Power Amps 101

[ozzynotwood]

Hey everyone.

I need a lesson in rackmount poweramps for guitar. I really know nothing about these things.

I dont know......
What ins and outs are used to connect preamps.
Anything about ohms
How to match up a power amp to a cab without Kaboom
How many SS watts can I put thru a cab that will take 100tube watts
The sound difference between Mono and Stereo

The list goes on and on, so please feel free to educate me in this area. My preamps are a Johnson J-station, and a BOSS ME-50. I wouldnt run them together.

 

[jeremy]

Re: Power Amps 101

ins and outs depend on the amp, some use 1/4" some use xlr

ss amps will have a rating at x ohms, 100w @ 4 ohms for example. that usually means that you dont want to use anything lower than that (2 ohms for example) and using something over that (ex. 16 ohms) will reduce power but usually wont hurt anything.

for a guitar amp/cab combo you usually dont want to over power a cab so if you have a 100w cab a 100w amp is as high as you usually want to go.

100w is 100w best not to risk it

as far as mono vs stereo there are a few things to consider.
a 100w mono amp has a single 100w power section, it can power multiple cabs but you dont have independant control over them. a "100w" stereo amp is usually two 50w amps in one box which means that you can use them independantly, some can be mono bridged to get the full 100w some cant. having a stereo amp lets you use two preamps with one amp, something that cant be done with a mono amp as easily

 

[ozzynotwood]

Re: Power Amps 101

so lets say i wanted to run the ME-50 in stereo into 2 2x12 cabs without losing any power. I'd need a 50w/50w power amp with 2 cabs that would take the exactly the same ohms as what the power amp is pumping out?

 

[Artie]

Re: Power Amps 101

for a guitar amp/cab combo you usually dont want to over power a cab so if you have a 100w cab a 100w amp is as high as you usually want to go.

100w is 100w best not to risk it

Jeremy; I don't know if it would be different in a guitar application, (I don't think so), but generally, (with SS), you want twice the amp power compared to the speaker rating. (3db headroom.) The reason for this is that the speaker rating is usually its RMS, or continuous rating. It can generally handle peaks of twice that amount. Note that almost all guitar speakers have a peak rating of twice their RMS rating.

On the amp side of things, you still want the power to be clean, (unclipped), for those peaks. Ergo, double the amp power. I would use a 200WRMS amp, or 100WRMS x2 with that setup. And again, I'm only refering to SS here. Tubes is a whole 'nother animal.

 

[ShredFetus]

Re: Power Amps 101

Most guitar power amps are switchable between 16/8 and sometimes 4 ohms, so that should make things easier with cab choice. I was considering running through a solidstate PA amp type thing for a while, but often they are only suited for 2/4 ohms.

 

[Benjy_26]

Re: Power Amps 101

I try to match the power amp to the speaker cab's ohm rating.

If you plan on using it with a modeler, try to get one with1/4" inputs and outputs. It'll make it easier to use in a guitar rig.

BTW, I don't think a ME50 will be the best choicð

 

[jeremy]

Re: Power Amps 101

artie, for pa and bass applications you are totally correct but you are also trying to get a "clean" sound.
speakers dont like disortion so if you put 200w of raw distorted tone thru a 100w speaker its very possible youll kill it.

ss amps dont usually have switchable impedance, tube amps do. a ss amp will run at different loads but give you less power at higher impedances