Re: [Harp-L] 520DX as workbench element tester?

[G <gigs@xxxxxxxxxxxxxxx>]

Date: Thu, 13 Apr 2006 19:32:16 +0000
From: nonidesign@xxxxxxx
Subject: [Harp-L] 520DX as workbench element tester?
To: harp-l@xxxxxxxxxx

>I want to have a mic for workbench use only to test elements with. 
>Is there any reason I couldn't buy a Shure 520DX, remove the element,
>and outfit the lead wires with mini alligator clips for this
purpose?
>Should I remove the volume pot? Would that make any difference either
>way (because the 520DX's stock element is a dynamic)?
>
>Also, are there any sites that are "how to" places for guys like me
who
>know just enough to be dangerous when trying to learn how to work on
>/ modify their own harp mics?

Hi there,
  Rather than fork out good money for a brand new 520DX (an utter rip
off IMO), you can hunt around for 2nd hand bullet shells on eBay and
the like, or even get one from a harp mic tech
http://www.angelfire.com/music/harmonica/ampdmics.html#mictechs

  If you're wanting a bullet shell as a test bed for different
elements I suggest you get a JT30 shell instead. Check the link above
for sources.

There are a couple of reasons I suggest the JT30 shell over the GB as
a test bed:
* The grill is much easier to install with a tight fitting gasket than
the 520 - the grill screws are sturdier and in a better position, so
you're far less likely to mangle them with regular assembly/disassembly.
* You can purchase good tight fitting JT30 gaskets for both CM and
Crystal sized elements from Tim Dougherty
http://www.harpmicgaskets.com/
  The same isn't true for the GB.

I wish I'd been told of the importance of a decent bullet gasket
earlier.  If you have a good element, a poor fitting gasket can make
it really wimpy.

  With MC151 crystal elements, if the unit you plug it into doesn't have high 
enough resistance over the input (5MOhm), then you may end up with a weak 
harsh tone.  The only way to fix this is either use something in between
like a 
preamp that has the correct impedance over the input, or get your unit 
modified.   You can make up your own bullet mic impedance matching device - 
Mike Curtis has posted a description of how to build it.

In terms of wiring, it's usually perfectly safe, the only time you might be 
exposed to lethal levels is if the amplifier you're using isn't wired
safely - 
generally they're old models and lack proper grounding.  Plenty of threads in 
the harp-L archives about that.  When rewiring mics I always unplug them.

  Be sure to have wire in a good grounding to the shell (from cable &
element): you can use the spring that goes from the cable into the shell if
you have that setup; if it has a good pot, you can use it for ground;  in
some instances I drill a hole, tap it and install a screw a hole inside the
shell and connect the ground to that.
  If you run into hiccups, it's not a bad idea to take a volume pot out of
the equation.  All my mics have an on/off switch or are hard wired.

I think the biggest concern is not to cook or damage your elements. 
When you get an element, if it doesn't have wires soldered to the
contacts, do it immediately - don't overheat them, do a good job of it, and
from then on do any soldering and connectings to the wires, not the element's 
contacts.  Make sure they have enough extra length that there's no concern
about snipping them back from time to time, and tin the exposed ends.  
If you use alligator clips I recommend you make sure the signal lead
connection is well shielded.  - you don't want that shorting during 
a gig.   Heat shrink is relatively cheap, you could get a good length of it
and 
a cheap heat gun, or I guess, use insulation tape.

Take care and good luck,
-- G.