BSIAB II: Smoking Bullet mod

[Bucksears]

Ok, I'm no engineer, but after playing around with the BSIAB II for a LONG while now (three years?) I've got a combination of parts that I REALLY like.
I originally was suggesting to clip the two .0022uF caps just before the volume. Lately, I've been feeling that this was too bright, since I'd have to roll the tone back pretty far to get a chunky, darker sound. I made a small change this weekend that really impressed me.
I'm calling this config the 'Smoking Bullet' mod. Nothing major, but here's the rundown:

• Use 2N5457 transistors for all
• Replace the C5 (470pF) with a 560pF cap
• Replace C13 (.0022uF) with a .001uF cap
• Remove C14 altogether

This seemed to warm up the high-end without getting it muddy - nice, classic Marshall rhythm sounds and midrangey (but not nasal) lead tones.
I'm not taking any credit for the BSIAB II, but this set of changes yielded some excellent results for me. I'm going to try the C13/C14 mod with the stock transistors and C5 (basically just changing the LPF) and hear how that sounds. There are so many great (and significantly different) sounds to be had just by changing a part here or there.
Try this and let me know what you think.

Buck

[Rockon4ever]

Thanks for the mod tip! I am a huge fan of the pedal/circuit and am lookng forward to experimenting more with it. I built one about 4 months ago and was shocked at how it compared to my Timmy

[Deville2Rocket]

Originally Posted by Rockon4ever

...I built one about 4 months ago and was shocked at how it compared to my Timmy

R u serious?

[Bucksears]

SLIGHT UPDATE:
Ok, I'm keeping the 'Smoking Bullet Mod' like a separate recipe. What I did do over the last couple of nights was try a couple of other configs and here are the results:

#1
Using a basically stock config (3 x 2N5457, 2 x J201, 470pF cap for C5), and used the .001uF cap for C13, removed C14. It was a little darker/muddier, closer to the stock version. Not an 'inspiring' sound to play with, so I moved on.

#2
Stock transistors as above, 560pF for C5, no caps for C13 or C14.
Man, what a sound. The 560pF brings up the mids a little, no LPF caps makes it much brighter and sizzles. The J201s are higher gain than the 2N5457s, so with the gain maxed, this config has a total 'hot rod Marshall' sound. This, to me, is the early VH sound. Bright, gainy, not a lot of bass, harmonics all over the place.

I think the key is the 560pF cap for C5. That midrange cuts through nicely without being harsh. I'll probably keep my current BSIAB II with the #2 config above and build another for the 'Smoking Bullet' mod.
Please take all of this with a grain of salt and remember this is all IMHO. Sorry to sound like this is hype, but I'm excited about it. Try it for yourself and maybe you'll like it too.
thx,
Buck

[jamison162]

Clips?

[B_of_H]

I've tried these mods and many more.

I personally thinks it's best with a J201 in Q1, C14 removed, and C13 at a lower value.

great pedal though and I gig with it regularly.

[fr8_trane]

Hey Buckears have you tried lowering C5?

That R/C treble boost circuit is found in every 60's and 70's marshall. The plexi's used the 470pf but the JTM45 and the fender bassman used a 250pf cap and this added some low midrange grunt to the sound. I haven't tried it yet myself but the 560pf seems like it would add more hi midrange which is something I think the Brownie already has in spades.

[DreamTheaterRules]

Thanks Buck and fr8. I have a full kit and a board for another one in house now, and I watch every thread you guys have about mods for this thing. Can't wait to get them up and running!

[Bucksears]

fr8_trane,
You are correct on the JTM45/Bassman specs. I've seen some JTM45 schems with the 250pF as well.
I'll try that tonight. I just bought some 250pF caps for another purpose and will pop one in tonight. Ooooo.......a 'Bassman' mod for the BSIAB II...... (BMIAB?)

The 470pF and stock trannies didn't seem like a lot of upper mids to me, but who knows. I definitely could tell a difference after the 560pF cap was in there.

B_of_H,
Sounds cool. That's the amazing thing about this circuit - a couple of tweaks and you have a sound that's what YOU want.

DreamTheaterRules,
You GOTTA have at least TWO! :AOK

[Ed G.]

Originally Posted by Bucksears

SLIGHT UPDATE:
Ok, I'm keeping the 'Smoking Bullet Mod' like a separate recipe. What I did do over the last couple of nights was try a couple of other configs and here are the results:

#1
Using a basically stock config (3 x 2N5457, 2 x J201, 470pF cap for C5), and used the .001uF cap for C13, removed C14. It was a little darker/muddier, closer to the stock version. Not an 'inspiring' sound to play with, so I moved on.

#2
Stock transistors as above, 560pF for C5, no caps for C13 or C14.
Man, what a sound. The 560pF brings up the mids a little, no LPF caps makes it much brighter and sizzles. The J201s are higher gain than the 2N5457s, so with the gain maxed, this config has a total 'hot rod Marshall' sound. This, to me, is the early VH sound. Bright, gainy, not a lot of bass, harmonics all over the place.

I think the key is the 560pF cap for C5. That midrange cuts through nicely without being harsh. I'll probably keep my current BSIAB II with the #2 config above and build another for the 'Smoking Bullet' mod.
Please take all of this with a grain of salt and remember this is all IMHO. Sorry to sound like this is hype, but I'm excited about it. Try it for yourself and maybe you'll like it too.
thx,
Buck

I really like Mouser's polystyrene caps here for the 560pf. They sound clear but not harsh. REally smooth. I find silver mica gives them a 'bite' that doesn't work with my fender rig, but it might be good in darker amps.

[Bucksears]

Originally Posted by Ed G.

I really like Mouser's polystyrene caps here for the 560pf. They sound clear but not harsh. REally smooth. I find silver mica gives them a 'bite' that doesn't work with my fender rig, but it might be good in darker amps.

I might have to look at that. I'm using a ceramic disc for my 560pF. Seems fine for now.