Power attenuators are an essential tool for many guitarists, both professional and amateur, who need to tame their valve (tube) amp and save their hearing!
What is a Power Attenuator?
Power attenuators are a useful tool which are placed between the power amp and the speaker section of a guitar amp. There is no need for me to go into technical specifics, but if you're interested in finding out exactly how an attenuator works, there's plenty of information on the UG.com forums, however, in essence, a power attenuator converts some of the sound energy created by the amp into heat energy before it reaches the speaker.
Why should I bother with a Power Attenuator on a Master Volume amp?
As we all know, valve amps are extremely loud. Although many people don't know it, every day when they power up that 100w half stack, they are playing at volume levels well over the 'safe' 90db limit. So what is the problem? Can't they just turn down? On many amps (a classic example being the Marshall JCM800). The bright cap in this amp only kicks in when you raise the volume, meaning it will sound very thin without keeping the master volume above 4-5. If this component is removed from the circuit, it ruins the amps tone. With a power attenuator you can easily regulate your volume without having to drop your master volume to a level where you stop enjoying your tone, and yet retain your hearing!
How should I use my Power Attenuator?
Disconnect the speaker in your amp or unplug the cab from your head. Take a speaker cable and connect it from the speaker out (usually on your amps rear panel) to the corresponding input jack on your attenuator (read the manual if you are unsure which this is). Then, run another speaker cable from the speaker out jack on the attenuator (again, check your manual) to the cab/speaker in. Power up your amp (make sure you only do this after everything is correctly connected or you will blow out your amps Output Transformer), crank the master volume to an appropriately loud level, and then use your attenuators volume control to regulate the sound to an appropriate level. After a while, you should be able to find the 'sweet spot' where the amp is sounding its best, and then you can pretty much leave the attenuator alone.
Common Myths Dispelled
1. Power Attenuators Suck Tone: This isn't strictly a myth, but it comes from to many people who expect a power attenuator to magically turn their 100w non master volume amps into bedroom amps! Attenuators aren't designed to be run at maximum levels of attenuation, and at this point ANY attenuator will suck tone. Also, some people buy the cheapest attenuator they can - attenuators are just like any other piece of gear! The more you pay, the better you get. Higher end attenuators will suck little or no tone from your amp as long as they are used correctly
2. Power Attenuators can Damage your Amp: If you connect the fan (or just make sure that your attenuator isn't getting too hot) and connect your power attenuator correctly, there is no reason a correctly functioning power attenuator would harm your amp. They can, however, cause your power tubes to rise to higher temperatures, meaning that they might wear out more quickly.