Suspiciously EMF sensitive electric piano. Problem narrowed down, makes no sense - Page 1
Forum section: electronics / beginners

author: cincin
author_rank: Regular Contributor
timestamp: June 08, 2025, 08:46:26 pm
content: I have a Yamaha P-60 electric piano that catches some serious digital-sounding interferences in my living room, but not in my basement.I've really narrowed it down as much as possible, but the problem persists. I'm trying to sell the piano, and I want to make sure it is 100% healthy before I do so.So the question is: Is this EMF sensitivity a design flaw, or symptom of a problem. (And if it is a design flaw, how can I alleviate it.)Here are the facts / what I've triedThe internal setup is simple, the analog audio comes out of the digital board, goes through the volume fader, and onto the power amp board, then out to the speakers/headphones.The interferences are present in both the headphones and the speakers. Mostly on the right channel but definitely also present on the left.- It's the only synth/piano I own that catches EMFs there, and it's very loud.- The interferences are present when the piano is powered by a battery pack (not a ground problem)- The interferences come in on the amp board, because they are present when I disconnect the audio coming in from the volume fader- The interferences come in on the signal path, before the power amp IC, and not the ground, because they disappear when I ground the signal path before the IC- I've tried manually grounding various ground points, it doesn't seem to affect the interferences. Doesn't seem to be a bad ground connection.Please take a look at the attached schematic. The trace from the audio coming in from the volume fader (CN202) to the power amp IC is very short, it's surrounded by ground planes, and I have now replaced all the components between the connector and the power amp IC: R225, R245, C245, C265, R226, R246, C246, C266. Still the interferences remain.How?!Where else could this be coming in?Is it really a design flaw?Can I beef it up? I've tried waving a grounded piece of tin foil around the board and it doesn't seem to do much. A full Faraday cage would be a bit difficult to implement.I'm not sure what to try next. Halp!Cheers!

author: SuzyC
author_rank: Frequent Contributor
timestamp: June 08, 2025, 10:16:38 pm
content: Strong clue, "digital-sounding interferences in my living room, but not in my basement."Any exposed wires going to each piano key switch need to be RF shielded with aluminum foil and grounded. Probably pickup noise from a TV Wi-Fi or from terrestial TV and/or LTE strong phone transponders nearby. An efficient shield can can be made using two sheets of aluminum foil separated by a piece of paper or plastic and grounded. Must be made to fit over/under so as to make a RF shield fpr the exposed switch wiring and possibly the PCB connected to the key switches.Might also try connecting .1uF caps between IC203 pin 1-2 and (the second) cap between pin 7-6

author: radiolistener
author_rank: Super Contributor
timestamp: June 08, 2025, 10:45:19 pm
content: Quote from: cincin on June 08, 2025, 08:46:26 pmYou might want to check if there's a Wi-Fi router or other RF-emitting device located near your synthesizer. Strong RF fields, especially from 2.4 GHz Wi-Fi, can sometimes induce low-frequency interference by rectifying on nearby semiconductors or unshielded inputs.It's also possible that a cellular base station is located near your home. These installations can emit relatively high total power - often up to 500-1000 W across all channels (50 W per channel) at GHz range bands and may cause issues for electronics that are sensitive to electromagnetic fields.

author: cincin
author_rank: Regular Contributor
timestamp: June 08, 2025, 11:09:06 pm
content: Quote from: SuzyC on June 08, 2025, 10:16:38 pmIn this case the interferences are being picked up somewhere between the connector on the amp board, and the power amp IC two inches away. It can't be the keys because the interferences are present when the digital board, keybed, and volume control, are disconnected. As far as I can tell, the interferences are being picked up in the 2" of trace between the connector and the power amp IC, assuming I'm not missing something.Quote from: radiolistener on June 08, 2025, 10:45:19 pmI've played many different pianos and keyboards in that location and never had that problem. It's entirely possible that this particular keyboard is more sensitive than most, by design, and that's sort of what I'm trying to assess. I'd like to sell the keyboard in good conscience, knowing that it is working as it did when it left the factory (or better). So I need to do my due diligence and make sure these interferences are not from a defect or component failure, and actually (sadly) just a bad design... it's a bit subjective, I do realize.Is there any way I can be sure that the keyboard is not faulty? Like I said in the original post, I changed every components between the connector and the power amp IC, and I'm relatively certain that's where the interference comes in, so... but I'm a beginner still at all of this, so I could be missing something entirely.Thanks for the help!

author: SuzyC
author_rank: Frequent Contributor
timestamp: June 08, 2025, 11:25:30 pm
content: Your equipment is most likely working as well as when it was new but its circuitry was probably designed before the many new phone and TV devices were to be found everywhere and generating strong microwave signals that can be unintentionally demodulated by sensitive circuits and be the cause of the audio interferrance.Try the makeshift RFI shield I suggested to see if this shielding idea fixes the problem.

author: cincin
author_rank: Regular Contributor
timestamp: June 08, 2025, 11:29:20 pm
content: Quote from: SuzyC on June 08, 2025, 11:25:30 pmThe keyboard is from 2002, not that old, but I guess WIFI and cell signals were different back then.Will try adding some caps and report back!Cheers!

author: cincin
author_rank: Regular Contributor
timestamp: June 08, 2025, 11:35:57 pm
content: Quote from: SuzyC on June 08, 2025, 11:25:30 pmActually, IC203 can't be responsible because it's in the pre-amp section. The interferences are present when CN202 is disconnected, when the pre-amp and volume control are out of the loop.The problematic area is, as far as I would assume, limited to the trace and components between CN202 and the power amp IC.

author: SuzyC
author_rank: Frequent Contributor
timestamp: June 08, 2025, 11:39:58 pm
content: Try the makeshift RFI shield I suggested over the sensitive PCB area to see if this shielding idea fixes the problem.

author: cincin
author_rank: Regular Contributor
timestamp: June 08, 2025, 11:58:43 pm
content: Quote from: SuzyC on June 08, 2025, 11:39:58 pmAh, you meant the foil. My badAs expected, if I completely wrap the amp board in grounded foil, the interferences are gone.

author: cincin
author_rank: Regular Contributor
timestamp: June 09, 2025, 12:05:59 am
content: I guess I could add copper tape to the plastic case where the board goes, the bottom of the keyboard is already foiled. Connect the two...It's a bit obvious. But that's assuming the sensitivity is because of a bad (or old) design, and not a component failure, which at this point seems more likely.Thanks. I wanted to make sure I wasn't missing something with all my assumptions.Cheers!

author: johansen
author_rank: Super Contributor
timestamp: June 09, 2025, 12:39:27 am
content: i cant' say for certain but i've dealt with a wide variety of 20+ yr old audio equipment over 20 years, and none of it has these problems.the idea that modern day cell phone signals or 5g or etc could cause a problem with analog or sub 100mhz processors in state of the art synthesizers of 20 years old audio equipment such as a yhamaha 60 keyboard... nonsense to me.there is simply no mechanism for the circuit board to be a rectifier for a higher frequency than it was already designed to deal with, regardless of the failure mode.

author: cincin
author_rank: Regular Contributor
timestamp: June 09, 2025, 01:50:07 am
content: Quote from: johansen on June 09, 2025, 12:39:27 amWhich would suggest some sort of failure or bad connection?But where could that possibly be?I'm seriously puzzled about the source of the EMI as well. It's strongest near the front wall of my house, but all the wires are passing through the back alley. I've disconnected every appliance, charger, led light, powered down computers, etc, on my main floor and the interference was still there.I've applied copper tape and connected it all to ground, but apparently that's not enough. Will add more.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 09, 2025, 06:45:58 am
content: Quote from: cincin on June 09, 2025, 01:50:07 amThere's obviously something that you missed. EMI doesn't just come from nowhere.

author: SteveThackery
author_rank: Super Contributor
timestamp: June 09, 2025, 11:46:59 am
content: Quote from: johansen on June 09, 2025, 12:39:27 amI'm thinking the same thing: the gap between 20kHz and 2.4GHz is so vast it is surely not feasible for WiFi or mobile network signals to induce audible noises in the amp, is it?

author: radiolistener
author_rank: Super Contributor
timestamp: June 09, 2025, 02:26:38 pm
content: Quote from: johansen on June 09, 2025, 12:39:27 amInterference from cell phones communicating with base stations often heard as a buzzing sound from speakers is a well-known issue nowadays. I'm surprised you haven't encountered it before. You can even listen that buzz sound from cell-phone communication on many videos.As for Wi-Fi, I have a router located near the area where I conduct my electronics experiments, and I've long observed that it induces low-frequency pulses at the inputs of operational amplifiers. It sounds like a woodpecker tapping. When there is network activity you can even hear changes in the pattern and if you power off WiFi router, or just disable it in software, this interference disappears completely. The interference is relatively weak, but it is clearly audible.I can record how WiFi interference on audio equipment sounds like if you want.Another potential source of audio interference is the presence of a high-power radar system nearby. These systems emit extremely strong pulses at GHz range, which can easily couple into and disrupt audio circuitry.

author: cincin
author_rank: Regular Contributor
timestamp: June 09, 2025, 02:29:13 pm
content: Quote from: Analog Kid on June 09, 2025, 06:45:58 amI can only assume so. I do live in a fairly dense city, I guess it could also come from the neighbours, but it's so strongly focussed in my living room.We have smart electric meters around here, meters that have their own WIFI that cannot be disconnected. so it could be that too. But the meter is sort of at the back of the house.Quote from: SteveThackery on June 09, 2025, 11:46:59 amI don't know what the source of the interferences is, but it sounds digital (bleeps, bloops and pulses).Symptom of a failure somewhere?Or just a bad design?

author: radiolistener
author_rank: Super Contributor
timestamp: June 09, 2025, 02:39:17 pm
content: Quote from: cincin on June 09, 2025, 02:29:13 pmits just a lack of shielding and lack of blocking capacitors across circuits to block induced RF currents.But also there is a sense to check field strength and identify noise source. If its so high, its not good and maybe there is a sense to remove or power off the source of that interference.

author: cincin
author_rank: Regular Contributor
timestamp: June 09, 2025, 02:41:22 pm
content: Bad design means I'll have to keep adding copper tape until it's goneCheers!

author: SteveThackery
author_rank: Super Contributor
timestamp: June 09, 2025, 02:53:00 pm
content: Quote from: radiolistener on June 09, 2025, 02:26:38 pmAh, yes, of course - thank you for correcting me. The noise comes from when the 2.4GHz is modulated. As you say, some of those modulating frequencies are evidently in the audio range.

author: radiolistener
author_rank: Super Contributor
timestamp: June 09, 2025, 04:24:10 pm
content: Quote from: SteveThackery on June 09, 2025, 02:53:00 pmyes, such interference looks like envelope for RF carrier. So when the transmitter carrier is enabled and disabled you can see pulses on oscilloscope connected to audio signal path.Also it affects DC bias offset.

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 06:02:39 pm
content: Two usual paths for EMI into audio systems:1. Rectification of strong modulated RF signals by semiconductors early in the audio chain.2. Rectification of RF by corroded copper connections (copper-oxide diodes).In both cases, the lower-frequency modulation of the higher-frequency carrier is turned into a signal in the audible range, and cannot be removed thereafter.In an elementary example, a transistor RIAA preamp often needs a small capacitor directly between base and emitter of the input transistor to remove the RF before rectification.

author: amyk
author_rank: Super Contributor
timestamp: June 10, 2025, 04:26:23 am
content: If you provide a recording of what the interference sounds like, I think a few members here would be able to tell you what's causing it. GSM TDMA interference sounds like this:

author: radiolistener
author_rank: Super Contributor
timestamp: June 10, 2025, 04:56:37 am
content: Quote from: amyk on June 10, 2025, 04:26:23 amyeah, this is what I hear when cellphone is placed near audio-amplifierWiFi interference has different sound, its like woodpecker tapping...Here is example:

author: cincin
author_rank: Regular Contributor
timestamp: June 10, 2025, 10:49:41 pm
content: Sure thing, here's the noise:Definitely not that familiar GSM TDMA sequence, and not WIFI either from the sound of it.More of an ongoing stream than a handshake?Could be multiple sources? Could be random analog noise for all I know about noise (not much).

author: Analog Kid
author_rank: Super Contributor
timestamp: June 10, 2025, 11:11:52 pm
content: Nonstandard WAV file (24 bits/sample): no can open. Try something standard (16 bits/sample, 44.1kHz, which yours is).Nevermind; was able to open it with Audacity. (Still a weird .wav format, though.)

author: cincin
author_rank: Regular Contributor
timestamp: June 10, 2025, 11:19:09 pm
content: Here's a more common MP3

author: radiolistener
author_rank: Super Contributor
timestamp: June 11, 2025, 12:56:04 am
content: looks like some digital interference from computer

author: cincin
author_rank: Regular Contributor
timestamp: June 11, 2025, 01:12:31 am
content: The only computer that I haven't completely unplugged in my testing is my workshop PC, which is located in a room where the Yamaha is silent.I'm starting to suspect the neighbours.Or the house's "smart" electricity meter that's WIFI aware, but again it's nowhere near the strongest interferences.Or a hidden surveillance device in my living room floor (can't forget to be a bit paranoid).I kinda feel like switching off the main breaker to see if my house is the source.

author: amyk
author_rank: Super Contributor
timestamp: June 11, 2025, 02:15:38 am
content: Quote from: Analog Kid on June 10, 2025, 11:11:52 pmWorked fine here on my old shop PC running XP.Agree that this sounds like something digital.

author: richnormand
author_rank: Unknown
timestamp: June 11, 2025, 07:55:17 pm
content: Can you hear this interference on an AM portable radio tuned between two stations? If so it should be easy to locate.My issue was a landline phone too close to a modem. Yours sounds more like a computer or computerised piece of equipment with a transmitter.Have you tried to move the piano across the room and see if the intensity changes. Plug it in a different power outlet, in case the noise is carried of the power line?Have you tried using some ferrite clamps or multiple loops on a ferrite donut on the input wiring to kill the RF or even internally near the amplifiers inputs.Plug CN202 in your diagram. You can get some that just clamp on the wire.Better shielding.Even better would be a tinySA to identify the frequency and walk around to the source.Good luck with it.

author: cincin
author_rank: Regular Contributor
timestamp: June 11, 2025, 08:05:53 pm
content: Quote from: richnormand on June 11, 2025, 07:55:17 pmI have tried sniffing around with an AM radio between stations, and also with a Mr.Carlson Super-Probe, and I can't find that same specific interference.I have tried moving the piano around, the location and orientation affects the interferences quite a bit. I've found that the interferences are strongest near the front wall of my house, but there's nothing there that could possibly send interferences.I have tried plugging it into a different outlet, and even a battery pack, and the location of the keyboard is what decides wether it's catching interferences or not, not the outlet it's connected to.I have not tried ferrite clamps on the cable before CN202, but the interferences are present when the cable is disconnected from CN202, so that's not where they come in.I have added some copper tape to the plastic case around the amp board, but apparently not enough because the interferences are still coming in strong.Thanks!

author: richnormand
author_rank: Unknown
timestamp: June 11, 2025, 09:39:34 pm
content: "interferences are strongest near the front wall of my house, but there's nothing there that could possibly send interferences."I have seen case where the interference signal was carried by the house AC wiring. Could you have an AC cable (or TV cable or telephone) inside that wall?One that drove me batty for a while was an elevated noise floor for the 10-15MHz region on shortwave. Would be intermittent, lasting a few hours and then disappearing, being present one night and totally fine another with a pretty random pattern.Spent a month turning the house breakers on and off when the noise was present. Turned out to be a battery tender with a buck power supply only when the battery needed a top up. That is why I got a tinySA spectrum analyser for next time...Keep fighting.

author: richnormand
author_rank: Unknown
timestamp: June 11, 2025, 09:48:39 pm
content: "strongest near the front wall of my house, but there's nothing there that could possibly send interferences."further though: electrical smart meter, water meter or other utility (camera, home stuff like Nest... wireless thermostat , some have batteries and will continue working even if the AC is off). All these can connect to a network in the several 100s MHz.I know here I can see my and my neighbours electrical and water meters ping regularly and then send data.

author: radiolistener
author_rank: Super Contributor
timestamp: June 11, 2025, 10:26:20 pm
content: Quote from: richnormand on June 11, 2025, 09:48:39 pmSome utility meters such as smart electricity and water meters may include wireless communication modules operating in sub-GHz bands (typically several hundreds of MHz). While this connectivity may offer convenience and enables remote monitoring, it also introduces very high security risks. Therefore, while such meters may offer convenience for personal or residential use, they pose a significant risk when employed for commercial or official metering purposes.Specifically, meters with communication channel have potentially unauthorized communication capabilities and pose a serious security vulnerability and a potential vector for fraud. These communication channels can be exploited - either by malicious actors or even by the service provider to remotely modify meter parameters without the user's knowledge.For instance, it's technically feasible for a supplier to artificially inflate consumption data or adjust billing logic via such a channel. Worse, if a user initiates an audit or inspection, the same communication channel could be used to silently restore original values or configurations and cleanup the logs file before the inspection takes place, making detection extremely difficult. Such incidents are known and, unfortunately, not uncommon.This kind of vulnerability leads to a serious risk in relying on devices with communication channels. For this reason, it's preferable to use meters that do not include any form of remote communication. By eliminating wireless or networked access, the risk of unauthorized remote tampering is greatly reduced. It ensures that any interaction with the meter must be done physically and transparently, making it much harder to manipulate the readings or use the device for fraudulent purposes without the user’s knowledge.In addition such meters may also generate electromagnetic interference that can disrupt the user's electronic or radio equipment.In many cases, such communication-enabled meters violate regulatory requirements and lack the necessary certifications and licenses. For example, I am aware of a legal case where it was revealed that a company had been installing meters while referencing a manufacturer's general quality certificate as if it were a valid telecommunications certification (which is actually not). They simply relied on legal loopholes and clever wordplay - subtle enough that someone without a technical background would be unlikely to notice the misrepresentation. In reality, the company held no licenses authorizing the use of communication technologies in commercial metering devices.

author: Analog Kid
author_rank: Super Contributor
timestamp: June 11, 2025, 11:43:21 pm
content: You may have already figured this out:It may turn out that you never find the specific source of the interference. But if you want to sell the piano in good faith you'll need to insulate it against the interference in any case, so maybe just concentrate on doing that: more foil, caps, whatever works.

author: cincin
author_rank: Regular Contributor
timestamp: June 12, 2025, 01:19:37 am
content: Quote from: Analog Kid on June 11, 2025, 11:43:21 pmYeah that's what I'm going for. I'll be adding more grounded copper tape etc.