Latest Franken-phone!

[zebra50]

Grizz Royer called one of my mics a 'frankenphone'. :razz: :shock:
Thought that was quite funny.

Anyway, my latest experiment is a twin-capsule cathode follower mic. MXL body, dual capsule curtesy of soundking (Thank you Ward). The design is based on Royer's small dipahragm design, with a 5840 tube, 4u7 poly output cap, and the biggest old Sowter (a 1:1) that I could squeeze in there. Sounds absolutely lovely through my G9. The output level is not that high, but the noise level is low enough to turn up the gain for quiet sources & it can take high signal levels. Tube heater is at 5.8V.

The construction is based around some thick copper wire out of some high current mains cable which I've bent & soldered to make the frame. Everything else kind of hangs off the frame.

Some pictures & schematic....

just thought I'd share
:thumb:

 

[zebra50]

I'm using it out of habit now. I have a few around, but also (as Dave Royer points out in his articles), it gives satisfactory polarisation of the capsule via grid leakage, as well as biasing itself by a similar process. I don't know if other tubes behave as well. And it's small enough to fit in small mics.
z50

 

[zebra50]

...I should add that the switch is there to swap between omni and cardioid modes. It works fine.

 

[Gus]

Very cool! I like how it is built.

 

[zebra50]

Thanks gus.
I think it is a bit of a mess, but everything is in the air so should hopefully be well behaved.

 

[neilium]

Zebra50,

That's great. I like the flying lead construction. Is there any way to make it figure 8. (I never understood how that works.)

 

[zebra50]

It's possible but things start to get a little more complex and we can't do it simply with the arrangement shown. For fig 8 we would need double the backplate voltage on the rear membrane. Our backplate is polarised to about 50V so we need about 100V. We could take this from B+ via a 1 gig resistor, but would have to add a cap to ground to complete the circuit.
Have a look at the Gyraf G7 mic and how he does the polaisation there. It is very neatly done.

 

[Bauman]

Now this is a minimalist design!

Great stuff!!

 

[zebra50]

[quote author="Bauman"]Now this is a minimalist design!

Great stuff!![/quote]

Yup, but I can't take any credit. It's Dave Royer's 'country boy' mic all the way .
Stewart :guinness: :sam:

 

[okgb]

pentode triode switch , anyone see a good use for this ?

regards Greg

 

[JustinS]

Hey Zebra,

Also is the 1:1 a 600:600?? Or is it a 10k:10k??

Justin.

 

[CroatianSensation]

Last night I wired up my own Franken-phone MXL 2001. I threw in a dual capsule and followed Zebra's plan. It works but only for a short period then fades out....weird. When I switch to cardiod I get some hum..in omni it's dead quiet. It's driving me nuts. :evil: Any suggestions?

 

[outoftune]

[quote author="JustinS"]Hey Zebra,

Also is the 1:1 a 600:600?? Or is it a 10k:10k??

Justin.[/quote]
old thread but just wondering if anyone can answer this question?

 

[skipwave]

Answer here:

http://groupdiy.com/index.php?topic=19546


Also, Zebra added a note below the schematic on his page:

"NOTE: Transformer should be between 2:1 and 4:1 ratio."

http://www.omnipressor.com/Other/Frankenmic.html

I used a 4:1 turns ratio, 10k:600 impedance ratio.

 

[outoftune]

thanks skipwave!