More BSIAB 2 Q's and mods

[DWBH]

For the past couple of weeks I haven't been fond of my BSIAB. I now find it to sound very JCM800-ish, very metally (what the heck is metally anyways? )
I'd like to make it more Plexi-ish, more full. It reminds me of the 80s, and I want it to remind me of the 70s.
Of course, this probably isn't the best way to achieve that sound. Nonetheless, I'd like to try some modifications.

Anyways, I've been searching the forum for mods, and have also looked up other similar designs, like Doug Hammond's Sweet 16.

What I've noticed is that in the BSIAB design, right before the last FET, there's a low pass filter, which the Sweet 16 doesn't have.
The corner frequency is in the 90Hz region, so I guess it's just making more bass pass through the FET and the tonestack.

After the tonestack (BSIAB) there are two low pass filters, corner frequency of 7kHz each. I'm having a bit trouble understanding what they're doing here, and... why two filters in series? Is the corner frequency doubled/divided?
First off I'm going to up C2 and C7 to about 0,22uF, and replace R8 with a mid/presence-control.
I'm also wondering about C4 and it's impact in sound.
I should say that I use the BSIAB with the gain at about 9, 10 o'clock, so I'm not using too much gain.
In fact, maybe there's even too much gain, and I've thought about subbing all transistors with 2n5457s, but I don't have those for now, so that'll have to wait.

So you can know, I really like the sound of Led Zep and Hendrix, and in the higher gain registry, maybe ACDC and Sabbath, but as I said, I normally use the gain low. It gets too fuzzy, or just 'too much' with the gain crancked.


PS: alterations in the tonestack, even substituting it with a marshall-like tonestack have crossed my mind. Somewhere along Sweet 16's tonestack lines....

[liquids]

I'm with you on the too much gain and wanting less 80's.  It's very doable, the circuit very tweakable even within the confines of the PCB.

I use two identical BSIABs with lots of mods as my core tone.  The mods might be closer to the '70's' thing your after as a starting point.

The easiest mod I can think of for lower gain/better gain range is increase R10 (as per the GGG) schematic significantly--3.3k has been a good option both for me and for others I've talked with, so start in that range and see what you think.   

I've liked C2and C7 at .1uF.  C4 and C12 as well, for that matter.  With the bigger caps I have not had any mushy bass issues, though your mileage may vary, and it's certainly not as tight as with the stock values.   I made C8 1uF as well, so there is less/no bass cut off on the tone stack when past noon.  It's a starting point, if nothing else.

Subbing 2N5457s for the J201s will not be that significant a change I say -- more a 'tonal' change than a gain change.   Don't drool over the parts you don't have -- you'll get better mileage from tweaking the source resistors in this circuit for now until the parts come in.  That being said, I do personally like MPF102s at the input -- I got more of a Plexi-style dynamic an volume cleanup....but you can mess with R3 similarly and significantly for similar effect, and/or pull C3 for an experiment and listen to what happens.    MPF102s are not known to be consistent, though, as a tradeoff....

About the filters - two caps are going to shave off more of the extreme high end than just one big cap would. It keeps the high end sweeter and less fizzy -- especially if your rig is single coils running into a fender amp clean (or clean solid state amp!) with the 'bright' switch on.   The tone stack has a lot you can mess with.  I find the C10 at 22n is too big, and made it more subtle with a 4.7n, though see what you prefer.  The typical amp tone stacks will reduce output significantly, and scoop your mids beyond recognition, into an inevitably mid-scooped amp.  Few here have liked that when they've tried it.   There are other tweaks too, but, first things first. 

[DWBH]

Thanks for the very useful tips!

I'm probably going to try the R10 mode, and C2/C7/C4 at 0,1uF. I'll have to pass the C8 1uF though, I once tried that and it sound blergh, but maybe I'll try it again after the mods.
By increasing C2/C7/C4 to 0,1uF I'll increase bass response you say?
I would like more dynamic response, so I'll definitely lower the gain in the first transistor (R3/C3).

Regarding C10, if I lower it to 4,7nF it seems to boost some lower mids - what do you mean more subtle?
How about messing with R8, 10k trimpot, for some mids adjustment? Have you tried this?

[liquids]

How are you running your tone pot?    If you like more dynamics, definitely audition some MPF102s when you can. It made a huge difference for me -- lots of volume knob clean up and very very sensitive to picking strength with reasonable gain levels.  Is this on the breadboard?  If you only have 2N5457s, try a very large value resistor for R3 - try 4.7K 10K, 22 K, 33K off the top of my head. Then start again with stock value for R31 but remove C3, and increase R3 to 1K, 2.2k, etc, slowly. Use your ears, see what you like and what yields the balance between dynamics, gain range, and tone you want.  The time invested will be well worth it.

Yes, increasing all those caps to 100nF/.1uF will add bass to some degree.  More so, 100nF is usually this is where I start with the average circuit.  Hearing it stock for the first time, it was 'nice and tight' but too much so for me.  I tried simply making C8 bigger as suggested for more bass, but it still was too much.  So I went to the 100n all over (C2 C4 C12) as a starting point, and wound up liking it, with no reason to need it any tighter than it was for my tastes, my use, and the low-mid gain range I dialed in...so I can't suggest how or which ones to tweak outside of that...make them all big and then if it's too much, I say, tweak them one by one and listen to how each affects the sound differently to achieve the desired effect...ahh, the beauty of breadboarding. 

C10 (in conjunction with R7) controls the high end roll off of the tone knob.  Making the cap smaller (All else being equal) means high mids are less affected, with it having more of an effect on the high end and leave more of the other signal alone.  I don't like the BMP tone stack values which shaves gain overall, and likewise will cut bass when it allows more treble to pass, and the opposite (shave highs, pass bass) in the other direction.  I tuned it so that, in conjunction with the larger cap for C8, it has little to no noticeable affect on the bass and more so acts as a high treble roll off.  I leave it full up most of the time unless shooting for a very smooth lead tone---where rolling it back shaves highs but can still be clear and cut in a band mix.

R8 - be careful.  Make it a 100K log pot if anything.  You'll perceive a mid dip as you descend onto 33k/22k/10k and it's dramatic below that (hence the linear control).  Weather it's a dip or a scoop depends on the tone stack values.  I leave it at or near stock here, but it's useful in moderation.  Stock, it's got a big full midrange that helps it cut...too little mid and you'll get lost in the mix, for one....

[punkin]

I couldn't pull it off but the one thing that comes to mind is the Tonemender circuit. If you can shoe horn that in place of the stock stack and pick up the lost level this should put you right there where you wanna be. http://www.runoffgroove.com/tonemender.html

Just a thought

[DWBH]

No, it's on pcb. I made the pedal a couple of years ago, but now I want to mod it.
Tweaking will be tougher, I'll solder some sockets.
I have 2n5457 and J201, like in the original schem.
The tone control really repends. Nowadays I've been running it at about noon, but I used to run it at about 3 o'clock. It varies between 12 and 3 o'clock.

Won't removing C3 reduce gain and some bass response?
What values do you recommend for C3/R3?

[waltk]

The typical amp tone stacks will reduce output significantly, and scoop your mids beyond recognition, into an inevitably mid-scooped amp.  Few here have liked that when they've tried it.

I had the same interest in getting a little more flexibility out of the BSIAB2 (which - out of the box - is the best distortion I've ever heard).  My solution was to replace the single-knob tone control with a Baxandall tone stack, and add a clean recovery (gain) stage at the end.  The Baxandall is more flexible than any of the other amp tone stacks, and doesn't have a built-in mid scoop.  I like this solution better than all the other mods (and I did try them).  The result was awesome.  If you have any interest in this, search for the "Infinity" thread here for ideas about how to implement it.

[liquids]

No, it's on pcb. I made the pedal a couple of years ago, but now I want to mod it.  Tweaking will be tougher, I'll solder some sockets.

I hear you, it will be tougher.  as I always say, if you can, re-breadboard it, as it will save you the time and trouble and potential damage to components with so much unsoldering and re-soldering.  Then you can go through it once with all the mods you settle on. If that isn't an option, sockets in key spots is a good compromise.  I'd socket all the JFETs slots either way, though, if they aren't already.

I have 2n5457 and J201, like in the original schem. The tone control really repends. Nowadays I've been running it at about noon, but I used to run it at about 3 o'clock. It varies between 12 and 3 o'clock.

Question -- have you tried a Box of Rock before, and if so, what do you think of it?  It's a good tonal reference for a Plexi kind of sound in a pedal, and can help figure out more of what you do and don't want, by comparison...

Usually I'd say put the C13 and/or C14 on toggles of some kind to control the darkness of the overall voicing, but it sounds like you don't mind the 'stock,' dark tone?  If your ideal 'plexi' has more high end clarity than the '80's' tone, try unsoldering C13 or C14 at some point and see if you like it more or less (in conjunction with the tone pot).

Lowering gain (Making R3 and or R10 bigger) will probably make it seem brighter, though.  I'd focus on getting the gain and dynamics more in your range first, before doing too much tone stack stuff depending on your wants.    If you get the dynamic response and gain range you like, but you're not using the tone control below noon, THEN I'd try making C10 smaller and/or modding C13, so the tone pot is more usable along it's whole range, but it may not be necessary if you like the range and don't find it overkill.

Won't removing C3 reduce gain and some bass response?
What values do you recommend for C3/R3?

Removing C3 should reduce gain, but will make the bass response bigger if anything, if I'm not mistaken.  C3 at around 1uF will have the effect of creating more gain, but does so more for for higher frequencies and tightens the bass to some degree.

I never tried messing with R3 with the 2N5457s in there, as I went right to the MPF102s at that stage and left them there much to my delight.   But from other expiriments, I'd guess and say, leave C3 in, Make R10 something slightly more middle of the road like 1K, and make R3 4.7k to start.  See if that makes it more dynamic and responsive to picking strength and more reasonable along the gain range.  Tweak from there. 

Reducing gain of the first stage (increasing R3) should serve to make the input stage more responsive to dynamics as it likewise lowers overall gain.  Likewise, tweaking R10 will more so hone in on the overall gain range....it all depends greatly on what your ears like and what equipment your using to drive it...

I had the same interest in getting a little more flexibility out of the BSIAB2 (which - out of the box - is the best distortion I've ever heard).  My solution was to replace the single-knob tone control with a Baxandall tone stack, and add a clean recovery (gain) stage at the end.  The Baxandall is more flexible than any of the other amp tone stacks, and doesn't have a built-in mid scoop.  I like this solution better than all the other mods (and I did try them).  The result was awesome.  If you have any interest in this, search for the "Infinity" thread here for ideas about how to implement it.

This interests me. But duncan's tone stack calculator with the 'James' (Baxandall) setting seems to be different than you describe.  With both controls set mid way, it's fairly flat, but has a LOT of gain loss (hence the recovery stage. Increasing treble or bass creates a BMP-type contours, and increasing both sure does scoop the mids like a stock BMP set midway.  The BSIAB style BMP tonestack is mid-humped, if anything.  So  I'm not seeing the advantages of such a complicated RC network over tweaking a BMP type...tell us more.   

[liquids]

So  I'm not seeing the advantages of such a complicated RC network over tweaking a BMP type...tell us more.   

Oh and while it is good information for other guys who can start from scratch and do a vero/perf/homebrew pcb themselves, the Baxandall or other tone stacks are not an easy option for those using the PCB, like the original poster...

[DWBH]

Question -- have you tried a Box of Rock before, and if so, what do you think of it?  It's a good tonal reference for a Plexi kind of sound in a pedal, and can help figure out more of what you do and don't want, by comparison...

Unfortunately I haven't.

However, I've seen some demos and it does sound good. It definitely has less gain than the stock BSIAB, and it seems to respond better to pick attack.
And the voicing is close to what I'm looking for. I will not say it is what I'm looking for, because I haven't tried one yet in person.

[DWBH]

EDIT: the original demo of the BoR sounds very good. However, in other demos it sounds too bassy.

[liquids]

Okay...I had a BoR which my BSIAB replaced, so I was going for that vein barring the excessive bass content, the drive knob having too little range of useful gain, and the way I grew to hear it 'fizz' with too much signal on the input from hot humbuckers, and needing to run the tone knob too low to not sound excessively harsh.  I know that sounds like a lot, but it is a great pedal, just close but no cigar, even for $200.

Thats also when I found out about the BSIAB, grew tired of swapping pedals a couple times a year, and decided to take the DIY plunge.  So I've tweaked my BSIAB 2 to address those issues, and I like the texture far better than the BoR, to boot.  The BoR is far brighter overall than the BSIAB despite having very similar tone stacks, if what I've heard and seen is correct.  With the mods I've proposed the BSIAB will still have more gain range, not be as harsh in the treble, clip a bit more gracefully, and will not be as unnaturally tubby on the bass.

[DWBH]

Thanks a lot liquid.
I'll give these mods a try this weekend or next week. I'll report back.

[waltk]

This interests me. But duncan's tone stack calculator with the 'James' (Baxandall) setting seems to be different than you describe.  With both controls set mid way, it's fairly flat, but has a LOT of gain loss (hence the recovery stage. Increasing treble or bass creates a BMP-type contours, and increasing both sure does scoop the mids like a stock BMP set midway.  The BSIAB style BMP tonestack is mid-humped, if anything.  So  I'm not seeing the advantages of such a complicated RC network over tweaking a BMP type...tell us more.   

OK. Imagine (or look at) the James (Baxandall) tone stack in Duncan's Tone Stack Calc.  With the knobs set in the middle, you have a fairly flat frequency curve with a 22 or 23 dB loss.  Now imagine you add a clean boost of about 23 dB.  The combined result is a flat frequency response curve at unity gain.  The good news is that you still have the two knobs set in the middle that you can turn up or down.  If you turn them both up, you have a mid-scooped frequency curve.  If you turn them both down, you have a mid-humped frequency curved.  In between these extremes, you can get any kind of curve you want.  If you make your booster variable in gain, you can adjust for any amount of attenuation or boost caused by the tone stack.

So how does that compare with individual tweaks to the stock components of the BSIAB?  IMHO, it's a lot more flexible.  You would probably be able to dial in a fantastic tone by swapping components - essentially shaping the frequency curve to sound good in one situation, but your single control knob still limits what you can adjust.  It only lets you wiggle the ends of your carefully modified frequency curve in opposite directions.  What if next week you want a different fundamental shape of your frequency curve because you are plugging into a different amp?

In practice, I was able to remove the tone and volume controls from the end of the BSIAB, and add the James tone stack with a variable gain boost.  The result was all the tone flexibility I was looking for (I almost couldn't believe how good it sounded).

Oh and while it is good information for other guys who can start from scratch and do a vero/perf/homebrew pcb themselves, the Baxandall or other tone stacks are not an easy option for those using the PCB, like the original poster...

Good point.  I know what it's like to have limited resources - but where there's a will, there's a way...  I would probably make him a new PCB if he asked.

[waltk]

Just a minor clarification from my last post (before someone else points it out)...

you can adjust for any amount of attenuation or boost caused by the tone stack

The tone stack, by itself, can only attenuate the signal.  When combined with a booster, though, you can get an overall boost as compared to the input.

Also, I still want to dial back the amount of distortion from the BSIAB - so I'm going to try one of mods mentioned above.  Thanks for sharing them.

[DWBH]

So I did a couple of mods.
Reduced gain in transistor before tonestack, and in Q1. Increased all those C2/C7/C4 caps.
Gain is more tamed, good.
Good bass response. Treble can be too much, but that's why the tone control is there.
However, it sounds a bit hollow in the mids. Any tips to increase it?
The way I hear it is that it's too hollow, missing some balls to it, and I think increasing the midrange would be a good mod.

[liquids]

Too much treble and lacking mids is not a typical complaint.  It could be that everything is correct and that's just how you hear it, but triple check the values you are using in the tone stack.  There should be plenty of mids even into a mid-scooped amp....I can't imagine someone finding this lacking mids compared to a a 'rectifier' circuit...the reason I love this thing so much is that it's got so much nice midrange (amongst other things), that you hardly know it's not tubes....

Some ideas of things to check...check to make sure C5 and C6 are the right values.  Make sure R5 is the right value, and is making connection, or else you'll be filtering everything through a 470pf cap exclusively.   Make sure R8 is 82k or 100K....triple check everything.

It's very easy to mistake 4.7k for 470k and visa versa...or '222' for '223', etc.  Look it over carefully...

There's no natural way to just 'add mids' here since it's so rich in mids... You can make C5 something like .01uF (103), which should 'enhance' the mids and low mids; one guy I know liked that.  560pf is another common swap, but might be more subtle.
Trimming fizzy highs carefully will make it seem thicker in the mids.   I like C6 in there, but you can clip C6 to reduce the sheen with lower gain knob settings.   You can trim the highs more via increasing C13 and C14--try making one or both bigger, .0033uF (332) or .0047uF (472), etc.  Lots to try.  Breadboard it if you can.

[DWBH]

I took C14 out. It sounds too 'closed' with it in. I don't mind the extra treble though. It's that midrange thing...
R10 is now 3,3k, and R3 is 2,2k
C4, C2 and C12 have 100n, 0,1 and 104K written on the surface, respectively. So they're all 100nF.
However, now that you're talking about checking values, C5 seems to have 2A472K written, which means 4,7nF, instead of 470pF.
And I think C1 isn't right either.

It sounds like marshall-y, but when compared to a Rat, for example, it lacks in mids. It's not ballsy.

[liquids]

Ah..while your swapping that 4.7n cap out, swap it in for C10.  That will make the tone control the high end more so, and have less affect on the midrange.  I've done that with both of mine, and prefer it.

[caspercody]

I tried the baxandall tone stack, and it make a huge difference in the sound. I want to try to get the sound of Wamplers Pinnacle pedal, and I read in another forum that he wrote how his pedal is designed;

Pinnacle (i think I stated this somewhere else, but can't find the thread)... basically a jfet mu-amp (bsiab-ish) setup, into that big muff style tone control, into a variable twin t type filter for mid control (contour), into a jfet (actually, your version just goes straight out to volume here, but the newer version goes into another jfet stage then to volume).

bright switch is a normal cap to ground off of the twin t, it just lifts it off ground.

The big box ecstasy had the bass control wired like the timmy pedal, just a pot off the feedback loop.

The pinnacle gain switch just changes the resistors on the mu-amp gates. As far as building kits, (and even pedals really...) you never make money by building pedals... you make money by SELLING pedals. And honestly, more time is spent in talking to customers than building pedals. If I had to build everything myself I wouldn't sell anything.

bw

I want to try this, but I am not sure what the variable twin t filter is? I think it may be like the AMZ presence control?

Would this be the 70's, 80's sound you are looking for? Would love to work on this with someone here?

Thanks
Rob