All guitar amplifiers comprise two distinct sections: the pre-amplifier (preamp) and the power amplifier (power amp). Understanding these sections and their roles is crucial in unravelling the nuances of guitar tones. The preamp takes the high-impedance electric guitar signal and amplifies it, making it electrically compatible with the amplifier's circuit. Typically, the preamp houses basic EQ controls like treble, mid, and bass, along with a gain control to set the level of amplification applied to the signal. After the preamp stage, the signal passes to the power amplifier, which drives a speaker to produce sound in the room. Importantly, these two sections operate independently, each with its unique compression and saturation characteristics.
In many valve guitar amplifier circuits, the sound produced by the speaker is a culmination of both the preamp and power amp sections, each exerting its individual influence on the original signal. For many vintage and revered amplifiers, it's the power amplifier stage that imparts the legendary "magic" sound that makes them highly sought after. However, there's a drawback to this magic—achieving it often requires extremely high volume levels. A 100-watt valve amplifier, for instance, can generate sound levels exceeding 120 decibels, akin to standing near a jet engine at a distance of around 180 feet. This level of volume is only practical in specialized facilities such as professional recording studios or dedicated rehearsal spaces, which are becoming increasingly scarce.
Adding to the challenge are modern noise regulations that restrict loud stage volumes during live performances. This confluence of factors creates a predicament where iconic amplifiers with magical sounds can never be practically used at the volume levels required to unlock their full sonic potential.
Furthermore, there's an issue with the rising prices of power valves and shortages in retail channels. Power valves, compared to preamp valves, have a relatively short lifespan when an amp is operated at full volume.
Evolution of Modern Valve Amp Designs
Given these challenges, modern valve amplifier designs have evolved to rely less on the sound of the power amplifier. Many manufacturers now design their valve amps to primarily depend on the preamp for producing overdriven tones. This shift has advantages, notably the ability to run amplifiers at quieter volume levels while still achieving a complete sound. However, it begs the question: What about the "magic" of the loud power section? While the appeal of vintage amplifier designs that produce a unique sound, often referred to as an amp "in the zone," is subjective, many players still believe that modern amps cannot replicate this sound. They argue that only high-volume valve power amplifiers operating at full tilt can achieve it. For those who've experienced this sound, it's an unforgettable and sought-after experience. With the availability of Neutron PowerPack profiles, more people can now enjoy this "loud amp sound" without getting in trouble for noise pollution or risking their hearing.
The Challenge of Capturing Power Amp Behaviour
In the world of digital modelling products, particularly those on the affordable end of the spectrum, accurately reproducing the power amp's sound is often a challenge. This complexity arises from the power amp's intricate combination of compression, even-order harmonic saturation, presence control (negative feedback loop), and the effects of voltage delivery, sag, and bias. Capturing and modelling this information is as complex as dealing with a preamp circuit, even if there are multiple gain stages. Consequently, the power section in some cases is reduced to a simplified algorithm that approximates its behaviour in a basic manner. In amp profiling, the power stage is sometimes blended with the rest of the sound, making it challenging to extract its independent, non-linear characteristics. This can result in a calculated sound that lacks the distinctive power stage behaviour, instead incorporating its effects on gain and overall EQ into the final result.
This discrepancy has less impact on modern high-gain amplifiers that derive their sound primarily from the preamp circuit. Consequently, many believe that if a profiling process successfully emulates a high-gain modern amp, it will do the same for vintage circuits where the power stage significantly contributes to the overall sound. The distinction lies in the fact that vintage amps possess a higher percentage of their character derived from the power amplifier and its non-linear behaviour. As fewer people experience the "loud amp sound" in person, modelling products and profiles place less emphasis on accurately replicating power amplifier behaviour.
Technology Comes to the Rescue
However, there's a silver lining. Thanks to the remarkable capabilities of Neural Amp Modeller, it is now possible to faithfully capture the behaviour of a valve power stage when profiled correctly. This process generates a profile that can be loaded into a plugin instance and used as a proxy for the real thing. This means you can continue using your favourite real valve preamp or the preamp section of your valve amplifier. In many cases, this approach allows you to leave your valve amp on standby, preserving the lifespan of the power valves. It's important to note that when using profiles or models of amps, you should source the sound from a preamp-only signal. If your amplifier has an effects loop send, this is the ideal signal to use.
Why Do You Want Power Amp Profiles?
Now, let's address the pivotal question: Why should you be interested in power amp profiles?
1. Enjoy the "Loud Amp Sound" at Normal Volumes: Power amp profiles enable you to use your real gear at regular volume levels while still relishing the incredible sound of high-volume power valves. This versatility is valuable for practice, recording, and live performances. It allows you to enjoy convenience without compromising on your guitar sound. Compared to running your amplifier into a reactive load at full blast all the time, particularly in light of current valve shortages, this approach is more economical. It's especially beneficial if your amplifier can use its preamp section while on standby.
2. Enhance Sound Accuracy: Profiling both the preamp and power amp sections separately leads to higher accuracy potential. While Neural Amp Modeller excels at profiling complex amplifier setups, dividing the process into two parts can further enhance accuracy. Although not an absolute necessity for NAM users, it can certainly upgrade your end result if ultimate accuracy and control are your top priorities. This approach can be particularly valuable when combined with preamp pedals, which are currently popular in the market.
3. Unlock New Tonal Possibilities: Power amp profiles open the door to exciting tonal possibilities by allowing you to combine preamp and power amp sections that wouldn't typically be found in production amps. For instance, you can pair a Fender Tweed Deluxe preamp with an EL34 power stage, letting your creativity run wild. Neutron has an extensive list of different power amps that will be released in due time, so stay tuned for updates!
In conclusion, power amp profiles offer guitarists the chance to enjoy the unique sound of high-volume power valves at manageable volumes. They also enhance accuracy by faithfully reproducing the behaviour of both the preamp and power amp sections. Moreover, they unlock new creative opportunities by allowing unconventional combinations of pre and power amp sections. With the advent of technology like Neural Amp Modeller, the "loud amp sound" is now more accessible than ever before.
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