If we tone-chasers had a pound for every hour we’ve spent discussing the finer points of electric guitar noises, we could all afford a pedal with a horse on it and an amp full of melted plastic. We find ourselves consumed by the issues of saturation, sag and signal path probably more than those of melody, modes and metre – and with good reason. Rock ‘n’ Roll is, to many, as much about the noise you make as the notes you make with it, and these noises are what often defines genres and inspires generations. No wonder we’re all a bit obsessed with it, right?
There are some accepted truths when it comes to guitar tone. Amps make a big difference, valve amps are better, vintage ones are best, volume is essential, sound engineers are your enemy. We know these all to be facts but the reasons why are a little more mysterious, so here’s a quick and basic lesson in how and why a vintage amp sounds the way it does. Spoiler: it’s not magic.
Let’s start at the beginning – with your guitar. Your pickup is an electromagnet which interprets the movement of a steel string as a little electrical signal. There are many imperfections in this interpretation, but we can leave the science of these differences to the pickup makers. For our purposes, we can simply sum them up as “awesome”. This tiny signal goes down your white, coily cable to the input of your amp, whose job it is to turn the signal into something big and useful enough to move the heavy speakers in your cab.
As we all know, this signal undergoes many changes before it gets to those speakers, which is a good thing. Anyone who’s plugged a guitar straight into a mixing desk will know it’s a far cry from a Rock ‘n’ Roll guitar tone. But, back in the 1940s when Muddy Waters invented electricity, this is what amplifier makers were trying to achieve, a completely neutral and clean guitar tone. All of the charm we associate with a good guitar tone came from the limitations of the technology – unintended consequences of an amp pushed too far.
The first gain stage in a valve amp is very important, as it makes changes to your signal that will be amplified an accentuated throughout the amp. Ever plugged into a JCM800 and noticed the biting, crashing tone when you dig in, or the fat mids of a Tweed Deluxe? Well, these characteristics are largely due to the first gain stage’s treatment of your signal, especially once you bring bright caps and switches into the equation.
So what about tone stacks? In pretty much any valve amp, the tone stack is passive, meaning you can only take away frequencies, not add them. The filtering done by one control is affected by the position of another, which gives us the interactive nature of a typical valve amp tone stack. There’s never really a “flat” setting, just settings that are “nice” or “not nice” (most of us actually find this more useful). You can make a big difference to the sound of an amp by changing the tone stack design. A Fender, a Vox and a simple amp with just a tone knob all sound very different, even when clean, and tone stack design has a big part to play. What’s even more important when thinking about the “magic” of vintage amps is the placement of the tone stack in the signal path.
In a classic, non-master volume amp (the ones we get misty-eyed about), the overdrive is mainly produced in the power amp – the last bit of amplification in the chain. As such, everything else in the amp happens before the distortion. In a modern amp, however, it’s common for the tone shaping to be placed after the distortion, which is created in the preamp. This important difference has a massive influence on the tone of the amp and completely changes your approach when using one.
A modern, master volume amp will typically have a very consistent character to the overdrive – curated, even. Not too harsh, not too woolly but always the same, with the ability to make big, precise EQ changes “cleanly”. All very practical and useful but this sort of amp can come off as cold or clinical to a more vintage-minded player.
In a vintage amp, on the other hand, placing the tone-shaping before the drive allows us to shape the tone that is being distorted. All of a sudden, turning the bass control takes us from a thick, fat tone to a tight, aggressive one. Messing with the treble knob lets us choose if our overdrive is warm or cutting. Sure, the end result gives us a bit less control overall but what we’re controlling is a lot more exciting. We’re shaping the kind of overdrive we want, rather than just making EQ changes to the overdrive we’re given. What’s more, because these tonal effects change with the amount of overdrive, we can influence the character of the drive by digging in, cleaning up and doing all the other stuff that helps us express ourselves as musicians.
Now we’ve opened the can of worms that is “preamp vs power amp overdrive”, let’s get into that. Yes, if you put it simply, a modern amp gets its overdrive in the preamp and a vintage amp gets its overdrive in the power amp, but it’s a bit more complicated than that.
In a modern amp, you can still overdrive the power amp but it might get in the way of other things you are trying to do, such as use an effects loop to cleanly amplify time-based effects. Also, as I’ve described above, the signal coming from the preamp might not lend itself as well to be being overdriven by the power amp. In an amp designed to get its overdrive from the preamp, pushing the output too far may just result in your once-controlled sound becoming indistinct and mushy, rather than the power valve magic you were expecting.
In a vintage, non-master volume amp, it’s not that only the power amp distorts, it’s just that it distorts first, and differently. Without venturing into nerdiness that exceeds the scope of this article, all valves distort differently, and the big ones used in power amps distort very differently from preamp valves. The actual configuration of the circuit has an impact too but…yeah…too nerdy.
So, once you’ve turned the amp up loud enough to overdrive the power amp, then what? Then the phase inverter will distort. This is the part of the circuit that takes the preamp signal, splits that wave into its positive and negative halves and feeds those to the power valves to do the heavy lifting. There are also different ways to configure a phase inverter circuit which overdrive differently. These factors make the distinction between the unruly fuzz of a Tweed Deluxe or a ‘70s Orange and the more mild-mannered and articulate overdrive of a Plexi or Twin Reverb. Push your old amp even further and the preamp will distort too, adding its own flavour into the mix. This is where we run into issues with the sound guy. Because this perfect interaction of amp bits only happens at a certain point on the dial, and because the valves in a big amp sound different to the valves in a little one, we might just find it necessary to bring a 100-Watt amp to the gig and turn it all the way up. Nothing else will do.
Getting an amp into this “sweet spot” brings yet more important elements into play. Because we’ve pushed the amp beyond what it was designed to do, other parts of the circuit can struggle. The much-discussed sag inherent to valve amps (particularly those with valve rectifiers) is simply the amp being asked for more voltage than the power supply can provide. During these periods of high demand (the loud bits of your playing), the voltage drops and so does the volume. This manifests itself as a special kind of compression that only the right amp can provide.
Demand even more from your amp and you may just run into “ghosting”, but this elusive phenomenon has been discussed in a previous Tech Tips, so we’ll leave that for now. The same goes for negative feedback, another building block in the character of your favourite amps. For the purposes of this article, let’s just say they’re other ingredients in our big, bubbly tone soup (new pedal name?).
Regardless of the details, it’s this combination of preamp, phase inverter and power amp overdrive, sag and even ghosting that gives us the glorious intermingling of harmonic complexity that is the magic of vintage amps. Different circuit elements all contributing their own brand of clipping, all of it responsive to our playing and offering an infinite palette of lovely, lovely tone. There’s even the “reactance” of a guitar speaker that elicits a certain response from an amp’s output transformer – the response that reactive loads seek to replicate. It all matters.
If you spend your time looking at Origin Effects products, you can probably see where this article is headed. The impracticalities of owning and running a fleet of unique, vintage valve amps are all too familiar to us – moving them, maintaining them, deafening people, things being very much on fire. These considerations are the reason we take our Analogue Amp Recreation pedals so seriously. Every single element of vintage amp design listed above is recreated in all-analogue circuitry, tested, tested again and not signed off until it behaves just like the real thing.
In something like the RevivalDRIVE Custom, you actually have control of the majority of these characteristics, allowing you to adjust the circuit itself to give you the tonal traits of multiple vintage amps – or even come up with your own combination! In our other designs, such as the BASSRIG pedals or DELUXE61, the same technology is put to work capturing the sound of single amp in nauseating detail.
More and more these days, it’s becoming impossible to use history’s finest amps in any real-world situations, and guitarists face the ongoing challenge of achieving those iconic tones without the weight, volume, expense, and complication of using the real thing. We’re not sure if there will ever be a better tone than our favourites from decades ago, and it’s only by respecting the role of every tiny part of these amps’ circuits that we have been able to create such worthy substitutes. Make no mistake, we love valve amps at Origin Effects – we just know when not to use them.
