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Luxman LV-105 hum
Luxman LV-105 hum
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Old 2nd February 2018, 12:45 PM   #1
Depaj is offline Depaj  France
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Default Luxman LV-105 hum

Hello,

I'm having some trouble finding the cause for a hum on a luxman LV-105 (not the u version). Also the right channel doesn't handle any load (dim bulb goes bright and relay opens). Sometimes, not always, the relay keeps kicking in and out without any load connected, at the same time dc offset get up to around 1.5v. The tubes are ok (putting in new ones doesn't change anything to the problem) and the hum is present before them (not in the tone amp though). The caps are all new (checked polarity carefully). Whenever I unplug the connector taking the + and - rails to the equalizer circuit the hum gets slightly lower and the right channel can accept a load again. It looks like the high voltage power supply can't keep up somehow.
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Old 2nd February 2018, 01:16 PM   #2
neptunes4you is offline neptunes4you  Hungary
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Luxman LV-105 hum
Quote:
Originally Posted by Depaj View Post
Hello,

I'm having some trouble finding the cause for a hum on a luxman LV-105 (not the u version). Also the right channel doesn't handle any load (dim bulb goes bright and relay opens). Sometimes, not always, the relay keeps kicking in and out without any load connected, at the same time dc offset get up to around 1.5v. The tubes are ok (putting in new ones doesn't change anything to the problem) and the hum is present before them (not in the tone amp though). The caps are all new (checked polarity carefully). Whenever I unplug the connector taking the + and - rails to the equalizer circuit the hum gets slightly lower and the right channel can accept a load again. It looks like the high voltage power supply can't keep up somehow.
Hi!
Are there capacitors in the signal line, or is DC coupled everywhere?
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Old 2nd February 2018, 01:19 PM   #3
Depaj is offline Depaj  France
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There are caps in the signal line at the output of the tone amp IC but from input to output of the power amp it's all dc coupled. I think it must be somewhere in the first stage, right before the tube based differential amp.
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Old 2nd February 2018, 01:29 PM   #4
neptunes4you is offline neptunes4you  Hungary
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Luxman LV-105 hum
Quote:
Originally Posted by Depaj View Post
There are caps in the signal line at the output of the tone amp IC but from input to output of the power amp it's all dc coupled. I think it must be somewhere in the first stage, right before the tube based differential amp.
Is the hum present when you connect the inputs to ground? Have you tried removing the tubes from the tube stage and checking the output noise with an oscilloscope?

Btw, i would try to find why is there a DC voltage on the output.
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Old 2nd February 2018, 01:50 PM   #5
Depaj is offline Depaj  France
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The hum is present with inputs shorted to ground yes.
The thing is, it's not consistent, it just moves up and then the relay opens almost immediately so there is no time to see why it does this . There is no dc when the I disconnect the equalizer circuit but there is still hum.
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Old 2nd February 2018, 01:51 PM   #6
neptunes4you is offline neptunes4you  Hungary
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Luxman LV-105 hum
So, i would check the equalizer first, try to find where that DC voltage comes from.
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Old 2nd February 2018, 01:54 PM   #7
Depaj is offline Depaj  France
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I doesn't come from the equalizer, that works ok, the extra load on the power supply seems to just agravate the problem, the output of the equalizer is not connected to the input of the amp so it can't be passing trough dc.
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Old 3rd February 2018, 09:51 AM   #8
neptunes4you is offline neptunes4you  Hungary
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Join Date: Oct 2012
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Luxman LV-105 hum
Quote:
Originally Posted by Depaj View Post
I doesn't come from the equalizer, that works ok, the extra load on the power supply seems to just agravate the problem, the output of the equalizer is not connected to the input of the amp so it can't be passing trough dc.
Are you sure there is no leaky capacitors in the amplifier?
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Old 3rd February 2018, 10:02 AM   #9
Depaj is offline Depaj  France
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I'm positive, they have all been replaced with high grade caps. Other than the hum it sounds ok through headphones, I haven't tested it with speakers because I don't want to risk damaging them.
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Old 3rd February 2018, 10:28 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
replaced with high grade caps
That worries me.
Some of the "Hi Grade" offering are scrap that have been relabelled.
__________________
regards Andrew T.
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