Have a couple questions about this idea I'm breadboarding (BMP into an active EQ)

kylewetton

Active member
Here's the schematic attached as a PDF, as you can see, the EQ (EarthQuaker Tone Job), has a buffer before and after the tone network, I'm wondering

1. Should this buffer be moved before the clipping stage of the BMP? If so, where should it go in relation to the input resistor and capacitor?

2. The coupling caps between the input buffer of the EQ, If I moved the buffer, what makes sense to take with it and what should be left behind? (I'm trying to avoid copy-past'ism and learn more)

I've breadboarded this and it sounds great, I just wonder if I'm doing anything redundant or odd here
 

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Yeah, if it sounds great, it is great.


Keep experimenting!

Since you've got it breadboarded, start moving things around, deleting things — see what sounds better to you.
Move the buffer right to the front of the Muff, then try removing the first transistor stage of the Muff so it's
Op-amp buffer > Muff clipping stage 1 > Muff clipping stage 2 > BMT tone-stack > [try op-amp buffer w/ no Muff recovery, and with recovery or even swap the 2nd op-amp stage as power-buffer and skip the final op-amp buffer altogether]


I suggest having a look at Mictester's 21st Century Muff (schematic). You should be able to find it online easily.
It's not exactly what you want, with a James tone-stack, but that's kind of the point — to show you there are many before you who've tweaked the Muff in one way or another and you could easily exchange the James for a BMT ...



Personally, I'd experiment with :
- having the first 3 stages of the Muff,
- ditch the Muff's tone & recovery stage, replace with a twin op-amp BMT such as the COLD TURKEY EQ.

The Cold Turkey is a BMT that only uses one TL072 compared to the Box And All's 2 x TL072. Wouldn't be hard to swap that into your breadboard to compare with what you have.

Once you compare, then you can decide which one to build up.



Here's another option, go modular:

Build a PPCB Muffin Man (basic Muff), but don't populate the tone-stack & recovery
Build the Box & All
Build the Cold Turkey

Box it all up with the Muff feeding a foot-switch that goes to either EQ and you've got a cool dual-channel Muff with separate EQs.



Next up, go even more modular.

Look at the Muffin Crumbs, get 4 so you can build each stage of the Muff separately,
1 INPUT​
2 CLIP 1​
3 CLIP 2​
4 RECOVERY​
then as before build each EQ on its own board,
now mix and match all the boards:
Clip 1 > Clip 2 > Box EQ
or
Cold Turkey EQ > Muff Clip 1 > Muff Tone > Muff Recovery
or
Muff input > Muff Clip1 > EQ > Muff Clip 2 > Recovery (or just OUT)
or
???


You can hook all that up to each other via the breadboard and have set pieces so you're not constantly ripping apart and rebuilding an entire breadboard set up, just swapping in/out modules...
 
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A
Yeah, if it sounds great, it is great.


Keep experimenting!

Since you've got it breadboarded, start moving things around, deleting things — see what sounds better to you.
Move the buffer right to the front of the Muff, then try removing the first transistor stage of the Muff so it's
Op-amp buffer > Muff clipping stage 1 > Muff clipping stage 2 > BMT tone-stack > [try op-amp buffer w/ no Muff recovery, and with recovery or even swap the 2nd op-amp stage as power-buffer and skip the final op-amp buffer altogether]


I suggest having a look at Mictester's 21st Century Muff (schematic). You should be able to find it online easily.
It's not exactly what you want, with a James tone-stack, but that's kind of the point — to show you there are many before you who've tweaked the Muff in one way or another and you could easily exchange the James for a BMT ...



Personally, I'd experiment with :
- having the first 3 stages of the Muff,
- ditch the Muff's tone & recovery stage, replace with a twin op-amp BMT such as the COLD TURKEY EQ.

The Cold Turkey is a BMT that only uses one TL072 compared to the Box And All's 2 x TL072. Wouldn't be hard to swap that into your breadboard to compare with what you have.

Once you compare, then you can decide which one to build up.



Here's another option, go modular:

Build a PPCB Muffin Man (basic Muff), but don't populate the tone-stack & recovery
Build the Box & All
Build the Cold Turkey

Box it all up with the Muff feeding a foot-switch that goes to either EQ and you've got a cool dual-channel Muff with separate EQs.



Next up, go even more modular.

Look at the Muffin Crumbs, get 4 so you can build each stage of the Muff separately,
1 INPUT​
2 CLIP 1​
3 CLIP 2​
4 RECOVERY​
then as before build each EQ on its own board,
now mix and match all the boards:
Clip 1 > Clip 2 > Box EQ
or
Cold Turkey EQ > Muff Clip 1 > Muff Tone > Muff Recovery
or
Muff input > Muff Clip1 > EQ > Muff Clip 2 > Recovery (or just OUT)
or
???


You can hook all that up to each other via the breadboard and have set pieces so you're not constantly ripping apart and rebuilding an entire breadboard set up, just swapping in/out modules...
Awesome that sounds like a lot to look into, thanks so much!
 
You can just dip your toes,
get your feet wet,
wade in up to your hips,
go in up to your neck,
plunge...


















...DEEP!​
 
The Thorpy Fallout Cloud is a BMP with a 2-band Baxandall tone stack at the end. They did it without opamps. Doing it with opamps is fine.

I recommend putting the LEVEL control ahead of the active tone stack because as drawn, you run the risk of overdriving U2A if any or all of the tone knobs are dimed. The way I would accomplish this is to replace the U1A buffer with the U2B level control circuit. Make C14 1uF, R25 47K and LEVEL A100K. Take the output from U2A, making sure you keep R27, C17 & R28. I just saved you an IC and a handful of parts.

The EQD 3-band tone stack is crap. If you set MID below 10:00 or above 2:00 it completely overrides the TREBLE & BASS controls. I know because I built a Chela and had to mod the tone circuit. Try it and you'll see what I mean. If you really want a 3-band tone stack, copy the one from the JHS Angry Charlie.

I just reread Feral's comments. The Cold Turkey is essentially the same circuit as the EQD 3-band Baxandall and will have the same problem.

22nF is kinds large for a brite cap (C7). With SUSTAIN at noon, it gives a 6dB bump starting around 300Hz. With SUSTAIN at zero, you get a HUGE boost above 7KHz. 1 or 2.2nF is more appropriate in my mind.

I notice that you dispensed with the feedback caps on the first three stages. You're going for a super brite tone, yes?

Do you want to explain the LED/1N914 clippers? They are not really any more asymmetric than using two identical diodes in this circuit. They just have a clipping threshold higher than two 1N914s and lower than two red LEDs. Personally, I like red LEDs all the way around. More dynamics. But to each is own.
 
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Thanks for weighing in Chuck!

So the GPCB TwEQ will require the same tweaks as the Cold Turkey, I suppose?

I once compared the two and they differed in some values but are essentially the same;
PPCB's Cold Turkey with annotations to turn it into a TwEQ:

COLD TURKEY EQ PEDALPCB convert to TwEQ.png
 
You still won't have what I recommended: the EQ section from the JHS Angry Charlie.

In any case, I would not remove C9, above.
 
That was just comparing the TwEQ and the Cold Turkey as an exercise, that's all. They're essentially the same so I figured same problems.
Alas, I've got a BUNCH of TwEQ boards :rolleyes:

A quick glance at the Angry Charles build doc... I'll probably be able to klodge the TwEQ to Angry Charles spec. I'll look at it more closely tomorrow.

Cheers,
FF
 
Just chiming in with a friendly reminder, if you drop the BMP recovery stage and swap it with opamp/buffers and you use the non-invertinf config for both opamp stages, your final signal output will be inverted. May want to consider using an inverting stage in there somewhere if that matters to you.
I think it's a good practice to try and not invert the signal whenever possible, provided it doesn't prove to be a PITA to implement. Others could care less but I love playing with parallel effects and dirt and it's a little more fun when I dont have to think about phase inversions and it just works.
Also, if you do percieve the opamp clipping, you could try a R2R opamp. TLC2272 or similar. There are some other considerations with going to a R2R but it won't hurt to just plug one in and listen.
 
Rail-to-rail give us a little more headroom. Might be enough to make a difference, might not.

Filters, any kind, change the phase and that phase change is frequency dependent. The whole inverted / non-inverted concept becomes a gray area when you run the signal thru an EQ.
 
The Thorpy Fallout Cloud is a BMP with a 2-band Baxandall tone stack at the end. They did it without opamps. Doing it with opamps is fine.

I recommend putting the LEVEL control ahead of the active tone stack because as drawn, you run the risk of overdriving U2A if any or all of the tone knobs are dimed. The way I would accomplish this is to replace the U1A buffer with the U2B level control circuit. Make C14 1uF, R25 47K and LEVEL A100K. Take the output from U2A, making sure you keep R27, C17 & R28. I just saved you an IC and a handful of parts.

The EQD 3-band tone stack is crap. If you set MID below 10:00 or above 2:00 it completely overrides the TREBLE & BASS controls. I know because I built a Chela and had to mod the tone circuit. Try it and you'll see what I mean. If you really want a 3-band tone stack, copy the one from the JHS Angry Charlie.

I just reread Feral's comments. The Cold Turkey is essentially the same circuit as the EQD 3-band Baxandall and will have the same problem.

22nF is kinds large for a brite cap (C7). With SUSTAIN at noon, it gives a 6dB bump starting around 300Hz. With SUSTAIN at zero, you get a HUGE boost above 7KHz. 1 or 2.2nF is more appropriate in my mind.

I notice that you dispensed with the feedback caps on the first three stages. You're going for a super brite tone, yes?

Do you want to explain the LED/1N914 clippers? They are not really any more asymmetric than using two identical diodes in this circuit. They just have a clipping threshold higher than two 1N914s and lower than two red LEDs. Personally, I like red LEDs all the way around. More dynamics. But to each is own.

Ah this is good info, thank you!
If you set MID below 10:00 or above 2:00 it completely overrides the TREBLE & BASS controls.

100% know what you mean, I'm experiencing that at the moment for sure

I notice that you dispensed with the feedback caps on the first three stages. You're going for a super brite tone, yes?

Well, in my naive mind, i was thinking I'd pass more treble to the EQ stack and let the treble knob have more range here, so trying to pass more to the EQ to play with. Is this the right way of thinking or not really?

Do you want to explain the LED/1N914 clippers? They are not really any more asymmetric than using two identical diodes in this circuit. They just have a clipping threshold higher than two 1N914s and lower than two red LEDs. Personally, I like red LEDs all the way around. More dynamics. But to each is own.

Just figured I'd try get it more asymmetric, I can't tell if I really heard much difference here, you're right. Any ideas on how to make it even more asymmetric to try out?
 
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With a limiter like the BMP, it is a good idea to limit the bandwidth of the signal going into the distortion stages so we can keep the harmonics under control. Non-linear stages (soft clippers, for example) act as frequency mixers. If we put a pure sine wave into a symmetric clipper (BMP is mostly symmetric), what comes out is the original sine wave freq plus some odd-order harmonics (3rd, 5th, 7th, etc.). But, if we put a more complex waveform in, say a single guitar note with some 2nd & 4th harmonics, then what comes out is all the possible combinations of those frequencies and their harmonics. Now inagine what happens if we play a chord. We have a bunch of frequencies, some of which are harmonically related and a bunch that aren't. All of the resultant frequencies can overwhelm the original signal with dissonant tones. But if we cut the high freq content at every stage (like the BMP does), then forest of harmonics is much less dense. We can always brighten the signal at the end using the tone stack.

Each distortion stage drives the diodes symmetrically when the signal level is moderate. If we drive harder, then the transistor's non-linearity becomes prominent enough that we get some asymmetry. If you want a lot of asymmetry, then omit the diodes in one or both stages and let the transistors clip the signal asymmetrically. The Colorsound Supa Tonebender does this. You can try putting a C100K pot in series with one or both diodes in the 2nd clipping stage (Q3) and see how that sounds (the Swollen Pickle does that). Installing that C100K pot will raise the clipping threshold and make the signal louder.

If we put the LEVEL control before the tone stack, then we can adjust the signal level going into the tone stack so that we don't overdrive the tone stack opamp (U2A in your schematic). An active filter is only an active filter if the active element (in this case, U2A) is operating in the linear region. If we overdrive U2A, then the tone knobs won't what they're supposed to do. I'm not sure why most pedal designers don't put the level control before the active filter. I have a pretty good idea why, but it's just my opinion. ;)
 
Take a look at the power section of the Angry Charles. You need a voltage divider to create Vref for the opamp’s virtual ground.
 
Did you connect Vref in the Angry Charles EQ section to Vref in your circuit?
I removed the Tone Job circuit, currently I chopped everything out before c12, guitar goes straight into it, have bypassed the BMP stuff too. TL072 has 8 and 4 from 9V to ground. Then there’s the voltage divider making 4.5V, connect 4.5v to pin 5. 6 jumps to 7, then 7 connects between 100u to ground and creates the VREF flag. At this point though, that VREF flag is 8.5V
 
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