Caution: High Voltage
Before even getting into the various uses of attenuators, it should be stated that tube amps carry lethal voltages and you shouldn’t go poking around your amp’s innards if you don’t know what you’re doing! Leave that to a qualified tech and save yourself to continue playing guitar another day. That said, this is not a technical article, and I won’t be asking you to take plate voltage readings or bias your amp, so let’s move on!
The Power and the Glory
Sometimes attenuators get a bad reputation for blowing up amps. There may have been some questionable designs in the past that put amps at risk, but these days there are a lot of great choices available that are safe to use. While I personally have never blown an amp while using an attenuator, I do know that if you dime your amp, any parts that are stressed are going to be exposed. And most of us running attenuators are using them because we like the tone of the amp full up, or close to that. Before you fear the attenuator will blow the output transformer on your favorite vintage amp, it might be wise to take it to a qualified tech and have it tuned up. What you may have thought of as a solid and safe amp (because you run an overdrive pedal in front of it with the volume on 3) could be teetering on the edge of destruction if you ramp it up. How are the tubes and tube sockets? What about the filter caps (especially on vintage amps)? Is it properly biased? So many things need to be right when you run an amp full out, just like a car in the Indy 500. And don’t let anyone tell you that vintage Marshalls, Hiwatts and the like weren’t designed to be run on 10. They were, and players have been using them that way for decades! Besides, even at a volume of 6, 7 or 8, you’re dealing with some serious power, so take care of your amp and know its running order before plugging it into an attenuator, or a speaker cabinet for that matter.
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!
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.
Creative Cabinet Choices
Ever wonder what a Superlead would sound like through an AC30 cab but were afraid to try for fear of blowing the Celestion AlNiCo Blues? Once again, as long as the impedance is set correctly, and the power is scaled back to accommodate the speakers, who says you have to use the same cab as the head was designed for? Many times I’ve been in the studio and knew that the tone of the amp was dialed in, but wanted a different color. Rather than running the typical, closed-back 4x12, I was able to choose between the many different cabs available by attenuating the signal down enough to allow safe operation. It’s a great way to experiment with tone and to further lessen the volume assault. This is great for live situations as well. Imagine how much easier it will be on your back to carry in a 1x12 cab for the gig. Heck, you usually only mic one speaker anyway. You can still get raging tone, just in a smaller footprint (physically and sonically).
Dummy Load/Line Out/Speaker Simulator
For recording or the ultra-adventurous live guitarist, how about ditching the cab altogether? These days with the myriad amp modeling programs and hardware devices, who says you even need a cab to produce a mic’d speaker tone? Dedicated devices like the Hughes & Kettner Red Box, the Palmer PDI-series of speaker simulators and the fabulous Axe-FX all offer ways of attaining a variety of speaker tones without speakers. As long as you have a dummy load and line out on the attenuator you can accomplish this easily. After setting the attenuator to “load,” take the line out and feed it directly into the hardware unit. The Red Box Classic offers settings for “combo” and “4x12,” while the Palmer offers an 8-ohm dummy load and multiple settings to simulate a variety of speaker configurations. Highly detailed speaker cab emulations as well as microphone models, reverbs and more can be obtained with the Axe-FX by Fractal Audio Systems.
If you’re in a recording scenario and like to use modeling software, consider bypassing the amp models and just use the mic and speaker models. The variety of software amp modelers is vast with, more products entering the market all the time. Each one of them has its own sound and the options are nearly endless. You’d be surprised how good they sound, and with the no-speaker option you can record at 2 a.m. with your favorite amp. Better yet, if you fire up the studio the next day and don’t particularly care for the sound of the mic/cab combination from the night before, you can change it, because the only thing that was recorded was the tone of the amp.
These are just a few options you can try out with most current production attenuators. There are certainly many more not covered in this article that would be helpful, but there’s only so much space available. The possibilities are endless. That said, we are in a new era of amps and tone, with more amplifier options than ever before. And while amp builders are certainly conscious of designing new amps with lower wattage and features such as power dampening or power scaling, we do still love our high-powered amps. Most of us won’t have the opportunity to play Madison Square Garden anytime soon, nor do a lot of us have amp rooms where we can crank our rigs up and jam without consequence. That’s why the attenuator is such a great device. Not only does it act as a big volume knob, it serves us in many creative ways… your imagination is really the only limit with what we have available today.