Author Topic: 1202 VLZ Pro - hum when pluggin in a jack  (Read 76 times)

fabiospark

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1202 VLZ Pro - hum when pluggin in a jack
« on: October 03, 2020, 05:37:27 PM »
I bought a passive pickup (K&K pure mini) for my acoustic guitar.
When I plugged it into a mic input of my Mackie 1202 VLZ Pro analog mixer with an instrument cable (mono jack to mono jack) I could here a strong hum. Troubleshooting the problem I noticed that the noise starts just when I plug a cable into a jack side of a mic channel, even if there is nothing attached to the other end of the cable (not a pickup problem, right?).
Using the same cable with the same pickup directly into a Focusrite 2i4 there is no noise at all. (not a cable problem, right?)
Even plugging in a mono jack with no cable at all the noise is still there (again, not a cable problem, right?)
If I plug in a stereo jack I get no noise.

I know that this input takes both balancend and unbalanced lines.
To help to understand let me show a couple of pictures taken from the Mackie manual:
https://ibb.co/7vQC9G7
https://ibb.co/YL1DZNx

I also noticed that the noise gets louder if I switch the mixer phantom power on, and I know from tha mixer manual that that works only with the XLR side of the mic channels.
After some further experiment I learnt that with nothing plugged in the jack socket, the channel is silent and also if I plug in an XLR cable with nothing on the other side it is still silent. So it seems that the cable is picking up the noise.


Could I use a balanced cable, with some "magic" wiring on one or both ends? (I can solder)

If I can't use a balanced cable to hook the pickup directly to the mixer, is there anything else I can try to sort the problem out, without having to buy a DI box?

Here some audio samples of the noise:
https://soundcloud.com/prik-m/cable-jack-plugged-in-phantom-off/s-ZSeStihXap4
https://soundcloud.com/prik-m/cable-jack-plugged-in-phantom-on/s-sGWanfXoQB2
https://soundcloud.com/prik-m/touching-the-tip-of-the-jack-phantom-off/s-IpWaQUL2Izf


Thanks.
fabio
« Last Edit: October 03, 2020, 06:46:29 PM by fabiospark »