Guitar Amp Technology

Analog Technology

Mesa/Boogie Duo-Class^TM Power A push-pull transformer operates in single-ended mode with zero net plate current through the transformer core.

Power Amp with Variable Harmonic Distortion The balance of the power amp input signal is user-controlled to vary the harmonic content of the power amp.

Mesa/Boogie Solo Control^TM footswitchable volume boost to enable the guitar player to "step forward in the mix for a spotlight feature in any mode"

Soldano SLO Global Feedback Controls "The combination of the Depth and Presence controls provides a powerful EQ section that goes well beyond a typical tone stack."

Davoli Bootstrapped Phase Inverter The circa 1965 Davoli Model 207 guitar amplifier from Parma, Italy has an unusual phase inverter with a split plate load.

Danelectro Differential Amplifier Many players have rediscovered the lo-fi bristle of Danelectro and Silvertone amps.

Ampeg Plate Follower Phase Inverter "It carries a mix-and-match bundle of ingredients found in a couple variations of a highly desirable blues and rock amp from another maker." -Dave Hunter

Guild Parallel LTP Phase Inverter Here is something not often seen in a guitar amp: a four-triode phase inverter!

Hughes & Kettner Relay Control Hughes & Kettner uses microcontrollers and relays to create a switched-channel, MIDI-controlled performance powerhouse.

Mesa/Boogie Switchable Grid Bias Supply The Dual Rectifier has a grid bias supply that is switchable to support EL34 power pentodes or 6L6 beam power tetrodes.

Magnatone Model MP3 Fixed Bias Preamp The first stage adds a strange 220kΩ resistor between the 140V plate supply and the cathode.

Guitar Amp Modeling

Digital Modeling of a Guitar Amplifier Tone Stack "We exhaustively worked out the equations for all the tone stacks by evaluating the mesh and node equations." -Fractal Audio Systems

Digital Modeling of Guitar Amplifier Preamp Distortion Gone are the days of applying a single, overly simplistic sigmoid function to a sample sequence to digitally model the distortion of an entire guitar amplifier.

Digital Modeling of a Guitar Amplifier Power Supply "Deviations in dynamic response can make an amplifier simulation feel too stiff or too spongy in comparison to the real amp." -Fractal Audio Systems

Output Transformer Lumped-Element Model A transformer model can be substantially simplified if distributed impedance is rolled up into a single lump.

Foldover Noise in Guitar Amplifier Digital Models For upsampling, Line 6 prefers linear interpolation. Here we look at a simpler method called "zero stuffing."

Miscellaneous Topics

Noise in Guitar Amplifier Preamps Thermal noise, microphonic noise, and tube noise can be particulary annoying when the amp sits idle in a quiet room.

Carbon Composition Resistors in Guitar Amplifiers "With some resistors the erratic sputtering sound predominates, whereas with others ... erratic sounds may be entirely missing." -George Conrad

James Tone Stack - Analysis Here we examine the other classic tone stack: the James, as used, for example, in the 120-watt Orange Graphic.

James Tone Stack - Create Your Own Design Our key concerns are the overall attenuation level at midrange and the transition frequencies between bass, midrange, and treble.

Ultralinear Guitar Amplifiers The 200-watt Marshall Model 1967 head has an "ultralinear" power amp. So does the Sunn Model T Super. Even Fender built an ultralinear amp.

Pentode Preamps - How Screen Voltage Affects Large-Signal Gain For large signals, the issue boils down to our basic definition of gain: output voltage swing divided by input voltage swing.

A Battery-Powered Guitar Amp The directly-heated cathode of a 1T4 battery pentode consumes almost 30-times less power than a 12AX7 heater!

Vacuum Tube Technology: A Perspective Circa 1950 The definitions listed here are from Standards on Electron Tubes: Definitions of Terms, published in 1950.