Discover how a critical difference between a self-contained guitar amp and a component rack system affects dynamic response and feel.
Playing guitar is an exercise in discovery. The more you do it, presumably, the better you get, and the more you learn about the instrument’s possibilities coupled with your own potential to advance. People often travel repeatedly to the same places. Not out of lack of imagination, but as an extension of the discovery process. Once you’ve seen the Eiffel Tower or Grand Canyon, you can go back and discover a nice bistro on a side street you’d never noticed, or a trail that may have been hidden previously. With that in mind, here’s a question that deserves repeated exploration: How do preamps and power amps—and rack systems in general—differ in dynamic behavior from self-contained guitar amps? And why? This was a hot topic during the heyday of rack systems. Technology has come a long way since then, so it’s worth revisiting the subject.
We’ve discussed the dynamic loop created by pick attack and playing volume, and how current demand from the power amp stage affects the preamp stage [“The Big Bang” and “The Sonic Legacy of Tube Amplification”]. To recap, a self-contained amplifier, consisting of a preamp stage and a power amp stage, gets its operating current from a common power supply (Fig. 1). When you play clean and at low volume, both the preamp and power amp benefit from a healthy reserve of available current. Once the volume goes up and pick attack intensifies, the power amp’s demand on the power supply increases exponentially, leaving whatever crumbs are left to the preamp. Now, to be fair, an amplifier’s power supply is normally designed to deliver sufficient juice to the preamp even under demanding conditions. But the truth is, a lot of what differentiates amplifier personality can be directly traced to the designer’s ideas about how much preamp voltage variability is acceptable or even desirable. This gives rise to terms ranging from “spongy” and “forgiving” to “dry” and “stiff,” and—sin of all sins—“unforgiving.”
So, let’s look at the rackmount preamp and power amp. In a system made up of separate components, the defining feature is that they each have their own dedicated power supply (Fig. 2). Right off the bat, this precludes that beast of a power amp from hogging all the juice to the preamp. The first thing we discover in playing this rig is that the dynamic feel is noticeably stiffer and absent some familiar gooeyness and bloom. In early rack systems, getting a group of components to feel like playing a normal amp usually took a back seat to the benefits of extensive signal switching and processing. My personal feeling was, and still is, that a well-executed rack system demands a power amp with a good range of control over frequency response and dynamic feel. Most of the time power output is less important than the kind of tube character you like, especially in a stereo power amp. I bring up stereo because this is a feature of rack power amps that always gets overlooked.
In a stereo power amp, the power supply is usually common to both channels, and therefore has to be sufficient to provide full output for them. It rarely occurs to players that if you only use one 50-watt channel of a stereo 100-watt power amp, you still have a 100-watt energy reservoir on tap. Naturally, that’s going to feel extra stiff compared to a single power-amp stage of a 50-watt head. If you expect to arrive at reliable conclusions about different power amps in A/B comparison tests, it’s important to run both channels to really understand what you’re hearing.
Some stereo power amps use a single 12AX7 for the input stage of both channels, while others have a separate tube for each channel. The reason this is important is not immediately obvious, but it certainly bears scrutiny. Crosstalk, or signal bleeding from channel A into channel B, often occurs in a power amp with non-isolated triodes, as opposed to isolated triodes. If you use a stereo FX processor to A/B test each design type with both channels operating, the amp with non-isolated triodes will sound practically mono due to signal bleed at the first preamp stage, while the amp with isolated triodes will deliver a markedly superior stereo image. If you compare these two design styles side by side, one channel at a time, you’d totally miss the significance of isolated triodes on the input stages.
Those two simple subjects—power supply capacity and crosstalk—play a major role in the difference between rack gear and self-contained amps. Here, a seemingly benign question offers an opportunity to understand nuances of amplifier design that are rarely discussed.
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“Clean platform” may be the current buzzword in guitar amplification, but the truth is, we’ve been here before.
Much has been written about how Fender and Marshall contributed to the early development of guitar amplification. As in every industry, there are pioneers and innovators who get the ball rolling, followed by inventors and entrepreneurs who seize on opportunities the originators may have overlooked. For instance, both Fender and Marshall were very late to the party on adopting increased gain and the master volume.
With the advent of the Marshall stack, guitarists experienced a major paradigm shift. Not only did this amp sound good and deliver on volume, it also offered an imposing visual announcement of intent. “We’re here to rock, so strap in and plug your ears!” In the beginning, this was more about coverage and clean power than circus theatrics. Onstage monitor systems were rudimentary at best, and sealed-back guitar cabs delivered beamy projection, which required several amps and cabs onstage to allow performers the freedom to move about. What started out as a matter of necessity ended up being an iconic statement of purpose.
Now, if you’ve ever played a full 100-watt stack—let alone two or three at once—you know you’re never going to need or even be able to use a fraction of that power, yet the mere presence of such an imposing backline was undeniable evidence that you meant business. And that leads to the long-held myth about big stacks—that they’re all dimed to the max and were the source of all the distortion. In fact, the opposite was true. The idea was maximum clean power and wide-area dispersion of sound.
Case in point: Pete Townshend decided early on that while Marshalls were certainly loud, there was something essential missing from the formula, thus setting the stage for his discovery of David Reeves and their mutual quest for the loudest, cleanest sound possible. While the dual 100-watt 4x12 stack remained the form factor of choice, Townshend’s quest led to the refinement of preamp tone and the ever-increasing power handling capacity of the speakers. Where the sealed-back Marshall cab made it possible to use lower-powered speakers, the original Sound City cabs, and later Hiwatt cabs, were vented in the back and loaded with progressively higher-powered cast-frame Fane speakers that featured high-temperature “glass fibre” voice-coil formers. A stiffer suspension allowed these speakers to withstand the punishing excursions that would easily destroy a typical Celestion of the period.
When Hendrix came to London, Townshend recommended he check out Sound City amps. Early on, Hendrix used both Marshall and Sound City, and there is plenty of archival evidence indicating this went on for about two years. Revisionist history now proposes that Hendrix used “the Marshall for distortion and the Sound City for clean.” While that may seem logical in hindsight, the facts suggest otherwise. It’s an accepted article of faith that most of the distortion in Hendrix’s live sound came courtesy of an Arbiter Fuzz Face, and between outbursts of sonic fury, his clean stage sound was gloriously deep and wide.
As bands became more popular, venue size increased, and the need to fill those venues with sound begat not only the need for more powerful and reliable guitar amplifiers, but also more powerful sound reinforcement systems to help singers and drummers keep up. And therein lies a tale of two competing philosophies of an otherwise similar engineering endgame: Power and reliability were the key imperatives for both guitar amps and sound systems, yet the latter needed to stay sonically pristine, while guitar amp designers had to embrace the expanding popularity of distortion and feedback.
With the current trend towards amps that provide a “clean platform” on which to sculpt unique and colorful soundscapes, it should be no surprise that this is really where it all started. What has changed is that sound systems have come a long way, baby. The live-sound engineer now has a lot of control over what the audience hears, as well as how much sound pressure level emanates directly from the stage.
Today, the big amp revolution is over as a practical matter, but there’s good reason many of us are not so quick to ditch the big rigs. The sense of power and dynamics at our fingertips is as undeniable as waiting at a stoplight in a ’69 Charger with a 440 Hemi. It feels ready to rip at the slightest touch. This sensation has come to be known as “footprint,” and big iron is the only way to get it.
In his new column, Fryette Amplification's head honcho riffs about taking a holistic view of the instrument.
Your sound. Every player’s quest for “that sound” is a journey—a lifelong pursuit that can lead to unexpected places. And we can go as deep as time, patience, and diligence will allow. For example, finding the ideal amplifier can be as simple as grabbing whatever you have at hand, plugging in, and playing, or as complex as scouring internet forums, poring over magazine articles, and investing time and cash in hands-on experimentation. Along the way, our path is littered with rabbit holes—some worth exploring, some not. This is how we gain knowledge and experience, and hopefully discover what works best for us.
In my many years on this road, I’ve come to understand the role of the amplifier—in particular, a tube amplifier—as the other half of the instrument that includes your guitar. I reject the concept of the guitar as the instrument and the amplifier as the less important appliance. It’s vital to understand how the guitar interacts with the amplifier and its speaker. I always think of the combination of guitar, amp, and speaker as the instrument.
When we play, the whole instrument reacts. The strings induce the pickups to send a voltage—the signal—to the amp, which sends a larger voltage to the speaker, which converts that voltage to acoustic sound, which impacts us directly via the speaker and indirectly via reflections in our playing environment. Our playing volume is determined by how we set the amp and by how much power we have at our disposal. If it’s a big amp played loud, there’ll be an immediate physical impact when we dig into the guitar and directly experience the amplifier driving the strings under our fingers. If it’s a little amp, we can more freely lay into it, and we enjoy the sound and fury generated by pushing it over the top. There’s a reason why players always say, “It sounded great just before it blew up.”
Yet, it’s how we play, not what we play, that matters most. To underscore the importance of the will of the player in this equation, it’s helpful to remember that both Dick Dale and Jimi Hendrix played Strats, and that live video exists of Hendrix playing through Fender Showmans with 15" JBLs, Dale’s iconic weapon of choice. Yet listening to each master, we’d never confuse one for the other.
Getting the right balance of tone, distortion, volume, and acoustic feedback, especially in a live performance, is as much about luck as it is planning. Of course, there’s tone-tweaking, where one can endlessly obsess about the subtleties of the rig’s component parts, and then there’s performing, where the goal is to leave all those obsessions behind and surrender to the moment. It often happens that the gig is where you’ll encounter every possible obstacle to a satisfying performance. Given that, a fair amount of planning is necessary, but experience tells us that preparation can be overdone. We’ve all had those nights when the music feels off and it seems your instrument just won’t cooperate. You think you sounded terrible, yet after the show people keep coming up to tell you it was the best they’d heard you play.
Being comfortable and conversant with your instrument—and remember, we’re talking about the entire length of the signal chain from fingertips to speaker cone—is one way to make sure your rig isn’t going to trip you up when the going gets rough. A very simple rig consisting of a guitar and small amp may leave you wanting for embellishment, but there’s no denying that a minimalist approach can give you a lot of opportunity to act on inspiration and impulse. A more complex rig demands more of your attention and skill—sometimes to the detriment of your overall performance. You may find that you’ve bitten off more than you can chew onstage, even though it all seemed so familiar and easy to navigate in rehearsal.
As soon as you pluck a guitar string, things start happening to the idea in your head that gave rise to that first note. The amp lights up, the room fills with sound, you hear it, feel it, react to it, and build on it until you’ve fulfilled that moment of inspiration. Exploring the limits of your ability and imagination provides you with a stepping stone to the next moment of inspired noise. Being in touch with your instrument, whether it’s a simple plug-and-play affair or an agonizingly vetted assemblage of odds and ends, is the indispensable part of getting there.
Can a lawn-mower flywheel lead to a “horrendous and beautiful” guitar sound?
From the age of 5, I'd begun taking things apart—toys in particular. For as long as I can remember, I've had an unyielding drive to learn how things worked. How my parents dealt with this was to either threaten never to buy another toy or, later, by offering more complex toys along with a stern warning that if it got taken apart, I had better figure out how to put it back together. What came of that was a developing gift for not only putting things back together, but to ensure that one couldn't tell I'd ever had them apart. Such was the intellectual battle in our house between young adults learning to be parents, and a kid struggling to outwit them.
One great respite from this tug-o'-war was spending two weeks every summer with my grandparents on their farm in rural Washington state. In a small familial community of Italian immigrant homesteaders, there were two ways of handling broken-down cars and appliances: Fix 'em yourself or put 'em out to pasture. For a super-curious kid with plenty of time on his hands, watching the grown-ups apply their dogged determination to eke out another season of utility from a lawn mower or chainsaw was a revelation. Grown-ups took things apart and put them back together, too! But what was, for me, merely a gnawing curiosity was, for them, perhaps having extra money in the savings jar for the electric bill.
One day I watched as Grampa Joe and Uncle John pulled apart a lawn mower engine to change the points and adjust the spark plug gap. I was consumed. If there was one thing you learned in an environment like this, it was how many barns in a half-mile radius housed a sidelined power mower. I remember lying awake most of that night waiting for the rooster to call out the sunrise, and soon I was off searching out an abandoned mower to play mechanic on. I struck pay dirt in Uncle John's barn, and in no time, I was hard at work—and a bit nervous. Could a lone 9-year-old kid with only rusty tools and zero experience replicate what two adults had accomplished the previous day?
I soon ran into my first major obstacle. Joe had rented a wheel-puller the day before to get that flywheel off. I'd never seen a wheel-puller before that, let alone a flywheel, but I understood the concept. The rented tool had been returned, so I made do by splitting a small block of wood into two doorstop-shaped pieces and gently inserting them under opposite sides of the flywheel. By carefully tapping alternate sides, I gradually lifted the flywheel off the main shaft, and soon I was filing the corroded ignition points and spark plug using Grandma Letizia's nail file. I had no way to gap the plug, so I had to wing it, tapping it with a rock to close the gap, and prying it open with a screwdriver until I thought it looked about right. Satisfied, I put the whole thing back together, poured in some fresh gasoline from a jug in the back of Letizia's Model T and gave the cord a yank. You can't imagine my surprise when that thing roared to life, and I just could not believe my luck.
Letizia had a garden around back of the house, and John's house was right next door, so I mowed a small patch of lawn near the garden to make sure everyone heard the noise of the newly revived mower. Sure enough, they all came out to see what was up. Uncle John was the first to ask me how I got that thing running. “I just did what you and Grandpa did yesterday." Uncle John's face went from surprise to a big, broad smile. He then reached into his pocket, pulled out a $5 bill and held it out to me. “No thanks," I said. “I don't want money." “Well, what do you want?" asked Grampa Joe. “I want that Philco radio in the spare bedroom."
I'd been eyeing that imposing 1936 floor-model radio for over a week. Grandma said it didn't work, and that's all anyone knew. Now it belonged to me and I immediately plugged it in and turned it on. It stood silent for a few minutes and then gradually a hum emerged from the large 13" electromagnetic speaker. Just a low insistent hum. No other sound, and no determined adults around to bail me out. Still, I was fascinated with that beast and I got permission to take it back home with me when my folks came to pick me up.
Within a couple of years, I was learning about electronics, reading library books, and making regular weekend bus trips to First Avenue—skid row—in downtown Seattle to visit a funky little surplus electronics store called Standard Radio. The place was dingy, with row after row of bins full of familiar and unfamiliar bits of mostly obsolete electronic parts and tangled cloth-covered wire that smelled of burnt varnish and decomposing wax. After a number of visits, the owner, a self-proclaimed “First Avenue Philosopher" gradually warmed up to the precocious kid with endless questions.
Over time, things my Standard Radio sage taught me began to mesh with the stuff I'd been reading at the library. On one of these visits, I took the plunge and bought a power supply I'd become fascinated with. It had a large power transformer, a big Coke-bottle-shaped rectifier tube, a couple of cylindrical metal capacitors, and a thing that I later learned was called a choke. I had purchased a voltmeter that I built from a kit, so I had a real piece of test equipment and just as the label on my new gadget said, this power supply was reading 450 volts! My folks never had a clue what I was up to. It all seemed harmless and only elicited the occasional “be careful" from Mom. Interestingly, the parts in that power supply closely resembled some of the parts in my prized Philco radio, and I began to realize I might actually have a shot at getting it to work.
From what I learned messing with that power supply, I replaced the filter cap and brought the Philco back to life. And the funny thing is, now that I knew a bit about what was going on in there, it started to lose its mystical hold on me. I guess I felt I'd conquered it. And then right about that time, something else happened: the Beatles. In an instant, my whole world changed.
I'd always been musically inclined, and music was omnipresent around our house, but this was something altogether new and exciting. It just obliterated everything else. My older brother and I started a band. We played local dances and people our age came over to play, and the neighbors were getting pissed off. From then on, I knew what I was going to do with my life.
Over time, however, the electronics bug reappeared, and I'd saved up enough money to buy a hi-fi amp kit. It started with a stereo preamp. I needed to save up for the power amp, and I was building speaker enclosures for my dream stereo system in wood shop at school. About that time, my brother got a Fender Concert amp for his birthday. It was big. And loud. It looked professional. And it was off limits.I was still the kid bro who took things apart and this amp wasn't going to be anyone's guinea pig.
Curious thing about that Concert: It had two big tubes in it with 6L6 printed on them, and they looked a lot like two of the tubes in the Philco, which had a pair of tubes labeled 6V6. By then I had learned that the first number designated the tube's filament voltage, and a trip to the library confirmed that the 6V6 was a lower-powered cousin of the 6L6. I was convinced the Philco housed a super power-amp stage behind that Clark Kent exterior, and I was determined to find out.
The Concert amp had the newer “miniature" preamp tubes in it, but I had learned that they were mostly modernized versions of those big Philco tubes, so I went about trying to determine which one was the preamp stage for the power amp. I didn't know what a phase inverter was yet, but I knew you needed the little tubes to boost the signal up enough to push the big ones. And I knew what a grid was. I also learned that touching some of the circuit parts gave you one hell of a shock, while others just made the amp give off a buzzing sound—a clue that noise was being amplified. For those of you wondering if I was ever going to get around to the point of this column, well, here's your first clue.
Without the benefit of a schematic diagram, which I had recently learned how to read (I was 12 at about this time), I had divined the input tube on the Philco power amp. Not only that, but its grid was conveniently located on top of the bottle. The number on the tube was 6K5. I know this because I still have that radio, and it still has the RCA plug I installed on it to use as an external input jack.
What happened next was as life changing as the first British Invasion. I plugged my stereo preamp into the Philco power amp, put an album on the turntable, and out came a loud, distorted, one-channel rendition of whatever that album was. What changed my life was not listening to the record, but the realization that I was just a short hop away from turning this contraption into a bona fide guitar amp. And that I did (Photo 1).
Fate had made our basement a rehearsal room and there were plenty of football practice sessions to keep my brother occupied after school. This afforded me the time to spirit his guitar up to my room and plug into the auxiliary input of my preamp. I flicked on the power switch, turned the volume all the way up, and there it was: a fearsome howling noise that was at once horrendous and beautiful. That feedback, crackling, and heinous speaker overload opened the door to a whole new universe for a musically inclined electronics nerd to explore.
About that time Jimi Hendrix had burst onto the scene, and the sound of that first album put the noise emanating from my Philco amp into sharp perspective. Later, Chicago Transit Authority was released, and the liner notes described the Bogen preamp-driven rig Terry Kath used to create the screaming sonic fury that was “Free Form Guitar." I couldn't believe the coincidence of these events, given the trajectory of my recent discoveries.
Something was pulling on me, and I was all in….
Welcome to my new column, Signal to Noise. My name is Steven Fryette. I took you on this long, convoluted introduction to illustrate, as best I can, where I came from, how I got here, and maybe attempt to explain why I can't imagine following a different path than the one I'm on today. This is where I live and where I belong. I hope you'll enjoy seeing this column unfold as much as I enjoy exploring the phenomenon of turning a small signal from the strings under your fingers into the glorious wall of harmonics that make up the beautiful noise of our lives.