More BSIAB 2 Q's and mods

[DWBH]

Thanks liquids. Apparently, that did it.
Now I see those mids you're talking about. I changed C5 to 470pF, just like it says on the schem, and C1 to 330pF.
Changed C10 to 4,7nF. More action on treble only.
I'll probably build another BSIAB, with other tonestacks and mods. This one is my first pedal, and I can't recall how many times I unscrewed those screws to peek inside and mod it.
Hopefully this will be the last time I close it. (or not!)

[liquids]

Thanks liquids. Apparently, that did it.
Now I see those mids you're talking about. I changed C5 to 470pF, just like it says on the schem, and C1 to 330pF.
Changed C10 to 4,7nF. More action on treble only.

At this point I've shared some of these simple mods with about a dozen people and it's a lot of (poor) typing and cloudy recollection every time...I've got to get around to just hacking out a schematic so I can say "here, try this."  Maybe today is the day I 'get around to it.'   

I forgot how integral that part of the tonestack mod I did to mine is.  My mind wrongly convinced me that the difference in values between 22n and 4.7n just make the treble end roll off darker vs less intense,  but when I looked at it on the tone stack calc, I realized -- holy crap, .022 that cuts a lot of mids out! No wonder I modded it.   I've talked to a few via PM and e-mail about mods and usually forget to mention that part...oops.    A switch for C10 makes sense too come to think of it.  I guess the 'contour mod' of making R7 a pot effectively does similar things, but is controllable in realtime, though the interaction between the 'contour' and 'tone' could be a little more overwhelming than choosing one cap or the other on the a switch...hmm, more ideas here.   

I'll probably build another BSIAB, with other tonestacks and mods. This one is my first pedal, and I can't recall how many times I unscrewed those screws to peek inside and mod it.
Hopefully this will be the last time I close it. (or not!)

Funny you mention that---the BSIAB was my first pedal, too.  And it's my main source of 'dirt' live.   I've breadboarded and re-breadboard it, and still, like you, have still 'unscrewed' that thing to peek and/or mod...both too many times to count!        though I'm incredibly happy with mine every time I play them, I endlessly fantasize and ponder how I could improve just about everything, so this no exception.  Since I was so new when I build them, when I now learn new things about circuits, I think back to how I could implement that knowledge into my BSIAB...  tweaker's 'disease.'   

So, how do you like it now?  Is it Plexi-ish and 70s enough, as you started out wishing?  Will you use it, or is it just another dirt pedal?

I think other tonestacks are interesting, though I'm mostly just sensitive to treble, so rather than need a baxandall, I added on-off-on switch to shape high end (C13 and C14) in conjunction with the tone stack, rather than needing anything radical like the baxandall provides, but it seems cool and highly versatile in theory if you can dial in the values for the right frequencies.

[earachemyeye]

This is a great thread! Thanks for the tips Liquids! I built one of these about a month ago and was not very pleased with it. It just didn't match up with my amp well at all. I desoldered the aformentioned caps and socketed them so I could play around with the values and I love it now. It's "tuned" to my amp. DIY rules.

[liquids]

Glad that helped!

I cracked open one of my BSIAB w/similar mods this week, and decided to mess with the socketed JFETs, because-- why not?    I'm much more familiar with the tones I get from after playing it for months than I was at first, and don't remember why I chose some of those JFETs.

I had the first stage as MPF102s, second pair as J201 (stock) and the third as 2N5457 (stock).  I decided to see what it would be like if I changed the J201s out.  2N5457s here made little to no difference to my ears.  I was going to close it up again, but just for the heck of it I swapped in MPF102s for that stage. 

Suddenly, it got even MORE dynamic and vintagey, which it already was with the MPF102s in the first stage, the gain and tone mods. My guitar's volume control became even more useful (like a cranked up amp) from mean to clean, and now no matter how the gain knob was set.  Previously there was more so a range on the pot where I could still clean it up with the guitar volume, but beyond a certain point the gain was too 'compressed' to clean up how I wanted.  To boot, the high end sweetened, and the maximum available gain went way down but it stillmore than enough gain for me.

Previously I used the gain knob at around 11 o'clock.  With the new arrangement, running the gain at max is about how much gain the previous arrangement would have been at 1-2 o'clock I'd guess, so it still gets hotter than I typically need, BUT, at that setting it cleans up really well, and is more dynamic and vintage sound, with slightly sweeter clipping tone overall to boot.  The 'tightness" switch I have became much more effective as well.

I finally made a schematic of all these mods I like: http://sites.google.com/site/liquidselectronics/bsiab-mods. 

You will want to click on the schematic image when you get there, to get rid of the frames.  Enjoy!   

[caspercody]

Do you happen to have a sound clip of your changes?

Thanks
Rob

[WGTP]

Beyond mods to morph...  Maybe some ideas... high gain... the tone control has a big mid notch...  cool sound...   

http://www.aronnelson.com/gallery/main.php/v/WGTP/Sweet16.gif.html?g2_imageViewsIndex=1

[liquids]

Do you happen to have a sound clip of your changes?

Thanks
Rob

No, sorry, it's unlikely I will anytime soon...since the variables are so high (guitar pickups, strings, amps, mic, soundcard, etc) I would want to do a soundclip in comparison to a stock BSIAB 2, otherwise the sound clips would be arbitrary to me.  I doubt I'll find the time to rig up a stock one anytime soon, you know how it is.  You'll easily have one breadboarded or build in far less time.  But maybe someday I'll get to it.    

The best I can say is, tonally, it's somewhere between the BSIAB and a tubescreamer, like a BoR without the tubby bass and a sweeter high end.  Definitely more mids than the BSIAB 2 stock.  Yet  not nasal like the tubescreamer.  Fairly bass neutral, dynamic rather than compressed (like the BoR),  far more friendly to cleanup, and far less fizzy than the BSIAB.   A focused tone, though not overly focused as I find tubescreamers to be.  that doesn't 'dissapear' when other instruments play; it works and cuts extremelywell live.   Hopefully that will make you try it for yourself.    

Also, I was able to put two of these side by side last night and A/B the differences.  The schematic reads MPF102s for the second stage, which I like on one hand, because it's super dynamic, open, and that is perfect for rhythm playing, very much vintage marshall, and VERY bluesy with the second filter cap bypassed, playing single notes and a neck pickup backed off to taste.  

For leads, however I'm using one with 2N5457s for the second mu-amp stage. Now that I've a/b'ed, I find it is noticeably nicer tonally than the J201s I had in there, but it has a bit more sustain for leads than the MPF102 version.  It still clean up very nicely like a BoR, but not as quickly as the 'rhythm' pedal with MPF102s.  So many good tones in there!  Pick your poison.  

[caspercody]

I have an extra BSIAB pcb board, almost threw it away, now I am going to build a second one with your changes.

Question, is the sound of your changes closer to the Brown sound than the original BSIAB?

Reason I ask is I bought Brian Wamplers book, how to build your own pedals, and he has a mu-amp pedal schematic in here that is so close to what you did. And I read a description he wrote about his Pinnacle pedal and that it is a BSIAB-ish design with a BMP tone stack with a variable twin t filter (not sure exactly what this looks like). I want to get this sound, similar to the Pinnacle, and just wondering if your changes sound closer to this?

Thanks

[liquids]

I don't know...wouldn't compare it to the brown sound, the stock one is probably closer.  I've never seen Brians book.  Maybe he can speak to that.

[DWBH]

Wow liquid, that vintage mods schematic looks tasty. Might have to build another one.
I've built a stock BSIAB w/ 2n5457s one all positions for a friend, and I have to compare it to mine.
But definitely, mine sounds more open, better bass response, less raspy and JCM-ish. More vintage-y for sure. Gain at 10 o'clock sounds a bit 'closed', but it opens up as you turn the gain up to 12, 1, 2 o'clock.

Great thread indeed.

[stringman]

Just to resurrect this thread. What is a good mod for the BSIAB for me to lessen the volume and add more gain? My BSIAB is a GGG spec to the parts, but I feel the gain is stale past 2 o'clock and the volume is beyond unity. I can't even use the volume past 12 o'clock. Also is i normal when I dim out the gain I lose the volume? Thanks!

[Subzero]

liquids, could you repost the schematics by any chance ? the link is dead.

Thnx

[WGTP]

When you cascade the 2 - 10k/2n2 networks, the filter frequency drops by 65% and becomes 12 db/oct instead of the 6 db/oct of a single filter.  You can vary the values and get different slopes.  Or, when you get older, you won't need them because you can't hear the highs anyway. 

[liquids]

IMO, and from spice simulations, it doesn't become 12dB/octave.  

It does however lower the cutoff frequency...so two cascaded 10k/2.2n low pass filters is is a 6db/octave filter similar if not identical to a single 27k/2.2n filter, not just a 20k/2.2n filter. 

Passive filters can't really be 12db/octave...you need an active element and utilize feedback to get there.

Ironically these cascaded passive LPFs are used time and time again in lots of pedals now...but if you don't mind the waste of 2 components, by all means, keep it stock.   

[liquids]

liquids, could you repost the schematics by any chance ? the link is dead.

Thnx

No, sorry.  Breadboard away...

[liquids]

Just to resurrect this thread. What is a good mod for the BSIAB for me to lessen the volume and add more gain? My BSIAB is a GGG spec to the parts, but I feel the gain is stale past 2 o'clock and the volume is beyond unity. I can't even use the volume past 12 o'clock. Also is i normal when I dim out the gain I lose the volume? Thanks!

You don't need the volume to be dimed for any reason, seems kind of silly...if unity is lower, set it lower.

The thing has more gain than it should.  There are many posts on here about the gain knob being useless or (fill in your favorite adjective) somewhere from 2 oclock on.

When you crank the gain knob you are causing the JFETs to go further into cutoff and conduction, so they squash a bit like neil youngs tweed deluxe and you 'lose volume.'

This is sort of an inherent design issue...but just keep the gain knob down where it sounds better to you, and for the reasons similar to why it happens when you turn it up, it won't happen anymore.

[liquids]

[WGTP]

Cool stuff Liquids.  Glad for the information.  I don't recall where I read that.  I suspect the 2 filters are not sufficiently isolated and act like a single as your simulation shows.  I have wondered about that.  What if the second resistor is 100k and the cap .22n or I guess that would be 220pf or a buffer is inbetween?  

That should probably have it's own post.   

[liquids]

Cool stuff Liquids.  Glad for the information.  I don't recall where I read that.  I suspect the 2 filters are not sufficiently isolated and act like a single as your simulation shows.  I have wondered about that.  What if the second resistor is 100k and the cap .22n or I guess that would be 220pf or a buffer is inbetween?  

That should probably have it's own post.  

I myself said something like that 2009 early in this thread "About the filters - two caps are going to shave off more of the extreme high end than just one big cap would."     I've learned a little since then....

Second resistor being 100k and the cap being 220pf would make it something somewhat unique.  But not too significantly different from a simple, lone 18k and 2.2n filter.

[WGTP]

http://www.aronnelson.com/gallery/main.php/v/WGTP/Boss+OS+Notch+Filter_.jpg.html?g2_imageViewsIndex=1

Here is a notch filter from the Boss OS-2 that you might try.

Liquids, I would consider it a favor if you would sim this and show us the response curves.