The Ibanez Tube Screamer is a guitar overdrive pedal, made by Ibanez. The pedal has a characteristic mid-boosted tone popular with blues and rock players. The "legendary" Tube Screamer has been used by countless guitarists to create their signature sound, and is one of the most successful, widely copied, and "modded" overdrive pedals in the history of the electric guitar.
The Tube Screamer has a drive knob, a tone knob, and a level knob. The drive knob adjusts gain, the tone knob adjusts treble and the level knob adjusts the output volume of the pedal. The pedal is used to try to mimic the sound of a vintage tube amplifier. The classic Tube Screamer sound includes a "mid-hump", which means that the circuit accentuates frequencies between the bass and treble ranges (mid-frequencies). Some guitarists prefer this sort of equalization, as it helps to keep their sound from getting lost in the overall mix of the band.
The pedal was produced with many variants:
The Tube Screamer pedal was preceded by the orange "Overdrive" (OD) and green "Overdrive-II" (OD-II). These came in narrower boxes without battery covers. There was also a reddish "Overdrive-II" which had a housing very similar to the TS-808/TS808. The green OD-II had a circuit similar to the TS808; however, the OD and OD-II had a more distorted circuit.
Once Ibanez discontinued the 9 series pedals, they introduced the "Master" or "L" series. These were only made in 1985, and did not have the Tube Screamer in the line-up.
The TS9 and TS808 pedals have been reissued, and according to the company, feature the same circuitry, electronics and design components that helped shape the famous Tube Screamer sound. Some musicians have a technician perform modifications to the unit to change the sound to their liking. Also, Maxon, who produced the original Tube Screamer pedals for the Ibanez brand in the 1970s-1980s, produce their own version of the Tube Screamer (called Overdrives: the OD-808 and OD-9 as opposed to Tube Screamer, TS).
According to Susumu Tamura () of Maxon, the designer of the Tube Screamer, the initial design concept was to create something to compete with BOSS OD-1 and MXR Distortion+. In doing so, he used an innovative circuit, using the monolithic operational amplifier device, introduced in early 70s, to create a pedal sound different from the "discrete" transistorized 60's fuzzes.
The overdrive is produced using two silicon diodes in anti-parallel arrangement into the negative feedback circuit of a operational amplifier ("op-amp") circuit, to produce soft, symmetrical distortion of the input waveform. When the output exceeds the forward volt drop of the diodes the amplifier gain is much lower, effectively limiting the output to + and - one diode volt-drop, although due to the exponential I-V curve of the diodes this is not a hard limit. A "drive" potentiomenter in the feedback path provides variable gain. The original 4558 based circuit uses transistor buffers at both the input and the output, to improve impedance matching. This is mathematically equivalent to mixing the input signal with a clipped version of itself, however. Thought of this way, it is said that this "preserves the original dynamics of the input signal which otherwise would get lost at the threshold of clipping" and "avoids muddiness and vastly improves clarity and responsiveness."
Characteristic of the distortion is the symmetrical nature, which produces mainly odd-order harmonics for a sine wave input. All this justifies the "vacuum tube" sound, and the "screaming" tone. As well, Tamura added a simple but effective post-distortion equalization circuit with a first-order high-pass shelving filter that "is linearly dependent on its gain", an approach called "progressivity". The overdrive stage is followed by a simple low-pass filter and active tone control circuit and volume control, using the second op-amp available on-chip.
The circuit uses transistor buffers at both the input and the output, and a modern electronic field-effect transistor (FET) "noiseless" bypass switching to turn the effect on and off. 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. Yet another variant is the Ibanez ST9 Super Tube that features a fourth knob ("Mid Boost"), which provides a harder attack.
Much has been made of the operational amplifier chips used in the various versions of the Tube Screamer pedal, and several "fairy tales" about the merits of these devices have been written on the subject. The JRC4558D chip is well-regarded by some.
The (RC)4558 is a low priced, general purpose dual operational amplifier, introduced mid 70's by Texas Instruments as an "improved" version of the early 741, and used in thousands of consumer and industrial designs. In fact, JRC4558D is nothing else than the licensed product manufactured by Japan Radio Company (), and identical to any other 4558 chip. Other popular chips used included the TL072 (a JFET input type, highly popular in 80's), "original" TI RC4558P, and OPA2134. The TA75558 (yet another version, made by Toshiba), standard in the TS10 alongside the 4558, is strangely regarded as the "ugly duckling of TS opamps".
The pedal was popularized by Stevie Ray Vaughan. Phish guitarist Trey Anastasio implements two TS9 Tube Screamers in his rig. It is widely used in genres as diverse as country, blues and metal. The Tube Screamer has since spawned many clones and modified versions. Possible modifications include use of mismatched, or different diodes (for example, a silicon and a germanium device), or more than two diodes in various arrangements, or modified tone circuits. It is also used by the majority of metal guitarists before the lead channel of the high gain amps to make distortion more focused and to cut the low end. Notable modifiers of the pedal include Robert Keeley of Keeley Electronics and Steve McKinley of Tube Screamer Mods.com.
And do remember that the op-amp has very little to do with the actual clipping in a TS circuit. It's just there to amplify the signal - the diodes [do] the clipping. Changing one or both of the diodes will make a huge impact on the overdrive character, while the differences incurred by different op-amps are minute.
in a guitar pedal there are a lot of factors that can modify the sound even more than the opamp can do: the components placement, values tolerance, circuit layout, the power supply, etc ... by actual listening test as well as oscilloscope traces and spectrum analysis, there is no audible difference between today's 0.5$ NJM4558D and the old ones.