more beef from bsiab II please

[nag hammadi]

i am loving these pedals, and some of my friends have had me build them for them.

i built them as per the ggg layout, but i have ommitted the 150 pf in the tone stack.  that gave a little more beef.

i need MORE low end.

any more suggestions?

[Bucksears]

I gotta be honest, the BSIAB II isn't really made for a bass-heavy sound, so there's probably only so far you can go with tweaking it to get more bass.
Have you considered a Dr. Boogey?

- Buck

[SolderBoy]

The tone stack is similar to the big muff... I would download the tonestack calculator programme from here:

http://www.duncanamps.com/tsc/

and put the parts in from the BSIAB, then tweak till that mole hill at 80 Hz looks more like a mountain...     


SB.

[pyrotek]

150pF? where is it?
nag, try this mods - change R10 to 100ohms and add a bypass capacitor, start with a value of 0.1uF
                           - change C2 to 0.1uF
                           - try lowering the value of R3 and instead of using 2 capacitors (C3a & C3b) use a capacitor with a higher value
                              i.e.2.2uF

[mojotron]

Your bass response is likely amp dependent. I wanted to do the same thing this is what I did:

referring to http://www.generalguitargadgets.com/diagrams/bsiab_2_sc.gif

I kept C6 - C6 is pretty important for the BSIAB II sound. You could bump it up to 330pF.... but really your just messing with the mids by lowering the upper mid response - which can sound good too - but just does not add a lot of low/low-mid - just tweaks the higher mids by passing more lower frequencies. I would target R6/C5 as that is the more significant low-freq Z in the stage1/stage2 transfer function. Stage 1 is all about boosting upper mids, R6/C5 passes a lot of the the upper mids from stage 1 and filters lower-end freqs - just like the Blue Magic and a few other Marshall-ish sounding (IMO) pedals - this 500k/470pF filter is in there too - so when I modded mine I wanted R6/C5 to be tweak-able so I make R6 a 1MB pot.

There's 2 ways to go for low/low-mid response:

• Permanate low-end
  - Take out R6 and C5
  - Put in a jumper across where R6 was
• Adjustable low-end (as mentioned above)
  - Replace R6 with a 1MB pot
  

The other thing to try would be to keep doubling the size of C5 until your happy with it, but I quickly got to the point, when I did this, that just doing #2 above became a better solution that did not change the nature of the BSIAB II.

[mojotron]

150pF? where is it?

Right next to Q3

nag, try this mods - change R10 to 100ohms and add a bypass capacitor, start with a value of 0.1uF
                           - change C2 to 0.1uF

Hmmm... Changing R10 just changes Q3's Vd - thus Q3/Q4's bias. The idea of a bypass-cap is a good idea, I have used this mod on Q5 to boost the upper-mids. On stage 2, any changes like a bypass-cap should also take into account the value of C7 as you can run into some differences in Q3 vs. Q4 freq response that might not be a sound you're looking for (keep in mind the affect of C2 and C3a/b - they produce a bit of a difference in Q1 vs. Q2 freq response too - although Q1/Q2 and  Q3/Q4 are not really push/pull circuits). I have generally left stage 2 alone because it drives Q5 to clip. So, for a change in tone - a bypass-cap on Q5 works better/simpler... IMHO. But, then again a bypass-cap is really pulling more mids into the tone and boosting upper-mids along with some lows: The sound to my ear is that I hear the upper-mids being boosted more by a bypass-cap on the source, due to it having a greater net effect on higher freqs. 

                           - try lowering the value of R3 and instead of using 2 capacitors (C3a & C3b) use a capacitor with a higher value
                              i.e.2.2uF

Same thing here; this would raise some mids/upper mids (which is a mod I have done myself and really like) and R3 really is there to bias Q1 - not really affect tone - it pushes Vs up to get the right Vds/Vgs for the FETs being used.