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Old 14th March 2012, 05:53 AM   #11
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Have u by any chance not shorted the two grounds(12V and 35 V returns).

Gajanan Phadte

Last edited by gmphadte; 14th March 2012 at 05:54 AM. Reason: added content
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Old 14th March 2012, 09:05 PM   #12
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Quote:
Originally Posted by Bonsai View Post
Where and how are you connecting your common ground between the amplifiers?
Tried Via Chassis, tried Via Direct Ground wire from Left Channel to Right Channel.
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Old 14th March 2012, 09:08 PM   #13
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Quote:
Originally Posted by gmphadte View Post
Have u by any chance not shorted the two grounds(12V and 35 V returns).

Gajanan Phadte
NAMASHKAR!!!!
The Grounds are shorted on the Amp board circuitry by default.
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Old 14th March 2012, 09:23 PM   #14
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connect transformer 35V "GND" directly to Filter "GND" (wire is missed in your drawing) - and NOT to common Ground or Chassis!
Do this for left and right channel separately. This transformer "GND" carries high current pikes for charging the capacitors. These should not interfere with signal wires, and also not with "Signal GND".

Same for connecting Filter's output "GND" directly to amp supply GND (the wire which is missed in your drawing). Not to common GND / chassis!
Question: On the amp board, is signal input GND and speaker output GND internally connected to supply GND? If yes, simply connect signal input GND of each amplifier to a single common chassis GND. Thats the GND star point. No supply wires, also no "supply GND" should directly be connected to that star GND.

Regards,
Guthorst

Last edited by Guthorst; 14th March 2012 at 09:29 PM.
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Old 14th March 2012, 11:53 PM   #15
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Quote:
Originally Posted by Guthorst View Post
connect transformer 35V "GND" directly to Filter "GND" (wire is missed in your drawing) - and NOT to common Ground or Chassis!
Do this for left and right channel separately. This transformer "GND" carries high current pikes for charging the capacitors. These should not interfere with signal wires, and also not with "Signal GND".

Same for connecting Filter's output "GND" directly to amp supply GND (the wire which is missed in your drawing). Not to common GND / chassis!
Question: On the amp board, is signal input GND and speaker output GND internally connected to supply GND? If yes, simply connect signal input GND of each amplifier to a single common chassis GND. Thats the GND star point. No supply wires, also no "supply GND" should directly be connected to that star GND.

Regards,
Guthorst
Thanks for the quote, Will try and update.

On the amp board, is signal input GND and speaker output GND internally connected to supply GND?
Ans) Yes.
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Old 15th March 2012, 04:50 AM   #16
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Draw a physical schematic of your GND wires and post.
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Old 15th March 2012, 09:37 AM   #17
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Quote:
Originally Posted by SLAK View Post
Thanks for the quote, Will try and update.

On the amp board, is signal input GND and speaker output GND internally connected to supply GND?
Ans) Yes.
That's no good idea. But follow my description and check if it works.

I think, there are some reservoir capacitors on amp board, connected between suppl (+/-12V and +/-35V) and GND. So, every charge and discharge pulse currents for these capacitors travel via dedicated GND wires. This will result in a noisy/humming GND wire. So, you should not use this supply/reservoir ground wire as signal return/signal GND.

The complete GND network should not have any loop. Use only one star point, which is connected to signal inputs (the most sensitive signals). This star point can be the metal enclosure of your amp.

If you had an additional connection from transformer GND or filter GND to that star point, this would result in a ground loop. Because the internally connection inside amp board will form that loop. But if there was not internally GND connection at the amp board, then it was required to connect the filter reservoir GND to your single common star point GND.

Regards,
Guthorst
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Old 15th March 2012, 04:18 PM   #18
kpapr1 is offline kpapr1  Greece
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Hello,

I had exactly the same problem with you and did what someone else suggested in this thread and it worked perfectly. I disconnected the input GNDs from left & right star ground points and connected them both straight to the chassis GND, where left and right star grounds meet. I think it will work for you, too.
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Old 15th March 2012, 04:22 PM   #19
kpapr1 is offline kpapr1  Greece
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Hello,

I had exactly the same problem with you and did what someone else suggested in this thread and worked perfectly. I disconnected left and right i/p GNDs from left & right star ground and connected them both to chassis ground, where left & right star GNDs meet. Now there's no hum when I short left & right i/p GNDs. I think it will work for you, too.
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Old 17th March 2012, 08:28 AM   #20
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Quote:
Originally Posted by Guthorst View Post
That's no good idea. But follow my description and check if it works.

I think, there are some reservoir capacitors on amp board, connected between suppl (+/-12V and +/-35V) and GND. So, every charge and discharge pulse currents for these capacitors travel via dedicated GND wires. This will result in a noisy/humming GND wire. So, you should not use this supply/reservoir ground wire as signal return/signal GND.

The complete GND network should not have any loop. Use only one star point, which is connected to signal inputs (the most sensitive signals). This star point can be the metal enclosure of your amp.

If you had an additional connection from transformer GND or filter GND to that star point, this would result in a ground loop. Because the internally connection inside amp board will form that loop. But if there was not internally GND connection at the amp board, then it was required to connect the filter reservoir GND to your single common star point GND.

Regards,
Guthorst
Thank you for the useful quote, will try and Update.
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