Having a hard time grasping this tone stack

[ayayay!]

Hello.  Here's the schem:  http://thebin.free.fr/FSTBX/bb2.pdf

And some other discussion about the tone stack.  http://www.diystompboxes.com/smfforum/index.php?topic=62784.msg494277#msg494277

I've done some mods and really enjoy the pedal now, but the *scope* if you will, of the tone control, is not what I would like.  I like it with the tone control turned all the way to only about 10% - 15% up.  Above that, it's still not harsh really (suprisingly) but just a bit thin sounding.  Even at that, the pedal sounds great with Tele/Strat/LP's, just not really the tone control I'd like.  If I could shift both the bottom and top of the range down simultaneously, that would help.  (Does that makes sense?)

I just don't get that tonestack.  It' confuses me.  It looks kinda BMP'ish, but then it has all those additional parts (under the tone control) that throw me:  C14, C21, R23, R24.  And, it looks like they all intersect and are active w/ one another. 

My first thought is to raise C13 a little and remove C21.  I just don't know.  Like I said, I'm confused.  ...and I have no access to the Duncan TS calculator for a while. 

[petemoore]

  Con4 makes one of it's two paths harder to get through.
  When Con4 pins 1 and 2 are connected, this ''easy path for all'' looks sorta all pass like, a 4u7 C-12 with no ohms except R29.
  R23, R24, are basically like a 100k pot permanently turned almost all the way down, a voltage divider.
  When Con4's pins 2 and 3 are connected:
  There's probably a ''buncha'' resistance [I can't add 39k and X until X, the R between Con4's pins 1 and 2 when high-set is known] when the pots turned away from the 4u7.
  So...we're mostly having signal pass R20, into a couple HP filtercap [in series with the signal, C's 21 and 13, both are 220nf's.
  Then getting by C14, a LP filter...
  All that and...
  Since you don't like the tone control...
  Suggestion is to try Duncans TSC, shop for a TS which has appealing shaped lines up as far on the graph as you can see there, the up part of course isn't so important if your other volume control has room to go up too.
  A big electrolytic such as C12, in an all-pass situation, might like some help at that position with the HF processing, utilizing the aid of say a .1uf or so might be barely noticed.

[ayayay!]

Thanks Pete.  For once that kinda made sense.  (Your posts are hard to decode )  But C12 is 4n7 (.0047uF), not 4.7uF.  

And I actually like the behavior of the tone stack, I just need a lower set frequency is all.  

[ayayay!]

Anyone else want to take a crack at it?   

[CynicalMan]

Looking at the Duncan TSC, I'd recommend changing R20 to 2.2k and R24 to 1k. These are approximate graphs of the limits of the tone control before and after the change:



The tone control would then go up to around 1/4 of its previous range, and extend down another 5.5 dB (around 3/4 of its range) below its previous range. The only problem would be that the mids would be reduced by around 5 dB, but this is the best I change I could find.

[ayayay!]

Thank you sir!  I wish I had access to the Duncan TSC but I won't until tomorrow.  (I'm on a job-owned PC here.  No chance of installing anything)

Either way, that will get me ball park enough to play w/ some different resistors.  Thank you again!

[ayayay!]

Thanks CynicalMan!  Those were a perfect fit. 

[ayayay!]

Okay I've got the TSC now, but realize I don't know which tonestack to use.  Did you use the BMP?  And how did you arrive at those values?  I'm afraid if it's not the normal tonestack plugged into the TSC that I'm quite lost.  Anyone have some pointers for me?  I'd love to get much better at using it.

Thank you! 

[CynicalMan]

I used the Fender tonestack. I just changed all of the values to match the values for the tonestack in the schematic. So, the top capacitor was 4.7n (it won't accept 4n7), and the other two were 220n. R1 was 5.6k, I changed the Bass control to 100k and turned it up all of the way, and I changed the mid control to 2.2k and turned it up all of the way. Then the tone is controlled by the treble control which is 20k linear. So, you can see the range of the tone control by moving the treble control, and you can play around with component changes.

In addition to the changes I suggested earlier, I would also recommend changing C12 (C1 in the TSC) to 22n. This helps to preserve the mids.

[ayayay!]

Gotcha, makes sense.  I thought maybe you had a way to create your own TS.  So a little trickery is all that's involved.  Thanks!

As far as C12, it's all good already, but thank you for the suggestion.  I'd already modified the pedal before the TS change, so what you suggested fit perfectly into what I needed.  The sweep is fantastic.  I'll play w/ the TSC more when I get home tonight and replicate your findings.  Thanks for the tips! 

Thanks again!