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Mackie cr5x !

hi, thanks for reading. .ive had a very odd fault on two parts of these speakers, my son was getting shocks when he touched his MacBook Air or mic or his audio interface, when he was at the same time touching his guitar which was plugged into his amp, his setup is quite straight forward. cr5x monitors. ...2 x XLR leads to his PreSonus usb interface with a Shure sm57 mic on his amp .(usb powered from laptop)...Mac bookair charger plugged in...just on internal these speakers are. " double insulated". i.e. no earth, the mains cable is just a two core live and as you can see from this setup there is no earth at all..his electric guitar is plugged into his orange amp and is earthed..via three pin mains plug..this earth is right through to the guitar strings ! with my volt meter (fluke digital) I tested from any metallic part of the speakers..including all the screw heads on the back panel of the side with the mains voltage going in to a known good earth the wall socket and I get around. 90 volts ac !way above what I would think was acceptable...I sent the speakers back to amazon and got a replacement pair. .I tested them straight out of the box and found exactly the same fault. I got in touch with mackies service dep here in the u.k. and was told this was normal with switched mode psu,s.and some people are more sensitive than others ! and was told just to make sure that I earthed them properly ! not sure how I can do this with this setup, there isn't an earth terminal on any part of it !...the return path for this earth fault is straight down my sons he darent even use them..! I send them a video/photos of the test results..but now they've just gone quite about this,, its a little bit worrying to think they aren't bothered ! I have since got him two krk rokit5 speakers, each one with its own three pin main plug so therefore earthed, and he now no longer is getting electric shocks !..I wonder has anyone else come across this, or maybe everyone that has these speakers has them plugged into some other equipment that is earthed, so therefore wouldnt be aware of this stray voltage ?thanks for reading


Boswell Sun, 11/01/2020 - 04:39

Sadly, this is a common behaviour when you have a laptop connected to consumer-level audio gear. Although the Mackie speakers may make no provision for grounding themselves through their power leads, they expect the screen of the audio cable to be grounded, which is not the case when connected to a laptop running from its battery.

I'm not surprised to see a reading of half the mains voltage when using a high-impedance multimeter to measure between true mains earth and the audio input sockets on an otherwise unconnected CR-x series monitor. This is due to leakage current through the isolation capacitance of the monitor's power supply. To distribute the blame a bit, you could try the same test on the laptop powered via its mains adaptor - my guess is that you would get a similar result.

Audio gear must be grounded for safety, even if it's done through a 13A mains plug with only a green/yellow wire trailing from it!

marcb Sun, 11/01/2020 - 07:19

hi , thanks for reply..I thought I was going mad.....but the voltage is defo there !..mackies agents in the uk told me it was quite normal , but some people were more sensitive to it than others !!!! unbelievable really..surprised these speakers have a CE sticker on the back as according to the regs...
Requirements for touch voltage
According to section 411.5.3 of BS7671:2008 Amendment 3, touch voltage must not exceed 50 V at any location on an installation...
I still think Mackie aught to do something about this , as my sons setup is not too unusual..and I'm surprised its not been discovered before !
cheers again



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