[Harp-L] SuproSupremeFinal clip and JAYPHAT box intro re-send for digest



It looks to me as though the digest originally barfed this post this
morning, as occasionally happens, so I am resending a version to fill
in the digest gap so that a series of posts makes more sense:

An amp demo clip I put up on the Harp-L parking lot at
http://google.com.groups/group/harp-l/files/ grew into a series of
clips demonstrating some microphone impedance matching issues.  For
those of you whose eyes glaze over at the mention of amplified gear,
the clear finding on these clips is that proper impedance matching for
your microphone can greatly accentuate your hand effects as you play,
amplifying not only your volume level but the expressive aspects of
your playing as well, making the whole rig more an extension of your
instrument.

These clips involve an outboard impedance matching box designed/built
by my friend Greg Schlacter ca. 2001.  What it does is buffer a high-
impedance mic from everything downstream of it, and provide a steady
4.4 Megohms of impedance loading for the mic element, minimizing loss
of signal to ground and maximizing the mic’s tone.  More on the box
later.

SuproSupremeFinal is my brother’s 1947 Supro Supreme amp I was
overhauling for sale, temporarily modified for harp with 0.1mfd
coupling caps to fatten tone and no bypass cap on the input stage (to
reduce preamp gain).  The first filter cap is 47 mfd.  This amp model
has push-pull 6V6GTs with 6SC7 inverter and 6J7 input tube, plus a 10”
field coil speaker; very common postwar amp sold as Supro, National,
Valco, Oahu, McKinney, I think Bronson, and more; the earliest ones
have no tone knob.  It is basically a 6V6 version of the National amp
that influenced Gerald Weber’s Kendrick harp amp design.  1947Supro at
the files page is a photo of this amp.  A design quirk is that it has
a very low input impedance of 100K; that dumps a lot of mic signal off
to ground, really doesn’t let older hi-Z mic designs do their best
work.

You will hear this to a comical degree when I switch to the MC-151
crystal mic w/ 5Meg volume pot, as both the lows and the overall level
disappear.  Using the outboard impedance box changes that
dramatically.  Using a controlled magnetic (CM) element straight in
sounds pretty good, but listen carefully to what happens on the 4D
when I add the impedance box: the sound with my hands open expands
dramatically.  The impedance box doesn’t induce serious feedback
problems with either mic--I was standing closer to the amp than I
would on a stage--but it really emphasizes what I’m doing with my
hands as I play.

I tried to play repetitive bits with tonal exaggeration on these clips
to emphasize the A/B differences.  Sorry if it gets boring.  Youtube
addicts are encouraged to print out the photo file of the Supro amp
and stare at the photo while listening, which is not much different
than watching some Youtube amp clips :-).

Stephen Schneider




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