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-   -   Solid state power amp (http://www.ultimate-guitar.com/forum/showthread.php?t=1576320)

GuitarUser 12-04-2012 07:34 PM

Solid state power amp
 
Hey guys,
I need a solid state power amp that should be loud enough for gigs, but I don't know much about these. I often use my gainiac on the return of whatever is available, but now I want my own power amp, so I'll be just borrowing the cabs lol.
I'm looking at some local brands (because I live in Brazil, and a rocktron velocity here is kinda expensive) and I found some really cool stuff, they are not really made for guitars but a power amp is a power amp, right?
The problem, is that I have no idea on how much power should do.
I was thinking about this one, it's a bit more expensive than some others with the same features, but it's light as hell (2.5 kg).
http://www.hotsound.com.br/spa_2150.html
It says:
Total power @ 4 Ohms 1% THD max. - 300 W (2x150w)
Total power @ 8 Ohms 1% THD max. - 150 W
I don't really understand what that means, as I'll be using only 1 channel (right?).
Can someone help me?
Is that enough power for gigs?
What about this impedance thing?
Thanks in advance!

woad_yurt 12-04-2012 09:36 PM

Can you get a Crate Powerblock? They're small and light and wigh 4 pounds or so. Would shipping be a lot from the USA? I ask because they're on eBay often enough for pretty cheap. I have one and love the thing. 150 watts, too.

It is definitely loud enough for gigs.

FatalGear41 12-04-2012 10:30 PM

Solid-state power amps are usually pretty reliable. That company is not well-known in the U.S.A., but if they've been around for 20 years, they must be doing something right.

The specs mean that when used with a 4-ohm load (two 8-ohm or one 4-ohm cabinet), you'll be driving 150 watts per channel, or 300 watts if you bridge the two channels of the amplifier into one channel. With an 8-ohm load, your levels will be one-half that of a 4-ohm load.

Even at 150 watts, that should be more than enough to cause people to lose control of their bowels in a club. If you are going into a cabinet, make sure it can handle the power load.

What you must remember, though, is that a power amplifier has no equalization controls. In other words, it has no tone controls. You'll need a preamp with equalization controls or you are going to sound horribly sterile. You'll need a preamp just to get your guitar's signal up to line level anyway.

A few guitarists have made a career out of using a sweet preamp into a run-of-the-mill power amp. All the power amp is doing is amplifying the signal. The good ones don't color your tone much. You get your tone from the preamp. There are a lot of good preamps out there, and some of them are quite reasonably priced. Let us know what brands are available in your sector and we can give you better assistance.

Good luck!

gumbilicious 12-04-2012 10:58 PM

a power amp is pretty much a power amp.

speakers come rated with an impedance, which is simplified as 'how much the speaker resists electric current. speakers (and speaker cabinets) are generally rated 4 ohm, 8 ohm or 16 ohm. depending on how many cabinets you run and how you connect the cabinets (if you run more than one) then the impedance the amp 'sees' changes.

for example, if you run two 8 ohm cabinets in parallel (parallel connection is generally how it connected) then the total impedance the amp 'sees' is 4 ohms.

solid state power amps don't have an output transformer, they provide max output at their min impedance ratings. you can always connect cabinets rated at a higher impedance, but it lowers the output of the amplifier.

Quote:
Originally Posted by GuitarUser
It says:
Total power @ 4 Ohms 1% THD max. - 300 W (2x150w)
Total power @ 8 Ohms 1% THD max. - 150 W
I don't really understand what that means, as I'll be using only 1 channel (right?).


since the amp is 'stereo', then it means it has a Left and Right output. combining outputs is referred to as 'bridging', this is also called 'running the amp in mono'.

most likely you will be running the amp in mono. this means that if you want to get 300 watts out of the amp then you need a[n exactly] 4 ohm cabinet rated at [at least] 300 watts.

if you use an 8 ohm rated cabinet then your cabinet only needs to be rated at 150 watts


Quote:
Originally Posted by GuitarUser
Is that enough power for gigs?


most likely. 300 watts is a considerable amount of power for a guitar amp, even 150 watts is quite a bit.

a 95 dB sensitivity speaker pushed at 150 watts is like 116 dB which is really loud. 95 dB is actually a bit of a conservative rating for a speaker, and you most likely won't be running the amp full out. but that 116 dB is roughly a conservative ballpark number of the volumes you can attain with that amp, and that should prove to be enough.

Quote:
Originally Posted by GuitarUser
What about this impedance thing?


you can get a 4 ohm cabinet, or you can daisy chain (connect two amps in parallel) two 8 ohm cabinets together for a 4 ohm load.

GuitarUser 12-05-2012 12:10 AM

Quote:
Originally Posted by woad_yurt
Can you get a Crate Powerblock?

Actually, I'm looking into rack mounted stuff... thanks


Quote:
Originally Posted by FatalGear41
Solid-state power amps are usually pretty reliable....You'll need a preamp just to get your guitar's signal up to line level anyway.

Yes, that's why I'm moving to them. Well, I have a rocktron Gainiac 2. It does the job.


Quote:
Originally Posted by gumbilicious
combining outputs is referred to as 'bridging'

How do I bridge?

Quote:
Originally Posted by gumbilicious
cabinet rated at [at least] 300 watts.

What if it's rated lower than 300w or 150w?


Thanks a lot everyone.

GuitarUser 12-05-2012 12:22 AM

Sorry for inconvenience, but, how would I hook the stuff with the following examples?
http://images.miretail.com/products...binet_input.jpg
http://intercitymusic.co.uk/Marshal...input_plate.jpg
http://www.musiciansbuy.com/mmMBCOM...nput%20Jack.jpg

gumbilicious 12-05-2012 12:32 AM

Quote:
Originally Posted by GuitarUser
How do I bridge?

usually there is a switch on the back to run the amp in bridged or stereo mode. it is usually near the speaker outs.

Quote:
Originally Posted by GuitarUser
What if it's rated lower than 300w or 150w?


if the cabinet is rated below the output of the amp, then the speakers will be stressed. some people actually find this favorable, they call it 'rounding' the speaker or speaker distortion. this may reduce the life of the speaker, much the same way driving really fast in a car reduces your tire's life.

if you run too much power through the speaker then the voice coil will get more current than it is rated for and could become damaged by melting the coils. technically you could also cause over-excursion of the speaker cone and pop a speaker (though melting the voice coil is much more probable).

Quote:
Originally Posted by GuitarUser

assuming the amp is bridged

A - run a speaker cable to the jack
B & C - run a speaker to the right jack cuz that is the one rated for mono

A - is rated at 8 ohm so your amp's output would be 150 watts
B - is rated at 8 ohm mono so your amp's output would be 150 watts
C - is rated at 4 ohm mono so your amp's output would be 300 watts

GuitarUser 12-05-2012 12:45 AM

Quote:
Originally Posted by gumbilicious
if the cabinet is rated below the output of the amp, then the speakers will be stressed. some people actually find this favorable, they call it 'rounding' the speaker or speaker distortion. this may reduce the life of the speaker, much the same way driving really fast in a car reduces your tire's life.
if you run too much power through the speaker then the voice coil will get more current than it is rated for and could become damaged by melting the coils. technically you could also cause over-excursion of the speaker cone and pop a speaker (though melting the voice coil is much more probable).

I see, but... This is only gonna happen if I use it for a long time right? Or may it happen with like 30 minutes of use?


Quote:
Originally Posted by gumbilicious
assuming the amp is bridged

A - run a speaker cable to the jack
B & C - run a speaker to the right jack cuz that is the one rated for mono

A - is rated at 8 ohm so your amp's output would be 150 watts
B - is rated at 8 ohm mono so your amp's output would be 150 watts
C - is rated at 4 ohm mono so your amp's output would be 300 watts


I might be saying shit, but..
At A, won't I burn something? Because the power amp output is rated 4ohms and the cabinet input is rated 8ohms? I heard that when you put something with a lower impedance than the speakers, you are gonna burn one of them.



Sorry for my lack of knowledge. Thanks a lot for your help!

Cathbard 12-05-2012 12:52 AM

A solid state amp will tell you the minimum impedance you can use. If they were worried about higher impedances don't you think they'd list a maximum impedance as well?

gumbilicious 12-05-2012 01:01 AM

Quote:
Originally Posted by GuitarUser
I see, but... This is only gonna happen if I use it for a long time right? Or may it happen with like 30 minutes of use?


no one call tell you, it all depends on the situation. you could blow the speakers out on the first strum, it could be fine for months and months.

the best bet is to start the amp off low and raise the volume (lower volume = less watts the speaker has to deal with).

as you raise the volume you will hear the speaker starting to distort, and as the distortion grows worse the speaker starts to sound really bad. you want to avoid that, it means the speaker is getting way too stressed.

note how high you can get the volume on the amp and don't go beyond in the future.

Quote:
Originally Posted by GuitarUser
I might be saying shit, but..
At A, won't I burn something? Because the power amp output is rated 4ohms and the cabinet input is rated 8ohms?


as cath (and i) mentioned earlier, the solid state amp only has a minimum impedance you must observe. any impedance higher than the min impedance will just reduce the amp's output. so your amp outputs 300 watts @ 4 ohms and 150 watts @ 8 ohms, so this means your amp will prob output something like 75 watts @ 16 ohms.

Quote:
Originally Posted by GuitarUser
I heard that when you put something with a lower impedance than the speakers, you are gonna burn one of them.


if you have a tube amp, then it has a transformer before the signal is sent to the speaker and you need to match the impedance. if you have a severe mismatch then the amp could be damaged.

GuitarUser 12-05-2012 01:14 AM

so CABINETS doesn't have a minumum impedance rate?

Cathbard 12-05-2012 01:17 AM

The cabinet is what it is. Some will have a switch to go between two values but once you hit the switch it is what it is. It doesn't give a crap what's connected to it as long as you don't try to pump too much power into it. It's the amp that cares about impedance and a SS amp only cares about the minimum impedance you can hang off it.

gumbilicious 12-05-2012 01:19 AM

Quote:
Originally Posted by GuitarUser
so CABINETS doesn't have a minumum impedance rate?


:confused:

the cabinet has a 'fixed' impedance and it will depend on the speakers that are in the cabinet and how they are wired together.

speaker cabinets provide the impedance, an amp needs to 'see' a certain impedance from the cabinet.

if your solid state amplifier has a minimum impedance requirement of 4 ohms, then the amplifier needs to see a cabinet that provides 4 ohms or more.

GuitarUser 12-05-2012 01:23 AM

OK GUYS, I FINALLY UNDERSTAND LOL.
Thanks a lot for your patience.


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