single knob mid scoop or hump tone stack

[gaussmarkov]

it occurred to me that a single knob tone control that produced both a mid scoop and a mid hump would be a cool thing.  and, after looking around, i can see that it has been suggested before.  as far as i have seen, jack orman designed a two-knob modifcation of the big muff pi tone stack that produces both (see the amz presence control).  his design produces some other useful filters including a treble boost. 

i am wondering how to create a single knob tone stack that moves between mid scoop and mid hump.  mark hammer has already proposed the idea as well.  so here's a half-baked idea for doing this: blending two big muff pi tone stacks.  jack's tone stack shows how the BMP tone stack can produce both scoops and humps.  here's a schem out of 5spice that tries to take advantage of this:



there are three pots indicated but R7 would be the tone control.  the other two pots are just for tweaking.

this idea is half-baked because i have not figured out what component values are best.  so i do not really know how well this can work.  it does get part way there with the values shown, at least according to SPICE.  here's a profile of this stack at fully ccw, at 35%, and at fully cw.

rather than tweak these values some more, i am asking whether there is something obviously wrong with this idea.  i found a previous suggestion for a way to do this based on the duncan amps tsc program that turned out to be a program artifact and not the real deal.  so i am cautious.

if this might work, everyone is welcome to try their hand at component values.  i don't have the knowledge to take this much further if the approach has legs.  if this has already been done, then that would be good to know, too.  thanks, gm

[puretube]

reply#15 ; look at X5 and surrounding components...

[GFR]

If you want an active circuit, look at puretube's suggestion.

If you want a passive circuit, I'm afraid there's no way without an inductor.

[gaussmarkov]

thank you! 

GFR, i was afraid it was not actually possible to do a successful passive circuit.  the hump/scoop that i did get was tantalizing, but i just couldn't seem to move to the right location for each.  and i could hear that little voice that says, "if it could be done, it would already be on the forum."    i appreciate getting the answer.

i have to admit that i had found stm's active 3 band eq, but had not appreciated all that was there.  thanks, puretube, for directing me back there.

[Mark Hammer]

The tone control I snagged from Alexandro Charrisis "Ballz Booster" and tacked onto my Chaos distortion does exactly that.  Round, nasal tone at one extreme, and metal scoop at the other.  For those who like that pedal, I think that's one ofthe main reasons why.

[GFR]

Sorry Mark, I can't see hammer.ampage.org, not at home and not at work. I'd be very thankful if someone could mail me the Chaos schematic, or temporarily mirror it.

I tried a simulation based on a quick trace of the tone control from Paul's PCB layout (it's very problable that I did a mistake somewhere), it looked not exactly like from notch to "boost", it looked more like from notch to low pass. Maybe with the rest of the pedal before it and with a good choice of frequencies it indeed sounds like from notch to boost (well, that's what matters anyway).

[Mark Hammer]

This URL ought to do it:  http://ampage.org/hammer/files/Chaos.gif

I can read it on my machine at work.

[gaussmarkov]

This URL ought to do it:  http://ampage.org/hammer/files/Chaos.gif

I can read it on my machine at work.

hey mark, when i was doing my research on this stuff i looked for a gif file  on your site that you mentioned.  i could not find it.  it was called flexiblemetaleq.gif.  is this still available?  did i overlook it?

thanks!

[Mark Hammer]

It's over at my photobucket page. http://img.photobucket.com/albums/v474/mhammer/FlexibleMetalEQ.gif

[GFR]

This URL ought to do it:  http://ampage.org/hammer/files/Chaos.gif

I can read it on my machine at work.

Here's what I get with http://ampage.org/hammer/files/Chaos.gif:

Server not found

Firefox can't find the server at www.ampage.org.

    *   Check the address for typing errors such as
          ww.example.com instead of
          www.example.com

    *   If you are unable to load any pages, check your computer's network
          connection.

    *   If your computer or network is protected by a firewall or proxy, make sure
          that Firefox is permitted to access the Web.

?

[Mark Hammer]

Weird.  I click on the link in your post and I get the file.

I downloaded it (with the link) and repost a copy over on photobucket.  Maybe it will be more accessible there.

http://img.photobucket.com/albums/v474/mhammer/Chaos.gif

[gaussmarkov]

just for clarification:  a passive circuit with one pot can yield a hump and a scoop, right?  my circuit does that according to the spice sims.  i inferred from GFR's comment that the problem is that you cannot get both hump and scoop centered in the midrange.  is that correct?  i was hopeful for the twin BMP TS because the insertion loss was about the same as one BMP tone stack.

my understanding from mark's comments here is that his circuit produces a scoop and a treble rolloff, not both a hump and a scoop.  it sounds like it does the job but with heavy insertion loss?

and maybe this is all academic, given that an midrange active filter like the one in stm's 3-band eq does the job?  thanks for your help.

[gaussmarkov]

double post.

[Mark Hammer]

just for clarification:  a passive circuit with one pot can yield a hump and a scoop, right?  my circuit does that according to the spice sims.  i inferred from GFR's comment that the problem is that you cannot get both hump and scoop centered in the midrange.  is that correct?  i was hopeful for the twin BMP TS because the insertion loss was about the same as one BMP tone stack.

my understanding from mark's comments here is that his circuit produces a scoop and a treble rolloff, not both a hump and a scoop.  it sounds like it does the job but with heavy insertion loss.

and maybe this is all academic, given that an midrange active filter like the one in stm's 3-band eq does the job?  thanks for your help.

There's passive and there's passive.  All those old inductor-based RCL equalizers used "passive" circuits rather than active gyrators, and were able to achieve boost and cut at resonant frequencies.  Contemporary circuits, like the one Sebastian shows in his schematic, or the ones RG Keen shows over at Geofex, are more easily tuned, and certainly far more compact, than the older RCL resonant circuts.

I suppose one could say there are "EQ-type" tone controls, and there are "personality" controls.  The scoop and rolloff control I described is more of the second type.  In other words, it is intended to place in one control the sorts of parameters one would change in several other controls if the purpose was to present a different character to the tone, not just fine tune the frequency content.

And yeah, BIG time insertion loss.  Definitely not the sort of thing you'd want to use for pre-clip EQ because the requisite compensating gain would likely result in too noisy an output.  If you suck out lots of signal, but none of the hiss, and then boost even more to make up for the signal loss, you get lots of hiss.

[GFR]

Weird.  I click on the link in your post and I get the file.

I downloaded it (with the link) and repost a copy over on photobucket.  Maybe it will be more accessible there.

http://img.photobucket.com/albums/v474/mhammer/Chaos.gif

Many thanks (oh and I confirmed my trace )

[gaussmarkov]

I suppose one could say there are "EQ-type" tone controls, and there are "personality" controls.  The scoop and rolloff control I described is more of the second type.  In other words, it is intended to place in one control the sorts of parameters one would change in several other controls if the purpose was to present a different character to the tone, not just fine tune the frequency content.

this makes sense, and its a helpful insight.  thanks mark!

[b_rogers]

what about the amz-bmp mod, find the sweet spot with the 100k pot and measure the resistance on each side of the pot. remove the pot and replace it with two resistors that match the readings from each side of the pot and send the signal from the junction of these two resistors. then there would only be the 25k mid knob and no high/low control, and you would only control the mid content. does this make sense? would this work? i am no expert but it seems to make sense to me anyway..

Brent