I’ve had a number of opportunities to sample overdrive pedals from all around the world, and here are four that have made quite an impression on me. Though not as

I’ve had a number of opportunities to sample overdrive pedals from all around the world, and here are four that have made quite an impression on me. Though not as well known as many of the standard overdrive pedals, they are all destined for greatness.

Guitar Tech Ulbrick 12AXE
From the Land Down Under comes the Ulbrick 12AXE, a true plug-andplay pedal. There are only three controls—volume, tone and overdrive—so using the pedal is quite selfexplanatory. The pedal has a bright blue LED to let you know when the pedal is in use or in bypass mode, and a solid steel casing that can hold up to extensive travel and abuse. A wide variety of tones can be found just by adjusting the tone and overdrive knobs, and the unit runs on a 9V battery or with a standard 9V DC power supply. If you like the idea of having something as good as an original TS-808 Tube Screamer at a third of the price, this pedal will do it for you.

The 12AXE is as close as you can get to adding another valve stage to your amp; it reacts much like a valve. Wind up the overdrive and it becomes a true distortion pedal, giving you really tasty and controlled grit. Back it off and you can have a very handy “slightly dirty” pedal for blues licks or crunchy chords. Be warned however, this is no “metal” pedal—it has way too much tone for that. If you are looking for a really smooth distortion/overdrive pedal to compliment your tube amp, the 12AXE might just be for you. I highly recommend it.

Guitar Tech Fuchs Plush Drive
Many of you are familiar with Fuchs Amplifiers, but here in the U.S., Andy Fuchs has really outdone himself with the Plush Drive. If you don’t own a boutique amp, this pedal will make you sound like you do. Andy designed the Plush Drive at a very reasonable price for those who want the true tone, response, and feel of boutique tube amps. It comes with four separate control knobs that cover all the important aspects of your tone. Right away I noticed that the gain and touch controls allow you to set distortion and pick response based on your own individual playing style. Once you set those, the tone level controls help you to set both your overall lead tone and solo level. Andy worked hard to develop a unique bi-fet integrated circuit and matched discrete FETs so players can emulate the smooth overload and distortion of a tube circuit with the utmost quality of sound. It’s impressive enough played through a clean amp, but add a great overdriven tone and this pedal will blow your mind.

Guitar Tech Rodenberg GAS-909
From Germany comes the GAS-909. Made by Rodenberg Amplification with Germanengineered components, this pedal is designed to blend seamlessly with your amp. It’s actually a step up from Rodenberg’s GAS-808, except with three times the gain. This increase in gain gives the pedal a totally even frequency response throughout the gain structure, while maintaining the crisp and accurate lead sounds that the original 808 offered. The pedal is extremely even when boosting the amplifier’s sound, so the guitar’s tone shines through.

Guitar Tech Pacifix Ltd. Stampede SOV-2
Of course, the list wouldn’t be complete without a Japanese offering. Made in Japan by Yuki Hayashi, the Stampede SOV- 2 OD pedal is designed to deliver natural overdrive without changing the tone of the guitar. Believe me, Japanese design is not one to be underestimated. Yuki has studied overdrive in depth, and I had the chance to visit with him personally about this pedal. His major focus was to produce a clean, crisp, quality overdrive pedal with unique characteristics that enhance tone without compromise. One particular unique feature of this pedal is the bipolar power supply that powers the internal circuitry with ±15 volts, providing more than three times the dynamic range of conventional 9-volt powered overdrives.

The clarity and smoothness of this pedal is outstanding. It has standard true bypass circuits where the instrument signal passes through two switch contacts when bypassed. In addition to indicating the pedal’s on or off status, a very hip LED provides visual battery power monitoring. Because the incoming power is so closely related to the performance of the internal circuitry, when the battery voltage drops below 5 volts the LED will become dimmer and begin to fade out. The effect will still operate at this voltage, but it lets you know it’s time for a change.

So there you have it—overdriving around the world. Of course, you can find your own global gear online, so visit these (and other) manufacturers’ websites and spend some time reading up on some lesserknown products. You may have your own four on the floor in no time. Plus, you can drive these without a license!

Rick Wheeler
Rick Wheeler currently works as Larry Carlton’s guitar tech and front of house engineer. He is also an accomplished jazz guitarist, vocalist, and educator. You can contact Rick at rickwheeler@hughes.net

A basic rundown for all those seeking basic amplifier and resistance knowledge and tips.

Hooking up a head to a single or group of cabinets is often a confusing topic. Most of us just want to play music and don’t have time to learn about watts and ohms. But this is an important topic to understand so you don’t damage you or your amp.

First, it’s important to use speaker cables when hooking up a head to your cabinet. Instrument cables used between your guitar and amp might look similar, but they are drastically different. Speaker cables are thicker and not shielded. Even gauge numbers can be confusing – just remember, the thicker the cable, the lower the number. Use at least an 18 or 16 gauge speaker cable so you don’t damage your rig.

Guitar Tech
Do the math before hooking up multiple cabinets, otherwise you might have a flaming amp on your hands
You will see the term “load” a lot with amps. A load is something that uses power to do something. A load could be a motor, light bulb, speaker, a group of speakers in a cabinet, or several cabinets hooked together. An amp head is used to power the load.

Impedance is a measure of resistance. When electricity flows to a load, some of the electricity is resisted or impeded. Impedance is measured in ohms – denoted with the Greek letter omega ( ). Most cabinets have an impedance of 4, 8 or 16 ohms. More ohms mean more resistance and with more resistance there is less power flowing to the speaker.

Amp heads specify how much power is sent to a load (a cabinet or group of cabinets) of a certain impedance (the amount of resistance measured in ohms). For example, you may see an amp rated “400W @ 4 ohms.” Likewise, a particular amp head might send 200 watts into an 8-ohm load, but the same amp will send 350 watts into 4 ohms. More power will flow from an amp as the ohm rating (resistance) decreases. If you went down to 2 ohms, that same amp might send 600 watts to the load.

All of this is important because amps are designed to work within a certain resistance. If there is not enough resistance, the amp will put out more juice than it can handle, leading to overheating, and eventually burning up!

You probably don’t want your amp catching fire, no matter how cool it looks onstage.

If you are running your head to one cabinet, things are pretty straightforward. If your head says 300W @ 4 ohms, you need to plug it into a 4-ohm cabinet that can handle 300 watts. If you plug it into an 8-ohm cabinet, you might only get 200 watts of power and you’ll probably get less volume. If you plug it into a 2-ohm cab, there’s not enough resistance and the amp will overwork itself, which results in FIRE!

When you hook up more than one speaker to an amp, there are two ways they can be arranged: series or parallel. Series means chaining the cabinets together, one to the next. Parallel means sending one output of the bass amp head to one cabinet and a second output from the head to another cabinet. Parallel is two or more side-byside connections.

When you add a second cabinet, realize there are now two places for the amp’s power to go. Adding a second cabinet causes the total impedance (amount of resistance) of the load to change.

It’s easiest having each cabinet with the same impedance (e.g. each cab is 4 ohms or 8 ohms). In order to determine the total impedance of the cabinets (all with the same impedance), take the impedance of one cabinet and divide that amount by the total number of cabinets. For instance, two 8-ohm cabinets wired in parallel will have a total impedance of 4 ohms; two 4-ohm cabinets would have an impedance of 2 ohms. Remember, if your amp can’t handle a 2-ohm load it could go up in flames – that’s why this is so important. If your amp says it can put out a certain number of watts at 4 ohms, you can only hookup a total load of 4 ohms, 8 ohms or greater – not 2 ohms!

If you are hooking up two cabinets of different impedances, there’s a little more math involved. For instance, if you have a 4-ohm cab and an 8-ohm cab, the equation is as follows: 4 x 8 = 32, then 4 + 8 = 12. Divide 32 by 12 and you get 2.667 ohms. If your amp is rated only for 4 ohms, you can’t use this configuration of cabinets with 2.667 ohms.

If you are still confused, get someone with experience to verify that your amp hookup is okay before you turn it on. Make sure you use the correct cables and have extras to avoid the temptation of using an instrument cable. Most importantly, know the specs of your head and cabs. If you’re heads up, you’ll be able to get down! Go forth and hook up!

Rick Wheeler
Rick Wheeler currently works as Larry Carlton’s guitar tech and front of house engineer. He is also an accomplished jazz guitarist, vocalist, and educator. You can contact Rick at rickwheeler@hughes.net

Two types of distortion explained

Most of us love good distortion. Saying that sounds weird, but distorting a signal in a musically useful way is an incredibly complex process. The simplest signal waveform, a sine wave, can help illustrate how it works, although a guitar produces a tone much more like a sawtooth wave than a sine wave. The trick is to clip the waveforms; here’s how it happens.

A sine wave is the purest tone possible, just a single frequency. No musical instrument produces a really pure sine wave, although tuning forks get close. The sine wave is smoothly rounded everywhere, with no sudden changes in direction.

If we take that same sine wave and electronically clip off the tops and bottoms at a set clipping level, a crazy thing happens. Just snipping off those tips has a big effect on the sound. A pure sine wave is somewhat generic sounding. Distorting the sine wave by clipping introduces a whole bunch of new sounds called “partials” or “harmonics”. The sound is much more interesting to listen to, as long as we don’t get too carried away with it.

In music, there are fundamentals and partials. A fundamental is the basic tone of any given note – for instance, the frequency A-440 is the standard for musical tuning, which is a sine wave that has a frequency of 440 Hz (Hz is short for Hertz, and stands for one cycle per second). We recognize that a tone of A-880 is one octave higher than A-440. Musicians refer to a musical note that has both A-440 and A-880 mixed as having a fundamental and the first partial. A frequency of three times the basic note frequency is also referred to as the third partial of the basic note. Four times the fundamental is the fourth partial and so on. Since harmonic is another name for a partial, when you hear the term “total harmonic distortion” it means whatever is left after taking out the fundamental sine wave in some waveform.

So there are really two kinds of distortion: simple harmonic distortion, which generates distortion related to the fundamental frequency and adds character to instrument sound, and intermodulation distortion (IMD), which produces non-musically related frequencies at multiples of the sum and differences of two frequencies, considered to
sound harsh to the ear.

Ultimately, the name of the game is to produce harmonic distortion, which makes musically good sounding notes, and to minimize IMD, which makes unmusical sounds and
harsh buzzes. Unfortunately, no matter how hard we try, we can never get all harmonic distortion and no IMD.

One way to keep mostly harmonic distortion is to not have sharp corners on the waves. Tubes help with this process. Tubes generally produce very softly rounded, squashed tops when done on square waves. A pure sine wave is almost devoid of information, having no wiggles or corners in that smoothly rounded top. However, if we took a square wave and massively amplified it, or a triangle wave, or a wave with spikes all over its top and did the same amplify/clip operation on it, we’d get exactly the same result as with the sine wave with massive clipping.

There are other distortion tricks besides clipping a signal. To get an octave sound, a process called full-wave rectification is used. What happens here is the negative half-wave of an alternating current is converted into a positive half-wave. This trick has been used to one degree or another in a number of pedals. Having the signal completely fullwave rectified eliminates the fundamental frequency. But if we half-wave rectify a sine wave, the result still has a lot of the fundamental in it, in addition to a noticeable octave sound. We can also partial full-wave rectify a signal, which makes for an even more noticeable octave sound.

Here’s the big trick: filtering of the signal both before and after the distortion usually has at least as much, if not more, to do with how the distortion sounds than the actual method of distortion. A combo amp with a speaker or two and an open back implements a multi-pole low-pass filter all by itself. This is at least one of the reasons that mic''ing
an amp is preferable to running a distortion signal directly into a PA mixer. The speaker cabinet’s low-pass action smooths off those offending treble shrieks. An electronic multipole low-pass filter is the essence of all the cabinet simulators you hear these days.

Filtering before the distortion is also interesting. Hendrix used a wah pedal before his Fuzz Face. The band-pass effect makes the signal bigger at the frequencies boosted by the wah, so those frequencies get distorted most. You get an interesting change in distortion depending on what notes you hit. This cuts a lot of the harsh sounding IMD, too.

If you are studying science in high school or physics in college and your teacher doesn’t like your long hair and your iPod, bring in a Tube Screamer and present this little distortion lesson to your class. Everyone will love you for it.

Rick Wheeler
Rick Wheeler currently works as Larry Carlton’s guitar tech and front of house engineer. He is also an accomplished jazz guitarist, vocalist, and educator. You can contact Rick at rickwheeler@hughes.net