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previous: Adam Frankowski I just recently bought a Big Muff P... -- 6/11/1997 9:07 AM View Thread

Re: Big Muff Pi Diffrences.

6/22/1997 8:40 PM
Mark Hammer
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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"  
tone.  
 
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  
has.  
 
Okay. Carry on.