Re: More on mics

[HAAndruss@xxxxxxx (Harvey Andruss)]

>Can you put a ceramic element into a mic that originally had a crystal
>one?

Didn't see a recent reply, so in a word, yes, eg. Andy Just runs a Shure
bullet cartridge in an Astatic shell.  Swapping guts of harmonicas is not
really any more involved than tuning or gapping your harmonicas.  Go for
it.  You can always go back to the original.

Also, ~mike on mikes~ (sounds like a new column in Vintage Guitar, or maybe
that's Data Communications Week ;-), you mentioned a while back off-list
about embedding a small buffer amp inside the jt30 shell once to take care
of the impedance mismatch. How did it turn out?  If it's too small of an
area, it seems there's another application for the pickle plug here ;-) I
am thinking of a Popper-like device that hangs from the bottom of the mike,
female xlr to the astatic, one simple low noise non-inverting op amp, a few
(very few, like a couple each) resitors and capacitors, a 9v battery, and a
female 1/4" on the other end.  You could use the volume control in the mike
or make a new one there. It wouldn't need to be 3-5 megs anymore.  Tape it
to the mike cord output it in a small light box.  Keeping it near the mike
rather than at the amp cuts down on the cord problems.  You could also add
a cap to minimize rf pickup, which can be a big problem at the high
impedances of the xtal elements.  When I get time, I think I'll strap one
of these together and comment on-list.

There's a lot on this in a new book out by Craig Anderton (1995) that I
mention now only because it has a whole section on designing preamps.  It's
focused on guitars, but the application for miked harmonica is very
germane. It's also written at hobbyist level, so anyone non-technical can
follow it.   Rkt has a circuit on the amp home page that uses more stages
and accomplishes the same thing.  But since Rkt's a bullet man these days
even with proper matching, I'm also starting to wonder.........but he's
also turned MIDI, so who can tell ;-))))

Speaking of midi, I have not seen any more info on the ECH and I know that
there have been several requests on and off-list. I hope we did not scare
RLS off the list and that the packet of info is ready (BTW, I hope most
know not to take me too seriously, esp. the preposterous)


Regarding mojo-dusting and such feats of magic, accelerated aging
techniques such as cycling the xtal element in hot/humid, hot/dry,
cold/dry, cold/wet would probably get you there (close anyway).  Then
~characterization~ involves running an audio signal pure sine wave
generator at a family of certain frequencies, low-mid-high, and monitoring
the change in response on a scope.  The spec talked about was probably
derived this way.  Not rocket science, but labor intensive and probably
worth it as mentioned previously (maybe even a patentable process). I would
guess that the impedance would also go down with this process (?) thereby
making the results of aging a combination of effects, freq response getting
more mid-rangy and impedance going down (??)

However, there are many variables in the physical aging process, so trying
to accelerate it doesn't always work well (speaking from experience with
magnetic materials), hence the ~finder's fees~.



-- Harv <HAAndruss@xxxxxxx>