Audiophiles - low hum emitting from left speaker? Please help!!!!!?

Basti

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Hi everybody, having a significant problem with my stereo. Please help if you can.
My setup is...

Amp = Philips Integrated System AH927
Speakers = 150 Tronic FL250 (brand name is Ultimate)
Turntable does not specify its model anywhere on its exterior.

When the Function Dial on my amp is set to "Phono", my left speaker emits a low hum/buzz that occurs with and without a record playing. The humming begins erratically, sometimes lasting for five minutes, sometimes lasting for an entire day. It increases as I turn the amp's volume up, so it is not something I can simply drown out.
It disappears as soon as I change from "Phono" to "Aux" or "FM", so it is exclusive to that channel. It grows louder as my hand gets closer to the head of the tonearm, however I don't believe it is the wiring in the tonearm causing this problem as I have taken the head off completely and the buzzing continues without it.
My good friend who sold me all three components of this stereo doesn't know what is wrong either. He has taken both the turntable and amp away with him on separate occasions, neither of which gave him any grief when he used them as part of his own setup for a couple of days. He has come up with a variety of diagnoses, none of which have stood up for terribly long. Originally the turntable's power cord was plugged into the amp, which he decided may have been the cause and told me to plug it into its own wall socket. This made no difference. Today I changed which wall socket the stereo was plugged into in my room, which he also believed could have been the problem, yet the buzzing still occurs.
He has taken the amp apart to have a look at it, and concluded that nothing was visibly wrong with its interior. I don't believe he is an expert in this field, however I take his opinion over mine. He says the problem couldn't be located inside the humming speaker, for if it was the buzzing would occur on any Function setting on the amp, not just "Phono."
Recently, when the buzzing occurs, the problematic speaker makes no other sound; if I'm playing an LP, the music comes from the right speaker only, the left making no noise except for the hum. This does not change when I change the speaker balance on the amp, or when I change the LP.

Please help me out here, I am clueless as to what the problem is.

I am hesitant to rely on my friend's help again, not only because he hasn't been able to find a solution but I feel guilty continually asking him to drive from the other end of town and help me out. I'd rather not go to a local audio expert, as they can charge crazy money. I have the option of getting my money back from my friend, however if the problem is easily sorted I'd rather keep hold of the stereo - when it works it sounds incredible.

Could anybody tell me where this issue derives from?

Let's run through this again. The humming sound occurs:

*erratically
*exclusively out of the left speaker
*exclusively on the "Phono" setting on my amp
*regardless of whether something is playing
*regardless of whether the head of the tonearm is attached or not
*regardless of where in the room the stereo is plugged in

Thanks so much, any and all help is appreciated.
 
My guess is its the phonocartridge and would simply need replacing, but it could also be the wiring in the tonearm, or phonostage of the reciever. First thing is to reverse the leads from the turntable to the reciever. If it changes channels its nothing in the phonostage of the receiver and is isolated at the turntable. Next putting the channels back, reverse leads to the cartridge. If it switches channels its clearly the wiring in the tonearm somewhere, if not then its the cartridge as I would suspect. Typically if its a ground issue like your having it would be in both channels.

Good luck

Kevin
40 years high end audio video specialist
 
You could make sure it's not the speaker by switching the wires @ the amplifier. That would be much more conclusive and informative, positively ruling speakers out and crediting the left channel. Now what i would do (assuming the first check played out as we expected) is switch the left and right RCA cables @ the amplifier. This will verify which unit should be the primary focus of these diagnostics. The buzz either follows the turntable's left channel or not. Turntables are more prone to problems like this because it sends a microphone level signal to the amplifier, not a preamp "line level" like all the other devices. I say more prone because both microphone level signal and line level signal are sensitive to picking up "Main's hum" (the microphone level more so than the line level) Borrow a different turntable and see if the buzz is still there. Then buy a replacement unit for the one that has the problem after you look closely for things like missing shield/shielding, broken solder for shield grounding, and anything close to power transformers and the power supply area of the device. Good luck!
 
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