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Signal Interferance with Plex Knock Monitor

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Hey guys,

I'm having some issues with signal interferance with my Plex V1, creating a kind of intermittent buzzing noise which is rendering it kinda useless.

It seems somehow related to the power supply (direct from the vehicle battery), as the tone seems to change depending on electrical load.

I'm going to try replacing the knock sensor lead with some shielded twisted-pair and see if that helps, but it doesn't seem like EMI could cause it and to be honest, its been fine up until recently - just wondering if anyone else has had similar issues with a Plex or other device and any thoughts?


Try powering the Plex from a separate battery. I'll bet it's alternator noise on the power lines. Might be able to put a filter (transformer, cap or ferrite bead) on the power leads.

Thanks David.

Ill try a separate power supply, although issue repeats on different vehicles so to me that suggests the unit itself. Will report back

Many Thanks


Ok so I spent an hour this morning altering the wiring arrangements on the Plex. Took the knock feed, power and ignition channel monitor to a 6-way DTM, swapped the knock lead for some shielded twisted 22awg, and sank the shield into the power supply ground.

Fed from a dedicated small 12v gel battery - Its made a significant difference!

Audio quality is better and most importantly, no interference - I highly recommend this, even if you are not having interference issues (as I was), the improvement in clarity is well worth it alone.



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