Recommend me a power amp that does 2 Ohms.

[geoffbyrne]

So we're looking at some PA speakers, but they are 4 Ohms each. We're still to get an amp, so what would work with 2 Ohms total? Looking at either a mixer head or a mixer desk, preferably powerful (500W/side) used & inexpensive.

G.

[Mr. Foxen]

Peavey. 8.5C come up for about £100 and are beefy. But there are loads of others. Open them up, hoover out the fluff and you are good to go.

[King Tut]

Behringer EP2500. Generally renowned for bucking the iffy reliability trend and happily run at 2 ohms.

[Ghost_Bass]

Practically every power amp in the market does 2Ohm! If i was to recommend you one it had to be the Phonic 3000 - the best thing i've heard - My band has two Phonic 3100 (the same but with sub-woofer out added and they sound amazing trough two pairs of Warfedale Pro 2x15"+2"H and 1x15"+1 1/2"H... They are expensive new but you could be lucky on e-bay. I don't recommend a powered mixer couse it's going to be too darn heavy.

Cheers

Edited November 1, 2010 by Ghost_Bass

[geoffbyrne]

Thanks for that, Guys. Didn't think of the powerd mixer/weight thing.

I've got my eye on something & it looks like we're not going for the cabs we were looking at originally (singer's buying, not me).

Mobile goalposts!!

G.

[Ghost_Bass]

Just another thing, before buying a monster (my phonics weight almost 60lbs each and are stupidly sharing the same rack! a nightmare to lift!) take a look at the class-D power amps. I know Crown does one and there are other manufaturers doing them. It will be a good investment in everybodys back health in the future. Probably worth saving a bit more for a tad more time

Cheers

[casapete]

Just sold a Crown XS500, which was a great amp. Reckoned to run 750w a side @2 ohms but we never did.

Personally would rather get a bigger output amp @ 4 ohms than run anything at 2 ohms if at all possible.
Peavey have in the past often claimed 2 ohm operation on a lot of their stuff, but am sure it would be happier / last longer etc
running at 4 ohms.
Just my sixpennorth....

[DirkThrust]

Does it really need to run at 2 ohms? Most PA amps are twin channel and they'll all happily run 4 ohms a side.

Edited November 2, 2010 by AndyMartin

[Ghost_Bass]

[i]NORMALLY[/i] power amps are designed to have maximum eficiency (put out the maximum wattage figures) when:

- run with a load of 4ohm per channel = total 2ohm load
or
- run bridged (just one active channel) with a load of 2ohm

This doesn't mean they won't run at higher impedances, just will have less output. Like a bass combo with extension speaker ability.
One of my band's power amps is feeding 2 8ohm cabs (1x15"+H) for the tops and we never felt lack of power when compared with the power we get from the other (same model) amp feeding 2 4ohm cabs (2x15"+H) on the bottom!

I'm currently between rigs so i'm running my bass trough a power amp (Norton KP600 - 600W@2Ohm) and a TL606 DIY 8ohm cab using only one channel - amp's not bridged - and i have plenty of volume! Didn't try bridging the amp becouse i think putting a 8ohm load on a 2ohm output would be pushing my luck! If anybody with knowledge can say i'm safe to do it i'll be glad to try!

Cheers

[LawrenceH]

[quote name='Ghost_Bass' post='1008090' date='Nov 1 2010, 03:46 AM']Practically every power amp in the market does 2Ohm![/quote]

Not for long though! Just because marketing specs quote an output at 2 ohms doesn't mean the amps will be happy about it long term. These figures are often short term 'burst' data and don't mean much. The thermal stress running at 2 ohms will be a lot more and the amp needs to have adequate heat-sinks and components or they'll run ok for a while and then fail, especially if you're putting a fair amount of bass through them. This applies to all flimsy cheap amps.

If you want something that'll really do it without much outlay, look secondhand. Something like a QSC PLX will do nicely. Those Peaveys Mr Foxen mentioned are probably up to it though I've never paid much attention to Peavey kit, or if you prefer new then the Behringers seem to have surprisingly good reports from people who flog them mercilessly. In general old heavy amps of proven design are your wallet's friend here, though not your back's.

[LawrenceH]

[quote name='Ghost_Bass' post='1011008' date='Nov 3 2010, 04:33 PM']I'm currently between rigs so i'm running my bass trough a power amp (Norton KP600 - 600W@2Ohm) and a TL606 DIY 8ohm cab using only one channel - amp's not bridged - and i have plenty of volume! Didn't try bridging the amp becouse i think putting a 8ohm load on a 2ohm output would be pushing my luck! If anybody with knowledge can say i'm safe to do it i'll be glad to try!

Cheers[/quote]

This seems backwards - an 8 ohm cab will be fine even on a minimum 4 ohm power amp that's bridgeable. I'm not familiar with your Norton but it should do it no problem. It's a low impedance cab you need to be wary of.

[Ghost_Bass]

[quote name='LawrenceH' post='1011474' date='Nov 3 2010, 10:52 PM']This seems backwards - an 8 ohm cab will be fine even on a minimum 4 ohm power amp that's bridgeable. I'm not familiar with your Norton but it should do it no problem. It's a low impedance cab you need to be wary of.[/quote]

I think i didn't explain right. My cab is 8ohm and the amp is running 4ohms per channel. I use it in one channel without concern becouse i know it's safe to do it.

My doubt is: If i bridge the amp i supose it'll become 2ohm in the only active channel. My fear is to link a 8ohm cab to a 2ohm power amp output! I realy don't need the extra power but the headroom i get would be apreciated

Sorry for the hijack!

Edit: i've read your early ansewer again and now i think i'm seeing your point! I know that a 1ohm (ex.) cab would blow the amp up but doesn't high impedance cabs also cause the amp to heat due to bigger resistance to put out the energy the amp's generating?

Edited November 4, 2010 by Ghost_Bass

[DirkThrust]

[quote name='Ghost_Bass' post='1011940' date='Nov 4 2010, 12:31 PM']My doubt is: If i bridge the amp i supose it'll become 2ohm in the only active channel. My fear is to link a 8ohm cab to a 2ohm power amp output! I realy don't need the extra power but the headroom i get would be apreciated [/quote]

Unless your amp is a valve amp it doesn't matter. The 2 ohms figure in the spec is just a minimum load. It doesn't mean it's designed to only work with a 2ohm load

Edited November 7, 2010 by AndyMartin

[stevie]

[quote name='geoffbyrne' post='1008050' date='Nov 1 2010, 12:08 AM']So we're looking at some PA speakers, but they are 4 Ohms each. We're still to get an amp, so what would work with 2 Ohms total? Looking at either a mixer head or a mixer desk, preferably powerful (500W/side) used & inexpensive.[/quote]
Just get a bog standard *stereo* power amp or mixer amp - job done. You would only have to worry about a 2-ohm load if you connected both speakers to the same mono power amp.

[geoffbyrne]

Moot point now, as the singer has gone for something else!

Thanks for the input, Guys.

G.

[Ghost_Bass]

[quote name='AndyMartin' post='1014970' date='Nov 7 2010, 05:58 AM']Unless your amp is a valve amp it doesn't matter. The 2 ohms figure in the spec is just a minimum load. It doesn't mean it's designed to only work with a 2ohm load[/quote]

I've tryied it this weekend at two gigs and it worked fine, no overheating and the amp held on for three hours of gig without ever clipping or going into protection
This myth is busted!

Edited November 8, 2010 by Ghost_Bass

[DirkThrust]

Which myth is that?

[SteveO]

[quote name='Ghost_Bass' post='1011940' date='Nov 4 2010, 01:31 PM']I think i didn't explain right. My cab is 8ohm and the amp is running 4ohms per channel. I use it in one channel without concern becouse i know it's safe to do it.[/quote]

This bit is back to front. you cant 'set' the impedance on your amp. if you plug an 8 ohm cab into an amp it will see 8 ohms, whether running mono or bridged. the impedance rating on the amp is there as a warning, i.e. in your case "don't plug a cab (or combination) with total impedance less than 4 ohms per channel otherwise the amp may melt" Generally the rule of thumb is less impedance = more volume, but stay at or above the amps rating.