Could you help me find the better amp power for me?

[bassgod0dmw]

You've got a mix of heads and cabs there.

I'd take the Gallien Krueger RB-400 III that you list, but that only leaves you 150 left over for a cab. If you could swing the Hartke 4.5 XL that would be a pretty nice rig.

[J.Nuno]

Oh, I know 350 will hardly be enough

So the head has 280W at 4 Ohms and the cab 400 at 8 Ohms, meaning that the cab is more than enough to take the head's full power, but the head doesn't have the standard 300W, right? Would this rig still be enough?

[bassgod0dmw]

Originally Posted by J.Nuno

So the head has 280W at 4 Ohms and the cab 400 at 8 Ohms, meaning that the cab is more than enough to take the head's full power, but the head doesn't have the standard 300W, right? Would this rig still be enough?

The head is going to put out less power at 8 ohms, probably around 150w.

300w is just a figure that is generally agreed upon to be a good starting point. More or less is not bad, just a situational thing. Some bassists push 1000w or more, and some do fine with 100w.

I can't say if it will be enough for you. I know it would be enough for me. My band is a 3 piece and we play reasonably loud but nothing crazy. In fact, I'll be gigging an older/original 400RB this weekend

I will say that GK heads are known for their honest power ratings and being very loud despite having "less" power than some competitors.

[96tbird]

Ohms. That's the resistance of the speaker array. 4 ohms is standard when stating amp power: 300 w into 4 ohms.

Plug an 8 ohm cab into the same amp and your watts will drop by about average 30% +- ymmv.

Now when you run 2- 8 ohm cabs, you will get 4 ohms resistance and full watts.
Why? think of water. You have two taps and 100 lbs pressure; open one and pressure remains constant. Open the other and it drops in both. Watts = pressure, ohms = points to release/reduce pressure. Easier work for the pump.

If you get an 8 ohm cab, you have the option to add cab for 4 ohms. You'll be moving more air with more speakers so it will be louder. Plus your head will develop full wattage.

If you got a 4 ohm, dead end because if you added another 4, there's not enough resistance, 2ohms, and you'll cook the amp.

A 410 8 ohm will give you lots of volume and your 300 watt head will be developing 200 watts, +- ymmv.

[J.Nuno]

Thanks again guys.

So before I begin to starting choosing which rig I’ll get I’d just like to ask you to check now if I got it all right this time.

So, hypothetically:

Using, say, a 300W head at 4 ohm, I can plug either a 4 or 8 ohm cab. If I use a 2ohm cab, there is not enough resistivity, the speakers will work off limits, may overheat and, as I’ve read elsewhere, may catch on fire!

Regarding the power: If the cab is 8 ohm, then the wattage from the head drops below the max 300W so if the cab is 300W that’s more than enough. If the cab is 4 ohm, than the head gives full wattage and the cab really has to be at least the 300W.

When plugging 2 cabs instead of one, if 2x 8 ohm cabs are used the total resistivity is 4 ohm, so the head will give full power (300W). Ohms are all good here but each cab needs to be at least 300W to support it.

So far, did I get it all right?


What still gets me a bit confused is when: 2x 4 ohm cabs are used. Here the total ohms are 2ohm. And in this case I’ve read that the amp (I assume the head) can’t handle such power from the load (that is, the cabs) and fries. But wasn’t it supposed to be the cabs that, being 2ohm when combined be vulnerable to the head and possibly fry?

[bongomania]

You got it right for the first bit, but missed on the last two paragraphs.

With two 8 ohm cabs, each only needs to handle half the wattage put out by the amp. Now, it's best to have a little safety zone anyway, because cab ratings are highly optimistic. So while you'll get by just fine if each was rated only 150 W, a higher cab rating is even safer.

The problem with the 2 ohm load is that the AMP will overheat. The speakers will probably be fine, unless the amp puts out a big wattage spike when it blows up.

[96tbird]

You also said a cab needs X watts to support it. No. You can run any cab with any watts but If your amp makes too many watts and you use too much volume you will blow a speaker.
You could also use an 800 watt speaker with a 300 watt amp. It could take 100% of the amps output would work and sound great until the amps limits are reached and severe distortion will result.

[J.Nuno]

Ok, let's try again, I'm starting to feel dumb :

Let’s split this in 3 parts.

1- Once we have 2 cabs instead of one, the power from the amp is split between the 2. So, with the 300W head, with 2 cabs, the max power that is going to be directed at each cab is 150W tops. Right? So with 2 cabs, half of the power of the single 300W cab becomes useless as only 150W of it will be used with this head?
By the way, in a case like this, would 2 exact same cabs (150+150 split) be much louder than 1 (full 300W)?

2- So the cabs don’t need the minimum Watts to support the head? The other way around I get it fine, 800 watt cab is ok to use with the 300W head because when the head has maxed the cab is still far from its limit (in this case, even though there is no physical damage to either parts, sound gets unpleasant when the head reaches its maximum power). But, if the cab’s power is 150W and the head 300W, doesn’t that mean that with the head at only 50% would already be pushing the cab to its limits?

3- So problem with the Ohms is that… 4ohm is kind of the standard lower limit of the heads? So, if a single CAB’s ohm is lower than the 4ohm of the head, the cab will fry. BUT, when there are 2 CABs, if their combined resistivity goes below 4ohm (say 2ohm) they will “demand” too much from the head and now the head will fry and not the CABs? Is that it?

Thanks for your patience, but I just like to understand this things to detail instead of just knowing what equipment to use

[RickenBoogie]

Cabs don't "make" watts, they "handle" them. Don't get hung up on wattage ratings. 2 identical cabs will split the amps power between them. I say identical because if you paired a 410 with a 115 for example, the 410 divides it's HALF of the power between 4 spkrs, while the 115 has to handle the entire load. And the word is impedance, when talking about a spkr cabs "ohms". So, most amps have a MINIMUM impedance of 4 ohms. You can run any combination of spkrs that add up to 4 ohms or anything higher, but cannot go below the minimum. And, it's always best to use two identical cabs with an amp, thus assuring that all spkrs are recieving equal power, and working together to create a BIG bass sound. And yes again, a spkr cabs wattage rating is generally the point at which the voice coil will overheat, so mechanically, they usually "handle" LESS than their rating- but you can use a 1000 watt head with a cab rated at 200 watts, IF YOU'RE CAREFUL, and likewise, you can run a 100 watt head through a cab rated at 800 watts without issue. Hope this helps.

[devilman666]

3x the power that the guitards are useing. So guitar head is 100 watts solid state then bass amp should be 300watts sold state .

[BassmanPaul]

Originally Posted by devilman666

3x the power that the guitards are useing. So guitar head is 100 watts solid state then bass amp should be 300watts sold state .

I prefer the 5x to 10x the guitar amp for my purposes.

[Zoa]

Originally Posted by J.Nuno

Ok, let's try again, I'm starting to feel dumb :

Let’s split this in 3 parts.

1- Once we have 2 cabs instead of one, the power from the amp is split between the 2. So, with the 300W head, with 2 cabs, the max power that is going to be directed at each cab is 150W tops. Right? Yes.

So with 2 cabs, half of the power of the single 300W cab becomes useless as only 150W of it will be used with this head?Not exactly sure what you mean here, but I am pretty sure you are misguided. Cabs to not make power, they can TAKE up to a certain amount (the wattage rating, though it is badly exaggerated in most cabs) from the head. In other words, a head's wattage rating is how much it puts out into a cab, a cab's wattage rating is how much it can take with out blowing up.
By the way, in a case like this, would 2 exact same cabs (150+150 split) be much louder than 1 (full 300W)? Yes they would.

2- So the cabs don’t need the minimum Watts to support the head? The other way around I get it fine, 800 watt cab is ok to use with the 300W head because when the head has maxed the cab is still far from its limit (in this case, even though there is no physical damage to either parts, sound gets unpleasant when the head reaches its maximum power). But, if the cab’s power is 150W and the head 300W, doesn’t that mean that with the head at only 50% would already be pushing the cab to its limits? This is correct.

3- So problem with the Ohms is that… 4ohm is kind of the standard lower limit of the heads? So, if a single CAB’s ohm is lower than the 4ohm of the head, the cab will fry. BUT, when there are 2 CABs, if their combined resistivity goes below 4ohm (say 2ohm) they will “demand” too much from the head and now the head will fry and not the CABs? Is that it? Doesn't matter if there is one cabinet or 300, if the resistance slips below the minimum, the head will fry.

Thanks for your patience, but I just like to understand this things to detail instead of just knowing what equipment to use

No problem. I advise getting a head with at least 200w (the GK 400RB is a fine choice for a first head) and an 8 ohm cab of some sort. If you need more volume, add a second cab of the same type. DO NOT mix cabs. What genre and how loud do you play, by the way?

[J.Nuno]

Prog Rock/Hard Rock are the main genera. It can get pretty loud .

[Downunderwonder]

Originally Posted by J.Nuno

Gallien Krueger RB-400 III - 200€
Trace eliot gp7sm head - 120€
Eden D112XLT Neo - 375€ (2x)

Are any of these good choices? (just to begin to learn what is good and what is bad).

The last 3 just have too little power right?

What rating is the Trace?

Here's the thing about ratings, they don't mean a thing until you play with the gear and see if it is any good.

Trace ratings are very conservative. Mine is a 250 but nobody would guess that comparing it with other amps blindfolded. It spits out 500W peaks that aren't distorted very much at all.

Most older amps are capabable of a lot more peak power than their rating. That was how it was done in the old days.

Everyone is so hung up on ratings that telling little lies has turned into telling big lies to sell equipment. Ratings on new gear are often Peak Burst Power, whatever that is, or RMS Music Power, another elusive measure. My estimation is my 250W amp would be at very least 500W on the shelf today.

Is the 2x 112 Eden cabs the pair for that price? It's enough cab to go a long way with either of those amps.

My advice is try to stay away from 4x10 type cabs with sideways mounted speakers. They don't have good dispersion for when your rig carries a whole room by itself with no PA.

Two 2x10 stacked up makes a great rig.

The bass problem:

The low frequencies take far more power than the higher frequencies to make them heard. The speaker must travel further with each sound wave made. If you cut back the lowest frequencies you can feed much more power before the speakers break. Manufacturers now take the fall back position that cabs are rated for melting with 1000hz thermal handling only, almost meaningless.

Even in the olden days of 1995, cab manufacturers were stretching the truth with cab ratings.

Roughly speaking, to give you half a clue, cabs rated double what the amp claims, will go a bit loud with that amp. You still need to be careful not to blow them up with low end if you want to crank the amp up to the max.

The 300W amp rule is pretty good for rock bands, nevermind my 250W amp blows away "300W" amps of today.

Something else to know since I ended up writing a book here. Amps often go as loud as they will go at less than 5/10 on the dial.

[J.Nuno]

Thanks for the help Downunderwonder!

The model of the Trace ends with "130" so I assume 130W?


"Here's the thing about ratings, they don't mean a thing until you play with the gear and see if it is any good."
I understand, but the problem is...I don't get to try most of the used things because thei're almost always far way. I can't drive 300km just to try an amp. So, for now, while I'm a virgin on the amp+cab rig situation, I have to rely on people's opinion and advice

[bassgod0dmw]

Originally Posted by J.Nuno

The model of the Trace ends with "130" so I assume 130W?

That might be true but don't assume it, just to be safe.

[Jeb]

I've done this for many years and I'm not the most technically inclined with all the verbage. But what I know is that the more watts the better. Back in the 80s I gigged a 250W Cerwin Vega head on a CV 2x15 cab. Huge rig and I hated it. Today I gig a Carvin Bx500 on top of a GK MBE2x12 (4ohm standalone) cab. Half the size, 1/3 the weight and twice the performance. I keep a Peavey TNT 1x15 combo in the rehearsal room, I practice new songs with a little amp with RCA inputs for the mp3 player and a headphone jack - and take the Carvin head/GK cab to work. I ran a separate pre-power amp rack over a Avatar 2x12 and enjoyed excellent performance, but I have to load and unload every weekend so the lightweight class D stuff that I've been using for the past two years has worked well and I wouldn't change a thing. For now.

[Jeb]

Wow, didn't know that my post would be a commercial with those blue links showing up. Let me just say that the blue links in no way represent my endorsements. Talk bass, you're welcome for my contribution. I won't attempt to charge you anything for that.

[bassgod0dmw]

That's probably only showing up for you.

Spyware or a plugin of some sort would be my guess.

[smogg]

That GK head will pair up nicely with the Hartke cab. It'll rock small/medium rooms no problem. I ran two XL410 cabs with an RB head from the late 1980's through most of the 1990's. Always had great tone for hard rock and what is now old school metal.