BSIAB II mid control?

[Bucksears]

I know there have been a lot of BSIAB II threads lately, but I have a quick question:
Can the 25k mid-pot be added in the same place in the stock tone control as it is located in the BMP tonestack mod?

I rehoused my BSIAB II recently and have 'rediscovered' it after playing with amp sim pedals lately. It's got so many harmonics when the gain is cranked, but still sounds great as a low-gain OD. My only gripe still is that it doesn't have quite enough treble (maybe it's my 16k-ohm Ibanez Super 58 bridge??), but that's not nearly enough for me to NOT have it on my pedal board. I'm hoping adding a mid control might brighten it up just a wee bit.

Thanks,
- Buck

[Bucksears]

bump

[mojotron]

bump

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,  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.. 

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. 

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

[Bucksears]

(Montgomery Burns voice) "Exxxxxcelllent.........."

Well, I know what I'M going to be doing in the next couple of days.

Thanks a bunch, Mojotron!

[mojotron]

Let me know if you have any questions.

[nero1985]

i tried using a 1M pot on R6 but its not that good cuz when the you have low resistance it kinda pushes the circuit more and kinda farts, at least it happended to me, what im doing now is adding a Marshall Tone Stack to mine right on the output just to give it that marshall type of tweak, altho i might use a different stack like this one http://www.runoffgroove.com/umble.html cuz as for what ROG says its a little more interactive that a stock marshall tone stack

cheers

[mojotron]

Hmmm..

With #1 you shouldn't get a farting sound. I have used this with an Ibanez S470 (w/Gibson a classic '57/'57+ combo) and a strat and I get a roll-off in the mids as I increase the resistance (at 1M) and get a warm mid-heavy crunch at minimum resistance (0 ohms) - keeping all the settings kind-of at around 50%. Other adjustments have a similar affect applied to them with the R6 pot. I used this at 0 ohms with my Ibanez S470 to make it sound a bit deeper giving if a great Les Paul sound.

With #2 I get a more subtle mid control. With .1uF for C2 it's higher range mid control and with C2 at .2uF you get a more upper-mid control. This one is subtle, but I find myself using it to compensate for differences in guitars - like jumping from HB to single coil guitars. My favorite setting is 0 ohms and C2 being .2uF - with all controls set to 50% this gives me a sound similar to a DS-1 maxed out with the DS-1 tone control at about 9 oclock - very much a heavier Vai sound.

With #1 and #2 I get a lot more gain out of the BSIAB2 and it is more mid heavy - so the pots roll these back to the original BSIAB2 sound.

[powerplayj]

Thanks for the mods.....tried 1M pot for the 470k resistor and it really did thicken things up at lower resistance.  I aslo, found the tone at higher resistance (~1M) to be useful for those piercing metal leads from 80's tunes from the likes of DiMartini or Lynch.  I haven't decided whether I'll stick with the pot or throw in a switch for using 3 resistor values.  Nice discovery!

#2 is next on the list !!!!!!!