[Harp-L] JAYPHAT multi-amp demo clip



Continuing my torrent of posts explaining a series of sound files I
posted:

The JAYPHATMulti-Amp sound file at http://groups.google.com/group/harp-l/files/
covers issues encountered when running a single hi-Z microphone into
multiple amps at once.  When you run a mic with a volume pot into an
amp, the mic element is already seeing  two parallel input impedances--
the pot and whatever the grid loading on the amp input is--and the
resulting overall impedance is going to be a fraction of whichever the
smaller impedance is.  As you have heard for yourself if you’ve
followed this cycle of files, inadequate input impedance can cost you
useful lows with vintage crystal mic designs and useful highs with
vintage CM/CR/dynamics, or freqs/detail across the range, as well as
overall output.

When you add the input impedance of a second or even third amp to your
signal chain, the overall input impedance drops even lower.  The
impact of that on your tone/volume may be compensated for somewhat by
having two or three amps pushing your sound out there, and the result
may sound fine to you--unless you hear how it sounds with the
impedance properly matched.

For this clip, I used three small amps: a 1949 Silvertone 1301 (5C1
Champ clone) with 5Meg of input impedance, 5V4 rectifier; a Crate
VC508 with 1 Meg of input impedance, the master volume mod somebody
posted on a guitar site, and a Weber ceramic Sig 8 w/ H dustcap; and a
Harmony H410A with 0.1 mfd coupling caps and  stock 400K input
impedance on its Mic input.   One 6”, one 8”, one 10”, barely 15w of
raw power at work here.  It would be louder if I’d put SS rectifiers
in the two vintage amps, but it was plenty loud to be in the room
with.  Yes, I have too many amps.  This clip is a feeble attempt to
justify owning some of them.

I ran the amps in pairs and as a trio, without and with the Jayphat
box, using mainly the 5Meg MC-151 heard on the other clips.  Pairing
the amps with the biggest input impedance differential has the biggest
impact on tone/volume.  Sorry for not having the time/patience to use
more mics,  but by this point you should have an idea how impedance
matching helps different types of mic elements.  I also did not really
think to demonstrate how to use the JAYPHAT box’s level boost to drive
multiple amps a little harder.

I tried to explain what I’m doing in the voice-over: usually I ran the
setup without matching first, then added the JAYPHAT.  I moved
segments around in the editing because I made the mistake of doing all
the pairs & trio unmatched first, then adding the box, but you will
hear the trio and each pair unmatched first, then matched.

I want to emphasize very strongly that any tone/volume loss you hear
is created by the multiple parallel impedances the mic element is
seeing plus the lengths of cord involved, ~not the switching devices
themselves~.  I did most of the segment on the excellent 3-way
switching box made by Fat Dog Amps; then I did a twin-amp demo with an
old Rapco A/B footswitch to demonstrate that switches sound pretty
much alike, it’s the overall impedance that matters.  I also did the
simplest multi-amp method, which is to chain two amps in parallel by
running the mic into one amp and running a patch cord out of its
second input and into the input of the second amp.   People sometimes
mistakenly call that running amps in series, but it’s really parallel.

I used a good vintage 10’ mic cord up front; I only had two mediocre
10’ cords to use after the switches, so I used a 6’ cord into the
VC508 and the 10s into the other two amps.  Think of it as roughly 20’
into any one amp.  I start the clip by playing the 10’ mic cord into
the VC508, then adding another 10’ cord so you can hear the difference
that makes, and finally putting the JAYPHAT box in the line too.  The
JAYPHAT can’t compensate for all the loss due to capacitance with
cords, but it does help.

Think that’s about it on this one.  One thing you could do if you
built a JAYPHAT box with parallel outputs is split amps out to the
sides of the stage and run your master volume from the JAYPHAT
wherever you are onstage.

You think you guys are tired of all these clips, you should talk to my
cats :-).




This archive was generated by a fusion of Pipermail 0.09 (Mailman edition) and MHonArc 2.6.8.