Whether you’re at the studio using your amp head as a preamp or jamming with headphones at home, it’s very important to know which circumstances require that you connect speakers to your amp. This article will break it down for you!
Using Headphones with Amps
Musical inspiration tends to strike at inopportune times, such as late at night and early in the morning when the neighbors are asleep. To allow for silent practice and jamming on riff ideas, many manufacturers today include headphone jacks on their amplifiers. If you have a combo amp with an integrated headphone jack like Carvin Audio’s MB Series bass amps, you can just plug and play.
But things can get a little more complicated if you have a separate head/cab setup. Some bass amplifier heads have quarter inch headphone jacks that make it easy for you to play without causing a disturbance. As long as the amplifier has a solid state output stage, you’re good to go and should not need to connect a speaker load to make use of this feature. Even so, you should consult your manual or just turn the master down if it does not affect the headphone output. This is always a good rule and if the amplifier section can be turned down without affecting the headphone or DI outputs it is good to turn it down.
Recording with a Solid State Amplifier’s DI
When using your solid state amplifier’s DI to connect directly to a mixing console, most DI outputs are separate from the master volume, so you can turn down your master if you are using only the DI output. Solid state amplifiers can usually handle no load and will be fine running with no load connected. Again, it’s good to check the manual or turn down the master if you can.
What About Hybrid Amps? Do I Need to Connect a Speaker?
There are many hybrid amps on the market with preamp tubes. As long as they have a solid state output stage, they are safe to use under the same conditions as solid state amps. Remember only the amplifier section drivers the speakers.
Going All-Tube? Connect a Speaker
This is where you need to be careful. If you have an amplifier with power tubes in the output section, then you cannot operate it without a speaker load connected.
Simply put, in the tube amp output section, the transformer performs the task of transforming the speaker load to a load the tubes want to see. For example, on an amp with four EL34 output tubes the transformer makes an 8 ohm load look like a 1200 ohm load for the tubes.
This is also why you should not mismatch your load to the impedance indicated or selected on the amp. If you are on the 4 ohm tap of the transformer it transforms the same 1200 ohm to the tubes. Tubes are happy. If you are on the 8 ohm tab with a 4 ohm load, the same transformer will put a 600 ohm load on the tubes and they will not perform correctly.
Now, if you do not connect a load, the transformer can not reflect a load and the tubes will only see the wire in the transformer and a big coil as a load. This is basically shorting the tubes to the high voltage and it will cause damage to the amplifier eventually. Another way to think of it is the power tubes pull on the transformer which magnetizes the output transformer; this in turn creates a voltage on the output of the transformer to drive the speaker load. If there is no load, all that energy has nowhere to go, so instead it will be fed back to the power tubes causing damage. Usually the tubes will go into a growing oscillation that eventually burns them. Most of the time the output transformer is ok, but if left on long enough it can also be damaged. And playing through an unloaded tube amp will only speed up the road to damaging the amp.
Dummy loads: Who’s the dummy?
A dummy load is a resistive load and in some cases a more advanced simulated speaker load that is used to load an amplifier when a speaker load is not wanted.
The Carvin Audio Vintage 16 tube amplifier has a dummy load built in and this can be found in other small tube amps. This is a selection on the impedance switch that connects an internal load to the amplifier allowing it to be used with no external load connected. There are also dummy load products on the market that will perform this feature for you as well, if you need to practice quietly or you are recording in the studio without a speaker connected.
Best to be on the cautious side and always connect a load, or turn down the master volume if you can when using headphones or a DI out without a load on a solid state amplifier. We all make mistakes, and if you accidently power on your tube amp without a speaker connected, it won’t blow up instantly. It should definitely be something that you make a conscious effort to avoid, though!