KLON!!!!! (now that i've got your attention...) tone control question.

[Lubdar]

Hey team,

Does anybody have an explanation (or reference) for what exactly the tone circuit topology is for the KLON?
From what I've gathered it looks like a dual inverting op-amp set up for more gain in the first half than the second. Where the first half of the op amp is providing a little bit of gain via the inverting input and the 392k resistor in the feedback path, presumably the 820pf is there for smoothing out harsh treble content. And the second half has 100k in the feedback loop in order to maintain the gain from the previous stage.

Maybe its the orientation of the topology in the schematic that's throwing me off, but are signal paths going in parallel through the 100k and 6.8k resistors.
If the tone pot is fully CW, then essentially the lug 2-3 path is wide open, and the signal would pass through the 6.8k, and 5n6 cap right? but when it is fully CCW, the lugs 1-2 path would be wide open and the signal would be sent through the 100k resistor and through the 5n6 and the 4k7?

I've looked through a couple KLON analysis articles, but everybody seems to focus on the dual-gang pot aspect and not on the tone control portion.

Any guidance/topology references/thoughts would be greatly appreciated

Best,
  Lubdar

[midwayfair]

I've explained this before somewhere ... maybe on TGP ... but I can't find it.

It's a combination of two active controls.

You've described what it's doing in the circuit, but to put you on the path as to why it works, you need to look up an active low-pass filter with op amps, and a basic active high-pass filter with op amps. It will be pretty easy to find an article that gives you examples for both non-inverting and inverting op amp stages.

The simplest way to put it is that CCW shorts more high frequencies in a somewhat fixed gain stage (producing more lows than highs from the gain) while CW shorts high frequencies across a gain limiting resistor in the same stage (producing more highs than lows from the gain). More of the CW causes less of the CCW effect and vice versa.

[Lubdar]

Ahhh, I think i found something useful, which describes what you have just stated
http://www.ecircuitcenter.com/Circuits/op_tone1/op_tone1.htm

Thanks once again