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Old 18th August 2002, 08:12 PM   #1
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Unhappy humm in sds headphone amp.

I just finished my first small ampproject, a SDS headphone amp but I got a problem: HUMMMMMMM. It's not very loud but is's there and when I approache the signal leads it get worse, I dont have to touch them to make it louder.
Since this is my first project and my understanding of EE and grounding is limited I'd appreciate some sugestions.

Ralph
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Old 18th August 2002, 08:25 PM   #2
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I built that amp two years ago. It isn't the greatest amp ever, but I didn't have any trouble with hum. With the headphones removed, is there a DC potential across the outputs? Check that first.

Does it actually produce music?

Is the circuit ground connected to earth? What about the chassis?
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Old 19th August 2002, 06:46 AM   #3
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It does produce music and with dance you can't hear the humm but with classical music it's all over the place.


Yes I got 2.08 mV of DC accross the output connector (what can I do about it.

The total amp is connected to earth with a starground.

Ralph
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Old 19th August 2002, 07:25 AM   #4
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Oops,

just rememver that I disconnected the POT on the input. With the POT in place I don't measure any DC.

When I disconnect the ground of the output the humm get really soft but the sound is breaking up (echo's)?!

Any suggestions???

Ralph
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Old 19th August 2002, 04:13 PM   #5
jwb is offline jwb  United States
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It is hard to diagnose something like this, without actually seeing the amp. My next best guess is a bad solder joint, possibly somewhere in your ground. Check continuity of the circuit ground, chassis, earth, headphone jack, etc.
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