This is not supposed to happen
- Thread starter adamdea
- Start date
adamdea
You are not a sound quality evaluation device
ATC said it's best not to put signal and mains next to each other but don't worry about doing it if you have to. Seriously though I don't think that whatever is getting in is doing it via the signal cables.
adamdea
You are not a sound quality evaluation device
That would be my luckMy impression is that you're dimmer is injecting RF back into the mains circuit. Having a 'screened' mains cable running to the speaker won't necessarily fix that as the crap is already being guided by the wiring. Indeed, a screen might help keep the RFI running along the wires. Its an example of the 'Russ Andrews flaw'.
Do you think there is any chance that the noise is being transmitted through the air rather than through the main. I am puzzled at why it affects one speaker more than the other, although I appreciate that it's possible- they do seem to have the same cable type and length
London Lad
pfm Member
Its quite possible that its coming through the air. Always try to eliminate the source rather than using filters etc. Whip the dimmer off and put a switch on to prove it. Do you really need the dimmer ?
westsea
Retirement present
It is not always good to belive experts, ATC generally is great engineering (I have Atc 100A,s) and they sound superb; quite envy your 40's from a domestic viewpoint. I would not dismiss the mains/signal cable completly though, although a very different environment in industry we did not run control/signal cables in the same trunking and even now when sorting out the rats nest I try and keep signal cables separate from mains. There was phrase 'avoid the need' when approaching problems. Anyway hope you sort out the problem
Sure, I realise you have excluded the signal cable injecting the interference. My point was that I have a hunch that mixing mains and signal cables is not permitted by the IEE/BS7671 wiring regs, unless the insulation on both is up to the highest voltage present in either or somesuch. Might be relevant fire regs too, can't remember, been awhile since I knew folk who did that kind of thing. And I'm quite possibly misremembering, but me, I'd check.
It shouldn't take you long to figure out the source of your problem and its path to your speakers. Wrt to a previous post, it is not impossible that the interference is airborne - the amp pack in ATCs is not shielded inside the speaker, so it might be a little defenceless.
Pity you're having this hassle, getting a pair of ATCs is one of the best moments in hifi.
adamdea
You are not a sound quality evaluation device
Yes. Good idea. In fact I think the first I'll do is to take out that particular bulb (there are others on the same switch circuit) to see whether it makes any difference
I quite agree. But unfortunately others differ on the need for dimmer switches. Fortunately the switches themselves are getting a bit sticky and may "need replacing".
adamdea
You are not a sound quality evaluation device
Don't get me wrong. I would not be doing it except that
1) there can be no wiring on the floor.
2) I'm not in the mood to get someone in to route new cabling through the walls and redecorate the whole room.
Hence the use of a quadrant at the bottom of the skirting board to route both cables.
Next time I redecorate I may reconsider.
adamdea
You are not a sound quality evaluation device
No worries. I'm very happy with the ATCs. This is only minor.
Jim Audiomisc
pfm Member
Its possible it is being radiated or coupled via the 'air'. However I think you said you'd disconnected the signal input and that didn't get rid of it. So I'm assuming it isn't getting in via the signal terminals/cable.
It *could* be being picked up by the power amp(s) in the speakers. Indeed, voice coils can act as effective 'loop antennas' if not well sheilded. You can check that by rotating the speaker slowly about 90 deg around its vertical axis whist listening with your ear against the tweeter. (Hey! Dancing with you speaker. You must love them.
)Did you swap the speakers over so each one was moved to where the other had been? If so, did the noise follow the speaker?
The speakers are likely to be closely matched in terms of audio. But dealing with RFI can be a real pig for designers as you have no idea what will happen in every case. Too many variables. And many audio components can behave unexpected at RF unless that is what they were designed for. Plus even one wire is a slightly different place inside the box, or a slightly imperfect join in something like a power rail might not show up in audio tests, but pick up RFI or convert it into audible crap.
All you need now is a nice Chord Hugo TT to do them justice.
One of the other best moments in hifi.
adamdea
You are not a sound quality evaluation device
Good idea, although tricky to execute as they are quite heavy and spiked into shoes. Then again I rarely get the chance for a danceIts possible it is being radiated or coupled via the 'air'. However I think you said you'd disconnected the signal input and that didn't get rid of it. So I'm assuming it isn't getting in via the signal terminals/cable.
It *could* be being picked up by the power amp(s) in the speakers. Indeed, voice coils can act as effective 'loop antennas' if not well sheilded. You can check that by rotating the speaker slowly about 90 deg around its vertical axis whist listening with your ear against the tweeter. (Hey! Dancing with you speaker. You must love them.
I only worked out what the problem was last night. I will begin messing about this evening
adamdea
You are not a sound quality evaluation device
Don't worry my F-dac will be here any minute.All you need now is a nice Chord Hugo TT to do them justice.
Does sound like a dimmer problem. It could be through the air, or through the cabling. If you can move the speaker, try moving the speaker further from the switch, and if the noise drops, it airborne. My guess would be air, and that the dimmer is at fault.
Best solution would be to replace with a standard switch and choose bulbs of an appropriate brightness rather than dimming them.
Best solution would be to replace with a standard switch and choose bulbs of an appropriate brightness rather than dimming them.
adamdea
You are not a sound quality evaluation device
I'm pretty sure it's the dimmer switch because I took the bulb out (ordinary incandescent) and the noise remains. Weirdly it's a switch unit with three knobs but only one of the 3 knobs/circuits affects the tweeter. I can't see what difference turning the circuit breaker off would make, as the noise goes when the switch is off.
London Lad
pfm Member
It won't prove any more than you already have. 'Engineer' the dumping of the dimmer ;-)
martin clark
pinko bodger
If it's a multigang dimmer and more than a couple of years old it is entirely possible that whatever suppression cap is in there on the affected 'way' (probably something miniscule, yellow, perhaps 0.047- 0.1uF / X1 and very cheap) has gradually lost its metallisation and is now doing nothing useful - IOW, it can appear perfectly functional, with no discolourd components , and yet noisier than its new replacement*.
Mains suppression caps don't last forever: it is part of a key design approach for safety (internal arcs or temporary overvoltage punches holes in the insulating layers, and the energy is dissipated in vaporising the very thin (tens of nm) metal film 'plates' into non-conductance locally - rather than causing internal shorts)
(*Which should be a 3-gang switch ; )
Mains suppression caps don't last forever: it is part of a key design approach for safety (internal arcs or temporary overvoltage punches holes in the insulating layers, and the energy is dissipated in vaporising the very thin (tens of nm) metal film 'plates' into non-conductance locally - rather than causing internal shorts)
(*Which should be a 3-gang switch ; )
adamdea
You are not a sound quality evaluation device
Thanks. I will suggest replacement with "more attractive" switches.
If I am outvoted on this, is there any particular sort of (3 gang?) dimmer which is less-audio unfriendly?
Jim Audiomisc
pfm Member
CPC do some fairly decent RFI filtered mains suppression distribution boards. If looking, though, watch out as many types only have 'spike' protection. Only some have RFI filters.