BMP tone stack variations - what would make a good mid hump?

[Les Paul Lover]

I'm asking for your help again as I've been staggered by the quality of your answers in the past.
I've rarely seen such a collection of helpful and knowledgeable people in one single place, really great forum.


So, i'm doing a BMP build, pretty straight forward, following this lay out:

http://pedalparts.co.uk/docs/MultiMuff.pdf

I'm doing the Ram's Head version.
A couple of variations, I've used a MPSA18 for Q1, and I've added 3 1N34A germanium diode on one side, and 2 1N4148 diodes on the other and a switch.


But I don't like the scooped tone stack of the BMP.
I want to keep it simply to one knob tone control (no extra body/mids control).

I keep looking around and I have played with the BMP tone stack calculator, but I believe downloading it might have given a virus to my laptop (thankfully my work laptop!!!), so I don't really want to download it again!!! 

I have studied the various lay outs here:
http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part4.html

Paying particular attention to the pharoah and the large beaver.
Simplifying the pharaoh and entering its values in the BMP tone stack calculator seemed to yield an interesting tone curve, with lots of low end and a good mids bump. (10nf  & 470ko on low pass, 25ko resistor instead of a pot & 22nf on high pass).

The large beaver has 10nf  & 22ko on low pass, 33ko resistor instead of a pot & 5.6nf on high pass.


They are such different values, I'm not too sure where to start with those. I know the pharaoh is highly thought of, but it's also used in a lot of heavier music, which isn't necessarily my thing. I mainly want to use it for creamy sustain rich leads.

Any advice you could give me please? What role does the pot play too? What impact would have a 100ko over a 250ko or 500ko?

[GibsonGM]

I suggest you breadboard, using a suitable circuit to input audio in, and tailor the components to taste   Don't forget, you can add a buffer to the output as well.      Should take about 1/2 hour to put input section, tone stack, and output buffer together!    There are no 'magic values'...what you see are what others' liked according to their taste, and within a few limiting parameters (impedance issues).

The pot will affect output impedance.  Play with that, too.  Might be pleasant for you, where another found it too muddy! etc.

[antonis]

I mainly want to use it for creamy sustain rich leads.

You may try a 100k trimpot with a 3n3 cap (I noticed that over 56k didn't have a remarkable difference) with the other filter of 39k and 10nF..

But JUST as starting point...

[GGBB]

The AMZ Presence Control page is a great resource for understanding the BMP tone control.

The BMP tone control is basically a low pass filter and a high pass filter that have a gap between their respective knee frequency. If you move the knees closer together, you get less scoop.  If you cross the knees, you get mid boost. If the resistor and cap in each section are the same for both sections, the knees are the same. The pot value affects how much scoop or low/high cut you get. As already mentioned, best thing is to breadboard it and play around. Sim programs are also a good idea if you like the visualization aspect.

[Les Paul Lover]

The AMZ Presence Control page is a great resource for understanding the BMP tone control.

The BMP tone control is basically a low pass filter and a high pass filter that have a gap between their respective knee frequency. If you move the knees closer together, you get less scoop.  If you cross the knees, you get mid boost. If the resistor and cap in each section are the same for both sections, the knees are the same. The pot value affects how much scoop or low/high cut you get. As already mentioned, best thing is to breadboard it and play around. Sim programs are also a good idea if you like the visualization aspect.

Thank, I had spent quite a bit of time perusing this, but it explains more what the AMZ presence control does.

What I'm really after is what sort of values will give me what within a single BMP tone control, without additional control.

[Les Paul Lover]

I suggest you breadboard, using a suitable circuit to input audio in, and tailor the components to taste   Don't forget, you can add a buffer to the output as well.      Should take about 1/2 hour to put input section, tone stack, and output buffer together!    There are no 'magic values'...what you see are what others' liked according to their taste, and within a few limiting parameters (impedance issues).

The pot will affect output impedance.  Play with that, too.  Might be pleasant for you, where another found it too muddy! etc.

Ideally I'd do that, but as an amateur / enthusiast, I dont have a breadboard at end. I can see one in my future, but not right now.

[Les Paul Lover]

I mainly want to use it for creamy sustain rich leads.

You may try a 100k trimpot with a 3n3 cap (I noticed that over 56k didn't have a remarkable difference) with the other filter of 39k and 10nF..

But JUST as starting point...

What results di you get with those? Why the trimpot?

[GGBB]

What I'm really after is what sort of values will give me what within a single BMP tone control, without additional control.

Which is what I was describing, assuming you had a basic understanding of RC filters.. You are essentially asking how the BMP tone stack works. The explanation for that isn't super simple. One component change doesn't correspond to only one thing, and there is more than one way to make similar changes (add mids or bass for example). You need a basic understand of RC filters at least. With that, you should be able to roughly imagine what will happen if you change one component value. The tone stack calculator is ideal for visualizing what does what. The one I downloaded from the Duncan Amps web site has no virus.

[Les Paul Lover]

What I'm really after is what sort of values will give me what within a single BMP tone control, without additional control.

Which is what I was describing, assuming you had a basic understanding of RC filters.. You are essentially asking how the BMP tone stack works. The explanation for that isn't super simple. One component change doesn't correspond to only one thing, and there is more than one way to make similar changes (add mids or bass for example). You need a basic understand of RC filters at least. With that, you should be able to roughly imagine what will happen if you change one component value. The tone stack calculator is ideal for visualizing what does what. The one I downloaded from the Duncan Amps web site has no virus.

Indeed, I understand the basic functioning of the BMP tone stack, but when it comes to what the various resistors and capacitors do, I'm totally lost.
I vaguely understand that they affect some frequency bandwith, but why and how isn't something I understand yet.

I suppose i'd better look for some audio RC filter for dummies now.....  

I might try again the duncan tone stack. I liked it a lot when I was playing with it.

[antonis]

I mainly want to use it for creamy sustain rich leads.

You may try a 100k trimpot with a 3n3 cap (I noticed that over 56k didn't have a remarkable difference) with the other filter of 39k and 10nF..
But JUST as starting point...

What results di you get with those? Why the trimpot?

Just what you've described above...
(but as you know, this is STRICTLY personal "feeling"..) 

The pot was used as variable resistor to find an "acceptable" point - if there is such a thing - of no mid loss (something like well described by GGBB "knees" crossing..)
(but I realized that - with some other minor modifications - it was NOT a BMPi anymore..) 

Unfortunately you have to make yourself familiar with RC filters calculations and some kind of results/changes visualazing AND listening AND listening AND listening AND listening AND listening AND listening AND listening AND listening AND listening...

And then you'll have to start listening...!!!


P.S.
Propably there are some well experienced guys who are able to feel the sound from a diagram but I'm not one of them..

[GibsonGM]

I suggest you breadboard, using a suitable circuit to input audio in, and tailor the components to taste   Don't forget, you can add a buffer to the output as well.      Should take about 1/2 hour to put input section, tone stack, and output buffer together!    There are no 'magic values'...what you see are what others' liked according to their taste, and within a few limiting parameters (impedance issues).

The pot will affect output impedance.  Play with that, too.  Might be pleasant for you, where another found it too muddy! etc.

Ideally I'd do that, but as an amateur / enthusiast, I dont have a breadboard at end. I can see one in my future, but not right now.

No breadboard?!   Dude, you can get one for $4 on Ebay....get 5    Once you start actually building these circuits and are able to change them, you won't need US anymore, ha ha.   Seriously, try to get a couple.   You will have a lot of fun with them and learn tons.

Good advise on all these replies.

[antonis]

No breadboard?!   Dude, you can get one for $4 on Ebay....get 5    Once you start actually building these circuits and are able to change them, you won't need US anymore, ha ha.   Seriously, try to get a couple.   You will have a lot of fun with them and learn tons.

You know Mike that there is a lot of people (including myself.. ) that are kind of lazy persons who are in a hurry to finish and plug n' play their build...
(even though they've most of the times disassembled the whole constraction and desolder parts and hitting their heads on the bench or on the wall - whatever comes closer...)

[GGBB]

Indeed, I understand the basic functioning of the BMP tone stack, but when it comes to what the various resistors and capacitors do, I'm totally lost.
I vaguely understand that they affect some frequency bandwith, but why and how isn't something I understand yet.

I suppose i'd better look for some audio RC filter for dummies now.....  

I might try again the duncan tone stack. I liked it a lot when I was playing with it.

That's totally cool - we all have to start somewhere. In addition to the Duncan calculator, here's another tool I've used regularly.

http://www.muzique.com/schem/filter.htm

[teemuk]

...I understand the basic functioning of the BMP tone stack

Roughly it's simplified to consist of a blend potentiometer blending between low-pass and high-pass signal paths.

In "BMP" both filters are generic 1st order RC, but if you dig around you find examples of same circuit idea but the filters may be higher order, LC instead of RC, or they may even be active gain stages that introduce the said filtering.

but when it comes to what the various resistors and capacitors do, I'm totally lost.
I vaguely understand that they affect some frequency bandwith, but why and how isn't something I understand yet.

RC filters have performance dictated by laws of electricity. The frequency points and all can be calculated. At that point we find out the filters are actually made of somewhat complex circuits and we need to "Thévenin" them to simpler forms. This is all a quite complex process and mapping out a frequency response, even in very low resolution, requires multiple math operations.

I encourage you that this is a nice and essential skill to learn but past that point...

...It's not worth the hassle when computer programs can do so much more in a fraction of a second.

For me it's enough to know the theory behind circuit's operation, and how different component values would affect that operation, but beyond that - when going into "details" like frequency response analysis - I much prefer to utilise computer software assistance (e.g. LTSpice, Duncan's Tonestack Calculator, etc.). Whatever fits.

I suppose i'd better look for some audio RC filter for dummies now.....  

Highly recommended if you feel that way.

[induction]

No breadboard?!   Dude, you can get one for $4 on Ebay....get 5    Once you start actually building these circuits and are able to change them, you won't need US anymore, ha ha.   Seriously, try to get a couple.   You will have a lot of fun with them and learn tons.

You know Mike that there is a lot of people (including myself.. ) that are kind of lazy persons who are in a hurry to finish and plug n' play their build...
(even though they've most of the times disassembled the whole constraction and desolder parts and hitting their heads on the bench or on the wall - whatever comes closer...)

With a breadboard, you can plug and play in much less time than it takes to complete a build. Then tweaking components is easy - it takes a few seconds to swap a cap on a breadboard.

The total time to build a circuit, then take it apart and swap a component or two, is more than the time required to breadboard it, tweak it until its perfect, then build it once. Not to mention that it's very easy to install a switch to audition components on the breadboard. For instance, use a switch to select between input caps. Then you can directly compared them, instead of relying on your memory of how it sounded before, which is extremely unreliable.

Breadboards are time savers, not time suckers. Take the leap, you'll kick yourself for not doing it sooner.

[Les Paul Lover]

Indeed, I understand the basic functioning of the BMP tone stack, but when it comes to what the various resistors and capacitors do, I'm totally lost.
I vaguely understand that they affect some frequency bandwith, but why and how isn't something I understand yet.

I suppose i'd better look for some audio RC filter for dummies now.....  

I might try again the duncan tone stack. I liked it a lot when I was playing with it.

That's totally cool - we all have to start somewhere. In addition to the Duncan calculator, here's another tool I've used regularly.

http://www.muzique.com/schem/filter.htm

I bit the bullet and downloaded the tone stack calculator.

between that and your link, I think I've devised a filter that i'll be really happy with:

33n & 22k high pass, 22k & 22n low pass.
Slight mids bump, especially around 300kh, and turning to either side should keep enough mids that all of the filter should be very useable!!!!

Thank you all for your help....



.... and yes, I can see how a breadboard could be useful.... I will get one.... sometime!!!!! 

[deadastronaut]

+1000 on breadboards...

essential must have tool.