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Old 19th October 2016, 08:08 PM   #1
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Default Grounding question

Hi all

just working out the wiring for a pair of Lang 20W Class A amps, and am a bit confused about the grounding.

http://gdurl.com/6Rsz

The amp uses 2 supplies - 20V @ 4A (output stages) and 24V @ 100mA (low level stages). As you can see on the board layout, there is a 0v connection, and a 'T' connection. Any ideas?

thanks
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Old 20th October 2016, 09:58 AM   #2
AndrewT is offline AndrewT  Scotland
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Every inter-module connection needs two wires.
Keep every two wire connection as a close coupled pair.
Twisted, or coaxial, is slightly better if the size and type of cable suits.

eg.
From power supply A you need two wires. A dual polarity PSU needs three wires, twist these as a triplet.
From power supply B you need two wires. A dual polarity PSU needs three wires, twist these as a triplet.
From Audio Source Left channel you need two wires.
From Audio Source Right channel you need two wires.
Speaker Left output needs two wires.
Speaker Right output needs two wires.
Transformer secondary to rectifier needs two wires.

Install all those two wire connections.
Now compare your assembly to the schematic and find any missing connections.

Unfortunately the PCB layout designer did not agree with this most basic philosophy.
He has provided many connections as single pads. He has forgotten that current cannot flow around a circuit unless a route is provided for the return current to go back to it's source.
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Last edited by AndrewT; 20th October 2016 at 10:06 AM.
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Old 20th October 2016, 10:05 AM   #3
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Thanks

it's more about the connections on the circuit board - there is one marked '0v', and one marked 'T'. My understanding is that the 'T' goes to the main star ground, but the '0V' - is that for the 0V return of the low current supply, or for the signal ground?
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Old 20th October 2016, 10:08 AM   #4
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this is what i use....
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File Type: jpg chassiswiring1.jpg (141.8 KB, 249 views)
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Old 20th October 2016, 10:12 AM   #5
AndrewT is offline AndrewT  Scotland
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post4 is wrong. Pavouk.org got it completely wrong and AJT should never have copied it. He has been told before and chooses to post this erroneous layout yet again.
Never take your audio ground to the main charging node between the smoothing capacitors ! NEVER !
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Old 20th October 2016, 10:16 AM   #6
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The problem is that there does not appear to be a signal ground connection on the board. Unless, as I said, that is the '0V' connection pin near the output transistors, which seems a bit odd.
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Old 20th October 2016, 10:20 AM   #7
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Quote:
Never take your audio ground to the main charging node between the smoothing capacitors ! NEVER !
never use the power supply ground return wire to run your signal grounds, use a separate wire....

run those wires separately to the psu common or zero point...
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Old 20th October 2016, 10:23 AM   #8
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Quote:
Originally Posted by AndrewT View Post
post4 is wrong. Pavouk.org got it completely wrong and AJT should never have copied it. He has been told before and chooses to post this erroneous layout yet again.
Never take your audio ground to the main charging node between the smoothing capacitors ! NEVER !
Many will disagree with you on that. The input gets it's return own path to the star ground. What's wrong with that?
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Old 20th October 2016, 10:24 AM   #9
AndrewT is offline AndrewT  Scotland
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Originally Posted by number7 View Post
The problem is that there does not appear to be a signal ground connection on the board. Unless, as I said, that is the '0V' connection pin near the output transistors, which seems a bit odd.
You need to do a bit of reverse engineering comparing the schematic to the layout to find the best place to tap into the return part of the circuit, for least interference.
That will not be easy.
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Old 20th October 2016, 10:26 AM   #10
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i have been using that layout even before Pavouk published it, as early as the early 90's
it works for me, no reason it will not work for others....

Quote:
That will not be easy.
nothing is....

the speaker negative or return wires go back to the star....
never use one wire for the two channels, run them using separate wires,
i never run speaker grounds to the board and then to the starr,
i use separate wires....
so you seem in the schematics there may be fewer lines,
but in the actual buildm there are more wires than the schematic called for....
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