where to put a tone control?

[foxfire]

is there a rule of thumb on where to add a tone stack to a circuit? for instance i just built a muff fuzz and i figured it would be a good pedal to learn on. i'm gonna go with the bmp tone stack and figure i could just put it in between volume lug 2 and the switch. that seems like the easiest place to put it but i wanted to ask if there is a better place for it?

[Processaurus]

usually they're before the volume and after the distortion.  Be warned the BMP tonestack eats a lot of the signal, which can be okay if the distortion can get really loud.  On the BMP, though, it was too quiet, so they had to add a boost (an LPB1) after it.

Check out this simulator for the BMP tonestack, if you haven't seen this before:
http://www.duncanamps.com/tsc/index.html
You can visually see what changes to the components do to the frequency response.

[foxfire]

i have a mac so i can't do too much with their program, but thanks anyway for the link and the tips.

[brett]

Hi
You can change the BMP values (e.g. lower resistors and a 10k pot) so that signal losses are reduced.
The main reason you'd use the standard values is if you have high output impedance from the previous section (which is true for the BMP, but not for many stages).
cheers

[Mark Hammer]

As noted and alluded to above, tonestacks work by selectively bleeding frequency content to ground, so they will always result in a lower signal level if they are passive.  Distortion pedals ALL work by having an input signal level that exceeds the circuit's capacity to apply X amount of gain and still come out clean.  If the tonestack precedes the clipping stage, then the signal coming from the tonestack IS the "input signal" and will be too low to produce clipping unless the gain of the clipping stage is bumped up or some gain stage is inserted between the tonestack and clipping stage.  Which of those is advisable and feasible will depend on a host of factors.

For that reason, you will generally find tonestacks after the clipping, frequently just before the output volume control.  In that location, there will likely be sufficient signal level in many pedals that the passive bleed will still leave plenty of signal level (i.e., you will still need to turn down the volume to have equal effect/bypass volume levels).

In some pedals, by virtue of how the clipping is done, and the properties of the tonestack (e.g., in the BMP, Superfuzz, Foxx Tone Machine), the volume loss/bleed is enough that a gain recovery stage is needed.  Note that these typically use silicon or even germanium diodes which will clamp the potential output level fairly low.  Subtracting the passive loss through the tone stack makes matters even worse.  If other diode types or quantities are used, such that the ceiling on signal level is raised (this will reduce clipping intensity, though), the added volume level may be sufficient to dispense with the gain-recovery stage.  I have an original Shin-Ei FY-2 fuzz, and the midscoop filter in it leaves juuuuuuuuust enough level that you can still get a volume boost when the volume pot is maxed, but not that much.  A gain recovery stage may be useful there.  When I insert a variable scoop pot and increase the resistance to ground of the filter (i.e., permit less signal to bleed to ground), the increase in volume is substantial enough that no gain recovery stage is even remotely needed.

Note that location of tone controls is not purely a question of relative signal levels.  The quality of the distortion will vary with the relative level of different parts of the frequency spectrum feeding the clipping circuit.  This is, after all, why you switch pickups and why some distortion pedals can sound great with a Les Paul and maybe not so great with a Danelectro or Gretsch.  Consequently, there is much to be commended about pre-distortion EQ.

What does one need in the way of pre vs post EQ?  Tough call.  Sometimes not much.  A simple change in input capacitor on something like a Bosstone or Fuzz Face can often completely change the character, and there is no end to the ways in which you can change how a Tube Screamer or Distortion+ souds simply by changing a single bass-shaving cap.  Certainly you can get a fairly wide range of sounds with some fairly simple tone-shaping before and after the clipping section. 

Here's a little experimental circuit (The "Boostnscoop") I whipped up recently that I think works great (It's been tested in perf form).

This sticks Craig Anderton's simple frequency booster circuit ahead of a slightly modded Distortion+, and follows it up with a slightly modded version of the midscoop filter found on the Superfuzz and a few other pedals.  Depending on the frequency/ies you select for the pre-boost, it will do "Money for Nothing" %^&*ed-wah sounds as well as metal-scoop sounds and a variety of standard bluesy sounds.  You can add selective boost before the clipping (or not) and shave away varying amounts of mids after the clipping.  Combining these in various ways yields lots of tonal variety.  Note that the clipping section uses two silicon diodes in series for a hotter output level to compensate for the passive loss of the scoop filter.  You can still get plenty of output level from this baby without the need for gain recovery.

[foxfire]

Hammer, thank you for the easy to understand explanation. i thnk i'm gonna try your "swtc" and make up a bmp tone stack on a board with sockets to play around with as Brett suggested. other than changing in/out caps i don't know too much about tone control so thanks for all the info.