freestompboxes.org

Here's my take on the BMP tone control. This goes from extreme mid-scoop with the bass and treble all the way up, to flat, with the controls halfway, to mid-humped (like a Tubescreamer) with the two controls down a bit. The output might be a bit low for some - add the original gain make-up stage after the FET if you want, but the FET prevents the tone control being loaded down which would spoil all the fab toneliness!
Enjoy!

This looks really cool! I have one question. Why the two 1n & two 10n pots in series on the 470K pot?

jrod wrote:This looks really cool! I have one question. Why the two 1n & two 10n pots in series on the 470K pot?

Simple - I didn't have 500pF and 5nF caps in stock, and 1nF and 10nF are much more common values. You could use 470pF and 4n7F caps (with a slight change in response), but it's easier to use the series caps!

This looks interesting, have you compared it to the AMZ Precence Control ?
http://www.muzique.com/lab/tone3.htm

A baxandall tone-control.....

....reminds me to the Ibanez OD-850 (first version)
http://analogguru.an.ohost.de/193/schem ... e_1974.gif
which uses an active baxandall-version without the signal loss.

analogguru

analogguru wrote: A baxandall tone-control.....

....reminds me to the Ibanez OD-850 (first version)
http://analogguru.an.ohost.de/193/schem ... e_1974.gif
which uses an active baxandall-version without the signal loss.

analogguru

i was going to mention the same style of tone control similar to this-
http://scopeboy.com/baxeq.html

haven't seen that 850 schem before, though. i like the idea of a single pot version. i came up with one using a dual 100K pot, but i'm always down with doing away with the dual pots if i am able to.

JshDnls wrote:This looks interesting, have you compared it to the AMZ Precence Control ?
http://www.muzique.com/lab/tone3.htm

Yes. It's not the same - my way, using the passive James / Baxendall configuration is much more effective (and I spent a lot of time getting the values right!).

The circuit as shown goes from flat through to extreme treble boost or cut and extreme bass boost or cut. Manipulation of the controls will give mid scoop, mid hump, thin toppy fizzy Telecaster into a Tonebender Mk III sounds, and lots of others. I've tried active versions at that point to remove the loss, but I found that the amplifier stage for the Baxendall would, itself, get driven to distortion which isn't a good idea (it sounds horrible) and the range of control available is smaller than with the passive version.

There's so much level available after the second clipper stage that I found that a gain make-up stage wasn't necessary - the "unity gain" point on the output pot was about halfway up so that the level was the same when the tone controls were set "flat" and true bypass was used.

The other point I modified was to put a FET in front of the input amplifier to raise the input impedance to modern standards - I made the first stage a FET/ bipolar hybrid. This made the signal through the effect have much more top end (the original input stage loads down a guitar pick-up, which is why it has that "mid" tone that has to be tamed by the bypass capacitors in the clippers and a scooped tone control.

If you put the FET circuit in, you then have to increase the values of the bypass capacitors in the clippers (I used 1n instead of 470p), or put in some kind of lowpass filter before the clipper stages to keep the sound the same.

I'll follow up with a schematic for the Big Muff Super-Plus which has a few other mods too (and is the one I use on stage).

analogguru wrote: A baxandall tone-control.....

analogguru

Actually, no. It's a "James" tone control, and pre-dates the Baxendall (which is the active version) by several years. I went passive because I didn't like the additional, nasty distortion added by the Baxendall amplifier stage getting driven hard by the huge level from the clipper stages. You could leave the tone control until after the level control, and go active, but you'd introduce unnecessary additional noise and still run the risk of distortion in that stage at higher level settings.

Also, there's the problem of "voicing" the Baxendall - it's difficult to get the actions of the tone controls close in frequency (like you really want in a guitar effect) - it's OK in a hi-fi amplifier where you're interested in a wide frequency response with treble and bass controls centred at 200 Hz and 8 kHz (with specifications quoted at 100 Hz and 12 kHz to show +/- 10dB of boost and cut). If you try to get the control ranges close together, you can get instability, noise and the range of control is disappointing anyway!

The values I use in the James circuit give a huge range of control at little cost, and with frequencies chosen to be musically useful with guitar. To "voice" for bass, just double all the capacitor values to take the controls down an octave!

Nice, thanks!
Any test with some low gain trannies or some Ge?

Duckman wrote:Nice, thanks!
Any test with some low gain trannies or some Ge?

There's no point whatsoever in building a Big Muff with germanium transistors - the effect of them is entirely swamped by the effect of the brutal clipping introduced by the diodes. I have tried germanium diodes for the clippers, but all it does is reduce the level at which the brutal clipping begins - the "sound" isn't really any different, because you're just going into squarewave territory anyway - you're not really going through the magical transition point where the V/I graph curves with germanium.

You can try low gain transistors, but again, there's no point. The Big Muff is designed to do what the Big Muff does best and really square the signal and then filter the hell out of the harmonically rich mess coming out of the clippers! All I've done is give you more control over the filtering, so that you have a wider range of tones available (some of which don't sound much like a Big Muff at all!).

Incidentally, I'm getting more and more anti-germanium. I have all sorts of issues with the temperature sensitivity of the transistors, and can't be bothered with the effort required to build compensation circuits to "fix" the problems introduced by old fashioned components. If you want the "soft" distortion introduced by gently driven germanium transistors, there are ways of doing it with modern FETs - in the usual "blind" tests even the "golden-eared" can't hear any difference.

Thanks again, mictester.

I'm not a germanium lover Just asking for curiosity

mictester wrote:The Big Muff is designed to do what the Big Muff does best and really square the signal and then filter the hell out of the harmonically rich mess coming out of the clippers!

Totally agree!

Slightly updated version - more top end because the guitar doesn't get loaded down as much! The FET input stage really makes a big difference.
Next, I'm going to put the final gain stage back on. Initial experiments using the FET buffer for some gain proved too noisy.

Duckman wrote:Thanks again, mictester.

I'm not a germanium lover Just asking for curiosity

mictester wrote:The Big Muff is designed to do what the Big Muff does best and really square the signal and then filter the hell out of the harmonically rich mess coming out of the clippers!

Totally agree!

duckman, see this thread: viewtopic.php?f=13&t=8856

i found that germs smoothened out my attack a lot more than silicon did, but the aggressive clipping is retained well. there were some seriously liquid lead tones, not really showcased in this clip though. will be updating the thread with a new layout, once it's verified.

mictester wrote: There's no point whatsoever in building a Big Muff with germanium transistors - the effect of them is entirely swamped by the effect of the brutal clipping introduced by the diodes. I have tried germanium diodes for the clippers, but all it does is reduce the level at which the brutal clipping begins - the "sound" isn't really any different, because you're just going into squarewave territory anyway - you're not really going through the magical transition point where the V/I graph curves with germanium.

I've tried over half a dozen different silicon transistors in the Muff circuit and you can hear a difference in different silicon transistors in the same gain range. I'm not saying that every single one sounds drastically different, but in testing different ones you can hear groups that sound similar, etc. There's a lot of diode clipping in the Muff for sure, but I definitely would not write off transistor selection if you plan on tweaking.

SpencerPedals wrote:
I've tried over half a dozen different silicon transistors in the Muff circuit and you can hear a difference in different silicon transistors in the same gain range. I'm not saying that every single one sounds drastically different, but in testing different ones you can hear groups that sound similar, etc. There's a lot of diode clipping in the Muff for sure, but I definitely would not write off transistor selection if you plan on tweaking.

In the last 30 years, I've built hundreds of Big Muffs, and I can assure you that you just need high gain transistors to get the classic Big Muff Pi sound. It doesn't matter which ones you use (any silicon transistor with an Hfe of > 250 will sound exactly the same). I've experimented with different transistors, different diodes, even germanium devices (though I'm very much against germanium these days). I've changed the value of every component in the circuit, and the best sounding version I've heard is the slightly modified "triangle" version that I turned into the Big Muff Plus with an improved tone control and an input buffer.

Please don't waste your money on expensive germanium parts!

I've got to side with Mictester here... I tried an all MPSA13 big muff first with one in each stage seperatley and then altogether.. could I hear a difference really? No.. it just saturated at the same point the diodes clipped anyway.

I also tried different diodes, sod all difference between 1N4001 and the stock 1N4148 (where as usually that would be fairly noticeable in another pedal) the combined clipping saturated once again at the same point, the only difference I really got was when removing a pair of diodes, then things changed drastically (and changed it into a Jumbo Tonebender)

mictester wrote: In the last 30 years, I've built hundreds of Big Muffs, and I can assure you that you just need high gain transistors to get the classic Big Muff Pi sound. It doesn't matter which ones you use (any silicon transistor with an Hfe of > 250 will sound exactly the same). I've experimented with different transistors, different diodes, even germanium devices (though I'm very much against germanium these days). I've changed the value of every component in the circuit, and the best sounding version I've heard is the slightly modified "triangle" version that I turned into the Big Muff Plus with an improved tone control and an input buffer.

Please don't waste your money on expensive germanium parts!

I definitely agree that all high gain silicons I've used did lead to a Muff sounding device, but would still have to disagree that they sound "exactly the same". The differences will be subtle, and far more so than a new tone control, but I was able to notice that some sound different. It's not a "booster overdriving other boosters" circuit, so saturation isn't as large a role, but I'd advise one to try a few transistors out. Certainly not if it's going to break the bank or if you're expecting it to sound like an entirely different circuit, though. I'll be getting a Muff on the breadboard next and look forward to playing more with the clipping stages, particularly trying out the Top Fuel style MOSFET clipping. The reworked tone control looks interesting as well. I'll be giving that a shot. The circuit has room for tweaking, hence much of Skreddy's earlier line. It was my favorite all-around fuzz prior to the addiction and continues to be. I look forward to the evolution of the Plus idea.

SpencerPedals wrote:
I definitely agree that all high gain silicons I've used did lead to a Muff sounding device, but would still have to disagree that they sound "exactly the same". The differences will be subtle, and far more so than a new tone control, but I was able to notice that some sound different. It's not a "booster overdriving other boosters" circuit, so saturation isn't as large a role, but I'd advise one to try a few transistors out. Certainly not if it's going to break the bank or if you're expecting it to sound like an entirely different circuit, though. I'll be getting a Muff on the breadboard next and look forward to playing more with the clipping stages, particularly trying out the Top Fuel style MOSFET clipping. The reworked tone control looks interesting as well. I'll be giving that a shot. The circuit has room for tweaking, hence much of Skreddy's earlier line. It was my favorite all-around fuzz prior to the addiction and continues to be. I look forward to the evolution of the Plus idea.

Fair enough. There is plenty of room to experiment. I don't really see the point in trying MOSFET clipping - it's going to be the same as using germanium diodes or LEDs - you'll just get the onset of clipping at different levels.

Someone else pointed out that it's worth removing or making one of the diode pairs switchable, so that you can get a Jumbo Tonebender option. I tried this, but found that the difference wasn't really worth it - the Jumbo Tonebender never really had enough gain for me (though many big names love the things), and I've built lots of those too.

mictester wrote: Someone else pointed out that it's worth removing or making one of the diode pairs switchable, so that you can get a Jumbo Tonebender option. I tried this, but found that the difference wasn't really worth it - the Jumbo Tonebender never really had enough gain for me (though many big names love the things), and I've built lots of those too.

In your experience, does removing the Q2 clippers raise the level enough to drive Q3 to saturation? I planned on playing with that idea, as it seems if you could pull it off you could get saturated transistor and diode clipping going on at the same time. Definitely leaving the traditional Muff sound, but it could be interesting if pulled off.

SpencerPedals wrote:

mictester wrote: Someone else pointed out that it's worth removing or making one of the diode pairs switchable, so that you can get a Jumbo Tonebender option. I tried this, but found that the difference wasn't really worth it - the Jumbo Tonebender never really had enough gain for me (though many big names love the things), and I've built lots of those too.

In your experience, does removing the Q2 clippers raise the level enough to drive Q3 to saturation? I planned on playing with that idea, as it seems if you could pull it off you could get saturated transistor and diode clipping going on at the same time. Definitely leaving the traditional Muff sound, but it could be interesting if pulled off.

Yes, but all you get of you remove the second diode pair is rail-bashing which sounds horrible, and if you remove the first pair, you have to increase the gain of Q2 a bit (I reduced the emitter resistor). This gives you the Super Tonebender, which is just the same sound as the Big Muff but with reduced sustain (and often gives increased noise). The original Tonebender variant had slightly different values in the tone control circuit, and always sounded pretty weedy to my ears.

The Big Muff was a major improvement. I can remember seeing my first one - in 1969 - and it stayed intact for about an hour, while I saw what it could do...

I can also remember being very disappointed when I took it apart and found what was in it, though unlike the other things I'd used before (two transistor fuzz faces, three transistor benders and so on) the Big Muff Pi had four transistors! I can remember also sketching the circuit of the thing, and building a duplicate on 0.15" pitch Veroboard (which you can't get any more). The one I had was a "triangle" type, with big diameter, serrated knobs that you could tweak with your foot. I gave it "true bypass" as soon as I discovered the treble reduction it caused, even when "bypassed", especially with single-coil pickups.

That first weekend, I made (I think) four or five of them for friends, two of which (I know) are still in use today! These clones were the first effects I ever built into diecast boxes, and their longevity suggests that all effects should be built into diecast boxes! (Either that or I built them well!). They used BC109C transistors and 1N914 diodes, and had "triangle" values otherwise. I was worried with the first one I built, in case the change of transistor would affect the magic, but the BC109C hissed less than the originals, and otherwise gave exactly the same sound, so I needn't have been concerned!

To this day, it's one of my favourite effects circuits. It's astonishingly simple, and it surprises me that nobody came up with that sort of idea before. Everybody else was really just doing variants of the Fuzz Face / Tonebender, though I did see one early op-amp Fuzz (diodes to ground after a simple inverting op-amp stage, using a metal-canned circular 301), which I think was made by Schaller, and sounded terrible!

Board layouts and modifications to follow soon! Also - how to use a CA3046 to make your Big Muff complete with LED indicator. Also - new project - using a 3046 for perfect transistor balance for your frequency doubler in a Superfuzz!