Tonestack design

[JRB]

Hello everybody,

I'm trying to design a tonestack with bass, mid and treble controls that interact less then the basic FMV tonestack.
So far I managed to piece this together:


Here is a screenshot of the frequency response in LTspice.


The graph has all controls at 50% of the pots rotation and then from top to bottom, Bass, Mid, Treble from 10% to 90% of the pots rotation.
As you can see the bass and treble don't interact that much. The mid does.

It seems that the bandwidth of the mid control is to big. Does anyone know either a good substitute or a way to lower the bandwidth of the mid control?

[Bill Mountain]

Could you label the pots on the schematic?

Wide mid controls can sound musical as well.  You don't really need precision.

I would use your ears on this one.

[GibsonGM]

It's very hard to get one that doesn't interact!    Try "Duncan's Tonestack Calculator", get it free online.  There are a few different models to play with....I like the James stack.   Like Bill said - it's going to be your ears that decide rather than the graphics.     Can't think of too many stacks that DON'T interact....an EQ is probably better for that kind of thing...

[bwanasonic]

"it's going to be your ears that decide rather than the graphics. "

Alas, this is the trap of obsessing over curves in software. I have spent (wasted?) so many hours tweaking virtual parts to achieve an ideal curve response that just doesn't  end up corresponding with the real-world knob-twiddling reality.

[tubegeek]

"real-world knob-twiddling reality."

What is this "reality" of which you speak?

[JRB]

The design has changed a bit and I think I'm going to build the new design as a test to see if I'll like it.
Ill have to upload some pictures when I got sometime (gigs etc who needs them  )

To answer your questions,
For the pots:
R9+R12= Mid
R5+R6=Bass
R1+R2=Treble

I did forget to mention there will be two tonestacks so one could switch between different settings, at the moment its two FVM tone stacks. The massive interaction between the knobs is making it really difficult to dial in settings that sound good and are roughly the same sound level.

I have looked at the duncan tonestack calculator the bench stack was really interesting if I would be able to get the required induction somehow I would have used that.
When reading up on the bench tone stack people suggested using the coils from a transformer the problem is I don't have the room for that.

And of course the good old use your ears comment is correct its just that running a sim usually gives you a decent idea if something is gonna work

[bwanasonic]

Is this is intended for a guitar amp? If so, keep in mind there is another major tone-shaping stage called the speaker  . That's why "flat response" is kind of tilting at windmills in a guitar amp tone stack.

[J0K3RX]

Well said both posts Kerry (bwanasonic) totally agree..

[bwanasonic]

And of course the good old use your ears comment is correct its just that running a sim usually gives you a decent idea if something is gonna work

And studying the Duncan Tonestack curves finally got me to where I understood how to use the typical BMT controls on a Fender style amp, mainly by teaching me to disregard the Bass Middle Treble labels. You're better off starting with the mids on 10 and bass and treble on 1-2 than the arbitrary all controls at 12 o'clock.

[JRB]

Is this is intended for a guitar amp? If so, keep in mind there is another major tone-shaping stage called the speaker  . That's why "flat response" is kind of tilting at windmills in a guitar amp tone stack.

Yes its for a amp, the whole thing is build and running I'm just "fixing" things in it like the tonestack being not to my liking.

New design, only thing that really changed is the mid, it doesn't act like a big volume control according to the sim.

[GibsonGM]

And of course the good old use your ears comment is correct its just that running a sim usually gives you a decent idea if something is gonna work

And studying the Duncan Tonestack curves finally got me to where I understood how to use the typical BMT controls on a Fender style amp, mainly by teaching me to disregard the Bass Middle Treble labels. You're better off starting with the mids on 10 and bass and treble on 1-2 than the arbitrary all controls at 12 o'clock.

Bing bing bing. ^^   

That's why, when you turn all the knobs to say, mid position, with the FMV - the response is NOT flat!  AND - if it WAS, you wouldn't hear it as being that way, anyway! 

The ears are strange, speakers are strange, and in general, audiophiles are too, ha ha.     Nothing is wrong with going experimenting, just as long a you know that in heading out in search of "A", you may in fact be headed right to "B" and not achieving much towards "A".   If that makes sense.

I HATE FMV mid response. So my instinct is just to make a filter that will handle those frequencies with a higher Q.    If I wanted it all, I'd leave the stack thing behind and add in 2 other filters.  Or perhaps 4 ;o)     Tone stacks have been around for almost 100 years, and they still haven't found a good way to please us yet, ha ha!   Altho some of the Mesa EQ amps have been pretty sweet!

[seedlings]

One way to modify/fix a FMV stack is to turn the 'dropping resistor' into a (100K?) variable resistor.  This brings the mids (and everything else) up to flat response.

CHAD