humm in sds headphone amp.

[rwagter]

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

 

[jwb]

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?

 

[rwagter]

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

 

[rwagter]

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

 

[jwb]

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.