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Old 30th December 2007, 05:32 AM   #1
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Question speaker terminals to chassis ground?

Hi! I just found a nice amplifier chassis in a thrift shop.and I see the "negative" speaker terminals are connected direct to chassis (very short)but the RCA ground are not connected direct to chassis .my question is:
can I do the same thing with my gainclone and connect the the speaker negative terminals and RCA grounds to chassis too?.that way I do not have to run the ground wire from input(RCA) to potentiometer,just the ground from potentiometer to boards and from boards to ground.I want to get the shortest wires as possible.is this a good technique or is something better?
thank you.
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Old 30th December 2007, 11:11 AM   #2
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Keeping the wiring inside an amp short is sensible from the point of view that you don't want signal wires too long and picking up 'rubbish' from the PSU section. But don't become obsessive about saving a few inches at the cost of proper grounding.

I would not want any part of my amp circuit to be in direct contact with the chassis, preferring instead to maintain my ground stars by using some extra wire.
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Old 30th December 2007, 03:11 PM   #3
AndrewT is online now AndrewT  Scotland
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I (and I really mean me) would always keep the audio ground separate from the Safety Earth including as it must do the chassis.
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Old 30th December 2007, 03:17 PM   #4
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Most amplifiers run their negative post to ground and or it makes its way to ground. This is true of everything I ever ran across with the exception of a bridge amplifier which neither uses a common connection between channel negatives or to chassis.
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Old 30th December 2007, 03:24 PM   #5
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isn't the ground at the end going to the the same place "chassis"?
I used a meter and checked the grounds in the board and all went to ground "beep sound".I am not saving wire just trying to get the shortest as possible.
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Old 30th December 2007, 03:41 PM   #6
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by lanchile07
isn't the ground at the end going to the the same place "chassis"?
No.
Safety ground must be attached to chassis.
Audio ground is usually separate from chassis.
They are two completely different animals.

However, to fully comply with the requirement that all exposed conductive parts must be connected to Safety Earth then many builders and some manufacturers adopt the debatable practice of directly connecting Audio Ground to Chassis.
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Old 31st December 2007, 12:17 AM   #7
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Question how many "grounds" are there?

OK! now I am really lost.I just checked my integrated amp LM3875 using a meter in "continuity mode" and from speakers negative terminals and RCA grounds and touched the chassis I got a beep telling me that there is "continuity".can someone please draw a schematic and show me the "right"way the AUDIO ground should be.I always thought there was "only"one ground...that was the chassis.mmmm where is the other ground.mmmm.
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Old 31st December 2007, 12:41 AM   #8
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Read about safely grounding your amp here.

I think it's asking for trouble by isolating the entire amp circuit from the safety ground. You must isolate the input signal ground from the main ground.
Use the ground loop breaker as detailed by Rod in the link above, but only if you need to.
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Old 31st December 2007, 01:08 AM   #9
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I think it's asking for trouble by isolating the entire amp circuit from the safety ground. You must isolate the input signal ground from the main ground.
Use the ground loop breaker as detailed by Rod in the link above, but only if you need to.


Hi! I am not "isolating the entire amp circuit".the safety ground is bolted to chassis. my question is:

if the chassis ground is not the same as the "audio Ground",how come when I touch the negative speakers terminals with meter (continuity) I hear a beep.that means it is some how connected to "chassis ground" right? check with your meter in continuity your gainclone and see if the negative from speaker terminal and chassis beep

PS: I have connected the signal ground to chassis.
the only things that I am worrie is: the speakers terminals(negative) are connected to chassis instead to board where the LM3875 is.
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Old 31st December 2007, 02:00 AM   #10
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Quote:
Originally posted by lanchile07


Hi! I am not "isolating the entire amp circuit".the safety ground is bolted to chassis. my question is:

if the chassis ground is not the same as the "audio Ground",how come when I touch the negative speakers terminals with meter (continuity) I hear a beep.that means it is some how connected to "chassis ground" right? check with your meter in continuity your gainclone and see if the negative from speaker terminal and chassis beep

PS: I have connected the signal ground to chassis.
the only things that I am worrie is: the speakers terminals(negative) are connected to chassis instead to board where the LM3875 is.
The safety ground (from the house current) must be connected to the chassis, along with the centre tap from the transformer.
The main star ground on the amp board should be connected to the chassis ground, but you can use the ground loop breaker circuit that is detailed on Rod's site (have a look, there is a very good, simple drawing).

The signal ground (from the source - preamp etc) should be isolated from the main star ground. Many use a 10 ohm resistor to do this. This is not a complete isolation, but it discourages high current from flowing into the signal ground.

The speaker return grounds will be connected to the main star ground, which should be connected to the chassis. That's why you have continuity.
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