trying to get rid of the "blattiness" of my Big Muff

[runmikeyrun]

I built a BMP from this schematic.  I'm using it with a 5 string bass guitar tuned to B standard.  It has that "blattiness" (sort of a peaked high-mid frequency) that is typical with some big muffs when used on bass, especially on the lowest notes.  I am trying to get rid of it.

I noticed that if i roll off my bass knob on the bass (it has 3 band active EQ) it smooths out the sound to how i like it, but obviously i lose low end.  If you'll notice, there is a cap blend mod on the input of the pedal, but turning it towards the smaller cap only reduces gain and the "blat" is still there, so i'm not sure it's an issue of too much bass, but maybe more the power of the low end overloading the input.  Using an audio probe, i notice the "blat" becomes really prominent after the 3rd gain stage.

I've tried numerous diode and transistor configurations and to no avail.  I'm currently using (3) 2N2059s and (1) MPSA18.  The MPSA18 is in the 3rd transistor socket, which has helped tame the "blat" a bit.  The 2N5089s are about 550 hfe, the MPSA18 about 900 hfe.

Does this make any sense?  I know that the sound is somewhat inherent to this circuit, but i really like the sound of it when i roll off my low end knob on the bass.  Does it sound like too much bass getting through to the 3rd gain stage?  Or is it just my active electronics screwing with the way the pedal reacts?  All transistors, clipping diodes, coupling caps, and caps on the clipping diodes are socketed so changing them is easy, it's just my ears are getting tired and i'm not sure what is helping or hurting anymore.

[azrael]

Try changing the 47n's in the clipping sections to 100n.

Also, reduce that 10uF output cap, maybe.

[jefe]

I've tried numerous diode and transistor configurations and to no avail.  I'm currently using (3) 2N2059s and (1) MPSA18.  The MPSA18 is in the 3rd transistor socket, which has helped tame the "blat" a bit. The 2N5089s are about 550 hfe, the MPSA18 about 900 hfe.

I've got a triangle big muff on the breadboard right now. I'm using 2N5088's (x4), all with hFE in the 305 - 315 range. Sooo... 550 and 900 seem really high to me. Maybe try some 2N5088's, or something else with a lower gain? I have absolutely no idea if that will help, but I thought I'd throw it out there.

Or is it just my active electronics screwing with the way the pedal reacts?

Seems like a possibility. Again, I'm just talking out my butt here, but don't active electronics put out a "hotter" signal? Maybe you're just feeding a bit too much signal in to your big muff?

I'm not much help, am I?

[runmikeyrun]

Thanks for the suggestions guys, i appreciate it.  I did change the 100n cap right after the sustain control to 10n, seemed to help a lot, without any appreciable loss in low end.  I had to go with big increases on the caps in the clipping sections to get any change in tone, but also with a huge decrease in fuzz.  I'm still working on it...  I did try some 2n3094s to see if it would make any difference, and it really didn't.  I'm going to continue to experiment.

[Mark Hammer]

I think you've nailed it when you allude to rolling off the bass from the input signal.  There are a couple of points where that can be done early in the signal path, such as the input cap before the first non-clipping gain stage, and the cap before and just after the "Sustain" control.

[Derringer]

A clean blend should do wonders for preserving your bottom end

check out the buff'n'blend circuit

[petemoore]

  Maybe the signal level entering the 3rd stage is enough larger than the 2nd stage to make it 'blat', try attenuate [increase that interstage resistor or put a 2nd sustain type deal in there is intrusive...but without a scope or even with, perhaps that stage is getting such a hot signal that the transistor or diodes clip so early on in the waves longer travels from Vbias.
   5 string bass is probably a lot of bass anyway.
  Suggestion that maybe some circuit re-voice [room for switch or even just the 'pullwire' can do wonders, try it out...yank the wire and then be glad you tried before installing a switch for that]..
  oh yea, similar to what you tried @ a bass guitar control but it took too much bass out, perhaps allow bass to grow until later in the circuit [up to after stage 2 or so] then HP filter it enough to tell whether that's a portion of the ticket to fat w/o blat.
  I say portion because voicing and gain staging structuring [making the clipping stages both clip unevenly or evenly] is a balancing act in which you start with 'someone elses center' [ie round and round it can go until some intuitiion about where your 'center' is as far as balancing the countless variations in attenuation/frequency/gain etc.
  Anyway sounds like it's pinned down to not before the 3rd stage, and some tricks ''pre-stage-3'' in your muff circuit might increase the fat before blat.
  Increasing the supply voltage is another possibility to try when curbing bass overdrive-blat, perhaps best to decide on a voltage or voltages for stage supplyies before doing gain structureing/diode seledtion etc. since it'll throw everything into or off center.

[WGTP]

There is always the Duncan Tone Stack calculator to experiment with different EQ settings in the tone control section... 

[Mark Hammer]

A clean blend should do wonders for preserving your bottom end

check out the buff'n'blend circuit

That would be the other strategy to deploy.  Keep in mind that the existing tone control already imposes a midscoop that exaggerates the amount of bass, or at least is capable of doing so.  My own instinct is to touch up the low end just a bit and see if that does the trick.  And if not, THEN opt for the clean+fuzz blend.

[Derringer]

A clean blend should do wonders for preserving your bottom end

check out the buff'n'blend circuit

That would be the other strategy to deploy.  Keep in mind that the existing tone control already imposes a midscoop that exaggerates the amount of bass, or at least is capable of doing so.  My own instinct is to touch up the low end just a bit and see if that does the trick.  And if not, THEN opt for the clean+fuzz blend.

right on, if you can get the sound you want by just changing some caps then by all means, do-it-to-it

I became a big fan of the clean-blend maneuver when I performed it on my bass player's stock big muff. You get that low end thunk along with the high end sizzle/drive.
Bass is such a different animal than guitar when it comes to getting a distorted sound that still yields functional low end

hell ... I'm talking to the guy who designed the Gruntbox though ... preaching / choir / etc 

[Mark Hammer]

Clean blend is a frequent feature for anything aimed squarely at bass players because - drum roll please - YOU ALWAYS GOTTAS HEAR THE FUNDAMENTAL CLEARLY FOR EVERYTHING ELSE TO HAVE ITS INTENDED IMPACT.

Having said that, however, Mikey only made clear what it was he didn't like about his tone, and not specifically what he was aiming for or how he was intending to use it.  So, it may be that all he really needs to do IS tame the bottom a bit on the input, and maybe tailor the tone-control a teensy bit, OR maybe he needs to pursue the other route and do a split-n-blend.

The nice thing about DIY, of course, is that one can pursue whichever course of action works best for one's own context, right?