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DIY Audio Analyzer with AK5397/AK5394A and AK4490
DIY Audio Analyzer with AK5397/AK5394A and AK4490
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Old 8th October 2018, 07:41 PM   #2421
zfe is offline zfe
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Here an own measurement, done with the RTX6001, from an genuine 24V laptop SMPS followed by a LM317 regulator circuit bringing it down to 21V. So definitely nothing special.
The RTX input was set to 0dBV:
NT 100OhmLast 0dbV.jpg
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Old 8th October 2018, 08:06 PM   #2422
Joseph K is offline Joseph K  Hungary
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Originally Posted by diyralf View Post
The EMU noise figures are excellent, but the THD is a little bit to high for a meassurment device.
It needs a bit of rework but one can reach the ~ same level of performance that the RTX..
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Old 8th October 2018, 10:11 PM   #2423
Terry Demol is offline Terry Demol  Australia
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Originally Posted by anatech View Post
Hi Demian, Chris,
I have to agree. Switching supplies can be made very quiet indeed. Using test equipment as an example couldn't be more effective.

-Chris
As with many things these days it is also convergence of technologies, namely that modern LDO regs also have much better HF PSRR.

For example, a low noise SMPS feeding LT3045 is a very effective, ultra low noise combination.

T
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Old 8th October 2018, 10:21 PM   #2424
chris719 is online now chris719  United States
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Yeah, the LT304x have good PSRR through 1 MHz
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Old 8th October 2018, 11:45 PM   #2425
anatech is offline anatech  Canada
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Hi Terry,
For sure! You won't get top performance without proper technique and component parts.

You can seal the switcher inside a box and bring out your filtered DC using feedthrough capacitors (old technology) and directly into your linear regulators. That ought to get you there.

-Chris
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Old 9th October 2018, 03:43 AM   #2426
1audio is offline 1audio  United States
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Implementation is always the hard part. Typically some small detail in the grounding and return current paths is overlooked and injects noise across the system. Split supplies can be the worst since that center tap represents multiple source and return currents. In one otherwise well designed system I had to reroute a connection around a transformer the long way or stray fields were coupled into the system. All of this was well below the spec performance floor but made a difference in the phase noise.
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Old 9th October 2018, 01:47 PM   #2427
anatech is offline anatech  Canada
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Hi Demian,
Stuff like that isn't normally self evident until you spark a new design up. At least it wasn't several problems all contributing to the mess that is the output. Those designs are best simply simpler to begin again from scratch. That would include most power supplies I run across in "high end" audio equipment. A few will be so bad that all you can do is move on to the next piece.

In a nutshell, I agree with you completely!

-Chris
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Old 9th October 2018, 06:17 PM   #2428
ergo is offline ergo  Estonia
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Originally Posted by diyralf View Post
The measurements were done from a 5V-DC power bank. I doubt that you get such noise values feed from a real SM-PSU.
What makes you think there is no DC-DC converter inside the 5V power bank. I'm pretty sure there is in most of them. How else would they keep the 5V until depleted etc.
So in that sense it would not be much different from a SM-PSU.
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