I am shopping for a cab and head to pair together. I get confused when thinking about matching watts and ohms, in other words, if I buy two used pieces, how do I know they are compatible?
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Rookie Question - Amp and Cab
- Thread starter riffermsytic
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What two pieces are you looking at specifically? Or just give examples of what you are considering. I would also start reading the Amp FAQs posted at the top of the forum.
Watts and ohms don't need to be matched..... Minimum ohms of the amp and ohms of the cabinet do.
If your head is minimum 4 ohms, you must use a cab of 4 or up. MOST Solid state Amos are minimum 4ohm.
If your head is 200 watts:
*your cabinet should handle 200 watts at the very least: you will have to be careful not to blow it by driving it to the limit of excursion or heat.
You can use a lower rated cab, but you will have to be VERY careful!
*You can use a 1000 watt cab but if you drive the amp too hard and it distorts the signal, you can burn the speaker coil.
*Now, if you want a modular setup that you can add a cab to later, you would want 8 ohm cabs. Two 8 ohm cabs together calculate to 4 ohms total. This is the most effective way to increase volume.
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Think of ohms this way: one cab is 8 ohms pushing against the amp restricting the flow. Add another cab and the amp now can dump energy into two paths and the resistance it experiences drops.
If resistance drops too low, the amp will electronically "run away" and overheat and die.
But adding two cabinets at 4, increases the speaker AREA therefore moving more air, therefore adding volume.
So, how many watts is the head you're looking at?
If your head is minimum 4 ohms, you must use a cab of 4 or up. MOST Solid state Amos are minimum 4ohm.
If your head is 200 watts:
*your cabinet should handle 200 watts at the very least: you will have to be careful not to blow it by driving it to the limit of excursion or heat.
You can use a lower rated cab, but you will have to be VERY careful!
*You can use a 1000 watt cab but if you drive the amp too hard and it distorts the signal, you can burn the speaker coil.
*Now, if you want a modular setup that you can add a cab to later, you would want 8 ohm cabs. Two 8 ohm cabs together calculate to 4 ohms total. This is the most effective way to increase volume.
- - -
Think of ohms this way: one cab is 8 ohms pushing against the amp restricting the flow. Add another cab and the amp now can dump energy into two paths and the resistance it experiences drops.
If resistance drops too low, the amp will electronically "run away" and overheat and die.
But adding two cabinets at 4, increases the speaker AREA therefore moving more air, therefore adding volume.
So, how many watts is the head you're looking at?
I believe that the amp is `125w at 4 Ohms? Either way it will work fine, but I would look for a better amp. The backline series was a budget level amp.
Roland GR 88
Commercial User
The Backline 250 is rated at 8ohms. The cab is an 8ohm cab. They will match fine.
The Backline 350 is a 4ohm head so you would need two 8ohm cabs for that one.
The Backline 350 is a 4ohm head so you would need two 8ohm cabs for that one.
No no no. The 350 will work fine with one 8 ohm. It has the ability to go with two 8's for 4.
It doesn't "NEED" two cabs. But it will handle two 8's.
Ok that 250 watt 210 cab is going to be touch and go with either of those amps. You'll have to be careful and use your ears so you don't cook them.
Personally I'd be looking in the area of 400 watt, 8 ohm cabs for those amps. Then in the case of the 350, you can get a second identical 8ohm cab in the future (yielding 4ohms) and get more volume.
Roland GR 88
Commercial User
If your amp puts out, lets say, 200 watts at 4 ohms....you could use one cab at 4 ohms. or you could use 2 8 ohm cabs connected in PARALLEL. Two 8 ohm cabs connected in parallel will give you 4 ohms.
You could also use one 8 ohm cab by itself. There will be a slight volume/power output if you do that. But it's perfectly o.k.
You don't want to do anything that drops the ohms total/combination to less than 4 in the example mentioned. Not good for that amp.
I read somewhere that it is best to match about two thirds of the amps watt output to the cab.
In other words if the amp puts out 200 watts then the cab should be no more than 300 watts.
Can't say for sure that amp/cab wattage ' bro' science' is written in stone though. I'm sure others will chime in with the anti-aircraft fire.....
IIRC the backline 250 will not run a 4 ohm load. 8 ohm minimum. A bit of an outlier in solid state bass heads. The two units the op posted will work with each other fine, but can't take a second cab later. OP, if you're specifically interested in that amp, double check the manual first. Honestly I'd skip the BP250 and go for the BP600- it will do 4ohm loads and has as much power at 8 ohms as the 250.
Look into the HA3500 or 4000 for a good amp you can get for cheap, too.
Back OT, I'm a "2x the amp watt rating" guy when I choose a cab. Maybe even 3x if you're shopping used for gear that was entry-level when it was new.
Look into the HA3500 or 4000 for a good amp you can get for cheap, too.
Back OT, I'm a "2x the amp watt rating" guy when I choose a cab. Maybe even 3x if you're shopping used for gear that was entry-level when it was new.
For around $30-50 more you can get a used Hartke LH500 head off GCs used site. Would be vastly superior to the Backline head:
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The EQ isn't the most flexible but when shopping used it's pretty much one of the best values out there. Sounds good too
And if you can swing a little more dough I know where you can get a brand new Genz Benz focus 115 cab for $300 plus shipping.
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The EQ isn't the most flexible but when shopping used it's pretty much one of the best values out there. Sounds good too
And if you can swing a little more dough I know where you can get a brand new Genz Benz focus 115 cab for $300 plus shipping.
DO NOT buy the GK Backline 250 (125-watts rms). It has a minimum ohm load of 8 ohms and tells you never to hook up more than one cab to it. Plus, I never could get a "good" sound out of it. Having previously used some GK gear and been quite happy with it, I made the mistake of purchasing that Backline amp with the GK 115blx as a "pack". From what I hear the next step up is much better, but, in my opinion, you're throwing away money if you get the bottom end of that series. It was all I could afford at the time and found it woefully inadequate to gig with. Heck, couldn't even get a decent sound out of it running to through the soundboard for the FOH system.
I got a usable sound out of it by adding a 4 ohm Sunn 212 cabinet wired in series so it was a 12 ohm load instead of a 2.67 ohm load. Was probably running about 85-watts with it hooked up that way. I replaced that amp as soon as I could. Still have it and may try to use it as a guitar amp down the road somewhere. From what I understand the Backline 600 (300 watts rms at 4ohm) is much better and at least expandable. Just stay away from that 250.
$150 + $60 shipping is $210, or the equivalent of what 3-4 Backline 250's are worth. $210 would buy you a pair of Backline 600's which is a much much better amp.
Could get a used MB200 or $100 away from a used MB500
Could get a used MB200 or $100 away from a used MB500
Never mismatch ohm loads on an amp unless it specifically says it can handle a certain ohm, running it risks damage. Just do it right the first time, and buy a head and cab(s) that match ohms for the best possible sound, and safety.
Later down the road if you ever venture in to tube amps, you can destroy the output transformers mismatching loads.
Later down the road if you ever venture in to tube amps, you can destroy the output transformers mismatching loads.
Or like most people he can learn a basic understanding of impedance instead of treating it like some scary monster under the bed. It takes about 2-3 minutes of reading.
If a head is 4 ohms you can run one of the following scenarios:
-1 8 ohm cab at less than max wattage (around 65%?)
-2 8 ohm cabs at full power
-1 4 ohm cab at full power
If the head is 8 ohms:
-1 8ohm cab at full power
-no 4ohm cabs whatsoever
-don't know of any 16 ohm bass cabs currently produced
thanks captain obvious. Even the op would know that by nowbecause other people have said it at least twice in this thread.
And no, a tube head rated 4 ohms can't run an 8 ohm load unless specifically designed to, it's still bad on the circuitry and can cause issues. Too much resistance is still a bad thing in some cases. Not every head is the same, so you can and may be able to do it safely on some, but not all.
