Modifiying Big Muff gain stage, Frequency Response

[blueduck577]

Reference Schematic: http://yfrog.com/13bigmuffp

I'm building a Big Muff clone for a friend of mine.  He said that he'd like to have a switchable built-in boost in front of the muff built into the same box.

Originally, I'd planned on wiring in an LPB-1 in front of the circuit, but then I realized: what if I simply changed the gain of the first gain stage in the big muff?

As it stands, the first stage is simply a clean boost used to drive the clipping stages.  After running some simulations, I determined changing R2 from 39K to 15K would create a significant boost.  However, I noticed this would cause the first transistor to clip, so I changed one of its bias resistors (R9) from 510K to 360K.  That ended the clipping.

However, since I'm trying to clone my own modded big muff for him, I don't want it to sound any different.  Would these changes affect the tone of the muff significantly enough to warrant other changes?

[Greg_G]

I think you'll find that the gain of the first stage is a function of R9 and R2.. so by decreasing R2 you've increased gain, and by decreasing R9 you've then decreased the gain again.

The changes shouldn't make any difference as far as eq goes.

[fuzzo]

I think to modifiy the EQ sound you've to play with the Tonestack, in tweaking it you can have a lot of different colors ,and I think , it's the only big change between all muff models (russian, sovteck, ram's head).

Nevertheless , you can increase (or reduce) the emetter Resistor of transistors. The creamy dreamer hasn't this resitor , the emetters are directely connected to the ground.

Removing clipping diodes, create a big boost volume.

I modded mine to have a mid boost (via a switch) and that sounds really good and really different compared to the regular sound.

[Gus]

R9 and R14 set the bias.  R9 is both a DC bias and AC feedback resistor.  It works with both the input series resistor 39K and the source(guitar another effect etc.) in front of the resistor.

What happens with a 22K or a 27K or a 33K or a 18K etc

15K and series pot of say 10K or ...

Did you sim with a 0 ohm generator?  That will be max gain.  You could have the 39K stock and add a parallel resistor for a increase in gain with a switch

I would adjust the 39K not the 510K

The eq part is the AC feedback caps and caps between stages as well as the tone control.  Lots of information on the web for adjusting a BMP.   All the way back to the "old" ampage days and maybe before that.  A search here and with a search engine should find all kinds of information on BMP adjustments.

[WGTP]

How about higher gain lower noise transistors like 2N5089 or MPSA018 or a Darlington?