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In Reply to: RE: Power Supply Noise Specsmanship. Caveat emptor.... posted by Lesage on July 12, 2016 at 04:12:37
Hi !
just to say that I agree with you.
Unfortunately spectra of power supplies are almost never provided.
I found an interesting article from Clifton Labs about this topic
I am attaching the link.
There is a very interesting picture of the 20 MHz spectra of different Power Supplies noise.
I honestly cannot image a more direct and better way to compare different power supplies.
Ok there is also reliability, MTBF, size, cost ... but speaking of residual noise/ripple ... I mean, I understand it even myself !
I love this kind of graphs.
What impresses me is that some very cheap smps have actually very decent performance.
But I am leaning towards good quality linear power supplies. They should have very low noise also beyond the audio band.
But a spectrum analyzer will tell almost everything about the quality of a power supply output. Very impressive instrument indeed.
I asked for some price and the good ones are very expensive.
If not I would buy one immediately.
If you have any source of spectral analysis on low voltage power supplies please share the link.
I would be very interested to know a little more.
Kind regards,
bg
Edits: 07/13/16 07/13/16Follow Ups:
There are some possibilities to do similar measurements at a fraction of the cost, with a computer + soundcard + software (for instance, look for Spectraplus.com)
And, of course, enough knowledge about electricity
But, by no way you will get enough bandwith to comply with the 20 MHz requirement from the Keysight/Agilent/HP Application note
Which is advertisement directed toward the industry/laboratories, widely exceeding what would really be useful for average audiophiles
Except those who use switching power supplies, switching power amps, high definition digital sources, etc.
Hi ! thanks for the kind and valuable reply." There are some possibilities to do similar measurements at a fraction of the cost, with a computer + soundcard + software (for instance, look for Spectraplus.com)
And, of course, enough knowledge about electricity
But, by no way you will get enough bandwith to comply with the 20 MHz requirement from the Keysight/Agilent/HP Application note "Yes. It is what I am doing with a soundcard that samples up to 192 kHz with 24bit. I get noise spectra up to 96kHz. Beyond that the mistery.
" Which is advertisement directed toward the industry/laboratories, widely exceeding what would really be useful for average audiophiles
Except those who use switching power supplies, switching power amps, high definition digital sources, etc. "Yes. I have already been advised to use linear power supplies that should be more quiet at higher Hz.
It is just that smps are so small and convenient.
For instance I have done some noise floor tests on my soundcard.
Up to 96kHz the noise floor does not change much using a very cheap but genuine smps from a major brand (i.e. like Dell, Sony, Lenovo) or a decent quality linear psu.
But the problems maybe arise at higher Hz ?
Kind regards,
bg
Edits: 07/14/16 07/14/16
Generally, lab PSs have different requirements from audio PSs.
Study the posted supply circuit diagram. You'll see protection resistors inline with the output that increases output impedance in favour of current limit. You'll see fans because these guys are trying to save on heatsinks.
For audio purposes, the lower the output impedance and the faster the output tracks the demand the better. Thus excellent transient response is important.
They used to say that preamps and amps are really their power supplies and this appears to have been forgotten in digital audio.
A $50 PS that says it has fighter jet technology is not credible. What it has is feedforward elimination of certain peaks, or a narrow range of peaks. The technology is well known in noise elimination headphones and has been around since the 70s.
Hi thanks a lot for the very interesting advice.
Just for fun i am trying some regulator kits i have bought from ebay
Unfortunately i have no instrument like a spectrum analyzer that would be so useful.
I have to rely on what i see with a SA software (only up to 96kHz)
However using a R-core transformer most of the kits based on lt1083cp are not that bad. And very cheap.
I am using one to power with 12VDC a usb soundcard and i feel some improvements sound-wise from the stock cheap smps.
Maybe i am just hearing things.
Without proper instruments it is practically impossible to test these regulators objectively.
Thanks a lot again.
Kind regards,
bg
Edits: 07/16/16
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