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The quest for silence and mains-bourne interference

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The quest for silence and mains-bourne interference

Postby Gary_W » Thu Sep 26, 2013 10:15 pm

Hello all,

If you've read any of my posts over the last few years, you'll probably realise that noise (other than my own bum-notes and fluffed chords) drives me nuts. I daresay I am preaching to the converted here.

Since moving my PC down the other end of the room, the horrible THX1138 noises are gone. Hooray. So now all I'm getting is single coil hum from my strat. I've screened it and, in positions 2 and 4 the hum goes away. So far, so good.

Curious thing is that I put the Kemper on during the day today and, even in positions 1, 3 an 5 it was SILENT with the noise gates off. Tipped the Strat all over the place (the familiar angle dance we all do!) and no noise. Happy ears, happy chap. Started to wonder if the usual buzz was all in my head.

My rejoicing went downhill fast - I plugged in tonight and it was buzzing like a bee. Much unplugging of equipment at this end made no difference.

I then discovered that the dimmer switch in the kitchen OR the lights in the hallway (energy saving lightbulbs) are the cause. On = buzz, off = bliss. The obvious solution that we sit in the dark for the sake of my sanity did not impress the long-suffering lady of the house even though she's fond of candles :bouncy:

The lights in the kitchen are a fair distance away from me and my guitar.... The only explanation I can come up with is that they are whacking interference onto the mains in the house. I have sockets not far from where I'm playing (where the Kemper etc are plugged in) but with those offending lights off they cause me no issue!

You would not believe how happy I am to have discovered this as it's the first stage of fixing it.

But before I go getting rid of dimmer switches elsewhere in the house and replacing energy efficient bulbs that are no-where near me, can anyone help me to understand how interference on the LIGHTING CIRCUIT is getting onto the RING MAIN? I guess it's possible if the lighting cables are laying next to the ring under the floorboards upstairs? Forgive me if this is a daft question but I'm wondering if a call to a qualified electrician is in order here?

I also wonder if one of these http://www.amazon.co.uk/dp/B002CIMZGU/ref=pe_385721_37986871_TE_item
would help? Granted, it'll do nowt for the 'wires in the walls picking up interference' but at least all of my trailing leads will then not bother passing it on? Thoughts please :)
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Re: The quest for silence and mains-bourne interference

Postby Gary_W » Fri Sep 27, 2013 6:51 am

Just to clarify - my theory is that the mains is noisy due to the dimmers in another room. The sockets / leads Nealer where I am playing are then radiating this noise through the air hence single coils picking it up.
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Re: The quest for silence and mains-bourne interference

Postby ef37a » Fri Sep 27, 2013 8:41 am

I suspect the interference is simply RF from the lamps and is getting into the Kemper input circuitry.
I don't want to knock the competition but not all companies put effective RFI stops in their amps!

This is a bit hard to prove. I have a pickup in a totally screened diecaste box that is obviously RF proof and if RF gets in using a decent 3mtr say, guitar cable with that, got to be the amp.

You could try some Maplin clip on ferrites on the lead? Probably best put at the amp end but if the filters are not in the amps to begin with it can be a bugger to keep RF out. Sometimes an external filter in a tin and a VERY short lead to the amp can help.

RFI is a tricky fellow, it can come down speaker leads. Ferrites can help here again as can filters but the inductors have to be way bigger.
And... you need to be systematic in your remedies. Often one thing will reduce RFI a little bit and you need to do more but measure the noise levels at every stage.
Dave.
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Re: The quest for silence and mains-bourne interference

Postby Gary_W » Sat Sep 28, 2013 11:49 pm

Thanks for the reply, Dave.

I was able to experiment in one of the ways you mentioned as I actually have a Blackstar HT1-r here. I plugged in the strat with the neck pickup selected and cranked it.

Same result as the Kemper - the hallway energy savers really send it wild, the kitchen dimmers also add noise.

I've whipped out the energy saving efforts from the hallway. I'll get LED for there but for the moment a conventional bulb is in and the problem is now gone provided the kitchen lights stay off.... That'll be more effort to fix but I have ideas.
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Re: The quest for silence and mains-bourne interference

Postby dmills » Sun Sep 29, 2013 12:26 am

Dimmer switches work by chopping the mains waveform to control the average power, and as such are somewhat notorious sources of (mostly radiated) emissions, the fast rise time can also couple into other circuits due to the non zero source impedance, but I would guess this is mostly radiated (Possibly magnetic coupling as well if there is some loop area).

Cheap energy saving bulbs are effectively tiny (and really shonky) switched mode power supplies, that have pretty much the same issues.

Either loose the dimmer or go to an autotransformer dimmer instead of a phase angle job (Bigger and expensive, but silent) and fit a low energy (But not as low) tungsten halogen in place of that CFL.

Regards, Dan.
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Re: The quest for silence and mains-bourne interference

Postby Gary_W » Sun Sep 29, 2013 11:32 pm

Thanks Dan,

It's sounding good now.... I do need to figure out a longer term solution out in the kitchen but it's minor compared with the sheer amount of horrors the energy efficient lightbulbs were putting out. Now I've got rid of those, it's much better.

The thing with the Kemper is that it is sooooo quiet and sensitive that you end up noticing EVERYTHING. But I'm now getting to a situation where even a single coil is virtually silent so can't complain!
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