O-12 Transformer with BlueFace Clone

Hi everyone, I decided to use a real O-12 transformer for my hairball blueface 1176 kit. I have no problem with the wiring hookup - see attached schematic - but the question I have is about the screen.

The original hairball kit has an alternate transformer with a screening can and ground connection. The O-12 transformer I have does not appear to have a screen. I do have a shielding can to place around it, but no connection to the chassis/internal transformer screen as there does not appear to even be one.

For anyone who has modified their Blueface 1176, any suggestions as to how to implement the original O-12 into the kit? I have the old kit from years ago just getting around to it.

Or anyone else maybe knows a suggestion?

Thanks,

Mike

PS Mods if this belongs in "The Lab" feel free to move; just seemed more logical here since it is an 1176. Thx.

Here's a schematic of the O-12 itself. I see double lines between the sets of pins, but does that mean there's an internal shield/screen? If so, how to access it?

Thx

Double line is the core.  If the transformer is not mounted to the chassis, just connect a wire from one of the mounting screws to ground. 

Was thinking about that Mike; good idea. From the schematic then the original O-12 is not shielded, correct? So best I can do is what you suggested?

Thanks,

Mike

It is shielded. The can acts as a shield. You need to connect it to chassis ground somehow.

I’m not sure if the aluminum case provides much shielding - it’s not mentioned in the spec sheet that it does...

Tho I agree that it should be referenced to 0V...

The Ouncers line uses the O-17 slip on shield for 25db of shielding - attached is a photo of a tube DI/Mic Pre I made, I used an O-8 for the input TX and an O-17 for shielding. You’ll see a soldier tab running from the top of the O-8, attatced with one of the 2-56 mounting screws, running to another lug on one of the output transformer mounting screws - this references the Ouncers case to chassis..

I have one of those Hairball 1176’s as well - and a few extra O-12’s - let us know how it goes when you get it up and running.

Thanks,
Timothy

Yes, the O-17 is great for mic input transformers like the O-1 and O-2.  However I think it is unnecessary for line level transformers like the O-12.

Thanks Mike , Timothy, and Ilya.

I'ts probably overkill but I did as suggested. I used the chassis itself to connect the two screws and ground both the can and the O-17 shield. I removed the paint off the top of the O-17 can and it is also touching the chassis, with removed paint metal to metal. I'm getting good grounding between both the O-12 and the chassis, and the O-17 and the chassis.

That sucker is GROUNDED lol!

I'll try to post a pic later.

Thx guys; very helpful!!

Mike