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Fabrizio Dadò by Fabrizio Dadò
On February 20, 2021

​Solid state amplifiers for the electric guitar: from tubes to transistors

How solid state amplifiers were born and how they work

In this article we’ll focus on electric guitar most popular and inexpensive amplifiers: solid state ones. We are going to explain how they work, how they spread and which are their pros and cons as compared to their tube “enemies”.

To get an overview on the electricguitar and its amplification development in the first half of the 20th century, please read the articleabout tube amps. Here we are going to talk about solidstate amplifiers (sometimes called transistor amplifiers or simply SS).

What is a transistor?


Studies on transistors started in the Twenties of the 20th century. The word transistor comes from merging the terms transfer and resistor. Transistors are electronic components based on the properties of some semiconductor elements such as Gallium, Germanium and Silicon. These elements substantially are non-conducting (or almost non-conducting), unless they undergo an electrical field; in this condition they start conducting at different levels.

To make a transistor, a “doped” crystal fragment of semiconductor is embedded in a case that can be made from several materials, such as plastic, metal, silicone, etc.; hence the solid state definition compared to the vacuum of tubes.

Making a heavy simplification, transistors operate by means of electron passing among three differently doped spots: the emitter (that’s where electron start moving), the base (an intermittent flow regulator), and the collector (the receiving spot). Whereas tubes work under high voltage variations, transistors work under low current variations. As a result in our area of interest, the incoming signal level increases and it is amplified.

Transistor schematic

Another possible function of a transistor is acting as an on/off switch, as it happens in digital devices for instance.

Transistors can be singly used as discrete parts, or placed in large quantity inside an integrated circuit (IC or chip); we usually find them as chips inside the circuit boards of amplifiers and effects.

Sound and distortion in solid states

Transistor circuitry

Whereas tube distortion is generally recognized as gradual, dynamic, rich of pleasant harmonics and middle to bass frequency focused (referring to the frequency range of an electric guitar), solid state amps generated distortion seems sudden, with levelled dynamics, “harsh” from odd harmonics and high frequencies focused. In a few words: no one would draw a project to get a mere distortion from a transistor amp. As far as guitar amplification, what’s good about transistors as compared to tubes can be summed up as follows:

  • great manufacturing economy of the component
  • low heat production
  • reduced size and weight
  • simpler and less frequent servicing (if the project is well done)
  • lower current consumption
  • higher resistance against impacts and vibrations
  • no need of an output transformer towards the speaker (a largely responsible component in tubes related sound)
  • smaller and cheaper power supply transformers.

Though it makes solid states still attractive today, a lesser highlighted feature is their restrained dynamics compared to tube amps; this makes them suitable for practice, rehearsal and use at home as well as in small spaces, even if they provide a certain power.

Cons to be accepted from solid state amps are:

  • more complex design to get good audio results
  • electrical and heating problems susceptibility
  • lesser volume level at same power
  • reduced dynamics range
  • clipping, or distortion advent in sound, rough, without an overdrive or saturation stage. (It’s clear that this happens in the regards of human ear, and when no circuital tricks are adopted; in fact very appreciated effects as the popular TubeScreamer boast a “tube” sound though they are solid state).


The Field Effect Transistor or FET is a very effective kind of transistor. It features a variable section link of doped semiconductor between the poles; its way of working reminds a regulated continuous flow rather than an on/off switch. To our purposes, the most known FETs are J-FETs (Junction-FETs) and MOS-FETs (Metal Oxide Semiconductor-FETs). MOS-FETs are very appreciated in the audio field for their soft clipping and a tube-like sound.

Transistors birth and rise

Since the time of first electrified instruments till the first Sixties at least, the dominant technology in amplifiers manufacturing, as well as that of any other electronic device, depended on thermionic tubes. With great strides, let’s summarize the diffusion of solid state amps for the electric guitar.

  • ’50s – A relentless diffusion of transistors starts in previously tube based analogue circuits, including amplifiers.
  • ’60s – Time for the boom of little transistor radios powered by batteries! Among the first solid state guitar amplifiers there are models from Italian Davoli Krundaal, American Kay, Kustom and Gibson, British Burns, Vox and WEM. Fender arrives in 1966 with the Super Showman amp (designed by humbucking pickup inventor Seth Lover). Meanwhile transistors are being used in legendary pedal effects such as the fuzz. At first they are Germanium made; due to the unsteadiness of this element, they will be replaced soon by Silicon based ones; also, silicon is a very cheap and diffused semi-metal.
  • ’70s – Transition to solid state is made, with the first transistor Marshalls, the powerful Sunns and the iconic Roland Jazz Chorus.
  • ’80s – It seems tubes are almost destined to extinction. All the big builders offer solid state models too, sometimes enhanced by effects as distortion, compression and modulation. Guitar players are giving in their tube amplifiers to buy new solid states, lighter, more manageable and cheaper.
  • ’90s – After tube amps withdrawal, changes of mind in musicians and the coexistence of both types of amplifiers – in mixed designs too – some heavy rock guitarists’ fame and the commitment of manufacturers the likes of Mesa/Boogie, Soldano, VHT and Rivera restore tube amps into favour. Solid states seem relegated to the budget and amateur range, but their live use by pro and semi-pro guitar players actually keeps on all over the world.

Soundsation Cream

The challenge continues…

During the ’90s and the 2000s, developments in electronics and computer science have reserved lots of sensational surprises, as a proof of technology driving force over music and musical instruments. This will be one of the next topics we’ll deal with: digital amplifiers.