From: META000 <META@UNB.CA>
Subject: analog flanger mods
Organization: The University of New Brunswick
Date: Thu, 12 Nov 1992 23:21:06 GMT

Several people had e-mailed me to ask for the flanger mods I had
hinted at in an earlier epistle.  Here they are.

Most analog delay devices (this includes delay lines a la DM-3, as
well as chorusses, and flangers) have two insertion points where a
few simple component changes, coupledwith a toggle switch or two can
yield a whole new palette of sounds.

The principle is simple.  Recirculation (aka regeneration or
resonance or repeat), and mixing (aka depth, intensity, etc.)
controls simply introduce different proportions of the delayed
signal back into the delay loop (with recirculation) or into the mix
(with the intensity or depth control).  One needn't be restricted to
simply AMOUNT of delay signal.  By use of different filtering
capacitors, one can also adjust WHAT gets recirculated or mixed.

For instance, ifyou trace the input to the recirculation control
(i.e., the one at left, looking from the back, with the lugs at 7to
5 o'clock) it should lead back to a capacitor anywhere from 0.1uf to
10uf in value.If you replace that cap with one half that value, the
lower frequency cutoff will be raised by one octave; if you replace
with a cap 1/4 the original value, the low end rolloff goes up two
octaves, and so on.  Do this and there will be disproportionately
more high end recirculating, which should lead to a sharper flanging
or chorus sound, and to a kind of "dub" echo sound for delay
lineswhere each iteration gets thinner and thinner.  If you perform
a similar replacement on the mix/intensity depth control, what you
get is that the bassier side of the flanged/chorussed/delayed signal
is less prominent in the mix.  Incidentally, I did this to the
reverb control on an old Gibson amp I used to have, and the reverb
went from annoying and boingy to bright and airy.  I recommend it.

Ideally, one would be wise to replace the original blocking
capacitor with one 1/10 the original value, andthen, using a 3-way
mini-toggle, switch in other capacitors inparallel to get something
around 1/4, and something roughly equal to the original value.
Depending on the space available, this may be hard to do, but need
notbe impossible in your basic floor box, as long as you're willing
to be creativeabout where the switch gets mounted.

A second, almost inverse, mod involves filtering outnot the LOW end
of the recirculated or delayed signal, but filtering out the HIGH
end.  There are two ways.  One involves soldering a capacitor (about
1000 - 2200pf should usually be enough) between the input to the
control(the leftmost lug again) and ground (usually the chassis of
the control).  The second involves connecting the same cap between the
wiper (centre lug) and ground.  The first one gives a fixed filter,
while the second one decreases the filtering effect as you turn the
control up.

I highly recommend this latter mod for delay lines (echo type). I
find it really cleans up the grit from sound that has recirculated
through a long delay.  You'll find that the sounds produced by
combinations of high-cut and low-cut of recirculated and delay
signal can make more natural sounding ambiences, and help to make
the delay and straight sounds distinct from each other, rather than
one being a slightly distorted copy of the other.

I'm not alone in these recommendations or design features.  PAiA
electronics' "hyperflange" employs a variable bass-cut circuit in
the recirculation path of its' premier flanger/chorus in order to
tame recirculation so that it doesn't oscillate into a squeal or
howl when you crank the resonance up.

Overall, this should cost you no more than $10 at RadioShack prices,
and should rejuvenate your analog delay devices.  I think you'll be
pleasantly surprised with the new palette that's available.

The only constraint or caveat I needto mention here is that you
should make sure any polarized caps you use or replace are oriented
at the same polarity (+/-), and that you perform such mods only on
clearly analog boxes whose mix and recirculation controls have one
lug (the rightmost) connected to ground, acting in attenuator mode.

Lastly, any ofthese mods will obviously void your warranty.

Mark Hammer