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Reduce SMPS ripple noise for PreAmp?
Reduce SMPS ripple noise for PreAmp?
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Old 8th February 2018, 05:17 AM   #41
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by forestsgump View Post
I am using a Meanwell SMPS (reads 200mv ripple noise) to power a NE5532 PreAmp to a Class D Amplifier.

Would the ripple noise a SQ concern the PreAmp?
Is there anyway, I can reduce this SMPS ripple noise?
I use a pair of Mean Well SMPS bricks in my DIFF PRE 8x2 differential preamp. You can see the performance plots on my website.

I use a CLC filter on the output of the switching modules. At least with modern parts, that provides plenty of ripple attenuation to ensure good performance of the overall preamp.

Not to knock your choice of opamp, but newer parts, such as the OPA1612, LME49720, etc. have much higher PSRR than the humble NE5532 and are worth considering in your application.

The trick with CLC filters is to pick the components such that you get meaningful attenuation at the switching frequency of the SMPS without causing (too much) peaking in the filter response. Ideally, you would optimize the filter for the lowest supply impedance as well.
I tend to shy away from CRC filters as they raise the supply impedance by 'R'.

In my HP-1 headphone amp, I use a pair of Mean Well switchers with a CLC filter and a pair of LM317/LM337 linear regulators. That provides stellar performance as well. You can see the plots here: HP-1: Ultra-High End Headphone Amplifier

Tom
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Old 8th February 2018, 03:53 PM   #42
forestsgump is offline forestsgump
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Thk Tomchar for sharing vast experience, any advice on the below situation:

Meanwell LRS-150 SMPS freq: 65KHz
Ripple =200mVpp
Output = 4.7A (i am using it on a integrated amp - so current drawn would be high)

appreciate any component & part value recommend...
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Old 15th February 2018, 04:01 AM   #43
tomchr is offline tomchr  Canada
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I don't know that specific supply, so I can't make a specific recommendation. If the switching frequency is 65 kHz, you'll want decent attenuation at that frequency. You'll want the filter bandwidth to be at least as wide as the SMPS's regulation bandwidth and you'll want to avoid peaking in the filter response.

To make a specific recommendation, I would need to know the regulation bandwidth of the supply. If I was to take a guess, I'd say mid-kHz range, maybe. So design a filter with that cutoff frequency and minimal peaking that gives you the best attenuation as you can get at 65 kHz. You'll need to include the parasitics (DCR/ESR) of the chosen components in your design. You'll also need to make sure that the inductor won't saturate at the output current you intend to draw.

Tom
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