Ground loop problem? - Page 1
Forum section: electronics / general

author: HobGoblyn
author_rank: Unknown
timestamp: June 05, 2024, 10:53:41 pm
content: Hi all, please bear with me while I try and explain my problem.Due to medical problems, I currently need to be able to use my music software while sitting in my armchair, hence need a computer and speakers on an over the chair/bed type table on wheels , and I have a 37 note midi controller keyboard that comfortably sits across my armchair.I have a MacBook Pro M1 with powered Presonus Eris 3.5 monitors attached.I’ve only had the Mac for two weeks, initially I had a mains powered soundbar plugged into it, and when using this, I didn’t notice the problem, unfortunately it sounded awful hence returned it and got the Presonus Eris 3.5’s instead.The left Presonus Eris speaker has all the controls/inputs/power socket on it, (right speaker simply has speaker cable socket on it with the speaker cable coming from the left speaker). It’s powered by one of those figure 8 plugs (C7) which can plug in either way round and obviously doesn’t use the earth pin in my UK plug or wall socket.First, the problem.Initially, I had a stereo 3.5mm jack to twin RCA, with the 3.5mm jack plugged into the MacBooks headphone port and the two RCA’s plugged into the speakers RCA ports.The MacBook wasn’t connected to the mains (MagSafe cable from mains charger not connected to MacBook)When using my MacBook Pro, after about 5 odd minutes, when I move my hand along the laptop case (when typing/using trackpad), I can feel a tingle where my hand touches it. If I hold my hand completely still on the case, I can’t feel anything , but as soon as I move it, tingling is there.Very hard to explain the sensation, almost kind of feels like some weird haptic feedback and sort of feels like there’s a slight resistance between the case and my moving hand. The slower I move my hand the greater the sensation.If I remove my hand completely, sometimes the sensation is still there when I put it back, other times it’s fine for a few mins before the problem returns.The second I unplug the mains plug for my new Eris 3.5 speakers, the problem goes away. When I plug it back in, it’s fine at first, then it comes back.I’ve got my wife to unplug and re plug in the Eris mains cable so I could see/feel with 100% certainty that unplugging them stopped the sensation immediately.What I’ve tried.1: Tried a stereo 3.5mm to 3.5mm cable from MacBook headphone port to the Aux in on my Eris speakers.2: I purchased a “Presonus Audiobox Go” audio interface.The Audiobox is connected to the speakers by two balanced 6.35mm TRS cablesThis came with a "USB C" to “USB A” connector to connect to the laptop, but as my MacBook only has USB C/ thunderbolt sockets, I tried with a spare USB C to USB C.3: Audiobox still connected to the speakers by two balanced 6.35mm TRS cablesUsed the USB C to USB A cable that came with the Audiobox, the USB C plugging into the Audiobox, the USB A plugging into Anker USB hub, the hub plugging into my MacBookWith any of the above (tried in all MacBook ports) the problem is still there.Before buying the Audiobox, I tried different wall sockets and a different fig 8 (c7) mains cable. Most tests were done without the MacBook being attached to the mains but I did a few with it charging, nothing made a difference.So currently the speakers are connected to my Audiobox by balanced cables, the Audiobox is connected to my Anker USB hub by USB C to USB A and My Anker USB hub is connected to one of the MacBooks USB C/Thunderbolt ports. The problems just as bad as as my original try and still, the second my speakers are unplugged, the problems gone.Any suggestions pleaseThanksLinks below to speakers etcEris 3.5 Speakershttps://www.amazon.co.uk/PreSonus-Eris-3-5-Gen-Studio-Quality/dp/B0CC36XVLM/ref=asc_df_B0CC36XVLM/?Audiobox Go Audio interfacehttps://www.amazon.co.uk/PreSonus-AudioBox-GO-production-Instruments/dp/B09N557CYK?Anker Hubhttps://www.amazon.co.uk/Anker-Upgraded-Delivery-Pixelbook-A83460A2-Gray/dp/B07ZVKTP53/ref=asc_df_B07ZVKTP53/?

author: tooki
author_rank: Super Contributor
timestamp: June 05, 2024, 11:03:58 pm
content: The tingle is from the interference suppression capacitors on an ungrounded switching power supply, a question that has come up many, many times here on the forums. It means your housing is floating at 1/2 mains voltage, but at an absolutely minuscule current, which is why this is not only allowed by code, but required, in order to meet EMI standards. This is normal and expected from a properly filtered supply. The fix is to actually have a ground, e.g. by tying the speakers’ case to ground (if it’s metal), or using your MacBook with the grounded mains cord (not the snap-on plug) on its power supply.

author: themadhippy
author_rank: Super Contributor
timestamp: June 05, 2024, 11:37:19 pm
content: passive DI box on the audio lines should clean things up

author: tooki
author_rank: Super Contributor
timestamp: June 06, 2024, 12:20:59 am
content: Quote from: themadhippy on June 05, 2024, 11:37:19 pmThis isn’t a ground loop problem, nor an impedance mismatch. So how exactly do you think the DI box would solve this? (Bear in mind that I already gave the solution above.)

author: themadhippy
author_rank: Super Contributor
timestamp: June 06, 2024, 01:49:04 am
content: it will break the physical connection between 2 items that when joined together are causing the tingle,which id guess is going from the speakers ground to the metal work of the un plugged mac.Being the speakers are using a 2 pole mains connector id bet its double insulated ,and adding an earth is a no no ,at least in the uk's electrical rules

author: Someone
author_rank: Super Contributor
timestamp: June 06, 2024, 03:33:33 am
content: Quote from: themadhippy on June 06, 2024, 01:49:04 amCitation required...Adding afunctionalconnection back to earth is perfectly safe and compatible with electrical compliance worldwide. Otherwise you'd be prohibited from connecting devices together (since once of them could have a functional earthing connection). This is all explicitly allowed (61010 3.2.2 for example) and not some sideways interpretation.

author: Ian.M
author_rank: Super Contributor
timestamp: June 06, 2024, 06:37:33 am
content: Its a bit old, but this summarises Apple's f***ed up grounding nicely:https://apple.stackexchange.com/questions/17575/how-to-properly-ground-a-macbook-proAlthough it fits, a 'figure-8' mains lead is unsuitable for an Apple PSU with a stud, as it does not provide a ground so wont ground the leakage current. You need a lead that properly grounds the stud, which will then ground the leakage current from both the Apple PSU and the speakers (via their audio signal cable shields).Apple duckbill mains extension cables for their PSUs, with three pin mains plugs *USUALLY* properly ground the stud. All the direct to wall socket adaptors, including the UK one do *NOT*, in spite of its metal ground pin on the BS1363 plug side.You need to confirm there is continuity from the PSU ground stud to the USB C plug shell, (just in case Apple have managed to f**k that up on new models!) then order a Apple Power Adapter Extension Cable (UK) from a supplier with a liberal enough returns policy that you can send it back if there's no ground contact in the slot the ground stud goes in. The first thing you should do, before you even uncoil the lead is check continuity from the ground pin to the slot.If both the PSU and its mains lead have ground continuity, your mains leakage current shock/'tickle' will just go away. N.B. if you connect more audio devices and any of them have a grounded PSU you may get a ground loop. If you get any hum as a result, first makes sure that the Apple PSU extension lead and the grounded audio device are plugged into the same extension lead or double wall socket, with their mains power leads right next to each other, and if that doesn't cure it you may have to resort to reverting to the Apple UK duckbill to wall socket adapter to remove one of the grounds to break the ground loop, and let the whole setup get its ground through the audio device. Don't hot-plug a grounded audio device if the Apple PSU is not grounded!

author: themadhippy
author_rank: Super Contributor
timestamp: June 06, 2024, 10:55:37 am
content: after a kip another solution past between the eyes,one ive use sevral times over the years when dealing with leaky guitar amps and singist getting a tingle from the mic,as your using a balanced line cut the the earth on the SIGNAL line.

author: themadhippy
author_rank: Super Contributor
timestamp: June 06, 2024, 11:42:17 am
content: QuoteFor the designer/manufacturer,not by some random bod in the street.

author: Shock
author_rank: Super Contributor
timestamp: June 06, 2024, 07:43:35 pm
content: "When using my MacBook Pro, after 5 minutes I can feel a tingle where my hand touches it."Use wireless speakers and grounded/earthed power adapters is the easiest way. If still an issue get the power adapters replaced under warranty then get a p.a.t. or electrician in to test your devices or wiring.If the midi keyboard or controller is connected to your laptop don't rule that out as a source of the issue either.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 06, 2024, 10:07:20 pm
content: FWIW, this is why I like class II isolated MOPP-rated (medical) AC-DC supplies: no tingles.Class I AC-DC supplies have a class Y capacitor between the DC side and the AC for keeping EMI down; class II do not.Per IEC60601-1, MOPP rated supply can leak at most 50µA from the DC side, 100µA in single failure condition, which should not only be safe, but also below the sense threshold (to 50/60Hz 120V/240V AC mains supply).I do also use digital isolators much more often in my own projects than others do, but it is at least as much about helping protect against my own blunders than anything else. We don't have polarized sockets here, and if a computer and a peripheral are powered from different sockets (different mains circuits), they may have different phases, which leads to ground currents between class I supplies. It also means that if connecting via USB serial to a separately-powered SBC or router, an isolator on the serial RX and TX lines will not only stop ground loops from happening and voltage (ground potential) differences from breaking anything, but also will nicely act as a voltage level translator.For analog audio, I'd use a transformer-based passive galvanic isolator, i.e. unbalanced-to-balanced audio transformer or "DI box" with "earth lift" (as themadhippy suggested). Eris 3.5 input impedance is 10kΩ, and frequency response 80Hz to 20kHz. As a dirt poor hobbyist, my choice would be a pair of Triad Magnetics' TY-250P fromMouser. The three-pin 3.5mm TRS audio connector would have Tip (Left) connected to pin 4 on one, and Ring (Right) to pin 4 on the other, and Sleeve (0V) to pin 2 of both. Both would have pins 6 and 7 linked, and the balanced output at pins 5 and 8 connected to 1/4" TRS connectors tips and rings, respectively. Sleeve would be unconnected, or both connected to the metal enclosure containing the transformers. Each TY-250P has -0.1dB to +0.6dB response from 80 Hz to 20 kHz at 10kΩ input impedance, which isn't "studio quality", but not too bad either. With either cables or female connectors, and using silicone to keep the transformers in place, it should all fit in e.g. Eddystone/Hammond 27969PSLA cast aluminium box.Quote from: tooki on June 06, 2024, 12:20:59 amA pair with "earth lift" will break the ground connection between the speakers and the Mac. The audio signals pass through the symmetric transformers, typically 600Ω:600Ω. The Eris 3.5 has two balanced inputs as 1/4" TRS connectors (sleeve is for ground/shield), so it will act as an unbalanced-to-balanced transformer also.Since there is no leakage current path to ground from the active speakers' ground to Mac chassis to human to physical ground, there would be no tingle either.The cables would be a bit funky: 3.5mm TRS in, sleeve/0V/GND connected to two transformers input only. Output is a pair of 1/4" TRS, with their sleeves possibly connected to the transformer enclosure (for shielding), but then that enclosure could give you the same tingle. I'm not sure such cables exist off-the-shelf.

author: HobGoblyn
author_rank: Unknown
timestamp: June 06, 2024, 10:23:38 pm
content: Thanks everyone.While electronics is one of my two hobbies, even after your much appreciated explanations, I would be lying if I said I fully understand exactly what’s going on.On a separate note, my bedside lamp is one of those all metal ones that you touch anywhere to turn on and off. It also has a usb socket.Normally it turns on and off at the slightest touch but if I plug my iPad into it to charge, sometimes I have to touch the lamp 3 or 4 times before it works, and thinking about it, when the iPads charging, I also get the same (but a bit stronger) tingling if I rub my fingers over it.I don’t want to use wireless speakers due to latency, I’ve tried Bluetooth ones and the latency was unbearable.The speaker cases aren’t metal (although I could try running an earth from one of the unused sockets on the back)The iPad charger is their 140w one.There sadly doesn’t appear to be any continuity from the psu ground stud to the usb-c. As Ian.M says, Apple do an extension cable that also connects to the ground stud and doing a lot of research today, a fair few people have said it solves their problem, but no continuity from mine so not worth buying.I did try running a cable from the wall sockets earth, and I touched it against the MacBooks metal case when the tingling was present. I thought this would have helped but it made the tingling much worse, hence me not fully understanding what’s going on.The midi keyboard will be connected to the Mac via the same Anker usb hub, haven’t got that far yet.I’ll double check the continuity tomorrow on the off chance I was doing something stupidNote: This is a 2nd hand MacBook hence changing the power adapter under warranty isn’t going to happen

author: wraper
author_rank: Unknown
timestamp: June 06, 2024, 10:51:31 pm
content: Quote from: tooki on June 05, 2024, 11:03:58 pmWell it's not really required, as you could use a shield between transformer windings and do other stuff. However it's the easiest and cheapest thing to do.

author: Someone
author_rank: Super Contributor
timestamp: June 06, 2024, 11:19:06 pm
content: Quote from: themadhippy on June 06, 2024, 11:42:17 amNo, as I said in the full quote.Quote from: Someone on June 06, 2024, 03:33:33 amAdding a technical earth can be as simple as a plug with the earth wire coming out the back of it. Which is a perfectly legal "appliance" and readily available. Nothing against the electrical rules there. Or going further to your newposition, very few jurisdictions restrict the owners of equipment from modifying it.So the challenge remains. What regulation/law/legislation is in the way? You say it exists but cannot point to it. I say it does not exist, I don't have to (and cannot) present a complete lack of that law.

author: Whales
author_rank: Super Contributor
timestamp: June 06, 2024, 11:43:47 pm
content: Quote from: HobGoblyn on June 06, 2024, 10:23:38 pmThe power bricks you are using (to charge your macbook and to power your other equipment) input dangerous mains electricity and output safe, isolated low-voltage electricity. They are "safety devices" that are designed toalmostguarantee that you cannot be electrocuted by anything plugged into the low voltage side, like a laptop, or even if you put the output lead into your mouth like a small kid might.The problem is that these power supplies are hyper-optimised for their goals of safety, radio compliance and low-cost. What if they gave you the sensation of being gently electrocuted, but don'tactuallyelectrocute you? That's perfectly fine! That doesn't break any of their goals. And if it makes them cheaper and emit less radio interference then that's even better.Seriously. That's the reason. That's the thinking behind it.I'd prefer to also give you some more technical detail on what's going on. Have a look at this circuit diagram of a power supply similar to what you might find in your laptop charger:(stolen fromhttps://www.electrothinks.com/2021/02/12V-2a-switch-mode-power-supply-with-lp2704a.html)On the bottom-left you can see the dangerous 240V mains coming in. On the right you can see the safe, isolated 12V coming out. I've highlighted the dangerous and safe halves of this circuit. Touch anything on the red side and you may get electrocuted, touch anything on the blue side and you'll be fine.There are three key components that bridge the dangerous and safe sides. From top to bottom: a capacitor (C6), a transformer (T1) and an optocoupler (U1).The transformer does a really good job at isolating the dangerous side from the safe side. It doesn't let electricity through directly, it smuggles the electricity through a magnetic field to get it from one side to another, and in a very controlled manner.The optocoupler similarly does a really good job at isolating the dangerous side from the safe side. It doesn't let electricity through directly, it smuggles the electricity by converting some to light and using something similar to a solar panel on the other side to detect it.The capacitor... it doesn't do so well. It straight up lets electricity from the dangerous side go to the safe side. It doesn't smuggle. It doesn't even launder. The only saving grace is that it only allows alittlebit across.That's your tingle.The evil class Y capacitor leaks a tiny bit of dangerous mains across to the safe side, into your laptop and then into you when you touch its case. It's enough to feel but not enough to harm you. (Technically it could harm you if you attach it to subdermal metal probes in your body, especially if they're close to your heart or in your brain. Please don't do that.)The evil class Y capacitor reduces the (unwanted) radio emissions of the power supply without needing to kill anybody, so the designers consider it a win.You can exorcise the evil in one of two ways:(1) Remove the capacitor, or(2) Attach the output GND to mains ground.Removing the cap is difficult because the power supply is in a welded or glued plastic shell. You probably don't want to muck with dangerous power supplies if you don't have much experience. Not to mention that operating a source of radio interference in a hospital is ethically questionable.Attaching the output GND to mains ground is a much easier solution. The key to understanding this is to imagine yourself as being at mains ground (close enough) and the two wires coming out of the power supply being at these voltages when compared to you:+12V: 12VDC + 90VAC of mains tingle from the Y class capacitorGND: 0VDC + 90VAC of mains tingle from the Y class capacitorIf you attach the power supply output GND to mains ground then you will suppress the tingle voltage:+12V: 12VDC + 1VAC of mainstinglefrom the Y class capacitorGND: 0VDC + 1VAC of mainstinglefrom the Y class capacitorYou can achieve this in many ways, including:* Attaching a USB cable between your macbook and something with mains ground (the USB shield will connect the earths)* Using a power supply with a three-prong plug (has mains ground) instead of a two-prong plug (ungrounded)Does that make sense? The technical section might have gone a bit off the rails, please feel free to ask questions.

author: themadhippy
author_rank: Super Contributor
timestamp: June 07, 2024, 12:25:10 am
content: Quote5.8.1 - Class II equipmentClass II equipment has reinforced or double insulation. As well as the basic insulation for live parts, there is a second layer of insulation, either to prevent contact with exposed conductive parts or to make sure that there can never be any contact between such parts and live parts. The outer case of the equipment need not be made of insulating material; if protected by double insulation, a metal case will not present any danger. It must never be connected with earth, so connecting leads are two-core, having no protective conductor. The symbol for a double-insulated appliance is shown in {Fig 5.20}.EN-60335 section 27 "Provision for earthing""Class 0 appliances, class II appliances and class III appliances shall have no provision for protective earthing. Class II and class III may incorporate earth for functional purposes"QuoteAdding a functional earth is a bit more than just chucking an earth in,can you guarantee exposed conductive parts parts wont became live in the event of a fault?Quoteuntil someone is seriously injured or killed thanks to your modification.

author: Someone
author_rank: Super Contributor
timestamp: June 07, 2024, 01:48:58 am
content: Quote from: themadhippy on June 07, 2024, 12:25:10 amBolded the bits where you are conflating things and arriving at your incorrect claim that users cannot connect a ground.Did you know there are class I and class II products and the only difference between them is the inlet/cord ? It is true a class II appliance cannot have aprotectiveground path, but that does not mean it is illegal or against the rules to add one, because then it becomes a class I appliance and that rule no longer applies. Cheap and easy to go in that direction, I'm unaware of any class II construction that would fail class I after bonding aprotectiveearth. This is aside from adding afunctionalortechnicalor earth which that quote backs up as a-ok and not prohibited as you first claimed.And again, you've chopped the quote to make it seem like I'm the one leaving things out:Quote from: Someone on June 06, 2024, 11:19:06 pmSo we're left with it being absolutely ok from the quote you are trying to use to support your (shown to be false) claim. Neither is that a clause prohibiting a class II appliance having a function earth, or a clause prohibiting the public from modifying their equipment.Quote from: themadhippy on June 07, 2024, 12:25:10 amWe already have that guarantee from the existing design. Adding a functional or technical earth is not changing any of that. It's what happens when you otherwise interconnect that equipment with a path back to ground through the audio cables.

author: themadhippy
author_rank: Super Contributor
timestamp: June 07, 2024, 02:26:22 am
content: QuoteAnd who certifys the device now fully complies? are you confident your certification will stand up in court? In this case the speaker manufacture has decided for proper functioning of the equipment no connection to earth is required.Quoteso were does the microphone thats fed into the speaker complete its path to ground?Or the double insulated (as most are) playback device?

author: Someone
author_rank: Super Contributor
timestamp: June 07, 2024, 03:15:13 am
content: Quote from: themadhippy on June 07, 2024, 02:26:22 amWhere is the requirement for a certification? People can generally do what they like with their own equipment. Note that no earth required does not imply no earth allowed.Quote from: themadhippy on June 07, 2024, 02:26:22 amThey don't have too, but they may.You said they may not, which is incorrect.It is clear you don't know what you're talking about but are intent on arguing away. How is this helping the OP?OP was uncomfortable with the tingle from leakage (which we assume is within safe limits, and can be checked), adding a technical earth will solve that without impacting safety or compliance. Perfectly legal and safe.

author: Someone
author_rank: Super Contributor
timestamp: June 07, 2024, 03:26:11 am
content: Quote from: HobGoblyn on June 06, 2024, 10:23:38 pmThe cases of those computers (as with many others) is anodized and non-conductive on the surface. A drain for the leakage needs to be electrically bonded to the system, such as a USB shell or the shields of the audio connectors. Easier would be to buy a power adaptor that already has the bonding built in. But that can/will cause ground loops as soon as you introduce another protectively earthed devices into the system.

author: tooki
author_rank: Super Contributor
timestamp: June 07, 2024, 08:21:50 am
content: Quote from: Nominal Animal on June 06, 2024, 10:07:20 pmQuote from: wraper on June 06, 2024, 10:51:31 pmThank you both for the clarification, much appreciated.

author: tooki
author_rank: Super Contributor
timestamp: June 07, 2024, 08:24:11 am
content: Quote from: Ian.M on June 06, 2024, 06:37:33 amBut this is the same as with any device powered by an ungrounded PSU.And in this instance, the MacBook wasn’t even plugged in, it was running off battery. It’s the leakage from the speaker PSU that OP was feeling.

author: Shock
author_rank: Super Contributor
timestamp: June 07, 2024, 11:06:32 am
content: Might want to check if your power adapter was part of a recall if you have an old one.

author: themadhippy
author_rank: Super Contributor
timestamp: June 07, 2024, 01:35:09 pm
content: QuoteYes you can,but the minute something goes wrong your on the hookQuote?? what i said i was "adding an earth is a no no ,at least in the uk's electrical rules"Quoteyour right i didn't spent a large part of the past 30+ years working in the events industry dealing with temporary electrical infrastructure . What i do know is a functional or technical earth is not just the shield on an audio cable. to quote the uk wiring regs definitionQuoteso your put a wire into plug most certainly isnt compliant,even if you used a pink cable.

author: HobGoblyn
author_rank: Unknown
timestamp: June 07, 2024, 05:01:53 pm
content: Quote from: Whales on June 06, 2024, 11:43:47 pmWow, many thanks, that's a very clear explanation, Had to respond rather than just hit the thanks button.Have learnt something new todayAgain many thanks

author: HobGoblyn
author_rank: Unknown
timestamp: June 07, 2024, 05:14:42 pm
content: Quote from: Someone on June 07, 2024, 03:26:11 amThanks, if I understand correctly, using balanced audio cables usually stops any ground loop hums?

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 07, 2024, 06:26:37 pm
content: Unbalanced audio is a voltage signal referenced to ground. A typical 3.5mm TRS jack has left audio signal on the tip, right audio signal on the ring, and the reference ("ground") on the sleeve.The power supply on your active speakers has that class Y interference-suppression capacitor between the ground and the AC. It only leaks about 1mA and isn't dangerous, but you do feel a tingle if that passes through your body (to true earth ground).Connecting to the speakers via say a cable with 3.5mm TRS male jack on the Mac end, and to two RCA male jacks on the powered speaker end, will connect the ground on the active speakers to the ground on your laptop, which allows the tiny leakage current (allowed by that class Y capacitor) to pass through the active speakers' ground to your Mac's audio ground to Mac chassis to your body and to true Earth ground, causing the tingle. It isleakage, not a "real" ground loop, if that distinction matters any.Typical audio mixers have continuity on the unbalanced audio connector "grounds", so won't change anything for HobGoblyn here.Balanced audio uses a pair of connections, adifferential pair, for each audio channel. The differential pair does not need a ground connection per se.Your Eris 3.5 active speakers have both unbalanced and balanced inputs. The balanced inputs are the larger, 1/4" TRS ("stereo") connectors, with tip and ring being the differential pair, and the sleeve the optional ground. Note, however, that this ground is almost certainly connected to its power supply ground, and thus will convey the "tingle" if connected to the ground on your Mac.Typical passive DI boxes (passive as in not requiring any power) are basically just an audio transformer to galvanically isolate balanced audio lines. Essentially, across each transformer, one audio channel is coupled over using a varying magnetic field. The properties of the transformer define what kind of frequency response you get at a given input and output impedances, so there are a huge variety of such audio transformers, with the "undetectable effect on the audio signal within extended human hearing range" costing several hundred USD apiece. The ones I'd use are about USD 6 apiece.Conversion from unbalanced to balanced is trivial with such an audio transformer: on the unbalanced side, the "ground" and the signal is connected to one coil; on the balanced side, the coil is connected to the differential pair.Many balanced audio cables have three conductors, often with the third being a shield around the differential pair. DI boxes that can break that connection between inputs and outputs usually call this breaking "Earth lift".In HobGoblyn's case, the need is to break the ground connection from the active speakers to the Mac, to stop the tingle, while allowing the audio signal to pass with high fidelity.I personally would do this DIY, using components that cost less than USD $30 off Mouser (and enclosure from a local Hammond importer,Uraltone, here in Finland). The enclosure would be placed close to the active speaker, perhaps on/in the speaker stand, or on the floor nearby. The connection from the enclosure to the active Eris speaker would use a pair of shielded audio cables (often called "microphone cable"), most likelyAdam Hall 5-star microphone cableor something like Belden 8451010100 (fromMouser) – a pair of conductors, and a separate shield – with two 1/4" TRS ("stereo") jacks at end, both connected to the active Eris 3.5 speaker. Their ground (sleeve) would be connected to the aluminium box, so that might give a tingle if touched. From the enclosure to your Mac or any other sound source with a 3.5mm TRS audio connector, I'd do a custom 3-conductor shielded cable, maybe Tasker C115 or Belden 22-24AWG 3-conductor shielded cable (likethis, link to my local store), where the shield is connected to the enclosure, but not to anything on the 3.5mm TRS male connector. This way, the audio signals should be pretty well shielded from typical electromagnetic noise that could otherwise couple to the audio signal, and cause annoying hum or buzzing, while breaking any direct electrical connection that could conduct the tiny leakage current that causes that tingling.The commercial option is to get two mono or one stereo DI box with "ground lift", and suitable cables. It/they will do the same thing, allowing the signal to pass without direct electrical connection across that box. While the problem here isnota groundloopper se, it is similar: both problems are fixed by breaking the direct electrical connection between the audio source (Mac) with a 3.5mm TRS audio output, and the active speakers.Because I'm poor and not interested in high-end audio stuff, I cannot help with links to suitable DI boxes or similar off-the-shelf products, but they definitely do exist.

author: nctnico
author_rank: Super Contributor
timestamp: June 07, 2024, 06:37:53 pm
content: Quote from: Nominal Animal on June 06, 2024, 10:07:20 pmI agree. Getting a signal tranformer / isolation transfer in between is an easy solution to break ground loops at the cost of frequency response flatness. Back in my audio gear design days, we always made it a point to have a ground on the amplifier and design the rest of the equipment to be double isolated (and powered using a transformer). That ensured no mains hum travelling along the ground of unbalanced audio lines. In cases that was not possible, we'd use a signal transformer to break a ground loop.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 07, 2024, 07:48:18 pm
content: Quote from: nctnico on June 07, 2024, 06:37:53 pmThe Triad Magnetics' TY-250P (fromMouser, 5.1€ each in singles; need two) I would DIY perreply #10is -0.6dB to +0.6dB within 20Hz .. 20kHz; if the active speaker input impedance is 10kΩ, it increases from +0.6dB to +1.2dB in 20kHz..30kHz.Other than "it would suffice for me", I don't know how good that is in practice, though, especially when used with active studio monitors like the Eris 3.5.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 07, 2024, 10:36:25 pm
content: There are tons of now cheap commercial DI boxes. If you're in Europe, just have a look at Thomann - if you're in the US, one equivalent shop would probably be Sweetwater.One of their cheapest:https://www.thomann.de/intl/millenium_die_dibox_passiv.htm

author: Someone
author_rank: Super Contributor
timestamp: June 07, 2024, 11:18:04 pm
content: Quote from: HobGoblyn on June 07, 2024, 05:14:42 pmReduces hum from different ground potentials, but doesnt eliminate it. Engineering rarely has true zero or infinity. You're in the middle of the balance:high impedance earth for improved interconnection performancelow impedance earth for improved RFI andtouch currentIt is not a group loop that is your problem, but the reverse, a too little current passing to ground.

author: themadhippy
author_rank: Super Contributor
timestamp: June 07, 2024, 11:25:39 pm
content: Quotepity about the £10 p+p ,maybehttps://www.studiospares.com/dual-passive-di-box-by-lambden-audio-449300.htmhowever if you want a known quantity your looking at 10x the price for something like the emo dual.

author: nctnico
author_rank: Super Contributor
timestamp: June 08, 2024, 09:08:43 am
content: Quote from: Nominal Animal on June 07, 2024, 07:48:18 pmMy old boss had a rule of thumb to either keep the response flat to approx. 25kHz or filter below 19kHz. So it would be a good idea to source and terminate the transformer close to 1 kOhm for optimal sound quality. This would mean a loss of 6dB though.

author: HobGoblyn
author_rank: Unknown
timestamp: June 08, 2024, 09:57:20 pm
content: Quote from: themadhippy on June 07, 2024, 11:25:39 pmTrue, I’d need two of the Thomann ones, so with postage would come to a total of £33.40The one you linked to with postage is. £26.98I presume they’re all as good as each other at that price range?Am I correct in thinking the Jack output is just a through for the input (it’s being sent straight back out) and I’d need to use the Xlr outputs? I’d also have to get a couple of Xlr to 6.35 cables as wellThanks

author: themadhippy
author_rank: Super Contributor
timestamp: June 08, 2024, 10:26:37 pm
content: QuoteyepQuoteor just cut off the jacks at one end of your existing leads and chuck on an xlr.

author: HobGoblyn
author_rank: Unknown
timestamp: June 09, 2024, 09:08:35 pm
content: Just ordered the one themadhippy linked to from studiosparesWas thinking of cutting existing leads and putting on Xlr but that would leave me short of leads, I need the existing leads to go from the Audio interface to the Di box, then need additional leads to go from Xlr on Di box to my Eris monitorsThanks

author: HobGoblyn
author_rank: Unknown
timestamp: June 11, 2024, 09:47:21 pm
content: Was talking to Presonus support about this and told them what both”tooki” said in reply 1 and what “Whales” said in reply 14.They responded with (confidential response but don’t think they would mind me quoting this bit)“I've no other reports of this issue but I would be interested in getting these speakers into a service centre for an inspection and we will replace these units”Personally after my learning experience in this thread, I don’t think anything is wrong with the speakers and I’ve told Presonus this. Still it’s nice to see a company taking issues seriously.

author: Someone
author_rank: Super Contributor
timestamp: June 11, 2024, 10:04:24 pm
content: Quote from: HobGoblyn on June 11, 2024, 09:47:21 pmSince you have not had the speakers tested for leakage, they are rightfully worried as there could be something wrong and indicative of future more serious problems. You do not know the speakers are operating within the safety requirements but its a routine test as already mentioned:Quote from: Shock on June 06, 2024, 07:43:35 pmThat is for catching faulty equipment before it becomes life threatening.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 12, 2024, 01:04:17 am
content: While the class Y capacitor in the supply should fail open, it is possible it was a dud or wrong one, or something like the flux used in manufacturing the board has reacted with the potting compound used to keep the big electrolytic caps from flapping in the wind and the resultinggunkis slightly capacitive and just happens to slightly couple over the isolation barrier. I think both are exactly the situations a responsible company would love to find out the details of, if they ever hear of or suspect it happening.Props for Presonus support for caring, methinks. If I was HobGoblyn, I'd try to have their service center check them out.

author: HobGoblyn
author_rank: Unknown
timestamp: June 14, 2024, 10:15:17 am
content: Sadly, that DI box cuts the audio to virtually nothing, turning volume up to hear it (still not very loud) and it distorts.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 15, 2024, 12:46:52 am
content: Quote from: HobGoblyn on June 14, 2024, 10:15:17 amThe DI box, being passive, attenuates the signal somewhat; this is calledinsertion loss. See if you can find it mentioned in the specifications for the boxes you use; it is typically specified in decibels (dB).Voltage amplitude is multiplied by 10-dB/20≃ exp(-0.115129dB) across the isolation transformer whendBis the insertion loss in decibels.Power or volume is multiplied by 10-dB/10≃ exp(-0.2302585dB).Did you have a small mixer at hand? Try putting the mixer between the Mac and the DI box, or the DI box and the monitors. Use the line out from the mixer. The idea is to boost the signal to account for the transformer attenuation, without clipping the output.In the DIY case, the Triad transformers I mentioned have less than 2.8dB insertion loss, which corresponds to about 28% reduction in voltage swing (×0.7244) and almost halving the output power or volume (×0.5248). One could amplify the input voltage by gain 1.38, without clipping up to output range of about -2.5V to +2.5V maximum, or -2.8V to +2.8V forpro gear–– far wider than normal audio amplifiers allow! –– to compensate for the losses in the isolation transformer.That makes it into an"active DI box with ground lift". The currents are very low, in single milliamps per channel. I would use for USB power, and a 5V to +12V and -12V isolated supply, perhaps Murata CRV1D0512SC or CMR0512S3C or Mean Well DPU01L-12, with both rails LC-filtered and linearly regulated down to +6V/-6V or so, with 0V referenced to the unbalanced audio ground (Mac ground), leaving about 3V between the rails and the output signal. That would allow the isolator to work from any supply – either the Mac, or from a class II isolated USB wall wart, or from a class I medical-rated USB wall wart.I know nothing of analog audio amplifiers or analog audio circuit design, but I assume a single dual opamp would suffice.

author: themadhippy
author_rank: Super Contributor
timestamp: June 15, 2024, 01:01:36 am
content: Quotepresume youve tried changing the attenuation switches on the box

author: HobGoblyn
author_rank: Unknown
timestamp: June 15, 2024, 09:45:51 pm
content: Quote from: themadhippy on June 15, 2024, 01:01:36 amYes

author: HobGoblyn
author_rank: Unknown
timestamp: June 15, 2024, 10:00:58 pm
content: Quote from: Nominal Animal on June 15, 2024, 12:46:52 amSadly there’s little information on their site and no leaflet/manual in the boxQuoteI do have one somewhere, I’ll dig it out.This all started as an easy and quick way for me to carry on my music while in my armchair, something that’s quick to move for my meals etc.Now I’ve got two monitors, a Di box, an Audio interface and now possibly a mixer tooQuoteThanks, I’m seriously thinking of going this route now

author: themadhippy
author_rank: Super Contributor
timestamp: June 15, 2024, 10:08:32 pm
content: Did you try cutting the earth on the signal cable?both channels of course.

author: HobGoblyn
author_rank: Unknown
timestamp: June 16, 2024, 06:09:08 pm
content: Things I've tried this afternoon (not using Di box), all with MacBook on battery.1) I unsoldered the earth in both jacks where they go into the monitors, exactly the same problem. (resoldered them before I continued)I then made up a lead, just the earth connected to UK 3 pin plug, and plugged into the same double socket as the monitors are in.2) Other end of earth connected to one of the jack inputs in the back of the monitor. Same problem, I unplugged the monitors and just left earth cable plugged in, still had same problem.3) Other end of earth connected to the Anker hub (Anker hub connects to MacBook via USB C, Audio Interface connects to Anker hub via USB 2), Same problem, I unplugged the monitors and just left earth cable plugged in, still had same problem.4) Other end of earth connected to MacBook case, problem still there but about twice as bad.That's all I can try today as have been summoned by my loverly wife.What's confusing me now is I THINK the above does what has been suggested such as attaching the output GND to mains ground. I thought one of these would have worked.Tomorrow I can insert my small mixer into the chain to see what happens and I might still go the DIY route onceI 100% understand what's going on. As I said somewhere above in an earlier post, previously when I've had the tingle with my right hand, touching metal on the monitors with my left hand such as one of the jacks instantly stopped it, hence I was convinced running earth from there to mains earth would solve my problem, seems I am still misunderstanding.I really appreciate all this helpthanks

author: HobGoblyn
author_rank: Unknown
timestamp: June 17, 2024, 04:47:11 pm
content: Quote from: Nominal Animal on June 15, 2024, 12:46:52 amToday I returned the DI box, but thought I would see what happens if I use the mixer.Macbook to Anker Hub via USB CAnker Hub to Audiobox Go (Audio Interface) via USB 2Audiobox to Behringer Xenyx 502 Mixer, Line in 2/3 via balanced 6.35 (1/4") cablesBehringer Mixer to Eris monitors via unbalanced 6.35 (1/4") cablesPerfect soundBeen using it for an hour and not one tingle, yayMixer specs here if anyones interested (exactly the same mixer as mine, but my mixer has Tracks on it where this manual says CD/Tape)https://mediadl.musictribe.com/media/sys_master/hdd/h5b/8850067685406.pdfMany thanks everyone

author: HobGoblyn
author_rank: Unknown
timestamp: June 23, 2024, 03:26:08 pm
content: It gets weirderToday I plugged everything into the same places (cables labelled, hence in exactly the same sockets) and the tingle was back.However, if I turn the fig 8 (c7) mains cable for the speakers 180 degrees, it completely goes away, if I turn it back again, its back.Tried two different cables, exactly the same

author: tooki
author_rank: Super Contributor
timestamp: June 23, 2024, 05:35:35 pm
content: Since it’s been suggested multiple times and (unless I overlooked it somewhere) youstillhaven’t tried it: what happens when you power the MacBook with a grounded mains cable? If you don’t have one, you can order it from Apple. (Not sure if the brick and mortar stores stock them.)

author: HobGoblyn
author_rank: Unknown
timestamp: June 23, 2024, 08:51:07 pm
content: I said in post 11, “ There sadly doesn’t appear to be any continuity from the psu ground stud to the usb-c. As Ian.M says, Apple do an extension cable that also connects to the ground stud and doing a lot of research today, a fair few people have said it solves their problem, but no continuity from mine so not worth buying”The MacBook also has a very long battery time and a very short fast charge time, I use it for hours on just the battery, all of the above experiences has been on battery although when I do charge, it makes no difference, tingling is still there.I also said in post 45 that I tried grounding the speakers to mains ground and the tingling still continued

author: Someone
author_rank: Super Contributor
timestamp: June 23, 2024, 10:15:08 pm
content: Everything you have said is consistent with mains leakage coming from the speakers and/or laptop power supply (could well have been both together and at different times). These are know issues with known solutions that you have failed to implement.Since you have been unable to control the problem with your efforts it is clear you need to obtain the services of someone who knows what they are doing and can test for safety, then rectify if needed. Sounds like the manufacturer of the speakers has offered this to you for free. The step beyond that of reducing the current below "safe" levels gets into specialists but they do exist.

author: themadhippy
author_rank: Super Contributor
timestamp: June 24, 2024, 11:53:49 am
content: QuoteThe thing inside the speaker thats causing the leakage is connected between one side of the mains supply and signal earth,with the mains lead connected one way around that part is connected to live ,rotate the mains lead and its now connected to neutral.Neutral and electrical earth normally are connected together somewhere on your incoming electrical supply so with the power lead that way around theirs no difference between the signal ground and electrical ground so nothing to raise a tingle.However with the power lead the other way around your signal earth is connected to live,and thats at a different potential to the electrical ground causing the tingle when you complete the circuit between signal earth and electrical ground

author: CaptainBucko
author_rank: Regular Contributor
timestamp: June 24, 2024, 12:29:54 pm
content: Quote from: Whales on June 06, 2024, 11:43:47 pmGreat write up - one of the best (and funniest too) I have read. It can (and has) blown up sensitive test equipment, I know of someone (not me) who blew up the front end of an extensive spectrum analyser which cost $30k AUD at the time to repair. After that, every laptop PSU adapter was modified to properly ground the laptop virtual ground. It was the RS-232 serial port that did the damage in the above example.

author: Ian.M
author_rank: Super Contributor
timestamp: June 24, 2024, 12:38:57 pm
content: You've made progress by discovering the polarity of the figure 8 connector matters. Mark the lead end and the back of the speakers so you can always set up for minimum touch current. Using an Apple grounded mains lead may also help as it gives the Apple PSU's AC leakage current a path to ground other than via the Mac and you, even though the USB C shell, and probably the 0V (Gnd) pin, aren't DC grounded to the stud and thus to mains PE. You can test this without the Apple grounded lead by using an ordinary figure 8 lead for the Apple PSU, and connecting a temporary PE ground to the stud.Some measurements of the touch current would help determine if its cause for concern. Use a DMM on AC V, with a 10K resistor in parallel, connected between the metal part you want to test and a known good ground. That will read 1V per 100uA of current. Don't simply use the DMM's AC mA range as it may not have enough sensitivity, and if there is a real fault, 10K resistors are much cheaper than multimeter fuses!

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 24, 2024, 02:09:18 pm
content: Quote from: HobGoblyn on June 24, 2024, 11:25:56 amIs that a typo, or did you really still get a tinglewiththe DI box with ground lift?I thought you wrote the tingle was gone but the audio too quiet to use.It matters a lot. If the tingle was still there with the DI box (with ground lift enabled), it means the leakage current path is not through the audio ground –– common signal in unbalanced stereo, at the sleeve of the 3.5mm TRRS connector ––, because the ground lift breaks that. It would have to be something else then. As audio signal lines have DC blocking capacitors, the leakage current must be mains-frequency AC; perhaps it gets coupled via the unbalanced signal lines? That would mean a serious fault in the speakers, as it is not supposed to try and inject AC signals on its inputs!

author: soldar
author_rank: Super Contributor
timestamp: June 24, 2024, 02:53:28 pm
content: Quote from: Someone on June 07, 2024, 01:48:58 amI agree with you 100% on this and I have had this argument before on this and other sites. And the problem is that the misunderstanding is so widespread that I have given up. I remember leaving a thread here on account of this.The simplest I can explain it:Devices need to comply with this rule and they can comply by meeting A or by meeting B. Any of the two is good.If a device meets both A and B it will be considered as B. In other words, B takes priority.Conclusion of those who misunderstand: A device which has A cannot have B.Well, that's not what the rule says.

author: HobGoblyn
author_rank: Unknown
timestamp: June 24, 2024, 04:11:46 pm
content: Quote from: Nominal Animal on June 24, 2024, 02:09:18 pmYes, the lift didn’t stop the tingle. I double checked before returning it, otherwise I would have tried it inserting my mixer into the chain first.

author: tooki
author_rank: Super Contributor
timestamp: June 24, 2024, 07:11:43 pm
content: Quote from: HobGoblyn on June 23, 2024, 08:51:07 pmApple USB-C laptop chargers don’t appear to ground the shield, but they definitely ground the ground pins, as is visible in teardowns of these chargers. I’d be very surprised if using the grounded corddidn’tsolve the problem. If it doesn’t, I suspect there are bigger problems here.

author: Someone
author_rank: Super Contributor
timestamp: June 24, 2024, 10:52:07 pm
content: Quote from: HobGoblyn on June 24, 2024, 11:25:56 amYou said you've tried several different ways to make a path back to mains earth. I believe you have made your best attempt at that. So now it is something along these lines:a) there is some subtle and non user fixable problem in your overall supply/system which needs a qualified and experienced person to checkorb) the problem is simple and your attempts didn't work for some reason you cannot see/understandEither way you're in over your head as the explanations so far have not solved your problem. How much free support do you expect to get? This needs someone with the skills and experience to get hands on with your setup and find out what has gone wrong. Noting that there is still the chance you have a damaged/failed item(s) that are dangerous (according to international standards), something which you ignore and gloss over rather than confirming.Given things are confusing and apparently not resolved by the normal solutions: step 1, confirm each item alone is of no danger.

author: Someone
author_rank: Super Contributor
timestamp: June 24, 2024, 11:02:49 pm
content: Quote from: tooki on June 24, 2024, 07:11:43 pmI've not checked every single adaptor model they make but I have never found protective bonding on Apple branded laptop supplies with the interchangeable mains plugs. When using the earthed plug to mains there is (on all I have measured) a 1k (exact!) impedance to mains earth from the secondary side. Usually enough to get rid of the tingle but not the fraction of an ohm a protective bond would provide.

author: HobGoblyn
author_rank: Unknown
timestamp: June 25, 2024, 06:27:40 am
content: Quote from: Someone on June 24, 2024, 10:52:07 pmAnother dig, sorry but I don’t need it. I appreciate your help but you are entitled to stop helping anytime you wish.I only continued my post when I discovered about the speaker plug polarity, I found it interesting and Ian.m explained it.I won’t bother explaining my progress any more and I won’t ask any more questions anywhere incase I’m exceeding my free quota.

author: tooki
author_rank: Super Contributor
timestamp: June 25, 2024, 06:58:16 am
content: Quote from: Someone on June 24, 2024, 11:02:49 pmI was just disputing OP’s claim that the ground stud is not connected at all. The low-power adapters that have detachable plugs but aren’t groundable use a plastic stud instead of the metal one.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 25, 2024, 07:56:12 am
content: I suppose Presonus is as interested in the particular fault pattern as I am, especially if the fault current bypasses a ground break and is thus coupled to the monitor inputs –– without affecting the actual sound generated.I think it is more likely that the ground lift on the DI box HobGoblyn used was faulty. For example, a solder bridge in the switch (assuming it has a ground lift slide switch). Reason is that if the tingle-causing leakage current was transmitted via the left or right signal line (instead of the unbalanced common line, "unbalanced ground"), I think it should have blown the output drivers in the Audiobox Go.The last resort is USB isolation. USB isolation does the same as a DI box ground lift, except between the Audiobox Go (or similar USB ADC/DAC) and the Mac. Because it is done at the digital signaling, it has zero effect on the data transferred and thus the quality of the audio, and there is no galvanic or even capacitively coupled connection to the host Mac.One I personally might consider, is theHifime High-Speed USB Isolator v2, although to me the price is quite high – as much as a new Audiobox Go costs hereabouts. You'd also need two female USB-C to male USB-A converters, or two USB-C male to USB-A male cables, too.I haven't torn one down myself, or even seen its circuit board image, but based on their specs, they didn't skimp on the isolated DC-DC converter –– and that is what matters the most.For USB Audio Class 1, and USB Low speed (LS, 1 Mbit/s) and full speed (FS, 12 Mbit/s), there are essentially two common chips to do USB isolation: Analog DevicesADuM3160andADuM4160. They are very easy to use, as they only need a couple of resistors and a few bypass capacitors, with everything needed included in the datasheet. The chip does not pass power, though, so the cheap $10 class full-speed isolators vary a lot in which isolated DC-DC converter they use. Most can only provide 200mA to the device, and require a 40mA or so load for their USB 5V to be within spec.For USB Audio Class 2 and 3, and USB LS, FS, and High Speed (HS, 480 Mbit/s), there are essentially five common chips to do the USB isolation: Analog DevicesADuM3165 and ADuM3166,ADuM4165 and ADuM4166, and Texas InstrumentsISOUSB211. They are only slightly more complicated, requiring a 24 MHz crystal oscillator, and preferably some voltage regulators –– they have some internal, but using external regulators reduces the thermal load within the chip, and is worth the extra cost. The Hifime one I linked to above is supposed to use ADuM4166.There is nothing special in USB Audio Classes, they are just standard USB protocols for audio. There are similar classes for USB webcams, which is why most don't need any dedicated drivers at all. The only thing that varies between the audio classes is whether they work at Full Speed (12 Mbit/s) or High Speed (480 Mbit/s); I do believe they are all specifically USB 2.0 (and not SuperSpeed).When picking an USB isolator, it is a Very Good Idea to check which isolator chip it uses, and how much current it provides downstream. There is very little that can go wrong with the data isolation – the datasheets cover it all, even suggesting specific PCB layouts! ––, so the isolated DC-DC conversion is what one should focus on when getting one.Isolated DC-DC converters are typically galvanically isolated, with no EMI-reducing capacitor across the isolation at all; it is just not needed.There are quite a few DIY projects and design guides to implement one oneself, too. For example, Mark Harris'full-speedandhigh-speedisolator projects at resources.altium.com, Stefan Wagner's (wagiminator)full-speedisolator at oshwlab.com, and so on. My ownfull-speed oneis what you typically get when you buy a <$10 USB isolator off eBay, except with soldered-in USB-A male and female connectors; mine is intended to be soldered in-line in a scavenged cable for minimal cost but sufficient functionality. Metal enclosure for the isolator helps reduce any electromagnetic interference, but should obviously be connected only to one of the grounds (host/Mac) and at one point only; perhaps even through a parallel resistor-capacitor network for limiting ESD and other spikes.Apologies for the long post.

author: themadhippy
author_rank: Super Contributor
timestamp: June 25, 2024, 11:25:50 am
content: QuoteI dont think so as they also tried physically breaking the signal earth on the cables,something more weird is at foot.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 25, 2024, 12:17:35 pm
content: Quote from: themadhippy on June 25, 2024, 11:25:50 amYep, coupling 50/60Hz mains AC via the signal pin is possible, but tingle currents (1-10mA range) are higher than the current passed in audio signals (less than milliamp); the isolation transformers are typically rated for just a few milliamps.Ah, but wait: the output on the Audiobox Go is a *headphone* output, which are typically able to drive somewhat higher currents, say 25mA, so if the tingle current is around 5mA or so, it could be capacitively conducted via the signal line instead of the ground/common line, with the headphone output drivers somehow sinking that to ground.(Also, transformer saturation/reaching its limits due to the back-fed AC signal might also explain the much higher than expected attenuation. DI boxes shouldn't do more than about halve the effective volume.)I would connect the Eris monitors to mains, with the IEC C8 plug in the tingle-causing orientation, but without any inputs connected. Then, I'd use a multimeter to measure the DC and AC voltage and current on the female RCA connector *inputs* on the Eris monitors. I would measure between left and right signals (centers), between left and ground (center and shell), right and ground (center and shell), and also from left, right, or ground, to a true ground (ground pin on a grounded mains socket). Make sure it is a true safe ground, not live or neutral, because mains live or neutral will blow the Eris inputs. If nothing else, this would satisfy my own curiosity.

author: Someone
author_rank: Super Contributor
timestamp: June 25, 2024, 10:20:53 pm
content: Quote from: Nominal Animal on June 25, 2024, 12:17:35 pmThat sort of current is up in the range of "involuntary muscular contractions likely", perception starts under 500uA and is highly variable across conditions and individuals. IEC 60479-1 is a good starting point.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 26, 2024, 07:10:43 pm
content: Quote from: soldar on June 24, 2024, 02:53:28 pmYeah. Given the fact that in the sockets of many (most?) countries, protective earth is glaringly user-accessible; AND that stuff like water piping, radiators, sometimes even kitchen sinks etc. can be directly bonded to the same protective earth, AND the fact that SELV power supplies bond their GND net directly into connectors such as outside metal barrel of a DC plug, or USB connector's metal case which you can't avoid touching, it seems pretty interesting that some people think connecting these two by the end user must be somehow dangerous and illegal. If it was, we would be all dead or in jail by now by doing mundane things like putting your laptop near the kitchen sink, so that once you unplug power or USB, the connector touches the kitchen sink (earthed by pipework) by accident.

author: soldar
author_rank: Super Contributor
timestamp: June 26, 2024, 09:10:03 pm
content: Quote from: Siwastaja on June 26, 2024, 07:10:43 pmI remember leaving a thread in frustration over this. I mean the proposition makes no sense whatsoever from any point of view. Why would they enact such an absurd rule? But, furthermore, you would need two separate universes of devices. You could not use a drill of one type on a device of the other type. You could not use an audio amplifier of one type with a receiver of the other type because their gnds would be connected. It is just absurd.There is always again in safety by grounding any exposed metal parts. Always.

author: HobGoblyn
author_rank: Unknown
timestamp: June 28, 2024, 06:25:58 pm
content: Quote from: Nominal Animal on June 25, 2024, 12:17:35 pmIt has a stereo headphone output on the front and both RCA and 6.35mm jack inputs on the back, I'm using the 6.35 jacks.My initial very first try before buying the Audiobox go was a cable going from the MacBook headphone socket to the aux in on the front of the Eris speakers, that's when I first noticed the tingle and decided to get an audio interface and do things properly.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 28, 2024, 07:06:55 pm
content: As you said it will be a few weeks before the Eris monitors can be checked out, have you considered using anUSB isolatorwith the Audiobox Go?With the likelihood that there really is something wrong in the Eris monitors, I think a high-speed USB isolator would be a good idea, to protect both yourself and your Mac. For one, it absolutely should get rid of the tingle, if the leakage source is the Eris monitors.

author: HobGoblyn
author_rank: Unknown
timestamp: June 28, 2024, 09:13:22 pm
content: Thanks, I’m considering it but it’s a little pricey for temp use.I’ll contact Presonus on Monday to see if they have any idea how long it will be before I get my new ones, then decide.

author: HobGoblyn
author_rank: Unknown
timestamp: June 28, 2024, 10:11:21 pm
content: Quote from: Ian.M on June 24, 2024, 12:38:57 pmQuote from: Someone on June 24, 2024, 11:02:49 pmQuote from: tooki on June 25, 2024, 06:58:16 amI’ve measured resistance from metal stud to the USB-C and it measures 1.02KHave made a cable to go from ground stud to mains earth as shown at end of post.When I plugged it all in, the tingling was gone on initial touching of MacBook case, but if I lightly rubbed a finger over the case (very lightly, like if you rubbed your finger down your arm so lightly that you’re just touching your skin) and after about 4 seconds of doing this, a very very very faint tingle could be felt. When I say faint, I mean faint, I wouldn’t have bothered starting this thread if it was that faint.Which isn’t really a worry, however I then turned the speakers off, MacBook still earthed, I got a tingle that felt at least twice as strong as the tingle that caused me to start this thread, causing my reflexes to instantly remove my finger, then no tingle at all.I tried various combinations of things, including repeating the above precisely, and never got that big tingle when turning off the speakers again, so not sure what was going on.So I repeated:When I plugged it all in, the tingling was gone on initial touching of MacBook case, but if I lightly rubbed a finger over the case (very lightly, like if you rubbed your finger down your arm so lightly that you’re just touching your skin) and after about 4 seconds of doing this, a very very very faint tingle could be felt.But now when I turn the speaker off, no tingle at all, no initial large tingle like what happened when I did exactly this a few mins ago, and no very very very slight tingle when I gently rub my finger on the case for about 4 seconds.Turn the speakers on, again no tingle but if I rub my finger very very lightly, after about 4 seconds I can feel that very very very slight tingle.So it looks like buying the cable will fix it, although I didn’t really want the MacBook plugged in all the time, still it’s no big deal, now all I’ve got to do is find one, extension leads on Apple UK have plastic for the ground lug to slot into.Quote from: Ian.M on June 24, 2024, 12:38:57 pmOddly tonight, I get a tingle whichever way round I plug the fig 8 cable into the speakers although it’s still a lot worse one way, the other day I had no tingle at all one way. Same cables, same sockets, nothing different (this was before carrying out the above tests)I can’t find a way of accurately measuring the touch current, tried two DMM, used resistor in parallel and I simply couldn’t get a reading from the case. This is with negative attached to mains ground and positive probe touching the metal case,I’ve had to stop for the night, will continue my testing tomorrow including the speaker ones Nominal Animal suggested a few days ago in post 64

author: tooki
author_rank: Super Contributor
timestamp: June 30, 2024, 02:11:46 pm
content: Quote from: HobGoblyn on June 28, 2024, 10:11:21 pmAnd what’s inside that slot is two metal spring contacts that firmly contact the ground stud. That’s how this system works. Apple has been using this system for over 20 years, not sure why you seem so skeptical of it.

author: HobGoblyn
author_rank: Unknown
timestamp: June 30, 2024, 05:29:44 pm
content: I'm not meaning to sound skeptical, from the pics I could see online, it didn't look like there was any metal in the slot.I also didn't want my MacBook plugged in all the time.Anyway, just ordered it from Apple, will be here Tuesday.Many thanks

author: HobGoblyn
author_rank: Unknown
timestamp: July 01, 2024, 12:22:35 pm
content: Quote from: HobGoblyn on June 30, 2024, 05:29:44 pmI'm being stupid as usual, plug socket switch does nothing to the ground, its always there, So I can simply leave the lead connected to my MacBook and only turn on when battery getting low.

author: HobGoblyn
author_rank: Unknown
timestamp: July 31, 2024, 09:25:56 pm
content: Quote from: Nominal Animal on June 25, 2024, 07:56:12 amJust received the following from Presonus“ Just updating you. I've tested these speakers on 3 setups and have no issues as described in this ticket. I assume the new speakers arrived and are working ok?”As I said in my previous post, with the extension lead from Apple that grounds the lug, I didn’t have the problem anymore.Still waiting for replacements, they’re coming through customs, will do a quick test without using the Apple extension lead, I suspect the tingle will be there, will be very odd if it isn't though, will let you know.Many thanks everyone

author: wraper
author_rank: Unknown
timestamp: July 31, 2024, 10:07:45 pm
content: Quote from: tooki on June 30, 2024, 02:11:46 pmFWIW in 2016/2019 Apple recalled apparently nearly all regional variants of this plug adapter except US sold since 2003https://support.apple.com/ac-wallplug-adapterhttps://www.apple.com/uk/newsroom/2019/04/important-notice-for-certain-ac-wall-plug-adapters-and-apple-world-travel-adapter-kits/