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What this article doesn't mention is why vacuum tubes are still used in guitar amplifiers: The "distorted guitar" sound common in rock music is a direct result

What this article doesn't mention is why vacuum tubes are still used in guitar amplifiers: The "distorted guitar" sound common in rock music is a direct result of nonlinear characteristics of tube amps (both the tubes themselves and the coupling transformers necessary to connect an output tube to a speaker). Tubes exhibit "soft clipping" when pushed to their limits, which has the effect of producing the harmonic content associated with distorted electric guitar. Rock and roll pioneers got their sound principally from driving tube amps past their limits. "Overdrive" pedals are usually just voltage boosters that make the amp's input signal louder, but this pushes the amplifier past its clean linear section into the nonlinear crunchy overdrive that guitar players want. Modern tube guitar amplifiers, even "new" designs, generally follow one a handful of basic circuit topologies, all derived from a few classic designs. Even the iconic Marshall "Plexi" amp was a close copy of an earlier Fender. These circuits are extremely simple; a handful of tubes, transformers, and passive components, often less complicated than the internals of a single LM741. Here's an example: https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Deluxe-5A3-Schematic.pdf https://www.thetubestore.com/lib/thetubestore/schematics/Fen... It's possible to mostly recreate this sound with digital signal processing or carefully-tuned solid-state analog circuitry, but players like the sound of tube amps and are willing to pay for them, and so the market exists as it does.

jhallenworld 8y ago
Capacitors are also important: http://www.gibson.com/News-Lifestyle/Features/en-us/3-Classic-Capacitors.aspx http://www.gibson.com/News-Lifestyle/Features/en-us/3-Classi... Some old leaky "bumblebee" capacitor is worth $75 if it happens to be the .022 uF value found in certain guitar tone control circuits.
- dangerbird2 8y ago
  One of the main source of innovation in guitar amps (aside from bells and whistles like alternate channels and effect loops) are typically the "tone stack", i.e. the capacitance of the tone control caps and their position relative to the power and pre-amp tubes in the circuit. The amplifier circuits themselves are mostly taken from RCA radio amps dating to the 1930s and licensed by Fender in the 50s.
hamiltonkibbe 8y ago
I’ve found that a really good proxy for how good an amp sounds is the number of line-items in he BOM. The fewer the better. A lot of the classic designs that sound good and still sell have exactly what they need to get the job done well and no more. It’s almost like all the major (and boutique) amp manufacturers took one of three or so amp designs and just threw components at the schematic until you couldn’t recognize it right away, and sell it as some revolutionary design. I wouldn’t be surprised to find that it it all came from some RCA reference design in 1950
- exabrial 8y ago
  There some truth to that, but not always. Ideally you would want each time to be fed with a noise free constant current supply. Having each tube on its own power supply would be incredibly expensive but sound awesome. Buffering the output of each tube would prevent blocking Distortion, but would also be fairly expensive (although now we have mosfets that can handle 500+, so that might not be as bad). Split audio path about, where the bass goes through cleanly and the treble is overdriven would also sound incredible, but be expensive. Designs end up being about compromise: the above features will add $5-$35 to the bom per tube, and in the end, a lot of people just end up buying on brand. My Laney Lionheart L5T has a really cool preamp that uses solid state surface mount components where they don't affect the signal. This drives the bom cost down but sounds incredible (fully buffered fx loop, fully buffered reverb tank).
  - i_am_proteus 8y ago
    And further counterpoint: some guitar players like the sound of overdriving a tube power supply (the attack on a loud note reaches current limits for the p/s rectifier tube, dropping rail voltage, increasing harmonic content). Mesa "dual rectifier" amps made this an option, letting players switch between tube and solid-state rectifiers. There's definitely room for "improving" guitar amplifiers; I personally think that many guitar players like classic sounds, buy on brand as you said, and the brands just try to reproduce classic designs with any deviations made for cost more than for any other reason.
Zardoz84 8y ago
Don't forget that transistors have a different and more loud background noise that vacuum tubes. I don't appreciate the difference but I know that some people could notice and appreciate the different kind of noise.
- dangerbird2 8y ago
  The main cause of hum in both tube and solid state amps are ground loops that pick up the 50/60hz signal of nearby AC appliances and wiring. These can be caused by grounding problems in the amp, the instrument, or even the cables. https://en.wikipedia.org/wiki/Ground_loop_(electricity) https://en.wikipedia.org/wiki/Ground_loop_(electricity)
KozmoNau7 8y ago
This is a great example of "worse is better". Unlike amplifiers made for listening to music, in a guitar amp you want that distortion and non-linearity, you want it to be wild and resonant and you want it to be sensitive to what you do on the input side. Not directly related to tubes, but see the enduring legacy and popularity of the Boss HM-2 distortion pedal in metal circles, very often employed with all the knobs turned to eleven for maximum crunch. It was used to great effect primarily by Swedish death metal bands such as Dismember, Entombed, At the Gates and their compatriots. The tone is rough and textured and just feels right for the genre, so much so that it is considered a clearly defining characteristic of that particular branch of death metal. Just like tube amps, it's preferred because it's imperfect in just the right ways to produce an artistic result.

jhallenworld 8y ago

Capacitors are also important: http://www.gibson.com/News-Lifestyle/Features/en-us/3-Classic-Capacitors.aspx http://www.gibson.com/News-Lifestyle/Features/en-us/3-Classi... Some old leaky "bumblebee" capacitor is worth $75 if it happens to be the .022 uF value found in certain guitar tone control circuits.

dangerbird2 8y ago
One of the main source of innovation in guitar amps (aside from bells and whistles like alternate channels and effect loops) are typically the "tone stack", i.e. the capacitance of the tone control caps and their position relative to the power and pre-amp tubes in the circuit. The amplifier circuits themselves are mostly taken from RCA radio amps dating to the 1930s and licensed by Fender in the 50s.

hamiltonkibbe 8y ago

I’ve found that a really good proxy for how good an amp sounds is the number of line-items in he BOM. The fewer the better. A lot of the classic designs that sound good and still sell have exactly what they need to get the job done well and no more. It’s almost like all the major (and boutique) amp manufacturers took one of three or so amp designs and just threw components at the schematic until you couldn’t recognize it right away, and sell it as some revolutionary design. I wouldn’t be surprised to find that it it all came from some RCA reference design in 1950

exabrial 8y ago
There some truth to that, but not always. Ideally you would want each time to be fed with a noise free constant current supply. Having each tube on its own power supply would be incredibly expensive but sound awesome. Buffering the output of each tube would prevent blocking Distortion, but would also be fairly expensive (although now we have mosfets that can handle 500+, so that might not be as bad). Split audio path about, where the bass goes through cleanly and the treble is overdriven would also sound incredible, but be expensive. Designs end up being about compromise: the above features will add $5-$35 to the bom per tube, and in the end, a lot of people just end up buying on brand. My Laney Lionheart L5T has a really cool preamp that uses solid state surface mount components where they don't affect the signal. This drives the bom cost down but sounds incredible (fully buffered fx loop, fully buffered reverb tank).
- i_am_proteus 8y ago
  And further counterpoint: some guitar players like the sound of overdriving a tube power supply (the attack on a loud note reaches current limits for the p/s rectifier tube, dropping rail voltage, increasing harmonic content). Mesa "dual rectifier" amps made this an option, letting players switch between tube and solid-state rectifiers. There's definitely room for "improving" guitar amplifiers; I personally think that many guitar players like classic sounds, buy on brand as you said, and the brands just try to reproduce classic designs with any deviations made for cost more than for any other reason.

Zardoz84 8y ago

Don't forget that transistors have a different and more loud background noise that vacuum tubes. I don't appreciate the difference but I know that some people could notice and appreciate the different kind of noise.

dangerbird2 8y ago
The main cause of hum in both tube and solid state amps are ground loops that pick up the 50/60hz signal of nearby AC appliances and wiring. These can be caused by grounding problems in the amp, the instrument, or even the cables. https://en.wikipedia.org/wiki/Ground_loop_(electricity) https://en.wikipedia.org/wiki/Ground_loop_(electricity)

KozmoNau7 8y ago

This is a great example of "worse is better". Unlike amplifiers made for listening to music, in a guitar amp you want that distortion and non-linearity, you want it to be wild and resonant and you want it to be sensitive to what you do on the input side. Not directly related to tubes, but see the enduring legacy and popularity of the Boss HM-2 distortion pedal in metal circles, very often employed with all the knobs turned to eleven for maximum crunch. It was used to great effect primarily by Swedish death metal bands such as Dismember, Entombed, At the Gates and their compatriots. The tone is rough and textured and just feels right for the genre, so much so that it is considered a clearly defining characteristic of that particular branch of death metal. Just like tube amps, it's preferred because it's imperfect in just the right ways to produce an artistic result.