Wierd Tone CTRL - what's the topology?

[Dave Z]

Screamer-type circuit but only 2 lugs of a 50K pot used.

Lug to ground goes through a 3 K resistor (minimum resistance) and a 100K trimpot "harmonics".

As you turn UP harmonics, resistance to ground INCREASES.
As you turn UP Tone (brighter), resistance to ground DECREASES

Go figure!

Also, there is a 1N4148 diode hanging off this circuit as well

Since caps block DC I am assuming the capacitor is in series before the tone pot..so this is not at all like a typical screamer tone control!

[puretube]

:?:

[RDV]

:?:  :?:

Give us a hint, eh?

RDV

[puretube]

twin-T involved?

[smoguzbenjamin]

Uh... what exactly is it you want to know? Do you want advice or is this a contest?  :?:

[Dave Z]

I am trying to figure out how the heck this thing works.

It's my Barber Direct Drive...I like the pedal & I'll be keeping it and will buy more Barber stuff in the future as I like his attitude (labels his components, has tweaks on his website for his stuff, vs Fuller who epoxies everything down & sands off component labels!)

Not trying to clone it but am building a SOS and since his design is an SOS-type, would like to incorporate his tone ctrl...it is a lot more effective than the one on another booteek pedal I have (which turns the signal immediately to mud!)

[brett]

Wild guess, but if you had the trimpot and pot as two resistors in a "T" and the cap as the stem (and DC decoupler) in the feedback loop of an op-amp, you might be able to get the kind of interactions you mention.  I seem to recall that the BluesBreaker had some funny (but not tunable)filtering in its feedback loop.  (LOVE the BB - a much under-rated pedal IMO)

But if you really want an answer you'll have to tell us a lot more about how this is connected.

cheers

[Dave Z]

Hi Brett -- "But if you really want an answer you'll have to tell us a lot more about how this is connected" yes, I understand..I was hoping it was a well-known circuit design and someone would ID it, but it looks like it may be fairly obscure. Hard to trace, as I'n not ripping the board out - that would be a major hassle.

I'll poke around a bit more tonight.

[puretube]

bump

[Dave Z]

Well...I gave up on figuring out the Barber...after I got my SOS done, and applied a few tweaks, it sounded better than the Barber so I sold the Barber. Maybe I got lucky but that SOS has some mojo...I added a mod that can give it the same kind of tweakability as the DD-SS (though in a different way) and the clarity is much better.

Still appreciate Barber's philosophy & will probably buy more of his stuff.