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Old 21st October 2008, 03:18 PM   #1
gain is offline gain  United States
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Default quick grounding question

i am building my first project (preamp) into an enclosure and just have a couple quick (newbie) grounding questions ...

if the enclosure is made of wood (or any non-conductive material):

-does the mains ground (aka house ground) need to be connected to the circuit ground (aka center tap of secondary side of trafo). in one of my vintage receivers that is made of wood, the power cord to it doesn't even bring in the ground line, just a two-prong hot and neutral. so circuit gound (CT of trafo) is not connected to mains ground.

if the enclosure is made of metal (or any conductive material):

- i know that the mains ground (aka house ground) MUST be connected to the chassis for saftey purposes. but must the mains ground be connected to the CT of the secondary side of the trafo as well? iow, should house ground be connected to the star point gnd on the PSU if enclosure is metal? or can they be separate because the primary and secondary side of trafo are two different circuits (isolation effect of trafo).

thanks guys. just want to make sure my project doesn't inadvertently 'tickle' someone someday!
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Old 21st October 2008, 03:38 PM   #2
AndrewT is online now AndrewT  Scotland
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any exposed conductive part must be permanently connected to Safety Earth.

Except for double insulated equipment, which you don't have the expertise nor equipment to build and check.
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Old 21st October 2008, 04:16 PM   #3
gain is offline gain  United States
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Hi Andrew. Good to see you and many thanks for your reply.

Quote:
Originally posted by AndrewT
any exposed conductive part must be permanently connected to Safety Earth.

does this include the negative sleeve on RCA female panel jacks? the metal shafts of pots?

ime repairing equipment, i have seen grounding done all four possible ways.

1. non-conductive enclosure, CT of secondary connected to safety earth.
2. non-conductive enclosure, CT of secondary not connected to safety earth.
3. conductive enclosure, CT of secondary connected to safety earth.
4. conductive enclosure, CT of secondary not connected to safety earth.

all worked without hum and without shocking the user. which wiring scheme is correct? or am i missing something?


Quote:
Originally posted by AndrewT
Except for double insulated equipment, which you don't have the expertise nor equipment to build and check.

you assume that? never forget what a.s.s.u.m.e. stands for.

again many thanks and hope you are doing well.
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Old 21st October 2008, 04:31 PM   #4
AndrewT is online now AndrewT  Scotland
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Default Safety Earth

the centre tap of the secondary is not exposed and does not directly need consideration.
It's all the metal/conductive fittings around the outside of the enclosure and/or the enclosure itself, that must be considered.
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Old 21st October 2008, 06:02 PM   #5
gain is offline gain  United States
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i should have been more clear, by CT of secondary i mean the PSU ground. aka circuit ground aka signal ground aka star point. i was asking from the point of view of a bipolar supply (+ and - rails and ground) hence thats why i was saying CT of secondary. obviously if this was a single ended supply (+ rail and gnd only, no - rail) this ground point i was referring to would be one of the hot legs of the secondary.

so if all metal/conductive fittings around the outside of the enclosure must be connected to safety earth as you stated, this would mean RCA negative sleeve would need to be connected, hence connecting signal ground (and psu gnd and CT of secondary in turn) to safety ground, correct?

also i have two metal pot shafts that will be exposed. the shafts are not brought out anywhere on pins on the device, so should i solder a wire to the metal mounting area of the pot and safety earth this also?

i dafs but all the posts i found relate to cuing hum/noise issues. i do not have those issues, my preamp is running on bench and is quiet as a mouse. i just want to make sure my project doesn't hurt or kill someone someday. if there is a thread anyone knows that discusses this issue a link would be appreciated very much.

kind regards.
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Old 22nd October 2008, 12:17 AM   #6
gain is offline gain  United States
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c'mon guys, i know someone out there has faced this situation before. all wood enclosure with only negative sleeve of female RCA and/or metal pot shafts hanging out (exposed) from the enclosure for conductive surfaces.

how did you deal with it?

did you ground it to safety earth, as Andrew calls it? (house/mains ground is what i call it but same thing)

did you ground it to your PSU ground (star point), w/o connection to safety earth?

did you use a circuit like the old timers talk of, aka a 5 ohm or so resistor in parallel with a 0.1uF or so cap between safety earth and and signal ground?

what were the results?

talk to me o wise and experienced diy audio members.
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Old 22nd October 2008, 12:25 AM   #7
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Try this out.

Earthing and how it effects sound.

You probably haven't gotten any detailed responses because there are multiple threads that have sufficiently addressed your questions and more. Search is your friend: there are more threads than just this one.
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Old 22nd October 2008, 03:19 PM   #8
gain is offline gain  United States
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thanks for the link zigzagflux, and yes search is your friend. but information overload isn't

thanks and take care
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