All about...Attenuators

Got a trillion Watt Marshall wall of 4x12's in your 1 bedroom apartment?

Just bought a 1957 Fender Tweed 50w combo, ultra rare for you upstairs bedsit, with a Wife and new born?

You'll know that it's impossible to play without waking the the next Town.

Attenuators might be the answer...take it away peter...far away, so I can hear again.

Attenuators, what they do and why you might need one.

Makes and models of traditional style attenuators are Marshall Powerbrake, THD Hotplate, Jetcity Jetenuator, Bugera PS1 Power Soak.

Attenuators come in many varieties and these different varieties do different things, however, the main job of all of these is to lower the output signal from your amplifier to your speaker and lose that attenuated signal as heat. There are two main types of circuit the attenuators use but we will come on to this a little later.

If we talk about tube amplifiers (although attenuators will work on solid state amplifiers). There is a distinct reason for using attenuators on tube amplifiers. That being that if you want power amp distortion, break up or overdrive (whatever you like to call it) and not have the neighbours banging to tell you how good you sound because you will need to run your amplifier at extremely high volumes. You can use an attenuator. We are not talking about pre amp distortion, break up or overdrive that is something different and happens in your amplifier at reasonably low volumes. It is the sound of a tube amplifier running at high volume. Think Paul Kossoff, Randy Rhoads, Michael Schenker, Angus Young, Pete Townshend.

All circuits and complex components can be measured in many different ways. For instance, if you were to measure a simple circuit you could measure its inductance, its resistance, its capacitance, its voltage, its current perhaps even its power. The reason I mention this is because components in a circuit that may on the face of it seem to be simple are quite complex and in amplifiers this can make a huge difference. In this case we will talk a little more about speakers and how attenuators ‘simulate’ these in an attenuator.

Speakers can be measured for their resistance (in the case of speakers this is a little more complex and is generally know as impedance) these are normally 8 or 16 ohm but sometimes they are 4 ohm and can be wired in different ways. (All very complicated and not necessarily required for this explanation)

They can also be measured for their capacitance and their inductance as the voice coil component is a essentially a coil of wire. This all affects what the amplifier ‘sees’ when they are plugged together and is know as the reactance of the speaker (how the amplifier reacts to the speaker and how the speaker reacts to the amplifier). Depending on all of these measurements of the speaker the amplifier and speaker will react together differently. So why am I telling you this?

Well attenuator circuits are either resistive or reactive. Purely resistive attenuators will generally be cheaper units and the circuits will be made up mainly of large resistors. As with all attenuators these will sit between your amplifier and your speaker and as the signal travels through these large resistors the voltage of the signal is reduced and becomes quieter allowing you to run your amplifier at a higher volume on the unit but have less volume at the speaker and as a bonus heating in your room. Purely resistive attenuators do not have a reactance as the circuit only contains resistors. This means that the amplifier does not ‘see’ anything that resembles a speaker and can sound sterile in comparison to ‘seeing’ something that resembles a speaker with reactance. The other type of attenuator circuit is a reactive attenuator. This type of circuit normally contains coils or transformers as well as resistors that mimic a speaker and as such make an amplifier ‘see’ something it recognises (and has been designed for). Therefore, if the circuit designer of the attenuator has done their job properly the sound should be similar to the amplifier without the attenuator in the circuit except quieter.

There is now a new generation of attenuator. Things like Universal Audio Ox Box, Boss Waza Craft Tube Amp Expander. Which do the same thing as a reactive attenuator but have additional functionality like having a speaker cab ir loader to more precisely imitate your favourite speaker cabinet. An effects loop, so you can use it with your old 60’s tube amplifier and put your pedals in the effects loop without having to pay an amp tech to deface your pride and joy. In some cases you can also use this new generation to plug directly into your DAW to capture the sound all at reduced or zero volume out of the speaker but with the ability to drive the power section of your amplifier into natural tube breakup. However this all comes at an increased price (over a grand)

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