Hello,
i want to build a BigMuff Pi and like to integrate some Trimpots for
fine Tuning/Biasing the Transistors (if nessesary and/or possible).
can anyone tell me, where to place the pots and whitch values?
thank you!
Oliver
P.S.: Is it important to select Transistors with certain hfe?
Hey.
The only place you may want the trimpots in is the tone section.
I see no use biasing the already biased silicone transistors.
A looooonnnnng time ago, RG Keen noted that when you have a design as simple as a Fuzz Face, every component value makes a difference.
In the case of the BMP, consider the criticality of each component to be reduced by virtue of the complexity of the effect. Note that I am not saying values are NON critical, just that criticality is diminished by virtue of all the other components.
Comments from those who have had the opportunity to compare different issues notes tonal differences between transistor types, so I am going to assume (notwithstanding all the feedback on my "I wonder if anyone could tell..." thread) that hfe MAY make a difference...although there is a whole helluva lot more to a transistor than its hfe.
The diodes make a difference as do the little caps in the base-collector loop of the gain stages.
Note as well that the BMP is fundamentally a cascaded fuzz. That is, there are two little diode-clipper fuzzes in there, one after the other. The signal gets boosted and clipped in stage 2 (after the Sustain control), then it gets boosted and clipped again. Personally, I'd be really curious to hear a BMP that uses a dual-ganged pot providing signal attenuation before each of the two gain stages. Right now it allows whatever grind is created in stage 2 to go unattenuated to stage 3. A dual-ganged 50k with a 47k fixed resistor to ground where the 1K resistor currently is would do a nice job of varying the grind by reducing the output level of the already distorted stage 2 so that it drives stage 3 less.
Check out Jack Orman's Fet Muff for some ideas.
Finally, as schematics everywhere note, the value of the cap in series with the diodes can be tweaked to taste with pleasing results.
Hi,
and Thank You for the detailed Information....
i will go for it with standard parts and try out your suggestions at the
caps to the clipping diodes.
bye
Oliver
someone else noted that the 8k2 R's in series with the clipper stage bases do make a difference. i remember trying it and liking it, but can't recall exactly what it did or what values i tried! sorry i couldn't be more use.
increasing the value would decrease the highs and decrease the gain, or vice versa... i reckon sounds good. also i liked low gain transistors. maybe try 'piggybacking' some 2N4401s or 2N3906s with a 10k B-E piggy resistor as well... this would be on my list of things to do but i'm playing my piggyback fuzz face pretty much all the time atm hehe
HTH...