Phono3S it's humming again.

[bikerhifinut]

thanks nigel i will bear it in mind.
Good to see you guys there too.
Sorry i didnt talk much more with you, I was whizzing round with my friend Terry and somehow the day just flew by.
had a good natter with Peter C at the Quad IAG room, some very nice sound from those big ESls!

andy.

[bob orbell]

Hey, nice one Nigel, and it has the two relays, plus diodes Andy .

[bikerhifinut]

Thanks Bob.
I am going to meter the connections through.
There's a "rabbit away" as we say up here.
I am suspecting that the Grado and also old Goldring cartridge I am using are picking up hum from somewhere.
If there was a fundamental issue with the stage it would surely hum whether there was an input or not?
And Phono3S has oodles of gain also which I reckon aint going to help.

Watch this space, its too effin cold to go rummaging in the garage tonight for stuff (It's hit minus5 already and theres 6 inches of snow and its started again!)

That'll teach me to buy a house on the side of a mountain!

I will suss it out yet.

A.

[bob orbell]

Yes, the cold wind from the east is a real bummer, last night our garden went down to -9, the wood burner has been burning almost continually for three weeks, so we are both warm, but the little birds out there are feeding from first light to just after dusk, they look ****ed off too. BOB

[John Caswell]

Andy, with all inputs removed does it still hum? If so try putting phono plugs with 100R soldered across them on input sockets to see if it still hums. If so, you need to look at the phono stage, if not it is hum pickup in the cartridge/leads/arm.

John

[bikerhifinut]

Originally Posted by John Caswell

Andy, with all inputs removed does it still hum? If so try putting phono plugs with 100R soldered across them on input sockets to see if it still hums. If so, you need to look at the phono stage, if not it is hum pickup in the cartridge/leads/arm.

John

Problem Solved John, as you pointed out there was no appreciable hum with the inputs disconnected and on mute (inputs shorted at the relays?) it was silent apart from a bit of valve noise.
I had the blessed thing apart this afternoon and everything metered fine, I reckon it did no harm as it had a good clean out in the process.
So back in the system. On the solid state commercial pre the hum was much reduced, this is a very quiet bit of kit and any extraneous noise shows up clearly. I moved the Phono vertically up whilst connected and when level with the TT the hum reduced to a very low level but still faintly in the background.
So I thought it has to be something like an unsheilded mains transformer transmitting a hum field.
I reconnected the homebrew valve pre amp (Pre3 casework with an Aikido ACF cathode follower buffer stage and Hi fi collective remote volume controller) and the hum was loud again. Moving the phono stage had much less effect this time.
Whatever it was had to be pretty close to the phono stage to do this.

Then the lightbulb moment occured. Theres a tiny plastic case with the Michell Gyro DC PSU in it and because the umbilical wire to the motor is a bit on the short side it sits behind the FM tuner on the second shelf of the equipment stand. It had somehow been disturbed and moved sideways no more than about 3 inches but that was all it needed, the hum field from the tiny transformer in it was enough to send the phono 3 into orbit, I suspect from the hanging loop of arm cable that dangles from the TT shelf and back up to the phono stage.

I had not thought to check that as I haven't moved the TT PSU during any other system alterations but somehow its been disturbed and that very small sideways and forwards shift was enough to couple its hum field into the arm leads.

I now have a silent phono stage again, all I get is valve hiss now.
And a practical eddication in how EM fields can propagate.

I am considering the practicalities of moving the Michell PSU into a metal diecast box to screen the innards. And of course when the snow melts and I get off the drive again, maplins in carlisle will be gone and they had a good selection of diecast boxes in store.

Thanks for all the offers of assistance and suggestions gents, it was a big help to me as I didnt fancy surgery to the relay board, it looks a right pig to remove.
When I redo the transformer pre in the big case i think I'll omit the WD relay board and make my own relay board up with very short pigtail leads from the RCA sockets on the back panel.

Andy

[bob orbell]

Well that's good news Andy, glad you are sorted, now then, what can you do about this **** weather? hmmm, . BOB

[bikerhifinut]

Originally Posted by bob orbell

Well that's good news Andy, glad you are sorted, now then, what can you do about this **** weather? hmmm, . BOB

I reckon its a question of just waiting it out Bob. The equinox will be with us soon and I hope we get a proper spring and summer this year instead of a washout.
We have short memories, certainly in my living memory we've had late winter nasties as late as Easter. 2 years ago at may bank holiday weekend we had a hard snowfall on the friday which caused a bit of mayhem on the road up teesdale and down to Alston. I know because i had to drive over it on my way to a motorbike weekend. I left the Triumph at home and took the car! Was still in North Yorkshire then.

A.

[John Caswell]

Hi Andy,
Placing a die cast case around the Gyro PSU will not help as it is an electromagnetic field the is causing the problem. Only mumetal or distance will help and that is a seriously expensive exercise.
Why not do as I did (cos I am lazy and cannot be bothered to change over the belt) and build yourself a new PSU with a toroidal transformer and switched voltages to change speeds, assuming that you have the DC motor, as opposed to the DC Papst motor. It is not very difficult using a standard 3 pin regulator. Of course if ll you play is 33 rpm is is even easier.

John

[Richard]

Well done Andy. Almost exactly the same thing caught me out too. My Thorens is a later one with (18V?) mains transformer and I had the TX sitting on the floor right under the WD3 set up. Moving it a foot away fixed things