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Know Your Knobs - Part 1: Amps 101

Posted on October 13 2017

Using Pedal Knobs

Welcome!

We’re here to help clarify the rights, wrongs, myths, grey areas, dos, don’ts, and give you a grounded understanding on how to utilize your beloved gear in the best way. We’ll cover different amplifier types, tubes, tones, effects, signal flow, and everything in between. Russo Music is has your back when it comes to knowing your knobs.

Section One: Amplifiers

[am-pluh-fahy-ers]
noun
1. an electronic device for increasing the amplitude of electrical signals, used chiefly in sound reproduction

Tube Vs. Solid State Vs. Digital Modeling

Tube amps use tubes to amplify signal, while solid state amps use solid state components to amplify signal. Digital modelers are solid state amps that have built in digital effects processors to allow the user to simulate different amps and effects all from one unit. Tube amplification provides a significantly more satisfying musical experience. Their harmonics, warmth, articulation, and speed are imitated by solid state amps but never quite duplicated. Solid state amps are cheaper to make and operate while tube amps can be more expensive and all require maintenance to perform optimally.

Class A vs. Class AB Tube Amps

While this section could be a novel in itself, the very simple explanation for this is as follows:

Class A amplifiers run constant power through the tubes, even when there is no note being played, so the amp is always “idling” around 50% power. The positive side of that is the tubes are always “ready to go”. On the converse, extremely high voltage is required and the amp runs rather inefficiently.

Class AB amplifiers use pairs of tubes working in conjunction with each other to accomplish the amplification. The tubes in a class AB push-pull amp are out of phase so each singular tube is only responsible for 50% of the sound wave. Meanwhile, in a true class A amp, each power tube is responsible for the entire wave itself. Single-ended class A amps (one straight signal path from tube to tube) are generally 5-10 watts. Push-Pull class AB amps are far more efficient and capable of producing significantly more power. Think about your 100 watt Marshall and Orange amps. These could never operate in true class A. Most Fender and Marshall amps are class AB while Vox amps are generally Class A.

The breakdown of Class A vs. Class AB

Class A - Always running, quick response, quicker breakup, richer upper secondary harmonics BUT shorter tube life, less efficient, lower maximum volumes.

Class AB - Idles at lower voltages/more efficient, higher power, more “headroom”, more low end bass response, longer tube life BUT slower response time, possibly less harmonic.

GAIN

Essentially the “loudness” of your amplifier. Input gain corresponds to overdrive, and output gain corresponds to overall volume level.

ARTICULATION

How your amp responds to playing dynamics and touch sensitivity.

PREAMP TUBES

The first stage in generating signal to the speakers. Preamp tubes are responsible for input signal - volume and tonality of the electric guitar that is then sent to the power amp section of the amplifier.

POWERAMP TUBES

The second stage in generating signal to the speakers. Power amp tubes are responsible for volume and clean headroom - the output signal.

WAIT, WHAT IS “HEADROOM”?

“Headroom” is the term used to describe the amount of volume an amplifier can produce before it distorts. Generally, higher wattage amps have more “headroom”.

Single Channel Vs. Channel Switching

With a single channel amplifier, you are most often dealing with one type of sound which is generally a clean tone. Any overdrive would be accomplished by increasing the gain and/or volume on the one channel. A channel switching amplifier will allow you to have two distinct sounds, most commonly clean and overdriven. By pressing a button you switch to a different portion of the amplifier for higher gain.

Combo Vs. Head and Cabinet

A combo is an amplifier and speaker contained within one physical package. The chassis holds the circuitry (and tubes if a tube amplifier) which connects to the speaker within the unit via speaker cable. A head is the amplifier itself, and a speaker cabinet houses the speaker(s) separately for the head to connect to. This provides the ability to “mix and match” different heads and cabs easily, be it for tonal reasons or simply convenience.

Popular Control Panels

Fender Dials Knobs

FENDER PRINCETON REVERB ‘65 REISSUE

Fender amps are, in many ways, the benchmark of where other amplifiers start. The earliest Fender control layouts were two volume knobs and a single tone control, and some Fender’s are still made this way. However, most Fender amps have a volume, treble, middle, and bass control. Some amps feature a Presence control, which adjusts high end from the power amp section, as opposed to the preamp section (treble). The most popular Fender amps feature a single reverb control, and a tremolo circuit - speed and intensity. This can be seen on any of the “-Reverb” amps - Deluxe Reverb, Princeton Reverb, and so on.

Vox Dials Knobs

VOX AC15

Vox amps are considered the sound of the “British Invasion” of the mid 1960s. Early Vox AC series amps had a volume for three channels - Normal, Brilliant, and Tremolo - and they could be blended by preference. For the EQ section, a Vox commonly has an “interactive” treble and bass section - which boosts or cuts mid range depending on their settings - and a “cut” control, which acts as a highpass filter at the end of the signal.

Marshall Dials Knobs

MARSHALL JCM800

Quite possibly the dominator of the amp world in rock, blues, and metal music from the late ‘60s through the ‘80s, a Marshall amp is benched off of a shared EQ section for two channels - treble, mid, bass, and presence. The two channels are a “High Treble” channel and a “Normal” channel. The magic of an early Marshall amp is to blend both channels to balance the right blend of brightness and boldness to attain some of the most quintessential electric guitar tones.

Orange Dials Knobs

ORANGE ROCKERVERB 50 MKIII

Orange amps have been known to be “fat” and warmer sounding than any of the UK’s popular amplifiers. They achieve volume through clean headroom more so than distortion, so they are made to be played loud! Classic Orange amps were on a single channel platform, with controls for volume, treble, bass, presence, and their “FAC” control - a 6-way rotary pot that controls bass response. Oranges are often favored to run loud and clean with a fuzz pedal, and can be associated with the sound of “doom” metal - but they have also been seen in Stevie Wonder’s backline in the ‘70s.

Mesa Dials Knobs

MESA MARK 5:25V

In the early ‘70s, Mesa took the Fender amp platform and sent it sprawling into new territories, giving the world the first “high gain” amplifier. This amp, which would be known as the Mark I, featured two stackable volume channels into a shared treble, middle, bass, and presence control layout. As time went on, Mesa entered the realm of channel switching amps, and their 40+ years of evolution and versatility can be best seen in the Mark V, which features three separate channels, each with independent EQ, and a staple in Mesa amplifiers - a five band graphic EQ.

Part 2 coming soon!


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