Since the 1930s, pipeless electric instruments have been available to produce similar sounds and perform similar roles to pipe organs. Many of these have been bought both by houses of worship and other potential pipe organ customers, and also by many musicians both professional and amateur for whom a pipe organ would not be a possibility. Far smaller and cheaper to buy than a corresponding pipe instrument, and in many cases portable, they have taken organ music into private homes and into dance bands and other new environments, and have almost completely replaced the reed organ.
The Hammond organ was the first successful electric organ, released in the 1930s. It used mechanical, rotating tonewheels to produce the sound waveforms. Its system of drawbars allowed for setting volumes for specific sounds, and it provided vibrato-like effects. The drawbars allow the player to choose volume levels. By emphasizing certain harmonics from the overtone series, desired sounds (such as 'brass' or 'string') can be imitated. Generally, the older Hammond drawbar organs had only preamplifiers and were connected to an external, amplified speaker. The Leslie speaker, which rotates to create a distinctive tremolo, became the most popular.
Though originally produced to replace organs in the church, the Hammond organ, especially the model B-3, became popular in jazz, particularly soul jazz, and in gospel music. Since these were the roots of rock and roll, the Hammond organ became a part of the rock and roll sound. It was widely used in rock and popular music during the 1960s and 1970s by bands like Emerson, Lake and Palmer, Procol Harum, Santana and Deep Purple. Its popularity resurged in pop music around 2000, in part due to the availability of clonewheel organs that were light enough for one person to carry.
In contrast to Hammond's electro-mechanical design, Allen Organ Company introduced the first totally electronic organ in 1938, based on the stable oscillator designed and patented by the Company's founder, Jerome Markowitz. Allen continued to advance analog tone generation through the 1960s with additional patents. In 1971, in collaboration with North American Rockwell, Allen introduced the world's first commercially-available digital musical instrument. The first Allen Digital Organ is now in the Smithsonian Institution.
Other analogue electronic
Frequency divider organs used oscillators instead of mechanical parts to make sound. These were even cheaper and more portable than the Hammond. They featured an ability to bend pitches.
In the 1940s until the 1970s, small organs were sold that simplified traditional organ stops. These instruments can be considered the predecessor to modern portable keyboards, as they included one-touch chords, rhythm and accompaniment devices, and other electronically assisted gadgets. Lowrey was the leading manufacturer of this type of organs in the smaller (spinet) instruments.
In the '60s and '70s, a type of simple, portable electronic organ called the combo organ was popular, especially with pop, Ska (in the late 1970s and early 1980s) and rock bands, and was a signature sound in the pop music of the period, such as The Doors and Iron Butterfly. The most popular combo organs were manufactured by Farfisa and Vox.
Conn-Selmer and Rodgers, dominant in the market for larger instruments, also made electronic organs that used separate oscillators for each note rather than frequency dividers, giving them a richer sound, closer to a pipe organ, due to the slight imperfections in tuning.
Hybrids, starting in the early 20th century, incorporate a few ranks of pipes to produce some sounds, and use electronic circuits or digital samples for other sounds and to resolve
borrowing collisions. Major manufacturers include Allen, Walker, Compton, Wicks, Marshall & Ogletree, Phoenix,
Wyvern Organs and Rodgers.
The development of the integrated circuit enabled another revolution in electronic keyboard instruments.
Digital organs sold since the 1970s utilize additive synthesis, then sampling technology (1980s) and physical modelling synthesis (1990s) are also utilized to produce the sound.
Virtual pipe organs use MIDI to access samples of real pipe organs stored on a computer, as opposed to digital organs that use DSP and processor hardware inside a console to produce the sounds or deliver the sound samples. Touch screen monitors allows the user to control the virtual organ console; a traditional console and its physical stop and coupler controls is not required. In such a basic form, a virtual organ can be obtained at a much lower cost than other digital classical organs.