Hello;
Switching noise coming from SMPS are over the audio band.
I saw some designs using LC filters to get rid of this unaudible noise.
I do not know the THD+N measurement details but the noise (+N) should be the noise in audio band right?
So could you please explain the reason of why these noise degrade performance of DAC chip or opamps?
Switching noise coming from SMPS are over the audio band.
I saw some designs using LC filters to get rid of this unaudible noise.
I do not know the THD+N measurement details but the noise (+N) should be the noise in audio band right?
So could you please explain the reason of why these noise degrade performance of DAC chip or opamps?
For a DAC, it could cause intermodulation between images of the signal and SMPS harmonics, for example.
If it crosstalks to the DAC's reference voltage, the DAC will multiply the ripple with the discrete-time audio signal. The discrete-time audio signal has copies of the audio spectrum (images) around all multiples of the sample rate. The multiplying with the ripple will convert some of these images into the audio band in much the same way as the RF signal is converted to IF by the mixer stage in a radio.
This doesn't matter if the ripple is at an exact multiple of the sample rate, because the converted image is then just a copy of the desired audio signal, but if the ripple is not at an exact multiple of the sample rate, it will cause a frequency-shifted version of the audio to be added to the desired signal.
If it crosstalks to the DAC's reference voltage, the DAC will multiply the ripple with the discrete-time audio signal. The discrete-time audio signal has copies of the audio spectrum (images) around all multiples of the sample rate. The multiplying with the ripple will convert some of these images into the audio band in much the same way as the RF signal is converted to IF by the mixer stage in a radio.
This doesn't matter if the ripple is at an exact multiple of the sample rate, because the converted image is then just a copy of the desired audio signal, but if the ripple is not at an exact multiple of the sample rate, it will cause a frequency-shifted version of the audio to be added to the desired signal.
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SMPS are garbage. I just bought a toslink-line level converter, & the power supply is causing rattles in the line level output. Toslink converters are all $12, they are all probably garbage. I'm going to throw the power supply away. I'll adapt a used wall transformer & splice the cable to fit the toslink converter.
Peavey Crown & allen organ, when they use a smps, they install it in a steel box, then put filters on AC input and DC outputs to keep the howl inside. $1000 products, not $12. Allen organs were $15000 in 1980.
Peavey Crown & allen organ, when they use a smps, they install it in a steel box, then put filters on AC input and DC outputs to keep the howl inside. $1000 products, not $12. Allen organs were $15000 in 1980.
Thanks very helpfull indeed.
I guess i will build low noise amplifier and try to discover the limits of high quality isolated smps.
The Peavey's & Crown switcher amps can last 20 years. Had smps blow in a cs800s @ 18 years. Light duty bar band use. 48 year old CS800 A B revision transformer power units are amping on. Broken transistor sockets fans & dust on heat sink take those out. Not the power supply.
Last year had a 10 year old 15 v 40 A SMPS organ power supply fail with ~10 hours use. $400. Sat on shelf 9 years after agency bankrupcy. Organ installation not completed yet. Replaced it with a 40 year old linear supply supply with replaced rail cap. No-brainer. Cleaning the dust off was the major challenge.
Bought a 42 year old Hammond 182 organ in 2010. Vacuum tubes & power transformers. Still working feebly, with e-caps keeping power down to 20% nominal. No buzzes, howls, screeches, fires. My transformer supply ST120 amp is 51 years old. No power problems with e-cap replacement @ 35 years. **** farnell HDTV converter developed switcher supply inadequacy @ 8 years. Needed new main caps. **** Apex HDTV converter quit @ 3 years. Went through 4 PC-ATX switcher supplies in this computer in 6 years. Garbage, garbage, garbage.
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I don't have anything else to say other than I'm very sorry for your terrible luck. I haven't ever had an SMPS fail on me, other than perhaps a USB charger or two.
And how much does that cost??
Transformer/choke for first-order 20Hz filter is usually more than we want to finance. Or lift.
Lol you're complaining about the longevity of switching supplies in bottom dollar products?
Anyone doing repairs or being in professional stuff knows the virtues of SMPS and that is not longevity but price. As a matter of fact these were developed solely for financial goals with the higher efficiency as important key-point.
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Components for low frequency are large, large components tend to have poor properties at high frequencies. Above a few 10s of kHz the geometry and size of components start to become a big factor. The stray capacitances and inductances, and the loops created by physical placement (layout) are all critical.
There are many good SMPS designs, but the cheapest of the cheap seem to be selected here on diy. I guess after many years of building linear supplies that often cost more then the signal circuit, the joy of having ready made small and light, and cheap supplies have blinded the audiophiliacs.
For success it may be wiser to invest in a proper industrial or 'medical' supply. They have strict specs in terms of durability and EMI. Be ware though that just because they pass the EMI specs, they are noisy at the switching frequency, and when lightly loaded they will skip - skipping creates low frequency beats which may or may not occur smack in the audio band.
Filters can reduce switching noise, but not totally eliminate them.
Filters must be made with components for the frequency of interest and it is ok to have several in series each with different frequency point, layout is critical.
SMPS can be very wise. I have to drop 150V in my tube amp, and am wasting about 10W just doing that linearly, this could easily be done with a simple buck and would waste <1W doing it. But lazy me I have yet to build the simple buck...
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"medical" is the magic word for SMPS that last and these are often more expensive than linear PSU's 🙂
Not blinded but experienced by profession and by hobby I can state that I have seen way too many defective and polluting switchers to be satisfied with them. If their output is clean (which is rare) then it is the mains side that is polluting mains voltage and/or radiating RF garbage. Many positive features yes: low weight, small heatsink, high efficiency, low heat, low price, relative high power in small package. They absolutely have their merits and in the industry I would not want to see them go but in audio under around 25VA a linear PSU beats them hands down in the important areas of interest.
Quality of many SMPS was not one of their design goals, just like quality of output voltage wasn't. Any standard linear design can beat them in terms of noise easily.
Not blinded but experienced by profession and by hobby I can state that I have seen way too many defective and polluting switchers to be satisfied with them. If their output is clean (which is rare) then it is the mains side that is polluting mains voltage and/or radiating RF garbage. Many positive features yes: low weight, small heatsink, high efficiency, low heat, low price, relative high power in small package. They absolutely have their merits and in the industry I would not want to see them go but in audio under around 25VA a linear PSU beats them hands down in the important areas of interest.
Quality of many SMPS was not one of their design goals, just like quality of output voltage wasn't. Any standard linear design can beat them in terms of noise easily.
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You could use an extra winding on the transformer when developing such a device and do it good by design.
Yes that would be optimum. I do not like switching devices near my analog. But thaen I need a custom xfrmr and I dont have that.
A good SMPS can have very low ripple with just one LC-filter.
(for example look at application notes from Vicor switcher VI-200)
Expect these to cost in excess of 10 times as much as an equivalent Meanwell SMPS.
Works very well for power amplifiers and I´m sure you could also make it work well for low-power and sensitive applications like preamps and the like.
(for example look at application notes from Vicor switcher VI-200)
Expect these to cost in excess of 10 times as much as an equivalent Meanwell SMPS.
Works very well for power amplifiers and I´m sure you could also make it work well for low-power and sensitive applications like preamps and the like.