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Reduce SMPS ripple noise for PreAmp?
Reduce SMPS ripple noise for PreAmp?
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Old 16th January 2018, 01:30 PM   #11
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by forestsgump View Post
what PSRR is needed to sufficient damp a 200mVpp ripple noise of SMPS?
I'd not rely on PSRR alone to reject SMPSU ripple. If you just want to rely on PSRR (and therefore, by extension linear modelling) then since your switching ripple is ultrasonic you can have any amount you like, it won't affect your audio because its above the audio band. But based on subjective observation, ultrasonic ripple does degrade SQ so there must be something else going on - which I take to be intermodulation distortion. The real circuit is somewhat non-linear, which means linear modelling doesn't cut it.
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Old 17th January 2018, 12:36 AM   #12
forestsgump is offline forestsgump
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what I do to sufficiently reduce those 200mVpp from SMPS?

if it is RC, any values to recommend? How to i connect it?
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Old 17th January 2018, 02:17 AM   #13
abraxalito is offline abraxalito  United Kingdom
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I've drawn a schematic in this post - Anyone tried to build LME49600 Headphone Amplifier Evaluation Board??
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Old 17th January 2018, 04:51 AM   #14
sarathssca is offline sarathssca  India
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How about approach in below link
TIDA-00571 Low Noise High PSRR LDO Reference Design for Powering Hi-Fi Audio Application | TI.com
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Old 17th January 2018, 06:30 AM   #15
trobbins is offline trobbins  Australia
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Is this a solution looking for a problem?

Every response is implicitly saying that the OP's power supply is too noisy and something has to be done to attenuate it or else (implicitly) the sound experience will suffer.

Maybe the OP wouldn't be able to hear any difference. If the post was on a hifi audio forum then its likely 100% of posters would be saying get a better amp (same outcome of a solution looking for a problem).

Just saying :-)
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Old 17th January 2018, 02:40 PM   #16
forestsgump is offline forestsgump
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Quote:
Originally Posted by trobbins View Post
Is this a solution looking for a problem?

Every response is implicitly saying that the OP's power supply is too noisy and something has to be done to attenuate it or else (implicitly) the sound experience will suffer.

Maybe the OP wouldn't be able to hear any difference. If the post was on a hifi audio forum then its likely 100% of posters would be saying get a better amp (same outcome of a solution looking for a problem).

Just saying :-)
isnt 200mV consider noisy for Pre-amp & DAC use?
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Old 17th January 2018, 07:09 PM   #17
trobbins is offline trobbins  Australia
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Do you hear any noise?
Can you measure any noise at the speaker terminals?
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Old 17th January 2018, 07:20 PM   #18
forestsgump is offline forestsgump
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Quote:
Originally Posted by trobbins View Post
Do you hear any noise?
Can you measure any noise at the speaker terminals?
-- Hear any noise?: Yes, as i can hear little hiss even volume (Potential gain knob) is at Zero, I had relatively quiet environment.

This little hiss tell me, that amplifier is powered-on.

-- 200mV ripple: presumably has some impact to pre-amp, and DAC on SQ.
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Old 17th January 2018, 07:57 PM   #19
trobbins is offline trobbins  Australia
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Quote:
Originally Posted by forestsgump View Post
-- Hear any noise?: Yes, as i can hear little hiss even volume (Potential gain knob) is at Zero, I had relatively quiet environment.
This little hiss tell me, that amplifier is powered-on.
That sounds like your amplifier is the main contributor to hiss/noise.

If you were inclined to test out the noise/hiss contribution from your preamp, then you need to appreciate that that noise/hiss may be from the preamp electronics, and nothing to do with the powering.

The simplest test for identifying if your preamp power supply is contributing noise/hiss that you can hear is to temporarily use a battery power supply for your preamp.

If you were able discern a difference between battery powering and MeanWell powering your preamp, then you need to somehow eliminate the other plausible causes of that noise/hiss that are unrelated to filtering any high frequency noise (as mostly recommended by the posts in this thread) - one area of concern is ground/HF loops through multiple mains AC connections.
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Old 17th January 2018, 08:37 PM   #20
tomchr is offline tomchr  Canada
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My HP-1 headphone amp uses two 24 V switching bricks + CLC filter + linear regulators to get down to 18 V. The HP-1 provides world class performance.

My DIFF PRE is powered by two 15 V switching bricks + CLC filter and gets stellar performance as well.

It is perfectly possible to get good audio performance from switching modules chosen with care. The switching frequency of the Mean Well units tends to be around 70 kHz. You can attenuation that with a well-designed CLC filter. Make sure to limit peaking in the filter as that will boost the noise (due to the resulting higher supply impedance) rather than suppress it.

One way to determine whether your preamp or power amp is the dominant noise contributor is to use a shorting plug on the power amp. Short its input. Measure the output noise. Then connect the preamp with the volume turned all the way down (or a shorting plug on the selected input). Measure the output noise. If the noise increases significantly when you attach the preamp, the preamp is dominating (or at least contributes as much as the power amp to the noise level).

Tom
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Last edited by tomchr; 17th January 2018 at 08:39 PM.
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