Shure Brothers 76B

[Moby]

I'm holding in my hands never-used 76B crystal mic. I can't believe that guy who gave me never used :wink: Here is data of, and i know it's for broadcast purposes, but i would like to know did somebody ever try to use something like this. I can't try before i found some pre with few Mohm impedance....
http://www.shure.com/pdf/discontinued/76b.pdf

 

[PRR]

Just use a Direct Box that has a very hi-Z input.

 

[NewYorkDave]

Get one of those "Hi-Z to Low-Z" inline mic transformers and you can use your crystal mic with any low-Z mic preamp with lots of gain.

Here's an example of an inline transformer:
http://www.shure.com/accessories/a95u.asp

You can also look for a UTC O-11 "Ouncer" mic transformer. The O-11 is specifically intended for use between a crystal mic and a low-Z line.

The important thing is to keep the connection between the mic and the transformer as short as possible.

I can't tell how good the mic is going to sound from looking at the spec-sheet, but I certainly wouldn't expect hi-fi response from it. It might be OK for voice. Since it's intended to be worn on a lapel and has an accentuated high-end response to compensate, it will probably sound overly-bright if you use it in a direct-address situation.

 

[Moby]

Thanks, i will let you know my impressions :wink: I like DI idea, wow how stupid i am

 

[PRR]

> Get one of those "Hi-Z to Low-Z" inline mic transformers

No, that will suck-out the bass, which is maybe the only good thing about a crystal (infinite bass response). Impedance needs to be better than 1,500pFd at the lowest frequency of interest, which means Megs of resistance or Thousands of Henries of inductance. There are no Thousands-Henries coils.

These transformers are more like 50K at 30Hz. Bass response fall-off will be in the 200Hz area.

Open-grid with a 4.7Meg resistor is ideal. An FET will be fine. Some DIrect Boxes claim 1Meg or higher input.

> keep the connection between the mic and the transformer as short as possible.

Won't hurt the treble. Drops the overall level (and actually helps with bass-loading). And if I am reading the antique specs correctly, it has plenty of output for home-studio length cables.

 

[NewYorkDave]

[quote author="PRR"]> Open-grid with a 4.7Meg resistor is ideal. [/quote]


Or a grid-leak biased stage with, say, a 10M resistor. Matter of fact, I think that's exactly what was used with crystal mics most of the time back in the day...

 

[Moby]

Thanks guys, im thinking about...first DI, then some tube elecronics is on the way. I will report when i do some test :wink: :guinness: