Phono3S hum

[soulminer]

Originally Posted by tomtidswell

how do you earth the top cover?

Simply scratch the paint off the the base plate around the screw hole nearest to the earth post and ensure that the paint is also removed around the corresponding screw hole on the top cover. For completeness you could also use a star washer between the top cover and base plate at the screw hole position you have just scratched the paint from.

HTH

Cheers

[John Caswell]

Hi all,
Sorry been at the Manchester show,
As HTH scrape says the paint away on both the inside of the top cover and around the hank bush on the chassis and I also recommend a star washer as well between cover and chassis.
The external hum pickup can and will vary depending where the Phono III is situated, mine is near a power cable buried in the wall and requires careful positioning for minimum hum pickup. Generally with all the covers on and earthed there should be no or very little hum at max volume.
I am investigating hum and other minor problems at present with the 3 items and will post on here when completed.
As far as levels are concerned ideally the vol control should be around 11o/c for normal to loud listening level so some attenuation maybe required or better still the shunt vol control mod. This will lose you 6dB or more if you adjust the series resistor accordingly.
eg a 47K series R with the 50K potr = -6dB ( a voltage drop of 2:1)
a 100k series R = -10dB ( a voltage drop of 3:1)
With Pre III this is a much better way of doing things as you still retain the very low output impedance which is a very good thing

John - Dr John

[tomtidswell]

Hi Greg,

Thank you for the reply - the instructions do not mention earthing the top cover - I will need to take it off and scratch some of the paintwork from the top cover with a corresponding patch on the base. Thanks for the advice.

Thanks

Tom

[tomtidswell]

And thanks to John as well (for some reason, your post hadn't displayed when I wrote my last one).

I will let you know the results.


Tom

[ArchieH]

Hi Tom
sorry to here you are also having problems. Further to my previous post the hum on phono 2 i/p is what i would consider normal mains hum but the hum on phono 1 and mute is slightly higher frequency. moving the phono3s or the pre3 around does not change the hum in any way.

Dr John any further thoughts on my problem ?

Archie

[ArchieH]

Dr John
Forgot to ask should the top cover on the Pre3 and Psu3 also be earthed.

Archie

[Greg.]

Archie,

Jumping in (no disrespect to John), yes, all chassis covers should be earthed using the described method.

Best wishes,

Greg

[John Caswell]

Yes I agree

John _ Dr John

[tomtidswell]

Phono Hum cured:

I earthed the chassis cover, and the hum from one of the channels has now nearly disappeared (i.e. not discernable with the volume up at loud levels, when it is audible, I would probably blow the speakers if any music was to be played).

I will do the following to the Pre3 and PSU3 covers to see if that improves matters - at the moment there is audible hum from the Pre3 if it sited too near to the PSU3.

The only other matter is some audible high frequency hiss from the phono3 - is this normal with valves? It is certainly noticeable at 3m away from the speakers when in between tracks on CD at moderate listening levels? Again, this does not interfere with listening to music - too busy enjoying re-hearing my record collection!. Peter has recommended input attenuators to my power amp (although other forum members council against this).

I will probably try the shunt mod, and earth the volume/control pots to the chassis to see if this improves.

Tomtidswell

[Greg.]

Tom,

Are you feeding your CD player into Phono 3 or straight into Pre 3?

Greg