Guide Needed for Bass Amp Head and Cabinet
 

Hi guys,

I'm trying to get an amp head and a cabinet but I dont really know how to mix and match the wattage and the ohms of the heads and cabinets.

In the event that I can find a matching wattage and ohms, what is the allowance of wattage btw the two? Or which can be higher than the other (in terms of both wattage and ohms)

Im looking at 250 watts, 4ohms / 180 watts, 8ohms bass amp head (think it has a dual mode) and either a 200 watt, 8ohms or a 300 watts, 4/8ohms.

Any help would be greatly appreciated!!! Thanks in advance :)

Any amp can play with (virtually) any cab.

To get the best out of a cab you should have around half the cab rated power on tap as a minimum.

The more power you have the easier you can blow up the cab if you don't pay attention to the cab complaining. But all amps have volume knobs.

Solid state amps have a minimum ohm loading. Ohms go down rapidly as more speakers are connected in parallel. Most are 4 ohm capable, so an 8 ohm cab is preferable, that you may add another identical cab later.

Older SS amps make more power into their lower ohm rating. This is generally not a reason to go for a 4 ohm cab. Most amps will drive the comaprable 8 ohm to the same volume level, only providing greater potential to blow up the 4 ohm one.

Sorry I dont quite get this, what do you mean by this? So shouls I get a higher wattage amp head than the cab? Or should my cab be preferably be higher wattage than my amp head?

Thabks in advance! :)

If your amp has at least half the rated power of the cab you aren't over investing in cab relative to amp. It's not a hard and fast rule or a target to aim at but if you find stuff for sale that meets the "standard" you can be confident it will make a bass noise.

I'm making mountains out molehills.

Your band volume requirements and budget are more to the point than any ohm power considerations. Generally a 300W (4 ohm) amp is held up as guaranteed for good clean fun. Find a cab and an amp and come back with more questions.

Too many speakers and not enough power will "overload" the amp... This is bad mmm k? ;) SS (solid state) amps have a min ohms level output per channel (sterio) typically and can be bridged together (bridged mono) if they have bi-amp capability for full amp power from 1 of the 2 outputs, usually the "left low" channel (make sure you read the owners manual to your amp!!). As long as your minimum ohm level on the cabinet is matched with, or greater than the minimum level output on the amp (8ohms Vs. 4ohms min load), and the amp is capable of delivering at least 1/2 or better (I like to go 3/4s (or more than the RMS watts of the cabinet and be careful of volume!!)) power of the RMS power handling of the cabinet, you should be fine. If you're going to eventually be running more than one cabinet, say two 410's, I would make sure your cabs are 8ohm cabs... That way, you can "daisy chain" (connecting the cabs together as 1 unit for the amp) the cabs together for a 4ohm min load on the amp and run the amps full power bridged mono. That's what I do ;) You can't do this safely with 4 ohm cabs unless your amp can handle a 2ohm load!! Just make sure your amp can handle at least 1/2 the power rating of the cab(s) or you'll overload the head and blow it up! Too much power to the cabs and you can blow them up if you're not careful ;) To answer your origional question, the cabinets can have more power handling capability RMS than the amp head... Just make sure the amp has a minimum of 1/2 or better power than the power handling RMS of the cabinet(s). For example: 750w or 1kw amp head paired with a 810 cab that has 1200w RMS. This would be ok and plenty loud btw!

Nonsense. You seem to be associating the "number of speakers" with the minimum load, but that is a false association.

To the OP, pay attention only to the part about the impedance (ohm) minimum load.
That's just baloney, please do not spread such garbage around.

The amp does not EVER "handle" the power rating of the cabs. A claim like that doesn't make sense on any level. An amp produces power, and cabs receive and use that power. The amp could put out 1 watt continuously and a cab rated for 2000 watts will handle it just fine, and nothing AT ALL will happen to the amp.

When he said:
He meant:
IOW, he was not saying you "should" have an amp rated for half the power of the cab, but that that's a very safe bet to start with. Be sure to re-read the other lines of his post, because there are useful truths there--basically, if the cabs start to complain (making farty clippy noises) then you need to turn down the volume on the amp. This will be the guiding principle to use no matter what wattage any amp or cab is rated for. The best way to reduce that problem generally is to buy cabs that have higher wattage ratings. You'll still have to listen to them and use common sense, but the higher the rating of the cab, the more power it is designed to handle before destructing.

Note: I made a major edit there!

Ah ic thanks all for the replies!!

As my hartke 1415 combo amp head is a little spoilt and hartke doesnt produce that anymore, no shops want to repair it for me. I tried repairing it myself but to no avail. When I jack in my bass, slight movement can cause sudden massive noise and cause the cab to move in and out vigourously. I tried soldering out an extension (a new jack) but the same problem persist and I dont know what's wrong with the jack.

Anyway I was thinking of getting a seperate amp head and replacing the hartke 1415 combo head. But the lowest wattage amp head I can find is the hartke HA2500 (250 watts) and the 1415 combo is 140 watts... so by plugging in that head into the cab that I have... it'll blow the cab no doubt?

It will be a little risky, but you can do it as long as you listen for those distorting noises, and turn the volume down until the distorting sounds go away. You can get back some volume by turning down the low EQ knob instead of turning down the volume knob, because the lows use the most wattage and move the speakers most. So reducing the lows reduces the amount of potential speaker damage, without cutting the overall comparable "loudness".

Ah ic, thanks to everyone who helped me on this topic :)

Another question, what is the difference between a 400 watts bass cab 4x10 and a 400 watts 1x15? Apart from the obvious 4 cones and 1 big cone xD

Cabs can have lots of differences in how they are "tuned", which means they can have a wide range of differences in how they sound based on the dimensions of the box, any porting, and internal structure. So one 410 can sound different from another 410.

If you were looking at a hypothetical410 and a 115 where "all else is equal", the 115 has less speaker surface area, so it will not be able to push as much air as the 410, so it will not have as much volume or low-end projection as the 410.

I think you've got my words mixed up and don't understand me or the points I was trying to make, either that or I didn't explain it clearly enough...

:scowl: I speak from experience about overloading amps. I've blown up 3 different power amps (individual situations) trying to run more than one cabinet where my amp wasn't powerful enough to power the cabinets together!

This is neither "garbage" nor "baloney."

I was just trying to help this guy so he doesn't make the same costly mistake I did by trying to run too many cabs (speakers) together with not enough power out of the amp to the cabs! Hence, overloading the amp ;)

In the 3 amps I blew up (not at the same time)... I had to replace a fuse in one amp (got lucky) but the other 2 I fried them (individual situations) beyond repair...

My cabs were fine because they could handle more power together than the amp could produce, but the amps were toast because I overloaded them! This was partially my fault though because I was trying to run the amp at a high volume to be heard in a band situation. My set up at that time probably would've been fine as a practice amp deal where I would'nt have had to turn up the amps "gain" and "volume" as much. But, I had to be heard in the band I was playing for at that time and made a few mistakes and learned my lessons after replacing 3 different amp heads.

Seriously!?? I know most cabs don't produce power! :spit:

There are some cabs that do "produce power" however FYI... In fact, GK has a whole new line of "powered cabs" in their series, look it up if you don't believe me...

You are right about this part though... The cabinet will in fact handle the amps power "just fine", but, you are WRONG in this same situation that you depicted because it IS in fact overloading an amp trying to push a cabinet capable of handling that much power... Especially if you want to be heard and turn up the amp :smug:

Lol, you could send all of "1 watt continously and a cab rated for 2000 watts" but you probably wouldn't hear much out of the cabinet (speakers)... In trying to do so, you would blow up the amp or at minimum, blow a fuse in the amp :D

Subscribed. :rollno::rollno:

What is garbage and baloney is the reason you attribute to the blowing of your amps. It is not because they were not powerful enough. It is because you asked them to produce more current than they were capable of. The fact that you blew a fuse is evidence of that. Fuses blow because they reach their limit of current. Power is voltage times current. In terms of voltage, an amp will produce only what its power supply can provide and that is essentially a constant. The variable is the current. According to Ohm's Law, current is voltage divided by impedence. If the impedence gets too low the current becomes very high which leads to blown fuses or, at worst, blown amps. The reason your amps blew is because the impedence was too low for the power they were driving.

Short version: the amps blew up because you connected them to too low of a total impedance. NOT because there were too many speakers, and NOT because of the wattage ratings of the amp or the cabs.

Yep...........

User error plain and simple.

Yup, it was and I had to learn it the "hard way"

Wow ok thanks alot to all who contributed here!! I really learned alot :)