DIY Ribbon Mic- Where's the bug?

[Haybee]

Hello everyone,

I recently started building my own ribbon mics and I'm at a point where I think I did everything right. Still I can't get any sound from my mics.
I thought I'd ask for a little help because I've tried everything in my power here.

(Check out the pic below)

Few informations:
The ribbon is aluminium foil (2.5 microns).
Continuity test between magnets and the ribbon/ clamps is negative.
Resistance between each clamp is about 1 ohm.
Ribbon has been corrugated with gears, like anyone does it.
The base of the motor is plexiglas, and wooden parts will hold the whole motor in its casing.
The transformer is RMX1 from Edcor, and is plugged to the XLR connector in such way: 1-Black, 2-Green, 3- Yellow.
I also tried soldering a bridge between the black lead and the XLR connector itself.
I tried switching with another transformer but it didn't solve the problem.
The magnets are magnetized through thickness and I checked that North and South are oriented in the same way for both magnets.

Any suggestion?

Thanks a lot,
Haybee

 

[shabtek]

is ribbon free to vibrate in gap?

are you plugging in to working preamp?

there should be hum with no screened enclosure, if not...

there is continuity across ribbon, is there continuity across coils of xfmr?--you will have to open 1 conection of primary to measure.
while you are at it check its right-way-round; lower Ω side is primary

i am gonna guess it is something simple--or a bad connection

black is the screen/foil iirc, that will attach to pin1/housing.

i am not clear on your description of magnetic lines but you should be getting something with enough gain--at least some hum

keep going, that is a nice DIY project!

 

[Marik]

Resistance between each clamp is about 1 ohm.

Is it with transformer connected, or disconnected?

 

[Spencerleehorton]

Looks like your ribbon is touching the magnet on the right?
Pre stretch the ribbon a little before install, and try and get the ribbon straighter when you corrugated it.
One if your wheels may be pulling it to one side.
Also try and match your magnets a bit better, they are lop sided.
When testing it put through a nice mic pre with lots of gain.
Shows some pictures of how you have wired to XLR as you may have made a mistake if your not getting any sound.

Regards

Spence.

 

[Haybee]

Hi thanks for all your replies.

I checked everything you asked and the thing is I had already soldered my transformer so the 1 ohm measure between the clamps wasn't right in the end!
A dumb mistake...
I glued a small piece of metal on the plexiglas for the bottom of the clamp and I could really read 1 ohm between the clamps, without the transformer.
My contact in the clamp was just not good enough so the loss was too high.

Thanks for all your replies, once I put everything working in the enclosure I will put in a few pictures