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Getting The Ultimate Guitar Sound – Part 2

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This post is part of a series called Getting The Ultimate Guitar Sound (Premium).
Getting The Ultimate Guitar Sound – Part 1
Getting The Ultimate Guitar Sound – Part 3

Getting a great guitar sound is a an almost endless journey for most guitar players, engineers and producers that requires time and too much money, to achieve a sound that may be only temporary. This series is based around my new book, The Ultimate Guitar Tone Handbook, where I’ll outline why acoustic and electric guitars, amplifiers, speaker cabinets and effects sound the way they do, and the best way to record and mix them after you’ve gotten the sound.


Also available in this series:

  1. Getting The Ultimate Guitar Sound – Part 1
  2. Getting The Ultimate Guitar Sound – Part 2
  3. Getting The Ultimate Guitar Sound – Part 3
  4. Getting The Ultimate Guitar Sound – Part 4
  5. Getting The Ultimate Guitar Sound – Part 5
  6. Getting The Ultimate Guitar Sound – Part 6
  7. Getting The Ultimate Guitar Sound – Part 7

In Part 2 of the series, we’ll look at the wide variety of elements that gives an guitar amp its sound.

Many musicians, engineers, producers are hip to different types, brands and models of guitar amplifiers, but few know the differences between them, and it’s those differences that often give the amp its unique sound. The special characters of an amp and speaker cabinet have everything to do with how a guitar blends into the mix, which is why the more you know about the gear you’re using, the easier it is to get just the right sound when you need it.

So what affects the tone quality of an amp? Let’s look at all the variables.


Amplifiers

There are two different categories of amps, tube and solid state, and a number of sub-categories as well. Let’s look at them individually.


Tube Amps

Tube amplifiers are based around those glowing cylinders of glass called the vacuum tube, which is an electronic amplification component. While tube amps are noted for their big, fat tone, they do have a lot of drawbacks.

  • The tubes themselves are available, but the best ones are getting difficult to find (almost none are made in the U.S any longer due to government environmental constraints and the costs involved with compliance) so they’ve now become expensive.
  • They give off an incredible amount of heat which eventually degrades the surrounding electronic components.
  • They require a large, heavy and expensive output transformer to transfer the amplified electronic energy to the speakers, as well as an equally large and heavy power supply transformer to supply the high DC voltage to the tubes. (See Figure 1.)
  • Tubes eventually wear out and need to be replaced, gradually changing the sound quality as they age.
  • Tubes are a very imprecise electronic component living in a world of high precision. No two are made exactly alike and each has slightly different specs, which means that it’s best to do an electronic setup every time you change power tubes, and have an audio audition when you change preamp tubes to be sure everything is optimized.

Figure 1. Marshall amp clone showing the power and output transformers

Regardless of those drawbacks, tube amps have the most important trait required by a guitar player - tone. Given the choice, most guitar players, engineers and producers will select a good sounding tube amp most of the time.


Circuit Design

The number of gain stages in an amplifier has a great deal to do with the sound of an amp. For instance, the normal number of gain stages from a typical Fender, Marshall or Vox amp is two gain stages, yet they don’t sound anything like one another. The difference is that in a Marshall the first gain stage (the preamp) feeds the volume control, which then drives the second amplifier stage (see Figure 2). When you turn up the volume control you begin to overdrive the second stage. This can’t happen in many Blackface and later Fender amps because the tone controls and volume control decrease the gain so much by the way they’re configured that it’s next to impossible to overload the second stage (see Figure 3). That’s why Fenders are generally cleaner sounding than Marshalls.


Figure 2 A Marshall Amp Gain Stage Block Diagram

Figure 3 A Fender Amp Gain Stage Block Diagram

But if you add another gain stage behind the tone stage, you suddenly have a lot more gain to work with, which happened as designers answered the requests of players looking for more distortion from the amp (see Figure 4). Some of the very high gain amps like some Boogies and Soldano’s even have four gain stages. That being said, most traditional amplifiers made before the 90’s only use two gain stages, while most of the newer amps use three or four.


Figure 4 A High-Gain Amp Gain Stage Block Diagram

Solid State Amps

Solid state refers to amplifiers built completely out of solid silicon material that makes up transistors, integrated circuits and microprocessors. Solid state amps have a lot of things going for them:

  • They’re very light because they don’t require large power supplies, high voltages and heavy output transformers.
  • They’re inexpensive because they don’t require a lot of expensive heavy components.
  • They’re very reliable because there are fewer components, no tubes to wear out and less heat to deal with.
  • They’re capable of much higher output power than tube amps.

The problem with solid-state amps, until recently, has always been about the sound. When they first came out in the 60’s solid state amps were sterile sounding, with little of the distortion characteristics that players loved (see Figure 5). While that kind of sound might’ve worked for bass players and jazz guitarists (who loved the solid state Polytone amps), it just didn’t cut it for the majority of guitar players doing real gigs.


Figure 5. A Roland JC-120 Solid State Amplifier

Amplifier Modeling

Virtually all solid-state amplifiers made today are built around modeling technology. Modeling digitally simulates the sound of various well-known guitar amps (most of which are usually based around tubes), cabinets, speakers and effects, right down to even how the cabinets of these amps are miked. A modeling amp is capable of a wide variety of tones and effects, all made available through the digital signal processing (DSP) of an on-board computer (see Figure 6).


Figure 6. Line 6 Spider II Modeling Amplifier

Solid state amps, especially the ones using modeling technology, now have a lot going for them sonically:

  • You have a huge variety of sounds to choose from.
  • Effects that used to require external stomp boxes are built in.
  • The output power can be high even in a relatively small and light package.
  • Different sounds can be selected almost instantly.

In the studio, a small modeling amp can sound so much like the amp it’s modeling that no one ever misses the real thing, especially if it’s placed back in the track a bit. In fact, a generation of guitar players has never used anything other than a modeling amp or software, and really doesn’t have a reference point as to how a real tube amp sounds as a result. They’ve been getting along just fine in the digital world of tone.


Speaker Cabinets

Just like amplifiers, there’s a lot more to speaker cabinets than meets the eye. Let’s look at some of the parameters.


Open or Closed-Back Cabinet

The typical combo amp has an open back (see Figure 7) so that the speakers are exposed at the rear and that affects the sound in a number of ways. An open-back cabinet:

  • spreads the sound around the room, but provide less low frequency response than a closed-back cabinet.
  • has a sound that’s harmonically complex, and a bit more open and even louder than a comparable closed-back cab because the sound from the back of the cabinet is reflecting off the room behind the amp and mixing with the sound that’s coming out its front.

    Figure 7, A Typical Open-Back Combo Amp
  • provides more miking possibilities than a closed back since you’re also able to mic the rear of the cabinet (watch the phase though).
  • enables you to easily change the sound of the cabinet by either placing it up off the floor on a chair or flight case, or placing it in the center of the studio away from the walls.

A closed-back cabinet (see Figure 8) seals the air inside the cabinet which compresses the sound coming from the rear of the speakers. That affects the speaker’s tone as a result.


Figure 8 A Typical Closed-Back Cabinet

A closed-back cabinet like a Marshall 4x12 or Fender 2x12:

  • has a tighter, punchier sound with more bottom end that’s a lot more directional sounding than the open-back because the sound is more focused.
  • has a sound that’s thicker, less airy, and harmonically simpler than an open-back cabinet.

Most closed-back cabinets have a resonance point of about 120Hz, which is equivalent to an open A note, which is why they’re seeming made for rock (although not as good for other types of music).


Cabinet Size

The size of the cabinet determines the lowest bass frequency that the cabinet can reproduce. The larger the internal space, and therefore the larger the cabinet, the lower the possible response. This is why bass cabinets are always a lot larger or deeper than guitar cabinets.


Construction Materials

The type of wood used to build a cabinet contributes to its tone. Cabinets, like guitars, can be built out of just about any kind of wood, but just like guitars, only a few kinds of wood are used because of their sound or cost.

  • Marshall cabinets are built out of 11 ply Baltic birch, a wood that’s known for its musicality, strength and light weight. This is one of the reasons (besides the speakers and the closed back) that nothing else sounds quite like a Marshall cabinet.
  • Early Fender cabinets were made of pine, which is light and has it’s own tone, but isn’t a particularly strong wood. Like most manufacturers, Fender slowly but surely changed their cabinet wood, first to marine plywood, and then particle board (known as MDF - medium density fiberboard).
  • Plywood and MDF has less cabinet resonance than solid woods like pine, cedar and birch. MDF is very strong and inexpensive, but is somewhat neutral sounding at best, and harmonically dissonant at worst. The resonance that occurs with MDF is often described as “dead” and “atonal.”

Construction Method

The way cabinets are constructed also makes a difference in their strength and the way they vibrate. Most quality made cabinets use finger or dovetail joints to join the pieces together and keep them solid (see Figure 9), while some even use reinforcement to hold everything secure.


Figure 9 A Combo Cabinet With Dovetail Joints

The Baffle

One of the most overlooked parts of a cabinet is the baffle (see Figure 10), which is the board that the speaker is directly mounted on. Perhaps more than any one piece of the cabinet, this has the most influence on the sound. The type of material (pine, birch, MDF), the thickness, and the way it’s mounted all contribute to how it affects the sound.


Figure 10 A Typical Speaker Baffle

Speaker Parameters

Here are some of the parameters that make speakers unique, without getting into transducer engineering.

Size

As you’ve probably noticed, an 8 inch speaker sounds different than a 10 inch, which sounds different from a 12 inch, which sounds different from a 15 inch speaker. The reason is simple physics; the larger the cone, the more energy it takes to get it moving so the high frequencies and the attack time won’t be as good as a speaker that’s smaller. Conversely, a smaller speaker has poorer low frequency response because it has less cone area to move air.

As a result, you’ll notice that an 8 inch speaker won’t have nearly as much bottom end as a 15 inch speaker, and the 15 won’t have quite the top end of a 10 inch speaker. That’s why 12 inch speakers are mostly used for guitar rigs; they’re a nice compromise between the two.

Number Of Speakers

That being said, the number of speakers in a cabinet can also have an affect on both the volume level and the low end. The more speakers that acoustically couple together, the more effective cone mass you have. As a result, a cabinet with two 12 inch speakers gives you 24 inches of cone mass while a a cabinet with four 10’s (like Fender’s original Bassman - see Figure 11) gives you 40 inches. Of course, other factors like resonant frequency are involved, but this is a simple way to look at it.


Figure 11 An Original Fender Bassman Amp

Speaker Wattage

Contrary to what you might think, lower wattage speakers usually sound better than high-wattage ones. High-wattage speakers have heavier cones that change the response of the speaker and therefore the tone. Because the cone is heavier, it’s slower to move when a signal is applied so the high frequency response isn’t as good as one with a thinner cone (see Figure 12).


Figure 12. The Highly Desirable And Low Powered Jensen P12N

Other things that change in a higher watt speaker is the diameter of the voice coil and the type of wire used, which makes it larger and again changes the speaker’s response. A heavier magnet is also required because the voice coil is a bit heavier to move.

As a result, what you have is a speaker that’s harder to blow up, but also one that has a different frequency response and doesn’t break up as easily, which may be an important trait of your sound.

Magnet Structure

There are three different types of materials used in speaker magnets, Alnico, Ceramic, and Neodymium, with each material having a distinctly different effect on the tonal characteristics of the speaker.

As you can see, there’s a huge amount of variables when it comes to amplifier sound (and we’ve only touched the surface here). Don’t get overwhelmed though, because in Part 3, we’ll look at ways to make big changes to a guitar sound without buying a new rig.

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