i dont understand a lot about amps --'

[perez]

hi,
i was just wondering...
if i have one of this cab: marshall mr 1960 A 300watts mono 4/16ohm
what head do i need?
a 300 w head?
please someone explain me :P

[tunghaichuan]

hi,
i was just wondering...
if i have one of this cab: marshall mr 1960 A 300watts mono 4/16ohm
what head do i need?
a 300 w head?
please someone explain me :P

300 watts is the maximum wattage you can put into the cabinet and not burn out the voice coils in the speakers. Since the 1960A is a 4x12" cab, I'm going to guess that each speaker is a 75-watt Celestion, probably the G12T-75. Those cabinets are generally used with 50 and 100 watt Marshall heads.

You don't need 300 watts to drive the cabinet. In fact, most Celestion speakers are very sensitive, meaning that it doesn't take much wattage at all to get loud volume levels. If the speakers in your cabinet are indeed G12T-75 speakers, their rated sensitivity is 97dB/watt/meter. That means if you put one watt of power into the speaker and measure the volume at one meter away, you get 97dB. And that is just for one speaker. Sensitivity goes up as you add speakers. A 1 watt or 5 watt amp cranked into that cabinet is going to be very loud.

The rule of thumb I like to follow is to never use an amplifier that is more than half the rated wattage for a cabinet. In your case, you wouldn't want to use an amplifier that produced more than 150 watts. You can go lower, of course.

[deeaa]

IMO those 300W cabs are good only for festival gigs and extreme thumping metal sounds...I love my ~100W 4x12" and use it with a 36W amp.

For years I played a 120W amp into a 140W cab to no ill effects ever. Also used a 50W cab with a 100W Fender tube head for many years...jus was careful to never totally crank it all the way.

[perez]

thanks for your answers, and i'm not planing to buy one (yet) it was just an example...

[tunghaichuan]

thanks for your answers, and i'm not planing to buy one (yet) it was just an example...

A couple of other things you might need to know:

With tube amps it is very important to match the impedance from the head to the cab. Some amps will tolerate a mismatch, but overall it is best to match them correctly. That means you always plug a 4 ohm head cab into a 4 ohm spaker cab, etc.

Solid state amps are a little different. They will usually have a stated minimum impedance. So if the minimum is say 4 ohms, using a 4 ohm cabinet will get the maximum power out of the amp. Using a 4 ohm amp with a 8 ohm cab or a 16 ohm cab is okay, but you get less power out. You should never go below the minimum stated impedance as doing so might cause your output transistors to burn up.

As dee stated above, you can get away with using cabinets that are not twice the rated power of the output of your amp. However, when the output of your amp equals the maximum power your cabinet can take, you do run the risk of blowing your speakers and amp. Say you have a 50 watt Marshall head and a 50 watt rated cabinet. 50 watts is what the Marshall amp puts out clean. When you crank it it puts out much more, 60-75W. So at 75W you're about 50% over the cabinet's rating. Taking it further, if your speakers blow, you are now running your amp into an open load, which is very bad for a tube amp.

[perez]

A couple of other things you might need to know:

With tube amps it is very important to match the impedance from the head to the cab. Some amps will tolerate a mismatch, but overall it is best to match them correctly. That means you always plug a 4 ohm head cab into a 4 ohm spaker cab, etc.

Solid state amps are a little different. They will usually have a stated minimum impedance. So if the minimum is say 4 ohms, using a 4 ohm cabinet will get the maximum power out of the amp. Using a 4 ohm amp with a 8 ohm cab or a 16 ohm cab is okay, but you get less power out. You should never go below the minimum stated impedance as doing so might cause your output transistors to burn up.

As dee stated above, you can get away with using cabinets that are not twice the rated power of the output of your amp. However, when the output of your amp equals the maximum power your cabinet can take, you do run the risk of blowing your speakers and amp. Say you have a 50 watt Marshall head and a 50 watt rated cabinet. 50 watts is what the Marshall amp puts out clean. When you crank it it puts out much more, 60-75W. So at 75W you're about 50% over the cabinet's rating. Taking it further, if your speakers blow, you are now running your amp into an open load, which is very bad for a tube amp.

thanks a lot for that explanation, anyway if i happen to have any other questions ill not hesitate on creating a thread.