Grounding question

[EdJ]

Hi,i am in the finishing stage of an Alembic Bass Preamp and i am using  one of Aron/Puretubes transformers for the High Voltage.
The thing now is that i am unable to find 220 to 12Volts AC adapters with an earth wire;the ones i can find only have 2 wires comming out of them so i am missing a ground connection for the chassis.
My question is are there adapters available  that have the 2 ac wires plus one earth wire and if not how do i get the chassis grounded?
Thanks very much in advance!
Ed

[aron]

hmmm... doesn't the chassis ground with the negative of the adaptor OR the grounds of the jacks? It can't be any different from the EH pedals right?

[EdJ]

Yes,that was what i thought too but since  i red it has to be powered from 12 Volts AC i have a problem.
I don`t know how it is done in the EH pedals but am kinda hoping Puretube drops in to help out on this.Unfortunately my problems are not over then too because i was given this Yamaha Power amp on which i hoped to hook the bass preamp to and the Yamaha has a 2 sprong(?)cord.
There is a screw on the back that says ground or Earth but why did Mr.Yamaha not use a grounded cord in the first place?
I am totally in the dark with this one too.
Ed

[aron]

>Yes,that was what i thought too but since i red it has to be powered from 12 Volts AC i have a problem.

What exactly is the problem that you are having with the tube circuit? Are you just wondering how the chassis will be grounded or?

As for the Yamaha, many older amps had 2 prongs and an earth screw.

[EdJ]

Well,there is no negative in AC is there?So do i take my ground point after i have rectfied it?
Glad you mentioned that of the Yamaha;i will put a new a 3 way cord on it.
Ed

[EdJ]

Hey, i think i answered my own question didn`t i?
Ed

[EdJ]

Ah,shoot!I still have the same problem because there is no connection between the ground point on the chassis and the mains ground.
Please help me out!
Ed

[aron]

From what I gather, you get AC in 12V.

Now you basically do 2 things:

Rectify/filter/regulate

and

Step up/Rectify/Filter.

So you get AC in, run that through a Bridge Rectifier, then filter,  then run that through a 12 volt regulator for the heaters.

The other side is 12 AC -> Transformer->Bridge Rectifier->filter = HV

On both, you ground to chassis after rectifying I believe.

How is this any different than say the Shaka Tube which uses 12AC as well?

I will ask Puretube.

Peter or Rob???

[niftydog]

There's no necessity to connect the chassis to earth. This is done for safety in mains powered equipment. But since you are feeding just 12VAC from a double insulated wall wart, you could get away without an earth connection. (EH pedals do!)

You should be able to find a wall wart with an earth connection, but I'm not saying it's going to be easy!

Now, as for GROUNDING (different to earthing)...

I'm assuming you've got a bipolar power supply? You have "created" an ground point by rectifying the AC voltage. Simply connect the chassis to that point. So yes, you have answered your own question!  

As for the whole two prong and earth screw thing... I have a vague recollection that it goes back to days when the mains sockets in the US didn't have an earth pin, they had an earth screw... but since I'm from the other side of the world I wouldn't know for sure!

[EdJ]

Thanks guys,i know what to do now.
Greetings,Ed