speaker terminals to chassis ground?

lanchile07

Member
2007-10-06 6:29 am
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.:smash:
 
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.
 
lanchile07 said:
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.
 

lanchile07

Member
2007-10-06 6:29 am
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.:smash:
 

MJL21193

Disabled Account
2007-03-10 1:20 am
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.
 

lanchile07

Member
2007-10-06 6:29 am
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 :smash:

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.
 

MJL21193

Disabled Account
2007-03-10 1:20 am
lanchile07 said:


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 :smash:

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.
 

lanchile07

Member
2007-10-06 6:29 am
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.

Well,from the transformer I have four wires(Plitron) they go to AC1/AC1 and AC2/AC2 and the V- PG- PG+ PG- go to the board that has the chip(LM3875). but where is the "CENTER TAP" from transformer?.I fallow the info at "Audiosector.com" and I do not see the 10 ohm resistor.
so can I leave the ground from speakers terminals connected to chassis.I make it clear...
instead connecting the ground from speaker terminal to board.can I just connect them to chassis?.I ask you this because,the chassis I got it has return grounds already connected to chassis.
or should I make new connections from terminals to boards.
the signal ground are connected to chassis.
 

lanchile07

Member
2007-10-06 6:29 am
So,is the "PG+" connected to Ground chassis?.because this "PG+" I have connected to the boards with the chip tha says "PG+".:smash:

I can see that "PG+" from power supply is going to "CHG" on chip board (CHASSIS GROUND)so if I just connect the "PG+"direct to Ground chassis it will be the same but will eliminate the "ground loop" or not?.
what about "V-" should this be connected to chassis ground too?
 

lanchile07

Member
2007-10-06 6:29 am
my transformer has dual secondaries, but does not have a center tap.I just connected them : two to "AC1" and the other two to "AC2"????:smash:
and from the V-,V+,PG- and PG+ are connected to same to the board that has LM3875 chip.but where is the "center tap"?that is suppost to be connected to chassis?
 
As mentioned above, the centertap is not relevant here as the boards were designed to work with dual secondaries, although they can be modified to work with CT as well: http://www.diyaudio.com/forums/showthread.php?postid=1196283#post1196283

There are basically 3 grounds:

signal ground (that starts with RCAs and connects to SG point on PCB)

the output ground (the center point on the ground plane, marked as OG which connects to negative binding post)

CHG, that is basically the same as OG and can be an optional point to connect chassis ground.

CHG, PG+ and PG- are all connected directly to ground plane.

When measuring continuity, you will notice that SG and OG are indeed connected, but SG is not directly on the ground plane but connected to it with a separate trace (that provides some isolation between signal and power grounds).

It is not recommended to connect negative binding posts directly to chassis in a stereo amp as that may create ground loops. It is not a problem to do it in monoblocks (separate chassis for each channel)

It is certainly not recommended to connect RCA to the chassis: a piece of wire is always better conductor than chassis material and it's also important that the ground from RCAs is connected to SG point on the board.

The chassis connects directly to Earth Ground, CHG connect to chassis through 10R resistors (and this is how you have audio ground and chassis ground separated).
 

vdi_nenna

Member
Paid Member
2000-10-10 7:27 pm
PA, USA
The chassis connects directly to Earth Ground, CHG connect to chassis through 10R resistors (and this is how you have audio ground and chassis ground separated).

Peter, is it ok to use a thermistor instead of a 10 ohm resistor?
I read in another thread using a resistor to chassis ground is not allowed in some countries because of safty standards. Is this correct?

thanks,

Vince