The AM Forum

Pictures of my newly-completed home made ribbon microphone are here:

http://mysite.verizon.net/sdp2/id16.html

It works!

Best regards
Stu

I heard you on around 10AM this morning talking with a 1 that I could barely hear.

Has anyone made a recording of your microphone, or have you gotten a sense of what it sounds like ?

Bear

My first try works... but sounds awful because of a high noise level. The frequency response appears to be ok. With a pop filter in front of it, I can get rid of loud crackles and pops. As has been pointed out by several consultants (who provided their advice during QSO's) I can get 20-30 dB of (noise-free)boost, before the first amplifier, by using a step-up transformer with a 10:1 - 30:1 turns ratio. That will help a good deal, but perhaps not enough. I may also need to fabricate some kind of magnetic shield around the microphone. At least it does not appear to be picking up RF (it sounds no worse when I transmit, and listen to it on my off-air monitor v. just listing to it directly).

Best regards
Stu

That's SO cool.
Well I presume that's what you were running when I heard you yesterday.

I'm off this week, and getting some house chores done -- plumber's here for the water conditioning system right now, but when that's done I'll stroll out and see if you're on the air and maybe catch a recording of you while conditions are good.

Stu,

While ur still experimenting with it, try slapping on some pole pieces that will run the length of the ribbon. Soft steel or better still iron will work well. It will likely increase ur output by a substantial amount.

       _-_-WBear2GCR

Cool! Do you have any idea of the output impedence? Maybe you could build in a rising peak around 2500 cycles and mount it on a G-stand? Just kidding... I think it's great. We need more tinkering and experimentation in the hobby. Well Done!

Hi Stu,

I've heard it on a few times !!! Except for the hum, it's not too bad, really.

Nice piece of work, to be sure !!

Regards,

Steve

Thanks for the nice comments guys!

The output impedance is very low (~ 1 ohm, or perhaps less)... not to be confused with the dc resistance of the aluminum ribbon.

I've ordered a miniature 1:22 audio step up transformer (nominally: 4 ohms primary and 2000 ohms secondary); which should give me about 27 dB of noise-free gain v. no transformer... but which may not help with respect to hum pick-up. Right now, it actually sounds pretty darn good... except for the hum. I'm using a miniature 1:2 audio step up transformer (half of the 600 ohm primary, and all of the 600 ohm secondary) until the new transformer arrives.

I've updated my web page http://mysite.verizon.net/sdp2/id16.html to show the latest improvements.

Cool! A Magneplanar in reverse

Not a Magnaplanar in reverse.

This is a true ribbon, the Maggies are foil or other conductive material on a substrate of polyester plastic film, usually with more than one turn inside the magnetic field (increases the impedance so direct drive is possible).

The true ribbon is (usually) a thin thin aluminium alloy foil, suspended in a magnetic field. Examples of these in speakers include the Decca/Kelly Ribbon Tweeters, and the Mids and Tweets on some of the Apogee speakers... very low Z... hard to drive with mere mortal amps (the Deccas have matching xfmrs).

         _-_-WBear2GCR