Although 99.9% of guitar effects / fuzz stomp boxes now use op-amp chips, if great tone is the goal, is it a question of should we be using op-amps instead of can?
By: Ringo Bones
If you are old – or rich - enough to experience the hi-fi wonders of the 1990s when 500 US dollar CD players began to sound as good as entry-level vinyl LP replay. Then it is more than likely that you heard the hype of the “tone enhancing” effects of premium-grade op-amp chips. After choosing to emulate my past experiments of using op-amp integrated circuit chips with audiophile credentials in guitar stomp boxes for ultimate tone. You could probably end up asking yourself should we – rather than can – be using op-amp based guitar stomp boxes? Before proceeding to the long-winded narration of my experiences with “boutique” op-amps, here’s a primer on what happens when an electric guitar is played.
Whenever you pluck the strings of your electric guitar or strum a chord, the guitar’s signal varies from a few millivolts to as high as 1 volt peak-to-peak depending upon how hard the strings are plucked or strummed or the kind of pick-up used. The electric guitar’s output signal when viewed on an oscilloscope is characterized by a sharp rise to a maximum value and then diminishes rapidly. This makes a tube-based electric guitar amplifier with a good vacuum tube pre-amp section or a fuzz box – i.e. distortion effects stomp box – a necessity if you want a pleasingly sustained tone from your electric guitar.
During the 1960s – when Jimi Hendrix and countless other guitarists – began experimenting with electric guitar effects boxes, most of these fuzz boxes were made with discrete small-signal transistors and germanium signal diodes. This provided those effect’s signature smooth tone and a long sustain compared to more recent op-amp chip based fuzz boxes. When the venerable 741 op-amp (LM741 op-amp and related variants) became available in 1966 after being made by most IC manufacturers, it was tried as an active amplifying device in guitar fuzz boxes to see how it compares to discrete small-signal transistors.
Sadly, many found out that the rate of decay is much faster than a conventional guitar fuzz box that uses discrete transistors. Op-amp based guitar fuzz boxes only became popular in the 1980s during the rise of high-decibel Heavy Metal music when the harsh sound of the op-amp based electric guitar effect fuzz box became de rigueur. Not to mention the silicon signal diodes that replaced the almost extinct germanium signal diodes only made the op-amp based fuzz boxes sound even harsher and Death Metal ready. Thus making the tonal versatility of a Marshall amp bristling with EL34 tubes really worth the very steep price premium.
By this time you could be asking yourself, if the “hi-fi world” can get away with using those gorgeously toned Electro-Harmonix reissued tubes, why can the “guitar world” benefit from using op-amps with audiophile credentials to improve the tone of their fuzz boxes? The short answer is music performance recordings, either from vinyl or CD (the two leading “state of the art” domestic mediums) has a vastly more complicated signal waveform in comparison to what a typical electric guitar produces no matter how beautifully played. Audiophile-grade JFET input op-amps like the AD845, LF356, or high slew rate types like the LM318 might be the cheapest way to make Iron Maiden or Veruca Salt sound as if they were playing right in your bedroom. But these premium grade op-amps don’t do squat – tone wise - when used in guitar fuzz boxes.
Audiophile-grade op-amps only shine when supplied with a well-regulated plus / minus 15 volts split power supply. You can’t tell the difference if you use them in place of your bog-standard LM741 found in your Hyper-Metal fuzz box being supplied by a 9-volt PP3 battery. And if you ever try to shoehorn a switching-mode power supply to power these audiophile-grade op-amps from a 9-volt PP3 in the hopes of a 12AX7 based preamplifier on the cheap. I tried it and it doesn’t work. Or it does play, but tone-wise you’re better off taking the all-tube route. An overwhelming number of fuzz boxes today are even using op-amps with much lower specs than the venerable LM741 op-amp. Good luck trying to find guitar stomp / fuzz boxes using high slew rate types like the LM318.
As it was in the 1960s as it is today, tube amps are still the best way to get the ultimate fuzz tone effects. If the contrary is true, how come I still see thirty-something housewives wearing a Lunachicks T-shirt hunched over their 1965 Fender Twin with soldering iron in one hand and a 6L6 tube in another? In truth, fuzz circuits do mirror the “quality hierarchy” found in the hi-fi world namely tubes are the best, followed by discrete transistors, and op-amps being the budget sector. Even though a skillful designer can still create great sounding gear using the right op-amp in the proper application.