Audio research LS2 hiss and hum... need help - diyAudio
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Old 6th May 2013, 01:33 PM   #1
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Default Audio research LS2 hiss and hum... need help

Hi,

Just buyed a second hand LS2 and when i plug it on my system, i heard hum and hiss. Hum is present when volume knob is low, disappear when the volume knob is about 1/3 coarse and then increase for the last of the coarse... Hum is present on all sources (also in Direct in) and disappear when mute key is on.
Hiss appear and disappear and sound like old phone internet modem...

First off all, i have change the tube with a NOS Philips ECC88... no change

I have recap all the HT capacitors... no change, all voltage are ok (just a little bit more).

Does anybody have same issue or can help me to fix it ?

By the way, sorry for my bad english. It come from a French guy...
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Old 6th May 2013, 01:42 PM   #2
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if both channels are in case , culprit is in PSU ( NT or auxiliary voltages - everything which is common for both channels )

look here for sch , if you don't have it : ARCDB - LS2
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Old 6th May 2013, 02:10 PM   #3
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Thanks for the link but i still have the schematic. By the way, the Fet Q3 (HT regulator) is very very hot, is it normal ?
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Old 6th May 2013, 03:17 PM   #4
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I resume it is normal - with 120V across it , and tiny heatsink ....... there must be at least 6-7W of dissipation ..... estimated without proper analysis of circuit itself ;

I wouldn't be surprised to find even more
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Old 7th May 2013, 04:05 AM   #5
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check the condition of the tube sockets. 90% of the time, hiss and pop are worn out tube sockets.
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