[JN] buzz goes away when volume is mid way.

Paul Seymour tallpaul999 at gmail.com
Wed Apr 17 23:01:30 CDT 2019


Thanks Stephen & all Joe's !

this suggestion RE earthing the top plate got me thinking.
I have a wooden top and I have placed the rectifier too close
to the 6sn7s.  In hindsight.  I noticed when going to earth the
valve plate socket that just my hand between the rectifier
and the 6sn7 almost fixed it. To further test it I placed an old
metal milk tin over the 6sn7 and then earthed it with a lead.

GONE. Quiet as a mouse.  See pics.
It was radiation from the rectifier. I might build an earth cage for
it but until then I put "flashing"   aluminium with sticky back under
the top and screwed and earth wire into it. The flashing is around
the 6sn7. Cured about 95% of it just with this.   I guess it only
affected 1 channel  due to the orientation of the tubes.

Many thanks,
Paul.


[image: image.png]


[image: image.png]

On Thu, Apr 18, 2019 at 3:37 AM Stephen Robinson via Sound <
sound at soundlist.org> wrote:

> I had something not too dissimilar recently and it was cured by earthing
> the plate the valves and transformers were mounted on; that wasn't the case
> work. Is the pot case earthed?
>
> Cheers,
>
> Stephen
> On 17/04/2019 18:04, Paul Seymour via Sound wrote:
>
>
> Hi Jo's
>
> can I ask for your wisdom, I am stumped on this one.
>
> I have a pre amp, similar to JELabs preamp with the 76 tube,
> except I have all 6SN7's.
>
> I have this BUZZ in right channel only.
> I switched inputs and output's and always this channel
> of the pre amp has the buzz.
>
> *Strangely if I turn up the volume pot on the pre amp *
> *to mid way the buzz vanishes. (* Pot is on the input and
> I've swapped inputs as said and it's the same result so it's
> not the phono stage prior. )
>
> *If the vol pot goes right up the buzz comes back.*
> *Only in the middle does the buzz disappear. *
>
> This bizarre symptom must point to something, but what?
>
> thanks,
> Paul.
>
>
>
> --
> Paul.
>
>
>
>
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-- 
Paul.
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