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Old 16th January 2017, 04:36 PM
pager8 pager8 is offline
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Join Date: Mar 2013
Location: Bristol
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Default Annoying Hum

Hi all,
I have just got hold of a WAD 300b Clone and upon swapping it with my WD88VA connected to a Pre3/Psu3 have the most awful hum. I have tried removing the earth from the Psu3 ( No joy) and replaced it. I have also tried different interconnects and they make it sound worse. I realise that this is likely to be the dreaded Earth loop so any help in this matter will as always be gratefully appreciated. The source is a CD Player which has no Earth ( Twin wire only) It also hums when the CD is connected to the 300b directly using the CDs variable output, and yet all worked perfectly with the WD88VA

Thanks in anticipation

pager8 (Geoff)
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Old 16th January 2017, 07:47 PM
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Phil Y Phil Y is offline
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Join Date: Jul 2006
Location: Bristol, UK
Posts: 764
Default Re: Annoying Hum

Hello Geoff,

What you need to do is put your '88 back into the system using all the same cables (including mains) and confirm things still work. You could have caused or aggravated a bad connection somewhere when swapping the amps over.

If all is well, plug a pair of shorted phono plugs and speakers into the 300b and switch on. If it is quiet, it is probably an earth loop. If humming, the amp has a problem.

Do this then report back and we can go from there.

Commission for Dark Skies (CfDS)
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Old 17th January 2017, 05:20 PM
John Caswell John Caswell is offline
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Default Re: Annoying Hum

Hi Geoff,
I assume that with the inputs shorted out you have adjusted the hum bucking pots for minimum hum.
If it hums with both the CD cables connected, try with one cable only and then the other only to see if the hum lessens. As the CD is double insulated (ie no earth) you cannot get an earth loop via the mains. It sounds more like an input earth loop to me.

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