When using a tube amplifier, you should always connect it to a speaker cabinet before turning it on – or a loadbox. The speaker cabinet (2, 4, 8 or 16 Ohms) must always be connected to the corresponding speaker output of your amplifier. Not doing so can lead to partial or complete destruction of the output stage of the tube amplifier. Most tube amp designers protect their products with fuses etc, but some amps do not have sufficient protection in place. Our general moto is that “It is impossible to predict the behavior of all the amplifiers on the market in case of use without a load (a speaker cabinet or a load box)”.

The electronic term that describes the speaker cabinet with respect to the amplifier is the “load”: we say the cabinet “loads” the amplifier. The term “load box” fits any product that embeds an electronic load. The main parameter of the load box is its impedance, and that is rated in “Ohms”. An 8-Ohm load box must be plugged to the 8-Ohm speaker output of the amplifier.

When using a Torpedo load box, the power sent to the load is turned into heat, so please follow the cooling recommendation of the load box – failure to do so may cause overheating which can lead to damage, both to the load box and to the amplifier. The Torpedo Reload, Live, Studio, Captor and Captor X are load boxes. This term indicates that these products feature a load which can electrically replace the speaker cabinet while safely dissipating (transforming into heat) the power coming out of the amplifier.

The embedded load in the Torpedo products is reactive: it embeds a specific circuit to simulate the complex impedance of a real speaker. This kind of system is widely used in the industry to silently test amplifiers.

Is the use of a loadbox totally silent?

We usually talk about “silent recording” when a load box is involved. If we compare the load box solution to a traditional cabinet miking solution, it is obviously several orders of magnitude quieter, but you will still experience some minor sounds, noises, that have to be taken into account:

  • Your guitar or bass strings can be heard. This is obvious, but it can be disturbing, depending on your environment if you are not used to it.
  • You may hear some noise coming out of your Torpedo when playing, like there is a tiny speaker inside the box. This is perfectly normal and there is no reason to worry. The sound is produced when power goes through the coil of the reactive load embedded on the Torpedo. The vibration is related to what power comes out of the amplifier connected to the Torpedo and to the signal’s frequency content (notes played are heard). Your amplifier may also produce similar noise, at the output transformer’s level. Such noise is usually not heard, simply because it is normally overcome by the sound coming from the loudspeaker.
  • The Torpedo embeds a fan, as there is quite a lot of power dissipated into heat inside the box. We selected a “silent fan”, but as it is running fast, it is never entirely silent. This said, you can consider that, in normal use (hearing your guitar through monitors, or headphones), you can barely hear that fan.

Care should be taken when using a load box

The correct use of your amplifier with a load box requires some precautions. Because of the fact that you may be playing “silently,” it is much easier to accidentally run your amplifier beyond the reasonable limits set by the manufacturer than when you are using an actual speaker cabinet. This can lead to faster tube wear and, in some cases, to more serious issues.

Keep in mind that the “sweet spot” — the perfect running point of the amplifier, the one that will give you the tone you are looking for—is rarely obtained at maximum volume. In addition, the volume control of the amplifier is usually logarithmic, which means that the volume goes up quickly on the first half of the potentiometer’s rotation, reaches its maximum at 12 o’clock, and will not change much beyond that point. Therefore, you can
reach the maximum volume of your amplifier even if the volume potentiometer is not set at maximum.

By reaching the maximum output power of your amplifier, you will hear a lot of distortion, which may not sound as good as you could hope. In fact, most amplifiers do not sound great at maximum volume. Always keep in mind that your amplifier may not have been conceived to be used at maximum volume for a long time. Running an amplifier at high volume will cause premature wear of the tubes and possible malfunctions or damages to the output stage.

  • When first testing the amplifier at high volume, monitor the color of the tubes and the general response of the amplifier. Red-glowing tubes or any appearance of smoke are signs of a problem that may result in partial or complete destruction of the amplifier.
  • The fact that the volume control of your amplifier is not set at maximum doesn’t mean your amplifier is not running at maximum volume. A good habit is to keep the usual volume setup you would use in rehearsal or on stage, rather than just following what the volume potentiometer indicates.

7 thoughts on “What is a load box?

  1. Raff says:

    Hello, I use my captor X 8ohm to a Princeton reverb head 8ohm. Can I then connect a speaker 16ohm to the Captor X to use it as an attenuator? Would it be considered a mismatch? Thanks

    • Jason Wilding says:

      This would be a mis-match – as the Captor X is looking at what the speaker is going rather than the amp (set in that way) – you should be fine, but take it easy!

  2. Michel Filliatrault says:


    I have a peavy artist 240 – instructions are mentioned that the speaker and ext are 4 ohms – which captors could fit with that amp ?
    Also I have a spider 330 bass amp with 2 speakers output at 4 ohms and one XLR DI output- same questions which models of captor will fit –
    I guess the answer is 4 and 8 ohms model – please confirm or precise

    • Jason Wilding says:

      Hey Michel!

      Having read the owner’s manual of the Peavey Artist 240 – this amp is rated at 4 Ohms.

      As for the bass amp, I assume it is the Ashdown 330 Spyder amp. If so, its power amp is solid state and is rated for a minimum of 4 Ohms. With this in mind, the best choice is the Torpedo Captor 4 – you will have perfect impedance match in all cases.

      If you wish to have DynIR cabinet simulation for better tones, headphones output, you can use a Torpedo Captor X, 8 Ohms version. You will have an impedance mismatch, albeit the tolerable one. This article will give you all the information and precautions you need to take when using an amp and a Torpedo product that are mismatched impedance-wise:


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