BSIAB II and a new tonestack

[YouAre]

I really like the BSIAB II that i built, but i think that all the problems i have with mine (tonal preference, not technical issues) stem from the tonestack. Has anyone put in a different tonestack, and gotten good results? If you have, can you please direct me to a good tonestack to replace the one that is currently in my BSIAB II?

And...can anyone report results of any experimenting they did with different transistors?
thanks,
Murad

[MartyMart]

The BSIAB II's tone stack is quite good, the problem for me ( and some others ) was the dual roll off
caps/r's at the end, not leaving quite enough high end.
Try removing one "pair" of these, but leave the TS "as is" and see what you think.
Otherwise, perhaps a TMB from the DR Boogey might work well.

MM

[YouAre]

i took out the two .0022 cabs, c13 and c14 i believe. it gets me closer to what i want, but not quite there. I'm guessing that by looking at the schem of the BSIAB, if you cut off the circuit from the beginning of the tonestack, you lose the tone control, and the volume. Is there a marshall type tonestack (TMB) and a volume control that would be more versatile than the current tonestack?

[Gringo]

Have you checked the duncan tone stack calculator? it has the big muff tone stack, and you can tinker and tweak til you find something you like

[jrc4558]

I honestly don't know what problems there are with the tone stack. What guitar/amp do you use? Do you feed BSIABII a buffered signal?

[alfafalfa]

I saved this post from Mike , at Mojotron, some time ago , it might be what you're looking for .
I liked it very much

BSIAB 2 mid control

Ok ok... I've been wanting to write these mods up and get them out there for a while now.. Here you go...

if you want more upper-mids... but in this circuit I like to add them actively rather than messing with the passive tone control - there's not enough done in the tone control to really make a set of changes there that adds mids that sound more like an amp adds mids (vs. how a speaker compresses the sonic range - nipping highs and lows like a passive tone control does to give you a kind of speaker simulation)....

So, thinking in terms of how an amp adds mids - staying faithful to the "Super Lead" sound - here are Mojo's favorite BSIAB2 mid tricks that I added to the BSIAB2 circuit in my quest to match more of a "Mullard 12AX7 equipped" pre-amp sound...

1) What I found was that I really liked a 1M pot in place of R6 in:

http://www.generalguitargadgets.com/diagrams/bsiab_2_sc.gif

And a polystyrene 470pF cap for C5, using the specified J201/2n5451 fets - this adds a low-mid boost.

With the R6 1M pot turned to low resistance - you get a lot more mids and low mids - without sacrificing the hi-mids/highs: At high resistance you get a bit less low-mids and more hi-mids.. kind of an in-line treb-boost sound. With a ceramic cap in C5 this still works, but sounds a little grainy and weak - that is - with a ceramic cap the signal seems to loose power as R6 approaches 1M.... The polystyrene cap seems to give you less loss of signal... but all of this is fairly controlled as you're not dumping signal to ground at this point in the circuit.

So, #1 only affects the amount of low mids you get... adding or removing the lower mids - you need to do #2 to boost upper mids.

2) Either put a pot (10 to 100k..) in front of C2 and make C2 like .2uF... or just play with values of C2 from .1uF to .2uF to tune the upper mid boost you want. The larger the cap, the more high-mids you add. Likewise, using a bigger cap, a resistance via a pot will allow you to tweak the upper-mid boost.

So, with #1 and #2 the combo will give you full control of the mids - boosting from the bottom and top to get the full mid-range boosted.

If you use an RC combo (using a pot for "R") in place of C2 - you get something that is very tunable. However, I simply use .1uF for C2.

3) Try #2 with C7.

When I played with these, it seemed to me that I liked the sound of adding mids prior to #1, but the last "boost" mod you have before Q5 is going to be the dominate one - thus I mention playing with higher values of C7.

4) Now,  icon_cool some times what you really need is a serious kick in the mid-section (figuratively) while keeping the gain at 1/3 to 1/2 of full rotation. This mod opens a whole can of whoop-**s in the upper-mids..  icon_eek

Ok, if you put a 5k pot with a 1uF to 2.2uF cap in series to bypass R15  - making an AC bypass from Q5 source to ground - you get a really great VH1 crunch that is quite addicting.  Grin

If I was to make like a BSIAB v3 - I would add all these mods together. It's a few extra knobs and it's a slight change to the original sound, the control you get is a fantastic change. I've been using these mods for about 6 months now, and what I did was to make #4 switchable for a lead boost kind of like is used on the Fulldrive - kind of a "crunch" control.

Give these a shot - let me know what you think....

--
Mike  ( Mojotron)

[powerplayj]

#1 mod from above thickens it up nicely and is a keeper in my opinion.  I like a resistance value around 100k. 

All this talk of the BSIAB2 made me add it back to my board alongside the Thunderchief.  It just has this sponginess that the Thunderchief doesn't have and it also seems to have more sustain and sweetness with neck pickups.  However, Thunderchief stacks much better with an OD and cleans up quite well.