Multipattern microphone selection

Hi !

I'm asking a question.

In typical Multipattern Tube microphone. (C12, G7)

the directivity is selected via a voltage divider
connected to the back electrode of the capsule.

Generally when in cardioid mode, C12 or G7 apply
the same (60v) voltage at the back electrode than at the backplate
in order to mute the Rear.

Why not simply leave the Rear electrode "in air". to obtain Cardioid figure,
and use the voltage divider only for the others figure, Omni, 8 and intermediate.

:roll:

the mics ive seen have 60 and 45 +- and the pattern is turning the front and back from equal omni ;back off= card; to back 45 super; back - for 8

OK,

but on the C12 and G7 :
Cardioid = Backplate 60v, Rear 60v.

So it's a good idea to "off" the rear for cardioid.

It has been done that way look at a u67 schematic.

Yes, that's right.

And if i do it this way :
http://img.photobucket.com/albums/v439/jazzy_pi/pattern.jpg

is there a problem with the components connected
to the rear electrode "in air" ?

in the U67, the switch is directly on the capsule
but i can't do it easily and don't want to add a hole on the mic body.

..you need the switch very, very close to the capsule. And you need very very high insulation resistance...

Ok, so it's not good to do it on the PSU.

if i do it like on the schematic
the results is :

1- nothing
2- a bit better than apply 60v
3- worse than apply 60v

?

Sorry to ressurect this old thread but I was hoping you could shed some more light on this comment Gyraf!I am about to install a replacement dual capsule CK67 into my existing A5500 tube mic which has a single in it, (and at the moment also has no pattern switch). I was going to install a small switch to let me switch between Omni and Cardioid buy simply puting the rear capsule in the circuit with the front one - and back out of circuit again (like U47 schematic).

What sort of switch provides "very very high insulation" ???

..you need the switch very, very close to the capsule. And you need very very high insulation resistance.../quote]  

Click to expand...

Easiest is probably a relay designed for low capacitance high impedance switching? Or look at the Neumann head assembleys for an idea of how to make this "mechanically".

Jakob E.

Nice idea, I'd very mush like to mod my A5500 this way too ;-) 

Where do you get the CK67 capsule?

What about Tim Campbell's C12 capsule? http://www.timcampbell.dk/index2b.htm

Guess many China mic owners would like this mod realized....  Have you replaced the transformer? or any other guts?

maby we could start a new thread to keep these "china mic mods"