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.