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Laptop source - cheap, bad power supply

trl

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Something odd happened today when I swapped the original SMPS from my Lenovo T440s laptop with an after market one (plug issue). An odd electronic noise comes up to my tweeter, something similar with the noise that RAM and VRAM does it on your computer speakers if your microphone cable is routed inside your computer's case. I repaired the original's PSU's plug and noise disappeared.

There's a .ZIP file attached containing an .M4A audio file inside (it should play with any modern media player). The first 15 sec. is the noise of the after-market SMPS PSU, the next about 10 sec. is with the original Lenovo PSU, the next about 5 sec. is again with the after-market PSU.

This is most likely to a badly design and cheap components inside the after-market PSU. A power-line filter will not improve anything here, although I wasn't tested yet.

The noise travels through the USB cable into the DAC (the XMOS transport inside is not isolated from the USB port). I haven't tried any workaround yet, but worth mentioning that if using a crappy power supply to your audio player (a laptop in my case) some noise might get injected into your amplifier/speakers/headphones and the final THD+N and SINAD will definitely get affected.

I'll probably try soon an isolation transformer to see if the noise drops, but I doubt it will do anything good. A mains filter will be tested as too, so in case it will do, I'll also update https://www.audiosciencereview.com/...rline-noise-on-hifi-linear-power-supply.7955/. and https://www.audiosciencereview.com/...o-use-how-to-choose-a-power-conditioner.9629/ as well.
 

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  • Lenovo-after_market_PSU.zip
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I've serialized an in-line DIY filter, but it did absolutely nothing.

I've added in front an isolation transformer and the silence got back again, like the original Lenovo SMPS. that was unexpected by me, because I was never able to find such a difference when added an isolation transformer in my audio chain.

However, the 250V transformer started to make some hum noise itself, even that my Laptop was drawing around 35-40VAfrom the outlet. I guess this after-market brick gets some DC-current back into the outlet, like the cheapo LED lights are doing.

Worth mentioning that mains ground was not lifted, so the noise was not caused by the mains ground!
 
You must use digital optical in this case as they completely isolate the motherboard from your DAC
 
If you went from a doubly insulated (2 prong) to a cheaper earth grounded (3 prong) PSU, it may be a ground loop.

I replaced my dell laptop's stock 3 prong PSU to an aftermarket doubly insulated 2 prong to get rid of a similar noise (but higher frequency).
 
Like I said, it's not a ground loop and it's the same 3 prong power cable, it's the cheapo after-market SMPS. Mains ground is still there, because my isolation transformer is not lifting the ground. After placing back the original Lenovo P/N the noise disappeared.

It has to be the DC that this SMPS injects into the mains or an extreme AC ripple. The main advantage of using such transformers is to block the DC coming from the mains.
 
I replaced my dell laptop's stock 3 prong PSU to an aftermarket doubly insulated 2 prong to get rid of a similar noise (but higher frequency).
I guess you're right, I removed the mains ground by using a 2-pole adapter (totally not recommended in most cases!) and that nasty noise from my speakers went away. Given the facts that the transformer I used had not a ground lift inside, I'm a bit puzzled. However, it's much safer to use an isolation transformer on ground-loops than to simply lift the ground (or at least using a Hum-X would be safe enough).

@DDF, thanks for the help, that was a good scenario after all. :)

BTW, placing back the original Lenovo P/N did resolved the issue.
 
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Computer SMPS are some of the worse noise injectors and offenders out there. You would be shocked. Some brands are more electrically noisy than others. I know because I use the older X10 signals to switch load controls and lights in my home and I test new electrical devices before I connect them. I must keep the computers and their PSUs behind some brick-wall style noise blocks designed specifically to stop SMPS from contaminating the entire power drop beyond that outlet. I'm not surprised at your findings. Lenovo tends to behave much better than many others but it's not completely silent. You can try something like this on the input power and output cords. I'm betting the Lenovo already has a smaller choke on the output where the input chokes are typically inside the case. Many no-name Chinese made SMPS units omit these "important" components (hence my earlier comments...) --> https://palomar-engineers.com/rfi-kits/acdc-power-line-chokes
Later.
 
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Would adding one or more ferrite chokes to the power cable have made a difference in this case?
 
Aftermarket non-genuine cheap Chinese laptop supplies are mostly dreadful.

Same goes for aftermarket (Canon/Nikon) camera battery chargers. Utter garbage.
 
You mean the third-party ones, right? Not the genuine Canon/Nikon chargers, right?

Absolutely. Some of the "fake" Nikon and Canon branded chargers will damage the batteries. (They kill the internal IC in the pack) and render the battery unable to be properly charged.

Lenovo and Dell genuine laptop supplies are really good. They have to hit every regulation in every country around the world (as they are universal) and are built beautifully.
 
Absolutely. Some of the "fake" Nikon and Canon branded chargers will damage the batteries. (They kill the internal IC in the pack) and render the battery unable to be properly charged.

Lenovo and Dell genuine laptop supplies are really good. They have to hit every regulation in every country around the world (as they are universal) and are built beautifully.
Understood. I have an original Nikon dual charger for all my original Nikon batteries. I wouldn't even think about using third-party stuff.

Meanwhile I have an Asus laptop and its corresponding original charger/adapter. It's got like two dozen different certifications on it. No induced noise in my audio system, as far as I can tell.
 
Would adding one or more ferrite chokes to the power cable have made a difference in this case?
Nope, I had ferrite inside the in-line EMI/RFI filter and it helped not.
What it really helped was the addition of an isolation transformer, but also removing the ground (not-safely) did helped as well.
All the equipment was powered on from the exact same power stripe and, of course, on the same electrical fuse...everything in the same room.
It sounds like a ground-loop indeed, although the isolation transformer didn't broke the mains-ground, so the 3-pron "after market" laptop brick did received Life, Neutral and Earth as well.

I don't have a differential probe to use my scope here (my PiscoScope can not measure voltages higher than 200V), but I might try adding a 230/115V choke/coil next weekend to see if something else gets changed after adding that isolation transformer or not.
 
^^^ Correct. If the electrical noise is EMF or backwash from the PSU then yes, ferrite loops and clamps can quiescence and sometime dead-stop that type of electrical noise from propagating down the electrical lines. If you crack open the "better PSUs", you will likely see them ferrite chokes as part of the unit.

With my X10 setups, I have to use noise blocks (which are basically ferrite chokes) on any UPS and most SMPS units to block the noise they can still manage to generate on the electrical circuits.

You guys are dead on... the OEMed PSU from Lenovo (IDK about Dell) are particular well designed to meet regs across the world. That's why I always buy OEM replacements and try really hard to only use PSU from Kepco and others that have UL/ETL and other certifications. Same thing for the Apple products. I've tried to educate people many times to only buy OEM or good branded (Anker, Belkin, and maybe a few others) chargers and cables if they value their $1000 iPhones.

If the noise is being caused by a nasty ground loop, then no. That has be addressed in several other possible ways. There are a few white papers floating around about how to properly address ground loops which can be a real PITA. Later.
 
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