Phono3S hum

[ArchieH]

Hello everyone and a happy new year
I am having a bit of a problem with my newly built Phono3s and Pre3. When I switch to Phono 2 ie the moving coil I/P I get a hum which gets louder the more I turn up the volume. If I switch to either the Phono 1 I/P or mute no hum but I do get a sort of mush, which is the best way I can describe the sound, again this gets louder the more I turn up the volume. I have used option 1 on the Phono3s build and have a DNM Aciore cartridge which I belive to be 5mV O/P. The other problem I have is with the Pre3 I do not have to turn the volume up very far on any I/P before the sound becomes to loud. The power amps are WAD 300B PSE. Any advice would be most welcome.
Thanks
Archie

[pre65]

Hi Archie-i'm still trying to find the hum on my Phono3s,but its not the same as you describe !

Try the shunt mod (see FAQ ) on your volume pot and that will help.




Philip

[FoxJT]

Hi ArchieH,

refering to your hi vol problem, check out this thread http://www.wduk.worldomain.net/forum...ead.php?t=3830 where we discussed matching the PRE3 to WAD amps.

I used the mod recommended to attenuate the PRE3 output into my amp and it works well.

Cheers,

Jeremy.

[John Caswell]

Hi Archie
Let us do one thing at a time.
I am pretty sure that the "mush" you describe is standard high gain valve shot noise so initailly do not worry about it. So...............
Does the Phono III Hum with the pickup leads removed from the inputs?
Do you have the cover bolted on and earthed as I said in another thread?

John - Dr John

[ArchieH]

Hi all
Just back from work, thanks for your replys. Dr john I think I will go with your suggestion of one thing at a time I will check the earthing to the cover and let you know.
thanks
Archie

[ArchieH]

Dr John
Checked my earthing and found cover was not earthed at all, also clips holding MC transformers were not earthed. Hum now on both phono 1 and phono 2 I/P and mute position no change if I disconnect the turntable also no change if I earth Phono3s to either Pre3 or Psu3. Have I done something to make things worse or am I on the right track with some way to go ?

Archie

[tomtidswell]

Dear ArchieH

I am having similar problems with the "mush" from the pre3 - this seems to be worst when turning on the amplifier, then reduces with time but still audible, however the gain is HUGE (i.e. 1 o'clock of the volume pot is loud), and it becomes relatively inaudible at lower voumes, but still greater than was present with my Quad44 into the Quad 405.

I rang Peter today at WD who recommends an attenuator at the phono leads to the power amp - they are being sent by post, so will let you know the results. I am also thinking of trying the shunt mod to the volume pot (if everyone gets this problem, should this be standard?).

As to the Phono3, I am also getting hum on Phono1, 2 and Mute - this seems to vary as to the position in the room of th Phono3, so I am hoping that correct positioning will reduce this (as will reduced gain from the pre3). I haven't tried earthing the cover to the Phono3 so will check this.

Still, despite this, once the music is on they both sound lovely.

Good luck to getting it sorted.

Tom

[tomtidswell]

Actually I have a question for Dr John (please),

When you mean to earth the cover - I have confirmed that the case (lower part) and transformer clips are earthed, but not the top cover - how do you earth the top cover? ( I can't find your reply in the thread, sorry).

TomTidswell

[Greg.]

Originally Posted by tomtidswell

Dear ArchieH
I rang Peter today at WD who recommends an attenuator at the phono leads to the power amp - they are being sent by post, so will let you know the results. I am also thinking of trying the shunt mod to the volume pot (if everyone gets this problem, should this be standard?).
Tom

The shunt mod has nothing to do with problem or fault solving. It is simply a better way of delivering the signal via a volume control. It actually surprises me that the commercial companies have not locked onto this as the cost is minimal and the effect is significant. Maybe they have another agenda

[Greg.]

Originally Posted by tomtidswell

Dear ArchieH
As to the Phono3, I am also getting hum on Phono1, 2 and Mute - this seems to vary as to the position in the room of th Phono3, so I am hoping that correct positioning will reduce this (as will reduced gain from the pre3). I haven't tried earthing the cover to the Phono3 so will check this.
Tom

I would expect the instructions to make it clear. At one point where the cover connects with the base chassis, being around a fixing point, to earth the cover, the paint on both mating surfaces needs to be scrapped away so there is metal to metal contact. Until you have done this, you will not be able to explore further if you have a hum problem.