popping crackling distortion that clears up after 2 mins Help!!

[Puggie]

I'm having problems with a Quad 405 fitted with a frequency splitting board from a rogers LS 5/8 loudspeaker.

when powered up the Bass section pops and crackles quite loudly (almost like electrical arcing) with some background hiss, after about 2 mins it settles down and behaves. I had this problem about 6 months ago and replaced most of the transistors and capacitors (mostly Tantalums which were replaced with electrolytics) which solved the problem but now it has re-appeared, any idea what the problem could be?

thanks

 

[edl]

What's your speakers impedance?

 

[Puggie]

8ohm IIRC, I tried it on a 4ohm midbass and that is no better/worse.

I have found with just the amp channel and no input I get a little popping and crackling, with the frequency splitter board it seems a little worse (but it may not be).

 

[edl]

Hmmm...
Then I would check the solderings, then the elkos.

Or maybe it's oscillating? You should use a scope to determine it.

 

[destroyer X]

Try this method....and the others ideas people will suggest too.

Touch with a soldering iron the components leads

This way you may find the defective component.

Do it with the amplifier switched on...no signal in the input..and listen to detect the noise..... wait component to absorb the heat from the soldering iron...listen at the speakers searching for the damaged part.

Of course sensitive stages will amplify the AC noise captured by your soldering iron metal chassis....when testing those stages reduce the volume for some seconds...remove the soldering iron and turn the volume up again.

regards,

Carlos

 

[Puggie]

I have today found out that tapping that amp board causes the speaker to 'crack' loudly so I think it would very well be a dry/broken joint.

 

[pinkmouse]

Blanket resolder, and go over all the traces with a magnifing glass to check for any cracks.

 

[Puggie]

Further to this, I have now solved the loud 'crack pop' noises, by blanket re-soldering the board and changing one Tant capacitor for a back to back pair of electros (was all I had to hand). but now the amp has quite a hiss and crackle which fades in at turn on which clears up after 30sec or so, Someone mentioned the electrolytic caps could be breaking down and healing as a voltage is applied, any ideas?