The new Spider V 30 is one of the latest models in Line 6’s long line of impressive modeling amps.

Modeling: In terms of guitar tone, modeling usually refers to a manufacturer’s software-based emulation of a physical device such as an amplifier, effects unit, speaker cabinet, microphone, or even the guitar or bass itself. With modeling, the software isn’t just programmed to sound like the real thing; it’s supposed to respond in real time like the device it’s modeled after. See also Profiling.

Negative feedback refers to a signal taken from the output and fed back through to one side of the phase splitter, thereby cancelling out sound waves that can cause unwanted distortion. “Unwanted” is the operative word here—if you’re looking for very clean sounds, an amp with a negative-feedback circuit might be the way to go. But there are some very famous amps—including many based on classic Vox designs—where negative feedback is intentionally decreased to add grit and harmonic complexity. Some amps have no negative feedback at all. Others allow you to adjust negative feedback either in total or at certain frequencies. The latter is the basis of the presence knob on the tweed Fender Bassman and Marshall amps.


As opposed to the printed green circuit boards we’re used to seeing in all sorts of modern electronics, this Carr Skylark’s wiring on an old-school turret board is an example of what guitarists mean when they say an amp is “point-to-point” wired.

Point-to-point is a method for wiring electric components directly to one another. For example, an amp’s input jack might be connected directly to a resistor that’s soldered onto the first tube’s socket. It’s a misnomer that all vintage or handbuilt amps are point-to-point. In fact, most have tag or turret boards, which are connected to inputs, tubes, and controls with wires. However, these old-school boards do allow techs to replace individual components and make other changes quite easily. See also Printed circuit board (PCB).

Printed circuit board (PCB): A circuit board made of epoxy with pre-etched conductive tracks for connecting components. PCBs are the standard for almost all mass-produced electronics today (including tube amps), and a well-designed PCB offers no sonic disadvantages over handwiring. They are, however, much harder to service and/or modify. See also Point-to-point.

Profiling is a software-based capability that allows one to capture (via a microphone) and analyze the characteristics of a specific device that one has access to (usually an amplifier) in order to create an accurate digital model of that device. See also Modeling.

By the same token, while solid-state amps have a reputation for sounding too clean and “sterile,” many classic guitar sounds are the product of a tube amp driven by a solid-state overdrive, distortion,
or fuzz pedal.

Push-pull: A power amplifier output section in which signal from the preamp is split into opposite polarities by a phase inverter (aka phase splitter). Each side of the phase inverter feeds one half of the power-tube complement—i.e., in an amp with two power tubes, one will have the positive side and one the negative. Each tube then feeds the output transformer, where the signal is summed to produce sound. Push-pull designs are more complex, but they’re also more flexible, require less expensive output transformers, and can produce more power. Push-pull is by far the most common design for mid- to high-power guitar amps. See also Class-A and class-AB, and Single-ended.

Rectifier: A device that converts alternating electrical current from the wall socket into the direct current needed in your amp. Rectifiers can be either tube or solid-state, and the correct type of rectifier depends on your amp’s power transformer (important if you’re replacing yours). Rectifier tubes don’t carry signal, but because they control the voltage going through the amp, they can have a noticeable impact on the tone, which is why players sometimes experiment with different brands and vintages of rectifier tubes. All other things being equal, solid-state rectifiers typically produce a tighter, more powerful sound, with less “sag,” give, or compression in responsiveness than tube rectifiers.

Single-ended: A power amplifier output section in which the entire sound wave from the preamp is amplified at a single polarity (see also Push-pull). Because it involves fewer parts, the single-ended design was especially popular for small practice tube amps. These days, it can also be found in some high-end boutique models. Many players love the overdriven sound of a single-ended amp, which can be lush with even-order harmonics. That said, single-ended amps are generally less powerful than their push-pull counterparts. Most single-ended amps operate in class A and have one power tube, but some designs can use more tubes (in parallel) to increase power. See also Class-A and class-AB.

Tone stack: The term derives from the way tone circuits appear on a schematic, and simply refers to the arrangement of resistors, capacitors, and potentiometers in a tone circuit. The most common tone stack for amps is known as FMV (Fender, Marshall, Vox) but there are many others, as well as many variations within the FMV family.


The 2011 debut of Kemper’s Profiling Amplifier rocked the gear world by giving players a method by which to digitally capture and model the tonal characteristics of amps they had access to.

The FMV usually has controls for treble and bass, with either a control or a fixed resistor setting the midrange. It’s flexible, but also considered to be “lossy” because it causes a drop in gain (though the Bassman and Marshall versions mitigate this loss by using a design known as a cathode follower).

A so-called “tweed” tone stack (based on the tweed Fender Deluxe) uses a single tone control that shapes the highs and upper midrange. It’s less flexible than the FMV and has more effect on the amp’s overall gain, but it’s also less lossy. Ampeg and others use a James (sometimes referred to as Baxandall) tone stack. It’s flexible, with relatively little signal loss. The “brownface” tone stack Fender used between the tweed and blackface eras is also becoming popular with boutique builders.

All this said, your amp’s tone stack isn’t the only element shaping its sound, especially in a tube amp. The way tube stages are arranged, connected to one another (coupled), and even the way they’re biased impacts the sound. The Matchless DC-30, for example, has a channel with no tone stack. Instead, its six-position tone switch changes the coupling capacitors between the preamp and power amp.

Tube vs. solid-state: Refers to the types of components used to amplify and shape the signal in an audio circuit. Both tubes and solid-state op amps can be used as voltage amplifiers—the devices that boost and shape your guitar’s signal. So which is better?

While most players will agree tube and solid-state devices sound and feel different, the pros and cons are too complex for generalizations. Tubes are cherished for their overdrive but they also seem to add pleasing harmonic complexity to clean sounds, especially if they’re pushed almost to overdrive. By the same token, while solid-state amps have a reputation for sounding too clean and “sterile,” many classic guitar sounds are the product of a tube amp driven by a solid-state overdrive, distortion, or fuzz pedal. There are great sounding solid-state amps, too—including many that use field-effect transistors (FETs) to emulate tubes. There are also lackluster, even horrible-sounding tube amps, both vintage and modern. Further, solid-state amps generally require less servicing, are less expensive, and usually weigh less.