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Old 18th September 2005, 08:09 AM   #1
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Default output hum

hey people i have just finished a 200wrms x 2 solidstate amp

we have alternate power at home and run off a modified sine wave inverter.

the problem is i need a way to (when the volume is right down) to eliminate the horrible hum

like i mean you cant even use headphones the hum iss so bad and loud


plz i need help

ps the hum is comming from the speakers @ 50 hz
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Old 18th September 2005, 11:10 AM   #2
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actualy is it easiest just to rewind the trnsformer agian so it has +/- 80 v in the caps and regulate it at +/- 60 v ?


sry we run a modified SQUARE wave inverter
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Old 18th September 2005, 11:53 AM   #3
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How have you grounded it? Stargrounded? Is the inputs shielded?

Regulated PSU isn't a very good alternative
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Old 18th September 2005, 12:55 PM   #4
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absolutly it was one of the first things i did and checked
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Old 18th September 2005, 04:49 PM   #5
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If you have grounded everything in a perfect way like a star then the hum might go right into the main pcb. Take it and put it far away from the transformer and see if it helps.

I assume you have rectified the AC and youre using significant big reservoir capacitors
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Old 19th September 2005, 07:22 AM   #6
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+/- 50v power

8000uF caps


200wrms x2 amp

the amp board is on the opposite end of the 17" box


thank u
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Old 19th September 2005, 09:08 PM   #7
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Except some very particular designs...
Normally heavy hum is not caused by the ripple on the DC rail.
Ripple on the DC rail usually causes just some hum, but not heavy hum. And typically this hum would be 100Hz, not 50Hz.

Do you have the hum also, if the amp is not connected to any
signal source? No computer, no TV, no radio etc....
Most often you get such heavy hum, when you connect two parts of equipment that both are grounded. ... grounded at different points and causing a ground loop between two (or more) parts of the equipment. So most suspect are computers (PSU always grounded), TV (antenna grounded), radio (antenna).

Good luck
Markus
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Old 19th September 2005, 09:47 PM   #8
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Sometimes you will need to seperate the Audio and PSU grounds to elliminate ground loops within your amplifier system.
Does the amplifier hum get worse when you connect a source to it's input terminals?
For a start seperate the input audio grounds and see if it goes away(attenuates is probably a better word)
Comman practice is to lift this ground away with a 47 ohm (or thereabouts) resistor.
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