All About Power Attenuators

Written by
Logan Tabor
Published on
January 22, 2021 10:21:48 AM PST January 22, 2021 10:21:48 AM PSTnd, January 22, 2021 10:21:48 AM PST
Power attenuators, in the realm of electric guitars, have been around and on the market since the 80s.  While their concept has undergone countless revolutions and refinements over many years, their designers always had one goal in mind: Keep the tone, drop the volume.  
There are a number of scenarios in which one might realize the need to decrease their amplifier’s volume level, either by 2dB or by 25dB.  But the general fear is that power attenuators will suck tone or cause problems within the amplifier, ultimately leading to the amp’s demise.  Perhaps in the past the market saw a few products whose circuitry inherently altered the tone coming from the amplifier, or whose design was flawed and caused electrical problems in the amp over time.  But these days, power attenuators are better and more user-friendly than ever; you’d be hard-pressed to find one that actually causes dramatic tonal changes or electrical breakdown. In today’s article, we are going to talk about how attenuators work, and what they can be used for; we’ll also be clearing up a few misconceptions about attenuators to try and shake the bad rap they’ve developed over time.  

In short, an attenuator works by “bleeding” some of the power coming from the output section of an amplifier, thus reducing the volume level, before sending the signal out to a speaker cabinet.  The attenuator is typically an external device that is connected to the speaker output jack of an amplifier and places the same load on the amplifier that a speaker normally would (provided the impedance of the amp and attenuator are matched).  Many will use a coil to convert excess wattage into heat or mechanical energy prior to sending the signal out to the desired location.  

The most common reason a player would use an attenuator is simply because their amplifier is too loud for a given setting.  We see them being used a lot with 50-100 Watt amps but the fact is, lower-wattage amps can get surprisingly loud as well.  It is commonly accepted that tube amplifiers sound best, and exhibit certain desirable tonal qualities, at higher volumes. This is because when the amp is pushed, the output transformer begins to saturate and the rectifier tube will start to sag when bigger notes are hit; these concepts give us that big, barking, compressed, and dynamic tube amp sound we all know and love.  But by the time an amp gets pushed that hard, it can literally be deafening. This is about the time the sound guy walks up and asks, “can you turn that down just a bit for me?” And as we all know, turning down the amp will immediately change its tone and touch response.  
Because an attenuator comes after the output section of an amp, it allows users to push the amp as hard as they want in order to hit that tonal “sweet-spot," while giving them the option to drop the volume level without affecting that mega rock tone!  

One common misconception is that a master volume control will achieve the same effect as an attenuator.  However, because a master volume knob is still a part of the amplifier's preamp section, it has an entirely different effect on the circuit -- and therefore, the overall tone.  The master volume knob essentially allows the user to push the preamp signal to a desired gain level before it hits the phase inverter and moves on to the output section of the amp, which is why when one turns the master volume knob they tend to notice a dramatic change in tone.  Pushing the master volume knob is a big part of what gives us that bold, fat, dynamic tone we all want in the first place. The attenuator, as previously mentioned, comes after the phase inverter, after the output tubes, and after the output transformer; it should theoretically have no influence over the actual tone or touch sensitivity the user has dialed in.  

Attenuators are all too often blamed for being tone suckers.  While many players will perceive a change in tone after implementing an attenuator and dialing back the volume, the attenuator itself may not actually be the culprit.  This phenomenon is typically attributed to two major factors:
Speakers - Speakers sound different at different volume levels, period.  Each speaker is designed differently and is made to handle unique frequency ranges and volume levels.  The frequency response of any given speaker will change from low volume to high volume. Because attenuators are placed between the amplifier’s output, and the speaker cabinet’s input, the intentional decrease in volume created by the attenuator will change the way the speakers vibrate.  This does not mean the attenuator changed the amplifier’s tone, though. It simply means the speakers are reacting differently to less power. As a way around this, many modern attenuators will provide some sort of treble and bass compensation controls.  
Human Ears - Similar to the way speakers react to volume, so do human ears.  Our ears are designed to perceive frequencies differently at different volume levels.  If the volume level of a sound source is decreased, the human ear will assuredly perceive its frequency composition differently than it would if that same sound source’s volume were dramatically increased.

Electrically speaking, it would make no real sense for an attenuator to damage an amplifier considering these devices come after the amp in the signal chain.  Problems do arise when players implement attenuators, but more often than not it is a result of having the amp pushed to its limits for hours at a time. The point of the attenuator is to allow users to push an amp as hard as they want in order to achieve a certain sound; if the amp is being pushed hard enough, it will be working at or near its maximum potential.  It is true that we can lower the volume level of our rig using an attenuator, but the amplifier is still working just as hard as ever in order to produce the desired sound.  
Imagine driving your Honda Civic at 95mph all day every day; it’s probably not going to last long.  Similarly, power tubes and output transformers are at risk of burning up quickly if they are constantly maxed out.  
What I’m saying is that sometimes players think they can push an amp even harder for even longer BECAUSE they have an attenuator, and because the volume level is no longer hurting anyone’s ears.  This ultimately leads to overworked amps which will, in time, malfunction. Best practice would be to find the amp’s sweet spot without exceeding the bounds of that sweet spot; don’t push it just because you can.  

For safe operation and optimal performance of an attenuator, there are two major specs that need consideration: Impedance and Wattage.  
The impedance of the attenuator needs to match that of the amp, just like a speaker would.  Luckily, many amps come with an impedance selector switch which allows the user to adapt to an external device such as an attenuator.  Likewise, many modern attenuators come with impedance selectors, or even the inherent ability to work with any input impedance. In any case, be familiar with your amp, and understand its needs in this regard.  Do the research on the attenuator and amp’s compatibility before making a purchase!
And what about wattage? You wouldn’t connect a 100 Watt amp to a 30 Watt speaker cab, right?  The same way a speaker setup needs to be able to accommodate the power of an amplifier, so does an attenuator.  Make sure the attenuator can handle the output of the amp, and leave some head room in there. A 100 Watt amp can easily reach peaks of up to 150 Watts, so make sure you account for this variance when making a purchase.  

While their primary use tends to be volume/power attenuation, modern attenuators can be used in a number of creative ways:  
Some attenuators can be used as dummy speaker loads, allowing a tech to safely work on an amp without having to connect it to a speaker cab. Setting bias, checking operating voltages, and other repair and maintenance work can be done without having to hear the hiss of a speaker cabinet.
Many attenuators will come with a line level output which allows for a wet/dry rig.  Some users will dial in a perfect dry tone, and then use the line level output on their attenuator to run through an effects rig, through an external power amp, and out to a separate cabinet.  This leaves their dry sound in place while adding effects on top of it as desired.  
Attenuators also allow users to play super high-wattage amps through low-wattage speakers without blowing the speaker(s).  After attenuating the high-wattage signal down to an appropriate level, one could connect their Triple Rectifier to a 1x12 extension cabinet loaded with a Celestion AlNiCo Blue (15 Watts) with no risk of harming the speaker.  Additionally, if the attenuator has a line level output, a user could experiment with speaker emulators rather than physical speaker cabinets.