic isolation from the pc could be beneficial because the power in the usb bus is dirty. Actually when i see something usb powered i am a little puzzled ... 5V/0.5A dirty do not leave much to play with. Much better 12V/2A with some uV of ripple.
But i understand there is no substitute for a direct measurement.
I am very curious to see how low i will go ... with a very cheap interface.
Thanks a lot again, gino
 
Nice and cheap tweak for this: JitterBug
I use one myself as part of my connection from a raspberry-pi to my USB-DAC. Better: don't know for sure how to describe the effect. Different: yes !!

Hi ! and thanks a lot for the advice.
I guess this device addresses the jitter.
I am still on noise :eek: i am starting my journey.
Also because i have the feeling that noise has an impact on everything ... less noise is always something very very good to have.
Like also low distortion. I am not a tube guy.
When i see the tests where they send 1kHz in and they get a series of other peaks at the output i am very puzzled.
Then i will try some distortion measurements.
But noise for me is important. I have been impressed by a very basic video on youtube that explained how bad is noise for audio. Very very bad.
It masks all the detail.
With no noise the detail pops up.
Thanks again, gino
 
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there is a blog from Archimago who does a lot of measurements. This article may perhaps give you an idea if you need to use a different power supply: Archimago's Musings: MEASUREMENTS: ODROID-C2 with Volumio 2, and USB digital music streaming.
There are a lot of interesting articles to read for all people who are having questions regarding digital audio

Hi ! thanks a lot for the very interesting advice
i am moving my first steps in measurements and i found this Arta software mentioned.
To be honest i have just a vague idea of what i am doing.
I am trying to learn something. My guess is that different usb interfaces will respond differently to better power supplies. So the only way to know is through measurements.
The idea is to select both an usb audio interface and the best power supply.
The ideal would be to have an interface very sensitive to the power supply ripple.
I am sure i could do better with the same interface and better power supply.
But i am exclusively interested in 12V power supply for my main project.
Thanks again, gino
 
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There's also the Schiit Audio WYRD USB Decrapifier. I've been interested in trying this myself.

From their website:

It seems like USB decrapification is really becoming a thing these days. Of course, other people call it different things, but let's face it: Wyrd was the first device to combine both a low-noise, linear power supply and USB hub chip (or "regeneration," if you want to be fancy) with a precision crystal oscillator. What does all this tech talk do for you? Simple. It can solve some sticky USB audio problems.

The Cure for Noise and Glitches
Have you ever heard strange noises from your USB DAC? Or have you had it “drop out” after the computer goes to sleep? Or does your computer have trouble recognizing your DAC at all? It could be due to noisy USB power, or USB port power management. Wyrd has you covered—Wyrd is the only USB decrapifier that includes a linear power supply (not a noisy switcher) and precision 2.5uV LM723 regulators with discrete pass elements for up to 200,000x less noise than what comes out of your USB port, up to 500mA—the full USB 2.0 spec.

Improves Sound, Color Printing, Data Stability
Yes. Some listeners say Wyrd improves the sound of their system. We won't make any such claim to sonic nirvana—sorry, creating expectation bias and neuro-lingustic programming ain't something that we do. Sonic improvements are for you to decide. The rest of it—color printing and data stability—that’s like saying charging your iPhone off Wyrd makes the battery last longer. Have fun with that one.

Works With Any USB DAC
Wyrd isn’t limited to working with Schiit products. You can use it with any USB DAC—2.0, 1.0, 32/384, DSD1024, whatever—it doesn’t care. All it’s doing is cleaning up the USB connection, and it supports all USB Audio Standards.


Schiit Audio, Headphone amps and DACs made in USA.
 
Hi !
there is a long thread on the subject here

http://www.diyaudio.com/forums/digital-line-level/290973-jitter-issue-usb-signals.html

the situation is still confusing. There is indeed a big marker of usb isolator, repeater, conditioner, anti-jitter and so on.
From what i understand if you keep the usb connections short and use good quality cables jitter should not be a problem.
Instead usb bus power is indeed a problem because it is weak and dirty.
I would try the device you mention for sure, give its low price also.
However there are many others.
Kind regards, gino