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Tube Amp Maintenance & Handling Tips

March 28, 2014 by · 1 Comment 

Guitar Amplifier ExplodesTo get the most out of your tube amp, which can be a hefty investment, here are some easy to follow handling and maintenance tips. There’s no arguing that tube amps still set the standard for tone – modern solid state and digital amps merely emulate the tube amps of the past. The unfortunate drawback however, is that tube amps are more expensive and fragile compared to solid state alternatives. Repairs and maintenance add to the already high costs of tube amps. Thankfully, some of these extra expenses can be avoided with proper care and maintenance. Read more

Field Guide to Guitar Amplifier Tubes – Everything You Need To Know

March 27, 2013 by · 3 Comments 

Guitar amplifier valve tubesWhat is a vacuum tube? — If the link between a light bulb and a raging Marshall stack doesn’t seem obvious, take a glance at those vacuum tubes glowing inside your amp. And then pay your respects to Thomas Edison, the Wizard of Menlo Park, New Jersey.

Edison produced an incandescent light bulb in the late 1870s by feeding an electric current to a filament until it burned bright red. He then sheathed the filament in a glass bulb and extracted the oxygen, thus creating a vacuum to prevent the filament from burning up.

During further experiments in 1883, Edison detected electrons flowing from the filament, through the vacuum and over to a metal plate he had placed inside the bulb. This discovery, named the Edison Effect, remained a minor phenomenon until another scientist, John Fleming, found that these electrons could be used to detect radio waves and convert them into electricity. Fleming added a second metal element to the bulb, thereby creating the first diode, or—to use a name more familiar to guitarists—rectifier. In 1906, inventor Lee de Forest added a third element to the bulb and found that the resulting triode could be used as both a switch and an amplifier. Today, the vacuum tube has evolved to include a complex assembly of plates, grids and heating elements that produce a more efficient part. Read more

How To Spot Fake Fender Guitars

January 25, 2013 by · 4 Comments 

How To Spot an Fender GuitarIt’s easy to get bamboozled if you’re purchasing a vintage Fender guitar. Because these instruments are bolted together, their parts can be swapped, stripped or replaced faster than you can say “rip-off.” A buddy of mine who has been in the vintage game for years recently estimated that between 15 and 20 percent of the “Sixties Strats” out on the market are bootlegged. And if that number sends a shiver down you fuzzy fretboard, the number of “all-original” Strats that feature replaced pickups, pots, bridges and other parts is even higher.

By and large, G-V has found that vintage guitar dealers who have a good reputation have earned it. Likewise, if the word on the street is that a certain seller is not on the up and up, he’s probably guilty as charged. Avoid him like the plague.

In short, proceed with caution, and get educated before you reach for your wallet. Here are a few helpful tips to get you started. Read more

11 Guitars That Sound Like the Future

January 11, 2013 by · 1 Comment 

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People in the 1950s thought that we’d all be wearing jetpacks and driving flying cars about now. But did they bother to predict what kind of guitars we’d be shredding on? No, they didn’t. Probably because they couldn’t imagine just how hard these eleven axes would rock. From robot-tuning to synth access, these guitars will have you dreaming of the possibilities.

First up is the Gibson HD.6X Pro Digital Guitar, an instrument that’s capable of making each string sound completely different than every other. Using fancy tech and hexaphonic pickups, the signal from each string is pushed through and Ethernet port to a computer, where you can tailor the sound, EQ and wave-shape. And did I mention that you can put a different effects signature and amplification on each string? Even though this guitar came out in 2007, it’s still pushing the envelope even now. Read more

History of Marshall JCM800 Guitar Amplifiers

January 6, 2013 by · 1 Comment 

Marshall jcm 800 guitar amplifierMarshall Amplification is a British company which is renowned for manufacturing some of the best and most versatile guitar amplification units out there. The sought after “crunch sound” which only Marshall Equipments have to offer remains unrivaled till date. Guitarists who prefer a heavier guitar sound have always invariably ended up selecting a Marshall. Read more

Electric Guitar Pickups 101

December 1, 2011 by · Leave a Comment 

How electric guitar pickups workAn electric guitar’s sound is deeply influenced by its pickups. For a musician who has little or no knowledge of electronics the matter can often seem to be incredibly complicated. When it comes to electronics in general, pickups are quite easy to wrap your brain around. This article will explain the connection between the electronics and sound. Read more

Basic Electric Guitar Circuits: Potentiometers and Tone Capacitors

September 15, 2011 by · Leave a Comment 

What is a Potentiometer?

Potentiometers, or “pots” for short, are used for volume and tone control in electric guitars.  They allow us to alter the electrical resistance in a circuit at the turn of a knob.

Potentiometers and Tone Capacitors

It’s useful to know the fundamental relationship between voltage, current and resistance known as Ohm’s Law when understanding how electric guitar circuits work.  The guitar pickups provide the voltage and current source, while the potentiometers provide the resistance.  From Ohm’s Law we can see how increasing resistance decreases the flow of current through a circuit, while decreasing the resistance increases the current flow.  If two circuit paths are provided from a common voltage source, more current will flow through the path of least resistance.
Potentiometers and Tone Capacitors

We can visualize the operation of a potentiometer from the drawing above.  Imagine a resistive track connected from terminal 1 to 3 of the pot.  Terminal 2 is connected to a wiper that sweeps along the resistive track when the potentiometer shaft is rotated from 0° to 300°.  This changes the resistance from terminals 1 to 2 and 2 to 3 simultaneously, while the resistance from terminal 1 to 3 remains the same.  As the resistance from terminal 1 to 2 increases, the resistance from terminal 2 to 3 decreases, and vice-versa.

Tone Control:  Variable Resistors & Tone Capacitors

Tone pots are connected using only terminals 1 and 2 for use as a variable resistor whose resistance increases with a clockwise shaft rotation.  The tone pot works in conjunction with the tone capacitor (“cap”) to serve as an adjustable high frequency drain for the signal produced by the pickups.  The tone pot’s resistance is the same for all signal frequencies; however, the capacitor has AC impedance which varies depending on both the signal frequency and the value of capacitance as shown in the equation below.  High frequencies see less impedance from the same capacitor than low frequencies.  The table below shows impedance calculations for three of the most common tone cap values at a low frequency (100 Hz) and a high frequency (5 kHz).

Potentiometers and Tone Capacitors

When the tone pot is set to its maximum resistance (e.g. 250k?), all of the frequencies (low and high) have a relatively high path of resistance to ground.  As we reduce the resistance of the tone pot to 0?, the impedance of the capacitor has more of an impact and we gradually lose more high frequencies to ground through the tone circuit.  If we use a higher value capacitor, we lose more high frequencies and get a darker, fatter sound than if we use a lower value.

Volume Control:  Variable Voltage Dividers

Volume pots are connected using all three terminals in a way that provides a variable voltage divider for the signal from the pickups.  The voltage produced by the pickups (input voltage) is connected between the volume pot terminals 1 and 3, while the guitar’s output jack (output voltage) is connected between terminals 1 and 2.  From the voltage divider equation below we can see that if R1 is 0? and R2 is 250k?, then the output voltage will be equal to the input voltage (full volume).  If R1 is 250k? and R2 is 0?, then the output voltage will be zero (no sound).

Potentiometers and Tone Capacitors

Potentiometer Taper

The taper of a potentiometer indicates how the output to input voltage ratio will change with respect to the shaft rotation.  The two taper curves below are examples of the two most common guitar pot tapers as they would be seen on a manufacturer’s data sheet.  The rotational travel refers to turning the potentiometer shaft clockwise from 0° to 300° as in the previous visual representation drawing.
Potentiometers and Tone Capacitors

How do you know when to use an audio or linear taper pot?

It’s really a matter of personal taste when it comes to volume control.  Notice how the rate of change is much more dramatic on the audio taper pot when traveling back from 100% to 50% rotation.  This means that the same amount of rotation would give you a more intense volume swell effect with an audio taper than with a linear taper.  Using a linear taper volume pot would give you a more gradual change in volume which might feel like you have more fine control with which to ease back the volume level.

For tone control, it’s basically standard practice to use an audio taper.  The effect of the tone circuit is not very noticeable until the resistance gets pretty low and you can get there quicker with an audio taper.

How do you know what value of potentiometer to use?

The actual value of the pot itself does not affect the input to output voltage ratio, but it does alter the peak frequency of the pickup.  If you want a brighter sound from your pickups, use a pot with a larger total resistance.  If you want a darker sound, use a smaller total resistance.  In general, 250K pots are used with single-coil pickups and 500K pots are used with humbucking pickups.

Specialized Pots

Potentiometers are used in all types of electronic products so it’s a good idea to look for potentiometers specifically designed to be used in electric guitars.  If you do a lot of volume swells, you’ll want to make sure the rotational torque of the shaft feels good to you and most pots designed specifically for guitar will have taken this into account.  When you start looking for guitar specific pots, you’ll also find specialty pots like push-pull pots, no-load pots and blend pots which are all great for getting creative and customizing your guitar once you understand how basic electric guitar circuits work.

Kurt Prange (BSEE) is the Sales Engineer for Amplified Parts (www.amplifiedparts.com) in Tempe, Arizona, United States.  Kurt began playing guitar at the age of nine in Kalamazoo, Michigan.  He is a guitar DIY’er and tube amp designer who enjoys helping other musicians along in the endless pursuit of tone.


Basic Electric Guitar Circuits | Guitar Pickups 101

August 26, 2011 by · Leave a Comment 

Guitar Pickups Single-Coil vs HumbuckerPassive (i.e. battery-free) electric guitar circuits are relatively simple and the possibilities for customization are endless.  A basic understanding of pickups, potentiometers, capacitors and switches is all you need to get creative and take more control of your instrument’s voice on an electronic level. Read more

Beer Can Guitar Amp

June 28, 2011 by · Leave a Comment 

Beer Can Guitar AmplifierThe first step in building your very own beer can amplifier will be to get an empty can of the beer of your choice. After you have your empty can you will need to remove the bottom of the can. With a little bit of patience and a razor knife, this can be done quite easily. Read more

Guitar Setup Is Essential

March 9, 2011 by · 4 Comments 

Guitar Lessons Have you ever noticed how your low ‘E’ string just never stays in tune? Wondering why it’s harder to play your guitar rather than your buddies’ slick Gibson? The secret to effortlessly traveling along the neck of an axe that melts like butter is probably in the setup. Read more

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