BSIAB II w/'Contour' (AMZ Presence) Control

Bucksears · July 13, 2009, 10:08:29 AM

Man, this is versatile.
Long story short, I built a 2nd BSIAB II (my main one is being rebuilt as well), with a couple of mods.
1) My tried-and-true removal of the two .0022uF caps in the low pass filter at the end of the circuit
2) I replaced the values in the stock BSIAB II tonestack with that of the AMZ Presence Mod #1; I labeled it 'Contour'

So, it's a four-knob BSIAB II. Where it really shines is that it goes from chunky, low mids, to a full-mid crunch, to an almost DS-1-like scoop. SO many sounds that I wish this thing had MIDI presets. The tone and contour are VERY interactive. Mainly, I would get the contour where I wanted it, then adjust the treble with the tone control. The 'Contour' does drop the volume a little when you rotate it fully clockwise.

I love the sound and versatility of the BSIAB II, but this really expands on that. I highly recommend it. I didn't want to go TOO over-the-top with this post, so feel free to ask any questions.

caspercody · July 13, 2009, 10:18:49 AM

This weekend I removed the tone control on the BSIAB2 and added a baxendall tone stack. What a difference this made.

alfafalfa · July 13, 2009, 11:36:36 AM

QuoteMy tried-and-true removal of the two .0022uF caps in the low pass filter at the end of the circuit

Did you leave the 2 - 10 K resistors then ? Or did you remove the two filters entirely ? That's not clear to me .

Alf

caspercody · July 13, 2009, 12:16:47 PM

I used the GGG schematic, and pcb. I removed everything after C9, up to the volume control.

Bucksears · July 13, 2009, 12:21:17 PM

Quote from: alfafalfa on July 13, 2009, 11:36:36 AM
QuoteMy tried-and-true removal of the two .0022uF caps in the low pass filter at the end of the circuit

Did you leave the 2 - 10 K resistors then ? Or did you remove the two filters entirely ? That's not clear to me .

Alf

I just removed the caps - I left the two 10k resistors in there. Works for me.

dschwartz · July 13, 2009, 06:26:42 PM

ds-1 have a scoop?..i´ve allways heard them a little mid-rangey...

isildur100 · July 13, 2009, 08:07:02 PM

Do you happen to have a schem of your full mod? The BSIAB2 is on top of my pedal to-do list and your mod looks interesting.

thanks

Morocotopo · July 13, 2009, 09:05:42 PM

Nice buck. A schem would be nice. And soundclips too.

jacobyjd · July 14, 2009, 08:36:36 AM

Yesterday I plugged in my BSIAB2 and gave it a whirl again. With my 30w Class A amp it sounds amazing. I think it might end up on my board after a re-house. I might check out this mod then

Bucksears · July 14, 2009, 09:37:21 AM

I used this:
http://www.muzique.com/lab/tone3.htm

It's just the Presence control #1 values (plus the 'body/contour' pot) in place of the BSIAB II's tone circuit values. That's it.
I'll work on doing some clips soon of this and some other stuff - I have a new Mojotone 2x12 cab being delivered today and I'm taking some time off in the next couple of weeks.

Ice-9 · July 14, 2009, 10:12:30 AM

I tried a similar aproach a few months back by changing the tone stack to the amz one (which is really the same as bmp/bsiabII stack just with the presence pot in) but i also left the 2 lowpass filters made up of the 10k and 0.0022 caps in after the tone control. I wasn't happy with the results at the time but then again i didn't tweak the values in the tone stack. I am going to go back to that and experiment a bit more with it now.

Bucksears · July 14, 2009, 11:13:46 AM

Quote from: Ice-9 on July 14, 2009, 10:12:30 AM
I tried a similar aproach a few months back by changing the tone stack to the amz one (which is really the same as bmp/bsiabII stack just with the presence pot in) but i also left the 2 lowpass filters made up of the 10k and 0.0022 caps in after the tone control. I wasn't happy with the results at the time but then again i didn't tweak the values in the tone stack. I am going to go back to that and experiment a bit more with it now.

Was it not bright enough? I almost scrapped the BSIAB II with those .0022uF caps at the end, but it's turned into my flagship distortion after they were removed. I left the two 10k resistors in.
Just clip those caps!

Ice-9 · July 14, 2009, 03:38:18 PM

I think in its standard form the BSIABII in my setup is bright enough, it give me that cranked twangy Marshall plexi sound. Then again i'm also going through a Marshall rig anyway and i have heard that on other amps the bsiab does have a different tonal context. the one i modified with the presence control had very little control over the sound that i wasnt worth boxing up, but as i say i didnt really do any tweaking of the tone control to make it useful. My next project will be exactly that.

I'm doing some mods to muamp bsiab circuits at the moment so if i get any good results i will try and post a few sound clips soon.

caspercody · July 27, 2009, 04:04:48 PM

Any more news on your mods? Plus, do you have any sound clips?

bdevlin · February 24, 2011, 08:32:23 PM

Quote from: Bucksears on July 14, 2009, 11:13:46 AM

Was it not bright enough? I almost scrapped the BSIAB II with those .0022uF caps at the end, but it's turned into my flagship distortion after they were removed. I left the two 10k resistors in.
Just clip those caps!

Bringing back an old topic merely to document success from someone recommendation. I just clipped these two caps and yes it turns it into a bit more of a beast for sure. I clipped c14 first and did not hear a big difference. After clipping c13 I heard a big change. Maybe start there to experiment.

News:

BSIAB II w/'Contour' (AMZ Presence) Control