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Luxman L-110 Pre-amp hum

K

kronos

New Member
I have a problem with my new aquisition! The humming is driving me insane... I have a Luxman L-110 which I purchased a little while ago and I have found that the pre-amp produces a hum which is quite bothersome.

I've removed the jumpers and connected an auxillary pre-amp (HK330b) and the hum disappears. I've connected the L-110's preamp to the HK330b's "main in" and the hum is still there....

I don't know what to do besides find a service manual and start re-capping.

Any thoughts or suggestions?
 
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If the hum is in both channels, it's more than likely a power supply issue. Replace the filter caps and you're more than likely done.

If the hum is in one channel, it's more than likely NOT a power supply issue. Get a schematic, start at one end of the signal path and start probing with your oscilloscope until you find the problem component. If you've got an ESR meter you can save yourself some time by checking all of the electrolytic caps in the bad channel in-circuit. If you're lucky you'll find one and you'll be done, but it may be a bad transistor or diode.

Dave
 
If it was the power supply capacitors why wouldn't this effect the "main in" function? I don't have a oscilloscope, but I would know what to look for I think... and that would be major ripple in the Vdc wave if the capacitors were bad?
 
kronos said:
If it was the power supply capacitors why wouldn't this effect the "main in" function? I don't have a oscilloscope, but I would know what to look for I think... and that would be major ripple in the Vdc wave if the capacitors were bad?
Click to expand...

It might be affecting the main in, but at a level which is inaudible. The preamp may add as much as another 20dB of gain. And yes, you'd see a 60Hz ripple on the power rail(s) if the filter caps aren't doing their job.

If you've got a turntable and the preamp has a phono section, fire that up and see if the hum is even louder.
 
Yes, the hum is louder when I play from a turntable. I don't have an oscilloscope so I can't test to look for ripple in the power supply side. Does anyone think it may be a grounding issue?
 
If you think you've got a floating ground, what's common to all of the inputs you've tested? Put one of your multimeter leads on the signal ground (outer ring of pre-out) and the other lead on the power supply ground between the filter caps. If it's not 000 check the ground connection between the pre-amp board and the power supply and/or amp board. Some amps use the chassis for grounding, some use wire-wrapped connections between boards, some use ribbon cables.

Actually an easier test would be to just use a lead with alligator clips to tie your signal ground to power supply ground. If the hum goes away you found your problem.

Don't rule out power supply caps just yet though...
 
Turned it on last night and the hum was gone.... odd. Didnt' do anything different besides let it sit for about 3 days. I'm confused.
 
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