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Post by greenstiles on Jul 13, 2013 10:09:30 GMT
Got a chap who says he's knows a lot and was in the industry for a while to build me a tone control unit, it works, but it hums on the treble (only) if the volume is right up and you touch the -/+ knob.........but if you touch any casework of other equipment or it's own casework most of the hum goes, only leaving some background noise.....the bass knob is totally silent regards hum etc.....any ideas ? willing to send to someone to sort out, just as long as it not cost an arm and leg please see link rockgrotto.proboards.com/thread/9180/stand-tone-control-unit-treble
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Post by Deleted on Jul 13, 2013 10:19:54 GMT
Got a chap who says he's knows a lot and was in the industry for a while to build me a tone control unit, it works, but it hums on the treble (only) if the volume is right up and you touch the -/+ knob.........but if you touch any casework of other equipment or it's own casework most of the hum goes, only leaving some background noise.....the bass knob is totally silent regards hum etc.....any ideas ? willing to send to someone to sort out, just as long as it not cost an arm and leg please see link rockgrotto.proboards.com/thread/9180/stand-tone-control-unit-trebleCheck that the metal of that potentiometer is properly grounded. Try connecting a wire between it and the case of the other pots. Alex
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Post by PinkFloyd on Jul 13, 2013 10:20:43 GMT
X2
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Post by greenstiles on Jul 13, 2013 10:27:51 GMT
hi that was my thought after reading about a similar prob......the pot is plastic covered, bar the tabs/connectors, so not sure where i'd attach a wire.............just a bit of extra info.......the knob is metal, the nut holding the pot in is metal, the shaft is plastic and the front panel is plastic.
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Post by greenstiles on Jul 13, 2013 10:36:06 GMT
Everything is as in pic, but he has recently, stuck (crammed) bigger caps in ? and re-routed the earth path...........i'm not electrically minded, but i know this guy does not know as much as he thinks he knows.............and to be honest, after this 3 fiddle, it is not sounding as transparent as it 1st did, it is sounding a little muted. £60 up the swanny i'm thinking
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Post by Deleted on Jul 13, 2013 10:39:54 GMT
Try connecting a wire between the metal of the case and the metal of the following case.
Alex
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Post by greenstiles on Jul 13, 2013 10:41:05 GMT
ok will do
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Post by greenstiles on Jul 13, 2013 10:55:14 GMT
that reduces the event of if i touch the treble knob it hums louder but hum is still there but does not get louder ( when i touch the knob )....but it has added a buzz which wasn't there before..........so when unit is active but tones bypassed was silent, now buzz, when tone active hum still there but not louder when knob is touched, but now with a buzz.
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Post by Deleted on Jul 13, 2013 10:55:32 GMT
It sounds like you have a problem due to lack of earthing. Is something powered by a switchmode PSU ? Alex
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Post by greenstiles on Jul 13, 2013 11:00:36 GMT
i wouldn't know what one of those is sorry...........my kit is (and i have tried with my other full size amp and another cd player) neco v3 bossfet (2 transformers) and a rotel cd player..........the ac/ac adaptor the guy supplied has a metal earth pin, all other adaptors i've ever used have plastic (is this a clue ? )
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Post by greenstiles on Jul 13, 2013 11:04:14 GMT
the pots are just a plastic sandwich of 2 sets of connectors rivited together, if they both have an earth, would it be worth joining them up and running to the case ?
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Post by Deleted on Jul 13, 2013 11:14:27 GMT
It could even have stability problems. I am surprised that the designer didn't use potentiometers with rear metal cases that could be connected together and perhaps earthed .to the case's metalwork.. I would recommend asking the designer of the tone control unit for advice.
Alext
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Post by greenstiles on Jul 13, 2013 11:27:51 GMT
I'm beginning to think, he is not so hot on things. It's been back to him 3 times, and he says it works fine for him, but he said last time, oh no hum in the bass knob, i keep telling him it's the other one.
I feel that either the pot is faulty or he has not put that pot in the circuit correctly......but that is just a guess on my part. I need someone else to look at it really as he keeps saying, it's fine,
I've tried it with other equipment and in other sockets in other rooms.......is there an outside chance i have a bad earth in the house ? but to me if that were the case the bass pot would do the same ?
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Post by Deleted on Jul 13, 2013 11:37:39 GMT
I've tried it with other equipment and in other sockets in other rooms.......is there an outside chance i have a bad earth in the house ? but to me if that were the case the bass pot would do the same ? Not likely. I would have at least used metal cased pots with their cases strapped together, and if possible, earthed. It sounds more like it's poorly implemented to me. Alex
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Post by greenstiles on Jul 13, 2013 11:42:08 GMT
I have suspected that, but assumed, if he can make a working unit, then the earth should be simple , but the guy has been in the electronics business for about 25 years inc MOD and hi-fi ind......so i took him at his word, but i'm thinking he's more of a ' half do-er'........been back to him 3 times, and he gets me to leave it in his bin, and collect it from there too, so there is some avoidence going on.
EDIT:
If i get some close ups, can someone walk me through identifiying and joining up the 2 earths ? (are there?)on the pot and i'll join them together and then to the case.....or i'll get a new pot and put that in please ?
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Post by greenstiles on Jul 15, 2013 7:13:24 GMT
EDIT: above
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Post by Deleted on Jul 15, 2013 7:23:45 GMT
I have suspected that, but assumed, if he can make a working unit, then the earth should be simple , but the guy has been in the electronics business for about 25 years inc MOD and hi-fi ind......so i took him at his word, but i'm thinking he's more of a ' half do-er'........been back to him 3 times, and he gets me to leave it in his bin, and collect it from there too, so there is some avoidence going on. EDIT: If i get some close ups, can someone walk me through identifiying and joining up the 2 earths ? (are there?)on the pot and i'll join them together and then to the case.....or i'll get a new pot and put that in please ? By all means post some close ups, but if the pots have plastic cases you won't be able to earth them. There is still the possibility that the unit isn't stable. Were you supplied with a schematic ? Alex
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Post by greenstiles on Jul 15, 2013 10:43:20 GMT
it's a diy job, i could try and get the scribbles the guy did i guess, would the pot have an earth solder tab on them ?? if so what do you think of this :
Well i did an experiment today, and i'm getting closer i hope with this earth issue.
I attached a wire to the ground wire you screwed into the chasis which lead off the neg on the back of the jack inputs, and the other end i attached to the nut that is holding the pot in place.......this had stopped the hum increasing when my fingers go near the metal control knob and/or nut.............i feel that if this pot has an earth solder tab on it ?? i would imagine so, then i just need to link the chasis to it and this may resolve the issue.........OR if the low/bass pot has no issue (and is earthed better) running a wire from it's earth tab to the earth tab of the high/treble earth tab.
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Post by Deleted on Jul 15, 2013 10:56:46 GMT
Most potentiometers have a metal case. You usually need to file s shiny small patch on the passivated finish of the case, and put a blob of solder on that section. You do that to all pots, then run a wire between each of them back to an earth point. You need a reasonable sized soldering iron to have enough heat for that. Another option could be to try something like a piece of copper clad PCB material, tin plate, aluminium etc. behind the front panel and provide mounting holes for the potentiometers. You then solder or screw a wire to the copper etc.and connect it to an earth point. Alex
P.S. Any other ideas from other members ?
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Post by Deleted on Jul 15, 2013 11:36:53 GMT
Two mad thoughts;
Wrap the pots in conductive, metallic tape and then earth the tape to chassis, making a sort of Faraday's cage for them.
OR
Replace the pots with metal cased jobbies for ease of earthing (of the same rating) and hope the plastic ones were not of some superior grade internally.
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Post by PinkFloyd on Jul 15, 2013 12:40:05 GMT
Any other ideas from other members ? Only happens when you touch the knob? IIRC those pots have plastic shafts but if they are metal then you could always replace the aluminium knobs with ABS plastic types.... unscrew the knobs and see if the shafts are plastic or metal.... if plastic then see if the problem is still there with the alu knobs removed.... if the shafts are metal cover them in insulating tape and see if the problems goes, if so then fit plastic knobs instead of the alu ones.
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Post by PinkFloyd on Jul 15, 2013 12:42:58 GMT
It looks like an OMEG pot:
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Post by PinkFloyd on Jul 15, 2013 12:46:05 GMT
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Post by PinkFloyd on Jul 15, 2013 12:57:19 GMT
What about a wire from the ground tags of the pot to the chassis ground?
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Post by PinkFloyd on Jul 15, 2013 13:00:41 GMT
Or.... make a new grounding point closer to the pot. OR..... go and hide in the blokes dustbin, tell him you've left it in there for him to look at..... when he opens the dustbin pop your head out in a "heeeeeeere's Johnny" style
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