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Old 31st December 2007, 05:29 AM   #11
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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.
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Old 31st December 2007, 05:40 AM   #12
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So,is the "PG+" connected to Ground chassis?.because this "PG+" I have connected to the boards with the chip tha says "PG+".

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?
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Old 31st December 2007, 06:22 AM   #13
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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"????
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?
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Old 31st December 2007, 07:34 AM   #14
Puffin is offline Puffin  United Kingdom
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If you have two secondary's and need a center tap, you will need to join the two wires closest to each other (from each pair) and this will give you ?v - Ov and ?v (?= the ac voltage)
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Old 31st December 2007, 11:13 AM   #15
AndrewT is offline AndrewT  Scotland
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Hi Lan,
your PSU is designed for dual secondaries and dual rectifiers.
Do not create a centre tap.
The common link between the rectifiers is the zero volt line. This connects to the Audio Ground.
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Old 31st December 2007, 02:45 PM   #16
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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/showt...83#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).
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Old 31st December 2007, 02:53 PM   #17
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Wow,now I have it clear! thank you so much for your help.
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Old 28th February 2008, 11:20 PM   #18
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Quote:
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
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Old 28th February 2008, 11:25 PM   #19
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Yes, thermistor will work fine too, maybe even better than resistor.
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Old 3rd April 2013, 02:48 PM   #20
troystg is offline troystg  United States
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Grounding 101....

Grounding and Shielding Audio Devices
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