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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 4th Jan 2024, 8:22 pm   #1
Dorian27
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Default Fidelity HF42

This record player has a loud acoustic hum when volume is turned up over half way it is differently acoustic it only comes on when record playing or arm put on record it has good volume and no hum only when playing records on high volum is this normal on this model
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Old 4th Jan 2024, 9:31 pm   #2
ben
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Default Re: Fedelity HF42

I think the arm's rubber bushings may have hardened, leading to acoustic feedback. Does it lean to one side at all?

Bear in mind these were low end units for playing 45s in childrens' bedrooms and the internal speaker 's proximity to the pickup means performance is pretty ropey at best.

You might be able to add some rubber grommets to add further isolation between speaker and plastic cabinet. But check the arm first.
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Old 4th Jan 2024, 9:38 pm   #3
Station X
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Default Re: Fedelity HF42

The one I had didn't hum at all. Try shorting the cartridge or its leads to confirm it's acoustic feedback and not mains hum.
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Old 4th Jan 2024, 9:57 pm   #4
Dorian27
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Default Re: Fidelity HF42

Yes it is definitely acoustic hum it only happens when playing lp works fine on 45
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Old 4th Jan 2024, 10:39 pm   #5
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Default Re: Fidelity HF42

It's probably the output from the speaker bouncing off the underside of the LP and being picked up by the cartridge.
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Old 4th Jan 2024, 10:57 pm   #6
slidertogrid
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Default Re: Fidelity HF42

That is exactly the problem. I used to repair these for a shop that sold them back in the day and it was a problem back then when they were new. They sold well judging by the amount around all these years later. Some are worse than others and the thickness of the record can have an effect on how bad it can be, the stylus can also have an effect, some have a metal end some plastic. Finally the medium output BSR cartridge used on these can vary, the output from some examples is higher than others. I would try a different cartridge on stubborn ones.
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Old 4th Jan 2024, 11:00 pm   #7
Dorian27
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Default Re: Fidelity HF42

Thanks everyone for your help I will inspect closer
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Old 5th Jan 2024, 8:35 am   #8
Edward Huggins
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Default Re: Fidelity HF42

The output from the IC amplifier on these is surprisingly powerful.
I agree with Ben in that because a 12" LP will partially mask the speaker, it is liable to create a back-pressure on the speaker's cone at certain volume levels.
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