Marshall Amplification is a British company which designs and manufactures electric guitar amplifiers. Marshall amplifiers are well known and highly popular among guitarists. The sight and sound of a Marshall stack amp with a Gibson Les Paul or Fender Stratocaster is an iconic image in pop-culture. To this day, top-line Marshall amplifiers still use valve preamp and poweramp stages instead of solid state devices (transistors), although Marshall also manufactures cheaper solid-state or hybrid devices. Valve amplifiers (known as "tubes" in North America) are generally considered to exhibit a "warmer" tone than that of transistors, particularly when overdriven; instead of abruptly clipping off the signal at cut-off and saturation levels, the signal is smoothly rounded off. Vacuum tubes also exhibit different harmonic effects than transistors (see tube sound for more about the sonic differences between transitors and vacuum tubes). Though technology continues to change, the most sought after, best sounding, and most expensive amps use technology that is considered quite obsolete. The sound of a Marshall Plexi or JCM800 amp is among the most recognized in popular music, and there is a constant demand for both cutting edge and vintage amplifiers.