Harp Mic Workbench by Fritz Hasenpusch

Microphone Choices
NITS and CHIGGERS—THE NASTY DETAILS INSIDE:
SWAPPING OUT FOR CRYSTAL, PART 1
“At The Harmonica Microphone Bench” with Fritz
Hasenpusch, Mel Bay’s HarmonicaSessions® eZine,
Edited by David Barrett
March 2012
I've got to admit that the squad of post-holiday helper elves still on duty down here in the
MICROPHONE DUNGEON were more than a little concerned with the working title of this
installment of THE MIC BENCH. They've requested that I state for the record: This is about
harpmics that utilize piezo-electric/Rochelle salt elements—or that we’ll be using these high
impedance devises. They've also asked me to request that the DEA please stand-down at this
time. Thank you…
During our last visit we looked at the aspects of compatibility between components when
installing a CONTROLLED-MAGNETIC or CONTROLLED-RELUCTANCE element into your
harpmic. On this visit we'll run down the checklist of requirements and methods when installing
the other perennial heavy hitter in the Harp Kingdom, the CRYSTAL element. Take a look at
the image below…
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Examples of full-sized CRYSTAL elements you may encounter include—from left to right with
top and bottom views: BRUSH DEVELOPMENT; Early ASTATIC '30' as found in the Model
'30' "Biscuit"; SHURE pre-R7 as found in "Brown Bullet" models; SHURE R7 as found in 707
models.
The first point on the checklist: Do you really need a CRYSTAL element in your arsenal of
Harpmics? Will a CRYSTAL element provide you with an indispensable sonic tool otherwise
unattainable? Are you willing to deal with their temperamental and fragile nature?...
The CRYSTAL ELEMENT GRAVEYARD... Many pro Tin Sandwich jockeys will answer in a
flash with a thunderous 'YES!'. There are many Harpsters who choose to use nothing else.
Onward…
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Let's concentrate on what has been by far the most widely used CRYSTAL element in recent
Harpdom history: The full-sized ASTATIC elements, most notably the units designated 101
thru 151…
In terms of physical dimensions, these elements—measuring 1.95" or 1 15/16" in diameter—
will fit in any and all of the familiar "bullet" mics from both ASTATIC and SHURE. As they were
stock factory equipment in all the ASTATIC mics fitting the "bullet" description this is no
surprise. However, they WILL NOT fit many of the popular ASTATIC "canister" mics by virtue
of their diameter (The '10' and some of the DN models). Any of the SHURE "bullet" mics—from
the 7A thru the 520 "Green Bullet" models—would be candidates for the swap. In addition,
TURNER base station mics present another hosting possibility for the full-sized ASTATIC
CRYSTAL elements. The TURNER '200' and '400' series mics have enough interior diameter
to make a swap possible, and have made TURNER "chops" (the mic head separated from the
base's neck) more common. Be aware that tight tolerances may make proper gasketing for
these a problem. We'll deal with that, too.
Whatever your choice for the mic body that will serve as the CRYSTAL element's delivery
vehicle, very specific precautions need to be observed when installing these tender beasts. If
you don't want your CRYSTAL to become a statistic, please take note…
THE INDISPENSABLE HEATSINK: Generally speaking, extreme temperatures are the enemy
of most audio electronic components. With CRYSTAL ELEMENTS they mean certain death.
Too often these fragile flowers are dead before ever seeing duty to the Tin Sandwich simply
because of exposure to excessive or prolonged heat while being soldered into the wiring of an
intended harpmic. Enter the HEATSINK. A HEATSINK is any material or method utilized to
wick-off heat from a subject item. In our case, it's the heat applied to the wiring terminals or
'lugs' of our subject, the CRYSTAL element.
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Our image below shows a spring-actuated heat sink made of aluminum from Radio Shack…
Placed between the heat source (soldering iron) and the base of the subject terminal, it will
help regulate/minimize the amount of heat entering the element's capsule and possibly doing
irreversible damage to the Rochelle Salt CRYSTAL within. I've found this design to be
effective, but clumsy to handle due to its thin/flat configuration.
Something more ergonomic and manageable would be an advantage at the MIC BENCH…
CAN YOU SAY "HEMOSTAT"?
Hemostats—or hemostatic clamps—are small needle-nose plier-like mechanical devises
commonly used to stem blood flow ("Hemo" from the Greek for blood) during medical
procedures. Their scissor-like action and looped handles utilize interlocking teeth to hold their
forward plier components in a fixed position at a level of pressure determined by the pressure
applied to the handles. They can be purchased new through crafts and technical supply sites
or found through medical surplus sources (my fave).
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Here’s an example of the smaller, finer versions…
Here’s an example of the larger, modified versions…
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Beyond medical applications, Hemostats can be used to remove fish hooks, manage and
handle tiny mechanical components, and—Hallelujah!—as very workable heatsinks. It's a fact
that the stainless steel they’re constructed of isn't as efficient at conducting heat and therefore
not as effective at wicking-off the soldering-generated simmer as aluminum. Still, I've never
lost a patient due to "heat stroke" when using them. Just be aware that they aren't a
guarantee, they're a precaution.
CUSTOM-FITTED HEMOSTATS: They're not just for vampires anymore! Some CRYSTAL
elements have soldering lugs that are very short and as a result have eyelets that are
extremely close to the element's body. The ASTATIC MC-151 is a prime example of this…
Modifying the gripping jaws of the Hemostat on a sharpening stone or bench grinder to fit the
limited margins available is the answer, producing a multi-use custom tool that can be utilized
over and over again.
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An especially versatile model is the customized CURVED Hemostat…
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HEMOSTATS IN PLACE, YOU'RE READY TO SOLDER: Just remember that the Hemostat is
there as a barrier to impede damaging heat from entering the CRYSTAL element via the base
of the soldering lug. MAKE CERTAIN you’re positioning the Hemostat between the base of the
soldering lug and the terminal you will be soldering, applying your soldering pencil's tip to the
wiring eyelet positioned ABOVE the Hemostat ONLY!...
We'll be showing ELEMENT INSTALLATION, GASKETING and wiring procedures in detail,
with pix to illustrate key points as we continue SWAPPING OUT FOR CRYSTAL, PART 2!
THE NEXT TIME WE VISIT…
THE MIC BENCH
For pictures and descriptions of most of the microphones listed visit
http://www.harmonicamasterclass.com/vintage_collection.htm
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