TECH TIPS: We’re Not Overreacting – Reactive Loads Are Important

September 16th, 2022 |  John Dines

Ever thought that a valve amp just “feels” better to play through? This is why. Sure, some people will tell you that it’s because it’s loud or because there’s “natural compression” or something like that. These are certainly contributary factors, but they’re not the whole story. Anyone who’s recorded guitar in a proper studio, sat in a separate room to the amp and listening through the monitors, will tell you that the feel of a good valve amp is still there even from a safe distance.

The reactive load is the key to this magic. When you think of a reactive load, your mind probably leaps immediately to attenuators, devices to safely dissipate all that power from your amp’s output and give you a line level signal to feed a cab sim or power amp. This means you can crank your valve amp up to the sweet spot, without annoying your neighbours, your sound engineer or flooding the studio with guitar when there’s a whole band to record. These are all good reasons to use an attenuator, but attenuators aren’t the only place you’ll find a reactive load – conventional guitar cabs are reactive loads themselves.

Though the impedance of a cab may be nominally rated at 8 or 16 Ohms, the reactance of a speaker causes this impedance to vary quite a lot across the frequency range, meaning that a speaker’s unique characteristics elicit a constantly varying response from the amp’s output transformer – and the valves connected to the other side of it. This means that these parts operate as a whole system, all working together to create what we experience as “valve amp feel”.

We won’t get into the definition of reactance here; it’d get a bit heavy on the science. But let’s just say that this important quality of speakers is crucial to getting the right behaviour from an amp. This is also the reason that the old amp attenuators of yesteryear were often criticised for ruining the response of the amp they were paired with. This is because many of these attenuators used a purely resistive load – just a great big resistor that could safely absorb all the energy from the amp’s output without causing damage.

These would protect the amp from harm, but a resistive load will not allow the power amp to behave as intended. The feel and frequency response are completely different. A good attenuator will have a reactive load, designed to mimic the relationship between impedance and frequency that you’d expect from a real speaker. Some reactive attenuators even let you change what speaker this is based on! In any case, this type of attenuator will let you experience your valve amp as nature intended, with the feel and response completely intact, albeit at a safe, ear-friendly level convenient for recording.

This crucial piece of the valve amp puzzle is something we at Origin Effects were keen to recreate when we designed the original RevivalDRIVE pedals. With the goal of simulating – in analogue – all the qualities and quirks of a great valve amp, we could hardly ignore this fundamental principle. The result? In addition to a preamp section, long tail pair phase inverter and a push-pull output stage, all recreated in miniature using high-quality solid-state parts, there’s also a little reactive load at the heart of all our Analogue Amp Recreation pedals.

It’s worth noting that the reactive load does not simulate the actual frequency response of a speaker – you’ll need a cabinet simulator for that. What it does mean is that the output from our Analogue Amp Recreation pedals already has that “real amp” feel baked in, without you having to worry about it being lost when running into a cab sim or neutral-sounding power amp.

So, this small but indispensable detail really does make a big difference. It’s one of the reasons our pedals are often accused of being the most “amp-like” overdrives and preamps out there, not only in terms of sound but also the all-important quality we call “feel”.

Lots of lovely oomph and bounce, brought to you by Origin Effects in collaboration with the humble reactive load.