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more... Amp DIYGigging AdviceRecording TipsMarch 2009

Quiet Please! Attenuators and Their Many Uses

Matching Up Impedance and Power Ratings
To get the best tone and safest performance out of your attenuator, make certain that you are accounting for the power rating of your amp, as well as the impedance that it’s set to. The good news is most high-powered tube amplifiers have selectable impedance settings to accommodate various speaker cabinets. Some amps are designed with dedicated 4-, 8- and 16-ohm speaker outputs, while amps like Marshalls have always had a switch or plug that sets the impedance. Attenuators, as in the case of the THD Hot Plate, offer individual models specifically tailored for 2, 2.7, 4, 8 and 16 ohms, while other units like the Weber MASS have adjustable impedance settings all in one unit (2, 4, 8, 16). Others still, such as the Ultimate Attenuator, are designed to accommodate any impedance amp. Every one of these will put their particular tonal stamp on the amp tone due to the various types of attenuation being used. These tonal variations are the subject of much heated debate in various forums, but that discussion is outside of the scope of this article.

Power handling is of utmost concern. You don’t ever want to use an attenuator that can’t take the juice of your amp. A 100-watt tube amp is easily capable of pushing out 150-watts or more peak power, so check with the manufacturer to see what it can handle before plugging in your favorite amp. Personally, I’ve used a Hot Plate for over a decade with my 50- and 100-watt heads and have never had an issue with them dimed for hours on end, five days a week. As long as you match the attenuator to your amp like you would a speaker cabinet, you’ll be in good shape… you’d never run a Hiwatt DR-103 full up through a 1x12 Celestion greenback cab unless you had a death wish for the speaker and the amp!

Load Up
Many attenuators have extra features on them that can be used for more than just volume reduction. Units like the THD Hot Plate and Weber MASS can be used as a dummy speaker load, allowing you to run the amp without a speaker cabinet. This is an invaluable tool for safely being able to set bias, check operating voltages or anything that requires the amp to be running to diagnose. Prior to specific dummy load devices, techs have used everything from light bulbs to giant resistors to dissipate power while working on a live amp. With the attenuator set to “load,” just plug the speaker output of the amp into the “amp input” or similarly named input and you’re ready to go. What’s nice about this is that while working on the amp you won’t have to deal with the noise coming from a speaker cabinet and all of the hiss that goes along with a loud amp. Just remember that although you don’t hear any sound or see that electricity, it’s there, and it’s lethal. Make sure you know what you’re doing, and re-read the caution at the beginning of this article.

The Wet/Dry Rig
If your attenuator has a line out available, you can use it to set up a Wet/Dry rig. A wet/ dry rig is great for keeping the dry tone of your amp intact while bringing in effects on a separate power amp and speaker. Once you have the dry tone set to your liking, take the line out of the attenuator and feed it into the desired effects, then into a separate power amp. Make sure you don’t overload the input of the effects by using the line out’s volume control to taste. From there, you can run a second speaker cabinet, effectively slaving the tone of the main amp but with the effects. Controlling the output of the power amp will bring up the “wet” level on the second cab, and you can mix to taste. Of course, this is best used for effects like delay, or any effect that you want on the back end of the tone. Pedals like compressors and distortion boxes are best left to the front end. Make sure if you’re using a delay or reverb that you set the effect to 100% so you’re not bleeding in the dry signal.

Line Out/New Power Amp
If you really want to tame the volume of an amp, but find that the lowest settings on the attenuator suck too much tone out for your liking, you can once again put that dummy load and line out to good use. First, set the attenuator to “load.” Then, like the wet/dry rig, use the line out to feed a power amp out to the speaker cab of your choice. In essence this is like using a “slave out” that used to be a big mod back in the eighties from the amp hot-rodders. Back then it was used to power yet another head, but these days it can be used to bring the volume down to a controllable level and still retain the full sound of the amp. Will it be exactly the same as with the power section of the main amp? No, but neither will it be the tone of a highly attenuated signal, so it’s a matter of taste.
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