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|previous: Adam Frankowski I just recently bought a Big Muff P... -- 6/11/1997 9:07 AM||View Thread|
|6/22/1997 8:40 PM|
|Mark Hammer||Re: Big Muff Pi Diffrences.|
Can't say what the tonal differences are
between the op-amp and transistor versions.
My guess is that any such differences are
likely to wash out when one considers the
variation in transistors, caps, diodes, etc.
that E-H likely used. You should bear in
mind that diodes show a fair amount of
variation in their voltage drop. There is
the usual difference between silicon and
germanium but even within standard 1N914
silicon types, any given diode in a pack of
20 or so can easily show a meter reading
between .52 to .7v clipping point. When you
use one pair of back to back diodes in a
conventional clipping circuit, such variation
may provide small, marginally audible
differences which wash out when you turn the
gain up higher or lower, and EQ it. The BMP,
however, has 3 such pairs cascaded, which
I suspect can have a more potent effect on
cumulative clipping, and tone. I'd be
curious to see if there are any folks out
there who have measured the diode
characteristics in "winner" and "so-so" BMP's.
Given the number of other active and passive
components in the mix, finding the "magic"
combination of parts for a BMP is probably
more difficult than finding the combination
for a winning TS-808 (or at least *as*
difficult). Ultimately, what you go for is
what your ears prefer. I find that fuzzes
can frequently be made to behave differently
with the right amount, and kind, of pre and
post eq-ing. Noise characteristics can often
be improved by goosing the signal ahead of the
fuzz (cleanly), and then turning down the
sensitivity of the fuzz itself. Sometimes,
prudent EQ-ing can do that job too. E.g.,
a nice hefty lower midrange boost from a
graphic or parametric EQ in the 300-800hz
range can elicit a wonderfully "gronky"
(think Billy Gibbons) tone from many
overdrives, and provide an overall signal-
level increase which allows you to set the
sensitivity/gain/fuzz/drive control a bit
lower and lower the noise component generated
by the fuzz itself at its output.
If you check the schematic, you'll see that
the tone control consists of single pole
(RC) high-pass and low-pass filters with a
100k pot to pan between them. The "cutoff"
values (i.e., the cap values) are selected
so that when the tone control is set to the
middle, it is equivalent to a "flat" or
"tone bypass" setting. If you want more of
"scooped-mid" or "death metal", all you have to
do is select cap values such that there is a
larger gap between the rolloffs of the high-pass
and low-pass sections. This doesn't increase the
bass like some of the BOSS units that have active
EQ-ing. Rather, it simply robs the signal of more
of the midrange. If you would like more
flexibility, then consider installing a DPDT toggle
(or slide) switch, that selects between the stock
cap values, and those that deliver the "scooped"
I haven't experimented with the values, but a
reasonable place to start is to select cap values
about 30% smaller for the high-pass section, and
30% larger for the low-pass section. Halfing or
doubling the value changes the rolloff by a full
octave, which may result in too pronounced a mid-
scoop. I suppose it may have some value to
*someone* as a valid sound, but do bear in mind
that pushing the envelope a bit too much with
the tone control will start to become useless as
a *variable* control, yielding only low end fart,
mosquito buzz, or a combination of the two, rather
than the somewhat smoother sweep the BMP normally
Okay. Carry on.