Blackfire Tone Control

[petemoore]

I'm reboxing the Blackfire, and thinking of adding a TC circuit to it.
 Any suggestions that you could recommend?
 I'm going to put some extra bells and whistles on it too !!!
 I mentioned this in another post which I'll check also.

[Phorhas]

You could try the Dumle Tone Stack

http://amps.zugster.net/articles/tonestacks/index.html#Dumble

[petemoore]

Those two N/C wires in the middle of the image, are those the in/out connections?
 Looks pretty extensive, like it could control tone in at least 20 different ways!!! Probly take a month to get used to what it's capable of doing !!!    
  Which is cool...

[petemoore]

Though if I need all that...I know I don't have the parts for it  right now.

[Mark Hammer]

Simplest thing is a one-knob Big Muff control.  See the article at AMZ on "presence" controls for tips on tweaking that classic circuit.

I was fooling around with my "Roseyray" dual clipper a few nights ago, and stumbled across something interesting which may be of use to some.  You can find the schematic at the top of the stack at http://hammer.ampage.org

Tired of the standard BMP thick-to-thin tone control (hey, wait, didn't I just compliment that one?), I tried something different.  Instead of panning between a lowpass and highpass version of the same signal (which is what the standard BMP tone control does), I wired up my tone control to pan between the lowpass-filtered output of my first clipping stage, and the scoop/notch-filtered sound of my second clipping stage in series with the first.  The intent was to pan from a smoother, mellower sound to something more intense and buzzier, but without losing bottom.  Worked like a charm but at highest gain settings there were some oscillations I still have to cure.

In experimenting with ways to cure them, the other night, I perfed another one, only this time I ran a small cap (470pf) from the wiper of the tone pot to ground.  

Here's where it gets interesting.

What that effectively does to the tone pot is make it a bidirectional lowpass filter, since both signals coming in each outside lug of the pot have to pass out via the wiper and each have treble shunted to ground via the cap.  When the pot is dead-centre, each signal is filtered at the same cutoff frequency.  As you rotate the control, though, one leg of the pot decreases in resistance (raising the cutoff frequency for anything coming in via that leg of the pot) while the other increases (lowering the cutoff frequency for that signal).  In essence, the same control not only pans between two signals, but provides variable filtering of them (Rat-style) at the same time.  

The effect is startling.  It starts to feel like one of those clickless pot-based switches you find on pedals/amps with DSP effects.  Turn it a bit and the sound changes.  Rotate the control fully and you pass through a panorama of timbral changes.

Applying this to a BMP-style tone control placed after a high-gain circuit (i.e., same signal from the same source, but differentially filtered before going to each outside lug of the tone pot), you can probably achieve a broader range of tones than the standard one does.  You'll need to do the math first to determine a suitable cap value.  E.g., assuming a 100k tone pot, a 470pf cap from wiper to ground yield a single pole lowpass from each "direction" with a cutoff of just under 6.8khz.  Rotate the pot in one direction so that the 100k of resistance is divided up 25k/75k, and you have a 13.5khz cutoff in one direction, and a 4.5khz cutoff in the other.  Bear in mind, these rolloffs are applied on top of whatever filtering precedes it.  So, for the treble side of the tone pot, at complete clockwise rotation (i.e., the 5 o'clock or max treble position), there is initially no practical/audible lowpass filtering applied, but as you start to rotate it to change the amount of bass-side signal mixed in, there is an increasing amount of additional lowpass filtering applied to the treble signal, so that it gets both toothier and rounder at the same time.

On the bass side, when the pot is rotated to 5:00 (full treble), not only is there much less bass signal mixed in, relative to treble, but there is additional lowpass filtering of whatever bass signal *does* get mixed in.  With a 100k pot and a 470pf cap, that rolloff starts at about 3.4khz.  As you start to turn the tone pot to the bass side, the cutoff frequency starts to go higher, until at the extreme bass setting (7:00, or zero ohms from wiper to lug), an interesting thing happens: the cap from wiper to ground is now placed in parallel with the cap to ground in the lowpass section preceding the tone control, at which point you move from a two-pole lowpass filter, to a one-pole with a different cutoff.  Total morph-o-rama, just by adding one cap.

Tack on Jack's suggested changes and one or two toggles, and you have a universe of tonal control in one little knob.  I'm VERY impressed.

Please note, however, that the Blackfire is impressively and remarkably responsive to guitar tone-control changes.  My hat gets tipped to Joe thricefold in this regard.  Roll off some treble at the guitar and the Blackfire changes tone noticeably, almost like you rolled it off at the pedal.  That's the long way of saying that you might not need a tone control, ANY tone control, whether simple, complex, or just plain brilliant  :wink:  as much as you think you do.

[petemoore]

Great write up Mark !!!
 Very interesting working concept.
 Schematic, and accompanying text is alone [I don't remem seeing anything quite like it] and alluring...Wide pallete of timbral changes etc.
 Just a bit more than a tone control...now I must go get more perf !!!
 That tone pot on a rocker wah... :idea: ...
 Thank you Mark ! I think you've 'hammered' out another great one!!

[Paul Marossy]

I put a Marshall-style tonestack on mine. It has no problem with volume drop or anything. Mine has so much output that I need to do something to drop it down some. Anyhow, I like the way it sounds with this circuit. Just something else to consider.

[Phorhas]

I'm planning to try out a 2 or 3 band active banaxall tone stack... maybe for a more powerfull tone shaping.

[petemoore]

In an old Quantum amp Frame !!!
 I put the AMZ [2nd one] tone control on it [a 100k and a 25k pot], works really nice. Great thing to have on there.
 We fired it up through his Boogie Mk4 and hafta say dials in excellent tones, with a fairly high degree of variability.
 Working excellent...He said: "That's a really good one".
 Nice to see the smile on his head, [his amp head seemed to be liking it too].
 Similar note..we tried out the SD-1 [4558 in it], and one that one he's like "Wow, ... Note Definition !!!".
 Anyway we saw the Boog crunching like never before.
 3PDT stomp/ indicator...a spdt stomp/boost kick...ToneStack on a Blackfire ... kwite the impressive unit !!!

[Paul Marossy]

I've heard good things about that boxendall tone circuit. I think I'm going to have to try that out one of these days.