what is needed to drive a power amp?

NateS · #1 10-01-2010, 11:45 PM

Hey all,

I have a seemingly simple question - in order to feed a power amp, how much signal is needed?

I've heard of people using various pre-amp pedals to run power amps without a seperate pre-amp module in the rack.

i have in my possession a yamaha EM-100 powered mixer, that can send a signal out through the monitor mixes outs at "+9dBm (2.2v), 5k ohm".

I want to feed these stereo outs into the seperate channels of my Ampeg B4-R head, but the manual for the B4-R has little info of specs...

will this work? I won't be able to test it until monday, but would like for someone else to say it'll work before i try it and damage something...

and, if this does work, should i use a speaker cable or a normal instrument cable?

bongomania · #2 10-02-2010, 12:29 AM

In the FAQ linked in my sig there is an article that answers most of these questions. The Yamaha is more than enough for any power amp.

The one thing is, the two inputs on your amp are not suitable for stereo input. They are not intended to work as a two-channel mixer, and the results will be lame.

Instead, just pan all of your audio hard to L or R on the mixer, and take just the one L or R monitor output from the mixer and feed that into the Ampeg.

Speaker cables are only for speakers. Instrument cables are good for what you want to do.

Son of Bovril · #3 10-02-2010, 01:10 AM

IME the preamps in most live mixing desks are not well suited to giving a great bass sound but maybe yours will give you the sound you are looking for...

what exactly is the purpose of doing this by the way, do you not like the sound from the pre section of your ampeg?

NateS · #4 10-02-2010, 06:35 AM

thanks for your help, you two! bongo, i'd read parts of your FAQ before bt i hadn't seen that one article, thank you.

the mixer gives an alright sound that i've beeen able to hear - feeding the two outputs into the two two inputs of my tascam. The main reason that i want to try this is that i was messing around with my pedals, and found that using the yamaha, i could finally use the stereo outs of my delay pedal for ping pong, which sounds awesome. i then also worked in the effect only output of my BSW, and finally got to where i'm using 5 of the 6 inputs of the yamaha for different parts of the sound. It's not so much that i don't like the pre section of the ampeg i'm thinking that if this functions nicely i'll draw my clean tone from that instead of the mixer.

Bongo, you said that the ampeg's power amp nput may not function as i intend to use it, why would that be? It struck me as the way it's meant to be used, unless i'm missing something.

bongomania · #5 10-02-2010, 12:19 PM

Quote:

Originally Posted by bassk81976

Bongo, you said that the ampeg's power amp nput may not function as i intend to use it, why would that be? It struck me as the way it's meant to be used, unless i'm missing something.

I didn't know (until I Googled it just now) that the B4R was a stereo unit.

I thought it was a mono head, like most others, and the two instrument inputs on those aren't meant for mixing. Assuming you have the amp and cabs wired up for stereo, then your plan will work.

NateS · #6 10-02-2010, 01:15 PM

Quote:

Originally Posted by bongomania

I didn't know (until I Googled it just now) that the B4R was a stereo unit.

I thought it was a mono head, like most others, and the two instrument inputs on those aren't meant for mixing. Assuming you have the amp and cabs wired up for stereo, then your plan will work.

Ah, I see what you mean. So the stereo power amp is to do what I want. If I take the pre-amp in, I can feed that into the mixer as a clean tone (assuming the input of the amp is the clean pre-effects) at line level?
This seems like it could be epic.

I know it sounds good through the tascam, I just hope it comes out the same through speakers.

Jerrold Tiers · #7 10-02-2010, 09:33 PM

Your 2.2V should be more than enough to drive the B4R power amps. They should take only about 1V to drive them.

NateS · #8 10-02-2010, 09:36 PM

Quote:

Originally Posted by Jerrold Tiers

Your 2.2V should be more than enough to drive the B4R power amps. They should take only about 1V to drive them.

it wouldn't harm them to be receiving double the voltage to drive them, would it?

it's also very awesome that there are legit tech people no here that WORK for companies (Not discounting Bongo at all, I have TONS of respect for him!)

T-Bird · #9 10-02-2010, 10:19 PM

Hi.

Quote:

Originally Posted by bassk81976

it wouldn't harm them to be receiving double the voltage to drive them, would it?

The inputs won't recieve double the voltage unless You feed that to them

. Inputs are also rather forgiving on most amps, the only thing that will happen is that the distortion increases, most times into clipping, but even that won't harm Your amp. Your speakers on the other hand can start complaining.

With any system, even with a more "matched" one, You often need to determine what gain structure gives you the best results. When the output signal of the "pre-amp" and the sensitivity of the power amp are close to eachother usually gives the most power with the least noise.

Regards
Sam

NateS · #10 10-02-2010, 10:29 PM

oh yea >_> that's what the volume knob is for...

thanks for all the help, everyone - i greatly appreciate. Monday i will try out my hopelessly over-complicated system on an actual rig! Very excited!