All Tube Amps are Not Created Equal

There are two main amplifier configurations in use today, the tube amp and the transistor amp. Most bass guitar players have a pretty strong preference for one or the other. Whichever you prefer, it’s important to have a good understanding of how each type works. The information below should help with that.

Tube Amplifiers

Most people associate tube amplifiers with classic rock ‘n’ roll music from the 1950s and 1960s. There’s a real reason for this association: for many years, tube amps were the only kind available. When transistor amps started appearing on the market in the 1970s, they were considered little more than toys compared to their more powerful and complex tube counterparts. Tube amps continued to dominate the scene even into the 1980s, when solid state technology grew sophisticated enough to seriously challenge their supremacy. Today’s most popular bass amps are typically hybrids, combining solid state preamps with tube power stages to deliver a combination of warm distortion and ample volume levels.

So how do tube amps work? In their most basic form, they consist of three main parts: an input stage that takes your instrument’s weak electrical signal and amplifies it; a power stage that takes this

So, you’re looking to buy a bass guitar amplifier? To start with, you can be sure that all tube amps are not created equally. If you are after a warm, vintage tone then it’s worth doing your research before buying a valve amp. With so much choice on the market and so many people singing the praises of valve amps, it is important to know what you are investing in.

We’ll look at some of the key differences between transistor and valve amps; but first, let’s take a look at their similarities.

Both types of amp have advantages and disadvantages but ultimately, your personal preference will determine which style of amp suits your musical needs. Some people prefer the tone from a valve amp while other people like the reliability and consistency of transistor amps.

If you want to know more about transistor and valve amps then read on…

This article is based on a talk I gave at the 2009 NAMM show in Anaheim. It was part of the session on “Old School vs. New School”, and was a direct response to some comments made in the main presentation.

The differences between tube and solid-state amps are not as simple as people make out. All tube amps are not created equal, and neither are transistor ones. The number of tubes is not necessarily related to sound quality or tone; neither is the number of transistors (although this might be an indicator of power output).

There are also some basic principles that are shared by all good amps, regardless of their technology. If you can understand what makes a great amp, you will have a better chance of getting one!

Valve amps can sound better than transistor amps, but not because of their valves. They sound better because they are more powerful and the power supply is much more robust.

So why do so many people believe that valve amps sound better? Well, because they do sound better. But that’s not because of the valves. Valves have a very small effect on the sound, and it’s widely agreed that the most important effect is to add a touch of compression in the output stage. If you want compression you can get it just as easily from a solid state amp by turning down the volume control.

Transistor amps can have a touch of distortion in them too (anyone who’s had an overdriven Marshall will know what I’m talking about). But that’s because transistor amps run into trouble when pushed hard. You might be able to get away with pushing a solid state amp hard if you don’t mind it sounding like an old school transistor organ.

Why do tube amps sound different?

There are a number of arguments made by advocates of both solid state and vacuum tube guitar amplifiers as to why their respective technology is superior. Solid State advocates often cite the amplifier’s speed, reliability and consistency as reasons for their preference. Tube advocates cite the amplifier’s harmonic distortion characteristics and its ability to change timbre when overdriven as reasons for their preference.

In order to gain some insight into this debate, we will focus on one aspect of tube guitar amps which has a direct bearing on how they sound: the nature of the power supply design.

A tube amp’s power supply is responsible for providing a constant B+ voltage, and for providing sufficient current to drive the loudspeakers. The power supply also influences the tone and “feel” of the amplifier, much like a capacitor or resistor changes an electronic circuit’s behaviour.

It’s a commonly held view that all valve amplifiers sound the same. This is patently not true. Even the most cursory of listening tests will show that there are some fundamental differences between the sound of different valve amps.

So why do people still hold to this view? And what does it mean for choosing an amplifier? Firstly, it’s important to understand that there are two main categories of valve amp:

Class A: The signal passes through the valves in one direction only. Class A amps always have a single-ended output stage (i.e. one output transformer and a single set of power valves)

Class AB: The signal passes through the valves in both directions (i.e. positive and negative). Class AB amps can have either a single-ended or push-pull output stage (i.e. two output transformers, two sets of power valves).

The great majority of “combo” amplifiers (those with an integral loudspeaker cabinet) are Class AB, push-pull designs. They work on the principle of using half the power valves to amplify half the signal, and then combining them at the output stage to produce the final amplified signal which is then routed through a loudspeaker cabinet.

Amp is the generic term for a device that amplifies an electrical signal. It has been used in this context since the very beginning of electronics and radio. In recent years it has also come to mean a device which serves as the central unit in a domestic sound system (stereo).

An amplifier is a device that takes in an input signal and produces an output signal which is larger than the input signal. The function of the amplifier is to increase the power level of a low power signal that has been generated by some other source. For example, a microphone can be used to generate voice waves into the amplifier, and the amplifier will convert these signals into large electrical impulses that can be used to drive loudspeakers (a type of transducer) that produce acoustic waves.

In musical applications, an amplifier may be used to supply electric guitar or keyboard with enough power for driving one or more loudspeakers.