*yawn* BSIAB2 question

[swinginguitar]

I built a couple of these back when (with contour pot...GGG version), and really liked how it gets very liquid/saturated, but found that it just wouldn't clean up (even with the gain low it was very gainy, and the volume knob on the guitar won't clean it up).

So I put them away and haven't given it much thought, but recently I was reading that different JFETs make it sound/feel different (IIRC I used J201s I had on hand).

Honestly, I was thinking about picking up a CMAT Brownie (heard some demos I really like), but am now wondering if I could just quickly/easily mod mine to match what he does. Thoughts? What JFETs are "stock" on the Brownie? Is it possible to get that liquid lead sound but still have it respond to attack/touch/volume knob?

Did I not bias it correctly?

[alphadog808]

Hey man.  I'm no expert, but I just built one.  I believe the BSIABII is supposed to have 2 J201s and 3 2N5457.  I think the J201s are Q3 and Q4.  

I messed around a little trying different combos of those jfets and from what I remember, the J201s made the pedal more aggressive and harsh.  The 2N5447s gave it a bit more mid/brown sound/feel.  However, I think I didn't like all of them being 2N5457 as it lost some clarity.  Bottom line, it does make a difference, but you have to just try and see.

As for bias, I believe the trimpot will take care of it.  However, I did notice a difference when I used matched J201s over 2 random J201s.  Seemed like it was hotter, in a good way.

Hope that helps.

[waltk]

I like all 2n5457's.  Cleans up a lot with the drive turned low.

[scott1568]

I agree. The pedal will be more compressed than say a fuzz though.

[swinginguitar]

concerning the bias pot - am I looking for 4.5v at the drain?

[waltk]

concerning the bias pot - am I looking for 4.5v at the drain?

Yes (on Q5).  The other thing to keep in mind is that Q1 and Q2 are a mu-amp, and Q3 and Q4 are a mu-amp.  Q1 and Q3 (the bottom sides of each mu-amp) are the ones that count.  They don't have to be matched with Q2 and Q4, and changing Q2 and Q4 will not change the sound much. (All references based on GGG BSIAB2 schematic)

[Ice-9]

concerning the bias pot - am I looking for 4.5v at the drain?

Just set the Drain bias pot by ear, then measure the voltage. You can always tweak it from there, but by ear is probably the best way. It will be obvious when it is at its correct point.

[swinginguitar]

concerning the bias pot - am I looking for 4.5v at the drain?

Just set the Drain bias pot by ear, then measure the voltage. You can always tweak it from there, but by ear is probably the best way. It will be obvious when it is at its correct point.

It's been a while, but I recall it having a wide sweet spot when I was adjusting it after the build.....more like it was obvious when it was at the wrong point...

Wish I could find some MPF102s locally....sigh

[duck_arse]

could you be a bit more specific with "locally"? you never know what people have laying around.

[swinginguitar]

could you be a bit more specific with "locally"? you never know what people have laying around.

Baton Rouge.

Check some local Rad Shacks - one of the transistor bins had the label where they clearanced them out and I missed it

They're cheap via mail, but shipping gets up there quick - may have to wait until I order some other stuff.

Just to clarify - I would do mpf102 for all but Q5, which would be j201?

[swinginguitar]

I have a bunch or 2n5088 and 2n3094 in stock....too far out of spec for this circuit?

[duck_arse]

I would say those 2 bjt's are a little off spec for a circuit calling for jfets.

[swinginguitar]

I would say those 2 bjt's are a little off spec for a circuit calling for jfets.

yikes...so i really was tired when i wrote that...