Author Topic: Some Triangle BMP mods and a question  (Read 1444 times)

mth5044

Some Triangle BMP mods and a question
« on: February 05, 2009, 12:03:54 AM »
Hello. I sent an email to Marc from Skreddy a while back and I was just reading over it again. Like he says in the email, it could be useful, so I thought I'd put it up here for ya. No need to hoard it for myself  :icon_razz:

"There are an awful lot of parameters in the Big Muff that can affect
the perceived level of flabbiness and buzziness.  One of those is the
amount of gain.  To decrease gain, decrease the value of the neg.
feedback resistors, usually 470k in the 1st 3 stages and 390k in the
4th.  Try 390k or even lower instead of 470k.  Another is how much
bass is permitted to pass through the clipping sections.  Usually
you'll find a .1uf cap in series with the clipping diodes.  Try going
lower to .047uf.  Try going higher to .22uf or even 1uf.  Experiment.
Finally, you can manage the amount of bass that comes through the
final stage with the capacitor that couples the tone stack to the base
of the 4th transistor.  Usually this is a .1uf cap.  I use something
smaller than this in the Pink Flesh to keep it from getting thumpy or
woofy.

A tip I got from Ed Rembold is to add a resistor between the tone
stack and the 4th transistor too.  You don't want to overdrive that
final stage unless you're really going for a raspy sound.  I usually
use 8.2k or as much as 18k in that spot.

Feel free to post this at diystompboxes.com if you like.  It's pretty
useful.

Best regards,

Marc
http://skreddypedals.com"

Some really good stuff in there.

Anyway, my question is about the last part he mentions. I've become OK at DIYing, but what parts do still eludes me. When he says to insert a resistor between the tonestack and the 4th tranny - using the GGG schem as a reference,

http://www.generalguitargadgets.com/pdf/ggg_bmp_tri_sc.pdf

would that mean I just cut the trace between C12 and the 'in' to Q4 and slap a resistor in there?  Or does that mean insert a resistor to ground like a volume pot? I'm guessing the later as 'overdrive that final stage' sounds like the volume going to it should be reduced.

Thanks for you help. I figure I might as well try some of this stuff out. It's not like it can be bad coming from Skreddy  :icon_mrgreen:

And if you read this Marc... thanks   :icon_cool: :)

petemoore

Re: Some Triangle BMP mods and a question
« Reply #1 on: February 05, 2009, 12:26:33 AM »
  A splice / R placement: in the line above the 'Q4' text in schematic, can put a little series resistance between the Q4 and it's input.
  I don't know if that's what's responsible for the BMP's ability to pronounce 'qua' and 'Kih' during the first milliseconds of pick attack, perhaps the intention is to let just enough input in so that at some very high level an 'edge' is hit, a parameter, turning the 'sustain' knob down introduces series resistance, albeit stages earlier.
  Personal choice, thanks Ed !
 
Convention creates following, following creates convention.

Ben N

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Re: Some Triangle BMP mods and a question
« Reply #2 on: February 05, 2009, 12:56:20 AM »
From the way he refers to the values (sort of suggesting that the higher the value, the greater the attenuation), I gathered he meant a series resistor, maybe just between the wiper of the tone pot and C12? I guess it works because that resistor and R21 form a voltage divider, at least for signals above the cutoff of the HP filter (C12 + R21). Plus, an 8.2k shunt there would probably steal too much signal. Although I imagine that a series resistor on the wiper might also alter (intensify) the operation of the tone stack, too, no?

I note that the disseminated schematic for his Mayo does not show a resistor there, but does show a 47pf cap to ground between the pot and the 0.1uf--an extra fizz-buster. The Top Fuel apparently does have a 10k series resistor.
« Last Edit: February 05, 2009, 01:02:02 AM by Ben N »

Nitefly182

Re: Some Triangle BMP mods and a question
« Reply #3 on: February 05, 2009, 01:46:02 AM »
The coupling caps are really where I think the magic is in a muff. The stock triangle is pretty thin and raspy sounding because the caps aren't big enough to let a good amount of bass into the next clipping stages. Double them from .1uf to .2uf and you get more saturation and a much thicker tone without sacrificing much it the way of tightness. Its certainly not tight like a high gain amp but its not all flab.

bumblebee

Re: Some Triangle BMP mods and a question
« Reply #4 on: February 05, 2009, 05:00:51 PM »
Quote
Another is how much
bass is permitted to pass through the clipping sections.  Usually
you'll find a .1uf cap in series with the clipping diodes.  Try going
lower to .047uf.
Changing these two caps to .047uF results in a woofy/boomy BMP (unusable with chords), the best value I have found for these two is from .22uF up to 1uF, I always use 1uF.