Thursday, 6 June 2013

Getting Amped Part 1

Amplifier technology has come a long way in the last 15 years.
When I first started in sound, amplifiers weighed more than me and delivered only a few hundred watts of power with dubious fidelity.

Those who have been around long enough will remember amps like the ZPE 500 which almost required a forklift to lift and delivered an (at the time) awesome 250 watts a channel.

These days there are multiple different types of amplifier design (called classes), the class of the amp is not an indication of its quality, it simply indicates what sort of design the amplifier circuit uses.

Amplifiers do three jobs, they convert the relatively high voltage / low current power supply that comes out of your wall socket into a format that speakers like (low voltage / high current), they store power so that it can be quickly released when needed and they take a low level signal from your mixing desk and turn it into a high power signal capable of driving speakers.

There is much more to an amp than Watts, in fact the power rating of an amp can be very deceptive.
If an amp does not have very much storage capacity then it might be able to deliver a large amount of power in a short burst before it 'runs out of guts'. When an amp 'runs out of guts' it is not a pleasant sound.

Things can get very technical here, so I'll try and keep it as simple as possible. If you learn nothing else from this post, it should be that the power rating is not the most important thing about an amplifier and that you generally get what you pay for. Generally, a cheap amp will never be a good amp, no matter how many bazzilion watts it claims to deliver.

Getting Loaded

The first thing to consider is the load the amp will be driving. Think of it like a car towing a trailer, the more stuff you put in the trailer, the harder the car has to work to tow it. Load is measured in Ohms (Resistance) but unlike the weight of a trailer, the lower the Ohms of the load, the harder the amp has to work to 'pull it'.
  • 16 Ohms is a light load.
  • 8 Ohms is an average load
  • 4 Ohms is pretty heavy going but should be within the reach of most modern amps.
  • 2 Ohms is where we separate the men from the boys
  • 1 Ohm will kill most amps and put them into protect mode
The more speakers you put on an amp channel (when wired in parallel), the higher the load (the lower the Ohms).
Most common individual speakers are 8 Ohms and by adding another one in you double the load to 4 Ohms. 2 Ohms is generally 3 x 8 Ohm speakers or possibly 2 x 4 Ohm speakers. It gets a bit messy when you start mixing speakers in series so I won't go into that here as that is a separate topic.

Got it?