BSIAB2 mod Question

[Ice-9]

Having built a few slightly modded BSIAB2 effects i was thinking of dropping the last trim that sets up the last FET devices bias. It occured to me that if the two previous stages have a CC source using another fet device to bias the fets is there any reason not to use the same method to bias the last stage instead of a trim pot ?

[liquids]

Why not.  I wondered that too when I was building it.  Try it!  See what you think of the differences.  Or contact Ed if your interested in his take on why it is the way it is rather than 3 mu-amp stages...

[jimma]

I don't see why it couldn't be done. I just breadboarded Doug Hammond's Sweet Thing and the last J-fet is set up that way. If you're a BSIAB fan (as I am) I recommend checking out the Sweet Thing, and also Aron's Booster 2.5, and to even get a true understanding of the lineage I also breadboarded Jack Orman's Mini-Booster-all similar, and all great, IMO.

[Ed G.]

Sure you can do it. Look at Jack Orman's Mini-Tubes, this is basically what that is.
I just found three mu-amp stages to be a bit too gainy. Then again, there are ways to control the gain.

[Ice-9]

I will start experimenting with this, The higher gain was one of my worries as i love the sound of the BSIAB2 i have any more gain would change the effect away from my aims . One of the other options iwas thinking of was to use an op amp in the final stage. I suppose its time to get the breadboard out Thanks for all the info.

[liquids]

I will start experimenting with this, The higher gain was one of my worries as i love the sound of the BSIAB2 i have any more gain would change the effect away from my aims . One of the other options iwas thinking of was to use an op amp in the final stage. I suppose its time to get the breadboard out Thanks for all the info.

Definitely breadboard it. I think it would be interesting to try, but to send all that jfet gain crashing into an op-amp will, I'd hypothesize, cause a difference to the quality of the distortion....different from the original sound the pedal was going for, but not necessarily worse or better on a fair playing field.

On the other hand I'm interested in the (presumably) subtle tonal differences yielded by the last stage being a mu-amp stage.  I had always assumed (never did an A/B I admit) that mu-amp stages were slightly more tame in gain over the 'trimmer' type jfet stages, all else being equal.  I never tried because I knew I was going to stick to the GGG boards, so it wouldn't be an option for my two final builds.  If I vero my next one (!), that would be good info.  But as Ed said, gain is controllable so you can easily tweak either one to have more or less gain.

One thing is true - removing the trimmer in favor of a mu-amp stage would probably yield more consistency, by removing the possibility for setting the trimmer poorly, and it's variable effect on tone...it would have that advantage.  One less thing to go wrong, one less knob to set incorrectly.   

Maybe this is the BSIAB 3 

As a side note, speaking of another BSIAB, anyone use this for that "bluesy neck pickup single coil" tone? I know the Blues Booster is out there, but I wasn't tweaking for that sound with my first few builds.   I really liked the Barber LTD I breadboarded for that tone, but now that I understand this circuit even more, I'm thinking I could easily get the core of the BSIAB/Blues Booster in that gain and EQ range, with more scooped mids settings from the BMP tone stack, tweak the low pass filters at the end, plus all that sweet guitar-volume controlability I get on the BSIAB, etc...man I want my workbench back!   

[Ice-9]

Yes i have to agree, my plan after a bit of thought is to breadboard the first 2 stages and then play about with a final stage. I will do the Mu amp as a 3rd stage and tweak components (all stages) to get what i am looking for.

I have used the BSIAB2 in the neck pickup and it also responds very well to the guitar vol knob. You can really get those "la grange" blues sounds brilliantly. Also fantasic for the verse tones of hendrix's "purple haze" then dial in the guitar knob and bridge pickup as everyone knows instant 78 vintage Van Halen. Such a versitile effect.
The only changes i made to my presend BSIAB is a resistor to ground from the gain pot so turning the gain down to "0" doesn't result in no vol at all. Also a few changes to the tone stack adding an extra pot to control the band that the tone effects.

[liquids]

I don't actually mind the signal dropping out with the gain pot zeroed, but for the sake of learning, can you explain how you physically wire this up?  Is it just a set resistor wired from the wiper to ground?   A picture would help.      I think this would be useful for certain volume controls...I'm not a big fan of the oversized volume pot, so I use smaller value log pots a lot of the time (10k, or even 1K  on a very loud effect with consistent gain levels) but there is little to no sense at starting from zero volume on other pedals...

[Ice-9]

I have drawn this version of the BSIAB2 the only changes are the mentioned resistor on the gain pot and an added section to the tone control. The resistor is conected to the pot end lug that was previously connected to the ground. (in the schematic its R17)



If Ed's about could you explain what the reason for the two parrallel caps in the first stage of the Muamp section are for (why not just one cap ?) In my sch they are caps 3 and 4.

[Caferacernoc]

Why not just change the last stage to a common drain buffer?

http://www.muzique.com/lab/buffers.htm

Then you know all the overdrive is from the minibooster stages and not from totally overwhelming the final stage with insane level boost.

[wampcat1]

Why not just change the last stage to a common drain buffer?

http://www.muzique.com/lab/buffers.htm

Then you know all the overdrive is from the minibooster stages and not from totally overwhelming the final stage with insane level boost.

That's part of the sound of the bsiab. 2 mu-amp stages beating the crap out of a simple jfet stage.  Here's a cool mod though... find Jack Orman's article about turning the big muff tone stack into a bass/treble stack. Follow that principle and replace the bsiab tone stack with the orman defined version of it. Simple bass and treble control and sounds good!
Even better - stick a buffer before the volume control and get a bit more volume out of the circuit.
bw

[Quackzed]

you can jumper over the last stage and see what it sounds like ...

[anchovie]

could you explain what the reason for the two parrallel caps in the first stage of the Muamp section are for (why not just one cap ?)

Because a 1.22uF cap might be considered a specialist item.