Design
Mr. S. Tamura, the designer of the Tube Screamer, used a subtle clipping circuit to create the pedal's sound. He mixed the input signal with the output signal of the clipping circuit, to "preserve the original dynamics of the input signal which otherwise would get lost at the threshold of clipping." In this fashion, it preserves the "original dynamics of the input signal avoids muddiness and vastly improves clarity and responsiveness." As well, Tamura added a post-clipping equalization circuit with a first-order high-pass shelving filter that "is linearly dependent on its gain," an approach called "progressivity." Characteristic of its clipping is the symmetrical nature.
The Tube Screamer uses electronic field-effect transistor (FET) bypass switching. The circuit uses transistor buffers at both the input and the output. The overdrive is produced using a variable gain operational amplifier ("op-amp") circuit with matched diodes in the feedback circuit to produce soft, symmetrical clipping of the input waveform. The overdrive stage is followed by a simple low-pass filter and active tone control circuit and volume control. The TS7 allows switching between a "TS9" mode, in which the circuit and all relevant component values are identical to the vintage model, and a "Hot" mode, which introduces an additional gain stage.
Much has been made of the operational amplifier chips used in the various versions of the Tube Screamer pedal, and several articles have been written on the subject. The JRC4558D chip is particularly well regarded. In fact, the JRC4558D is used in Analog Man's "Silver" modification. Other popular chips included the TL072, RC4558P, and OPA2134. The TA75558, standard in the TS10 alongside the 4558, is regarded as the "ugly duckling of TS opamps."
Yet another variant is the Ibanez ST9 Super Tube that features a fourth knob ("Mid Boost"), which provides a harder attack.
Read more about this topic: Ibanez Tube Screamer
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