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What is a load box? - bop01mo - 01.04.2022
What is a load box?
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.
High voltage test
The high voltage tester (also called dielectric strength test or hipot test) can be carried out using AC or DC. If the high voltage test is performed using DC, it is then combined with insulation; if the high voltage test is made using AC, this is more stressful for the sample and therefore carried out according to the sketch below.
Measurement of a high voltage test under alternating current is performed using an alternating voltage (50Hz) adjustable to an effective 50V to 1,500V. As is the case with direct current, the high voltage test detects any sudden rise of current up to a programmed threshold.
The short circuit test is maintained by default. The rise time is more than 500 ms and the application time at least one period.
Warning: The high voltage test under alternating current is penalised by the capacitive value of the tested equipment. It must be remembered that the generator power is limited to 5 mA.
signal generator, electronic test instrument that delivers an accurately calibrated signal at frequencies from the audio to the microwave ranges. It is valuable in the development and testing of electronic hardware. The signal generator provides a signal that can be adjusted according to frequency, output voltage, impedence, waveform, and modulation.
Signal generators are of five major types: oscillators, which generate sine waves useful in measuring the response of loudspeakers, amplifiers, microphones, transducers, and acoustic systems; standard signal generators, which generate sine waves over a wide range of output power and modulation, used, for example, to test radio receivers and measure gain, bandwidth, and signal-to-noise ratio; frequency synthesizers, which generate highly precise output frequencies over wide ranges; pulse generators, which produce pulsed signals at precise duration at precise frequencies; and random-noise generators, which produce a wideband noise for various types of electronic, mechanical, and psychological testing.
Power analyzer measurements
Power analyzers can make a variety of measurements dependent upon the manufacturer and the model, but typically power analyzers are likely to be able to measure parameters including: voltage; current; power; peak, mean and RMS parameters; harmonics; phase, and a variety of other parameters.
Some power analyzers are intended for high power measurements and may even have special high power sensors, whereas others may be intended for measuring the standby current parameters for various items of equipment.
In view of the many applications for these power analyzers, modern types often have data logging capabilities. Often they can stored the data on board to be downloaded at a later date of displayed in screen - the screens on some power analyzers can be quite large and able to provide very detailed data. It is also normally possible to communicate the data, often via Ethernet or USB with a computer so that further analysis can be undertaken.
As power energy analysers can often be used to monitor equipment over a long period of time, possible under a host of different conditions, the data communication capabilities are of great use.
Also it is often possible for the power analyzer to be controlled remotely. This enables the instrument to be located close to the item under test, whilst the computer and the engineer are located elsewhere. This can be very useful when an item is undergoing temperature or vibration testing.