RG Keen's Description of Tube Screamer Functionality

[Mike Sulzer]

I have not been able to locate any recent activity from RG, and so I will start a general discussion. In his description of the tube screamer circuit (http://www.geofex.com/article_folder...ch/tsxtech.htm. Also https://www.electrosmash.com/tube-screamer-analysis draws from RG's his description and has frequency plots, etc.) describes the operation of the tone circuit. Looking at the circuit carefully, I get a somewhat different picture of what is happening. RG says "When fully toward the (+) end [MS: that is.the tone pot slider turned to the positive op amp input], the capacitor shunts the frequencies above 3.2KHz to ground;". There is a 220 ohm resistor in series with this .22 micro farad capacitor, and so I think 3.2 KHz is where the capacitor stops having an effect. What this C does over most of the guitar frequency range is to act in parallel with the capacitor in the passive low pass filter, lowering the cutoff frequency by a factor of two. IMO, the function here is to restore after the clipping part of the bass removed before the clipping.

[Helmholtz]

Yes, I think yours is the better explanation as there are no longer 2 independent filters.
Don't understand why Electrosmash doesn't use a log frequency scale with the plots.

[Mike Sulzer]

Yes, I think yours is the better explanation as there are no longer 2 independent filters.
Don't understand why Electrosmash doesn't use a log frequency scale with the plots.

Look toward the bottom of the Electrosmash article. The overall frequency response is shown on both linear and log frequency scales, although not, IMO, as well as it could be, but much better than the linear.