Audiosector lm4780 dual mono grounding - diyAudio
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Old 5th February 2011, 03:02 AM   #1
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Default Audiosector lm4780 dual mono grounding

I am currently putting together an Audiosector lm4780 dual mono amp, 2 transformers and 2 PSU boards, is it recommended to create some kind of star ground between the psu boards and the amp boards?... meaning do I need to take all the negative connections to a single ground point on the metal chassis?

Also would I need to connect the speaker negative's to this ground star as well?
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Old 5th February 2011, 04:17 AM   #2
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Hi, If you have dual transformers then I would not do as you have suggested. I assume that the PS boards have a zero volts point, this is where your star ground for each channel should be (assumption as I have not seen the pcbs for the amps or ps, (some of the kits have separate +v and -ve zero volts points).

Certainly run the saftey earths to the same point on the chassis, but whether or not this comes from the PS star point I couldn't say without seeing the design.

I would personally run the speakers negative to the star points directly but again it depends a bit on the pcb designs of the audiosector PCB's (do they have a speaker negative point on the amp pcb?).

I believe that If you tie the separate channels zero-volts together you will lose some of the benefit of having dual mono, and you will get increased crosstalk between channels.

Tony.
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Old 5th February 2011, 10:19 AM   #3
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Depends on the voltage. You need to take measures against direct contact, if the voltage at the speaker terminals can reach or exceed 60 V DC (unlikely) or 25 V AC (possible depending on the transformer).

Then you have the choice between class I style and class II style. Class II style means to double-insulate all conductive parts. For speaker terminals and wires that is pretty impractical. So you'd rather use class I style which means to connect one end of the output, here the negative pole, to the chassis and install fuses in the rails that blow in case of a short to case. Once you do that and you have the chassis connected to PE, because you also did a Class I layout for the mains voltage, you have little choice but to create a star-ground to avoid ground loops.
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Old 5th February 2011, 10:30 AM   #4
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I seem to recall that AudioSector gives details and pics of exactly how to do the grounding.
They even show an alternative that allows for the use of a non recommended transformer.
Have you read? :
Audio Component Grounding and Interconnection
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Old 5th February 2011, 04:20 PM   #5
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In reply to wintermute this is the PS board http://www.audiosector.com/lm4780%20psu.pdf


In reply to AndrewT, I did spend quite some time looking over previous posts on here and most only show a setup with a single transformer, i couldn't find anything relating exactly to what I want to do
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Old 5th February 2011, 04:42 PM   #6
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Quote:
Originally Posted by mattjuk81 View Post
I am currently putting together an Audiosector lm4780 dual mono amp, 2 transformers and 2 PSU boards, is it recommended to create some kind of star ground between the psu boards and the amp boards?... meaning do I need to take all the negative connections to a single ground point on the metal chassis?

Also would I need to connect the speaker negative's to this ground star as well?
I assume you are using a single chassis.

There is no need for any additional star ground in case of dual mono setup, as each amp pcb features on board star ground.

The earth ground from power entry module connects directly to chassis and each amp board connects to the same ground point as well (run wires from CHG pads).

BTW, using rail fuses with LMXXXX chip amps is a bad idea; in case only one fuse blows, an excessive DC offset may occur and damage your speakers.
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Old 5th February 2011, 04:50 PM   #7
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Quote:
Originally Posted by Peter Daniel View Post
I assume you are using a single chassis.

There is no need for any additional star ground in case of dual mono setup, as each amp pcb features on board star ground.

The earth ground from power entry module connects directly to chassis and each amp board connects to the same ground point as well (run wires from CHG pads).

BTW, using rail fuses with LMXXXX chip amps is a bad idea; in case only one fuse blows, an excessive DC offset may occur and damage your speakers.
Yes I am using a single chassis.

Where abouts are the CHG pads on the lm4780 boards, I just had a look but can't see them?
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Old 5th February 2011, 04:54 PM   #8
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Indeed, I forgot I didn't marked them there.

The OG pad (output ground) is dual hole; use one of those for chassis ground.
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Old 5th February 2011, 05:29 PM   #9
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Originally Posted by Peter Daniel View Post
Indeed, I forgot I didn't marked them there.

The OG pad (output ground) is dual hole; use one of those for chassis ground.
Excellent thanks will I need to lift the ground with a resistor when connecting those pads to the chassis?
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Old 5th February 2011, 05:38 PM   #10
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You can connect them directly.
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