Ibanez Tube Screamer

Schematic from the TS-808 service manual

So much is written about the Tube Screamer. A lot of good info can be found on Analog Man's site.

The Maxon wikipedia page is currently (April 2015) proclaiming Tube Screamers was made back in 1974, which I have yet to see any evidence of. (From Maxon's own website: "The Tube Screamer as we know it today started in the late 70's with the TS-808 model...") 1979 is the earliest release date I've seen for the TS-808.

The Tube Screamer's success is often attributed to its use of symmetrical diode clipping within the feedback loop of a non-inverting op amp stage. Indeed, it is difficult to find an earlier example with this exact topology. Boss's OD-1 (1977) used the same op amp topology, but the diode clipping is asymmetrical (2 of one polarity, 1 of the other). The Electro Harmonix Big Muff was changed to an op amp design, also in 1977. The Muff uses symmetrical diode clipping, but it used an inverting topology with 6 diodes, and the Muff's distortion is much more intense than either the OD-1 or the TS-808. Unlike the OD or the TS, there is no control over the high gain of the Muff's clipping stage. The TS-808 happened upon a combination that just seems to work well for most people who want subtle boost and overdrive in front of a tube amplifier.