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Reduce SMPS ripple noise for PreAmp?
Reduce SMPS ripple noise for PreAmp?
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Old 7th January 2018, 02:06 PM   #1
forestsgump is offline forestsgump
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Default Reduce SMPS ripple noise for PreAmp?

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?

Last edited by forestsgump; 8th January 2018 at 01:20 PM.
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Old 7th January 2018, 02:53 PM   #2
abraxalito is offline abraxalito  United Kingdom
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You'll want to put at the very least an LC filter between the supply and your opamp(s).

Try an SLF7045T-471 (470uH) SLF7045T-471MR22-PF TDK | Mouser

in series with the supply rail with a Nichicon HZ UHZ1C102MPM6 Nichicon | Mouser
shunting to 0V on the opamp side of the inductor. Assuming that you're not using more than 16V.

In simulation this combination gives about 80dB attenuation at 40kHz.
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Old 7th January 2018, 03:01 PM   #3
Aatto is offline Aatto  United States
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smps+crclc+cap multiplier.
tried that setup for headamps and pre.
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Old 8th January 2018, 10:47 AM   #4
AndrewT is offline AndrewT  Scotland
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opamps and many discrete amplifiers can have very good PSRR at lower frequencies.
All have poor PSRR at higher frequencies.
The output of a switching supply is riddled with higher frequency interference.
You need something to attenuate the higher frequency interference. A 3pin IC regulator will not do !
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Old 8th January 2018, 01:18 PM   #5
forestsgump is offline forestsgump
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Quote:
Originally Posted by AndrewT View Post
opamps and many discrete amplifiers can have very good PSRR at lower frequencies.
All have poor PSRR at higher frequencies.
The output of a switching supply is riddled with higher frequency interference.
You need something to attenuate the higher frequency interference. A 3pin IC regulator will not do !
Thank you for all the inputs, some direction to focus ~ so zero-in action on the right area.

Search in diyaudio, some point out SMPS are usually well-considered design in disturbance reduction; while situation can become more complex when cross influence when supplying multiple devices.

Would appreciate any inputs which can leverage on; what actually was done to migrate and found effective.
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Old 9th January 2018, 07:12 PM   #6
martin clark is offline martin clark  Europe
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Very simple illustration of Andrew's point I wrote-up over a decade ago:

Using 3-pin regulators off-piste: part 2

Note - even a little C-R-C decoupling can help ahead of a 3-pin reg, very much; but you must be careful about where the '0v' ends of those capacitors return to. e
Effectively, they move the noise current from the input to wherever you connect them to - so their 0v termination must be on the 'dirty' 0v side, to return the HF current directly to the raw supply - and not pass across your 'clean' filtered 0v ground routes, anywhere. In other words - it's not enough to pick a preferred approach (LC, CRC, 'gyrator', whatever) - a good, well-considered layout is also an essential part of the solution.
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Old 10th January 2018, 03:06 AM   #7
HiFiNutNut is offline HiFiNutNut  Australia
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My BD player has SMPS PSU and it is very noisy. I put a number RC snubbers over the SMPS, multiple LCR filters, etc. but found that some ferrite cores wrapping around the output wires which go to the DAC board work wonders. I guess a lot of noise is CM noise so ferrite cores wrapping both V and 0 wires may work better than LCRs that mainly deal with differential noise. Please correct me if I am wrong.
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Old 10th January 2018, 03:16 AM   #8
abraxalito is offline abraxalito  United Kingdom
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CM noise is only an issue for connections to external units (for example the connection between a preamp and an amp, or between a source and preamp), not for the preamp itself. CM noise between units can be addressed by isolation transformers, slap-on ferrite cores (in effect they're CM chokes) only really help at very high frequencies.
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Old 16th January 2018, 01:14 PM   #9
forestsgump is offline forestsgump
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Got a amateurish question:

Did I understand correctly that i read somewhere that 10mV at switching frequency (psu) is sufficiently damped by 60dB PSRR? if so, what PSRR is needed to sufficient damp a 200mVpp ripple noise of SMPS?
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Old 16th January 2018, 01:18 PM   #10
nigelwright7557 is offline nigelwright7557  United Kingdom
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You could probably get away with just an RC filter.
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