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Old 5th August 2010, 02:07 PM   #1
Basill is offline Basill  Poland
diyAudio Member
Join Date: Apr 2007
Question Pearl Phono strange working

I've got problem with the pearl phono that I've finished yesterday. I pluged the pre with the input shortened to ground, pluged the otput to the oscilloscope and i've got very nice flat response (there was no noise), next i've plugged it to the amp, still no noise I was very happy . But when i plugged the turntable into it, it started to hum it gave very nice sine 100Hz . I've shortened the input again and there was again flat response. What can it be ? The same thing happened on differnet turntablas and cardridges i've got at home (MM and hi-output MC). Please help . I've made it P2P on a pref board. This is my second phono pre the first one was on tubes it gave some noise noticable on the scope, shortened and when the turntable was connected, but it wasn't audible.
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Old 5th August 2010, 02:42 PM   #2
teamacc is offline teamacc  Netherlands
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Join Date: Jan 2010
Does it give the noise too when only connected to the phono?
Sounds like a ground loop (100hz)
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Old 6th August 2010, 06:02 AM   #3
Basill is offline Basill  Poland
diyAudio Member
Join Date: Apr 2007
Yes it does, but what i know from my expirience with the tube phono pre i should have 100Hz also with the input shortened to the ground . I will try to modify the ground connections anyway, time will tell if it is the problem . The pre sounds nice only this hum is annoying :/.
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Old 7th August 2010, 09:50 AM   #4
Basill is offline Basill  Poland
diyAudio Member
Join Date: Apr 2007
So i've solved the problem, it appears that the hum maker was a LED power indicator strage becouse it was fed directly from mains 230V ? it only had contact on the power switch with the rest, removed it and there is silence now. Now i'm happy no hum on scope and no audible hum . Thread closed
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