2 small amps or one big one?

Is this amp OK?
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monekh
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2 small amps or one big one?

#1 Post by monekh » Wed Aug 23, 2017 12:46 pm

So... a predictable story for you all.

We just had our first outing of 8 T60s, having just completed another 4, which we were running off one MA3600. Limited at 55V, 2 ohms... bit dangerous.
We hadn't anticipated a drunk DJ bringing a bassline back in way past 0db on the mixer too fast (it seemed) for the limiter on the dbx pa2 to catch it, which blew the internal fuse in the 3600. Long story short, we rejigged everything with a spare smaller amp and carried on with 4 T60s. Many lessons learnt. We had fared fine with the dbx thus far, I suppose this proves the limiter is not brickwall, but then we were sailing pretty close to the wind running the amp that hard.

Anyway, wanted to get people's thoughts on our options to prevent this happening again...

My initial thought - get a bigger amp, still running at 2 ohms (4 T60s per channel) but with more room to accommodate incidents such as this.

However, someone who was present for this drama advised never running amps at 2 ohms, that they are much more stable at 4, and that it is therefore better to get 2 smaller amps, to provide double the channels in order to supply the same power at 4 ohms instead of 2 (2 amps, 4 channels, 2 T60s per channel).

Bearing in mind, getting another 3600 would work out about the same as selling the one we have and getting e.g. an MA5000...
However, I guess running 2 amps at 4 ohms means running twice as much cable... or maybe doing some 4 pole cable trickery.

Any advice greatly appreciated!

CoronaOperator
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Re: 2 small amps or one big one?

#2 Post by CoronaOperator » Wed Aug 23, 2017 12:50 pm

monekh wrote: However, someone who was present for this drama advised never running amps at 2 ohms,
^this, especially for sub amps. Way too much current.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

CoronaOperator
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Re: 2 small amps or one big one?

#3 Post by CoronaOperator » Wed Aug 23, 2017 12:54 pm

monekh wrote: We hadn't anticipated a drunk DJ bringing a bassline back in way past 0db on the mixer too fast (it seemed) for the limiter on the dbx pa2 to catch it, which blew the internal fuse in the 3600.
It will happen again, and again, and again.

Usually I run their mixer outputs into my mixer off to the side and then into the driverack. It gives you executive control over the output level and you can make adjustments without having to run up and interrupt his set while he is rocking out.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

djamps
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Re: 2 small amps or one big one?

#4 Post by djamps » Wed Aug 23, 2017 1:20 pm

chances are it was not a faulty limiter -- you were running so much current the fuses were already baking hot -- sitting on the limiter at the end pushed them over.

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MulletOver
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Re: 2 small amps or one big one?

#5 Post by MulletOver » Wed Aug 23, 2017 3:35 pm

I used a single 4 pole SpeakOn cable to drive 2 pair of T39's. Requires 2 plugs in each cabinet, an IN and OUT.
(8) 19" T39s (4xLab12, 4xDelta12LFA)
(4) SLA-PRO (4x6") Alpha6a
(1) Simplexx 10" wedge

Grant Bunter
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Re: 2 small amps or one big one?

#6 Post by Grant Bunter » Wed Aug 23, 2017 4:01 pm

monekh wrote:So... a predictable story for you all.

We just had our first outing of 8 T60s, having just completed another 4, which we were running off one MA3600. Limited at 55V, 2 ohms... bit dangerous.

Anyway, wanted to get people's thoughts on our options to prevent this happening again...

Any advice greatly appreciated!
Have a read of this excellent post:
http://billfitzmaurice.info/forum/viewt ... 45#p266748

There's two ways to solve 2 ohm loads.
The first is as you say, get another amp and run 2 cabs per channel to raise impedance into more like 4 ohms.

Or, if it has to be 1 amp, get one with sufficient power to serial wire pairs of cabs (using a breakout box), with the breakout box having a parallel feed to another serial out. Not sure what drivers you're using, but this will bring amp output impedance closer to 8 ohms than 2. The amp will run cooler, as the power supply will not be as taxed, and there will be less amperes in the speaker leads...
Built:
DR 250: x 2 (melded array) with March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

djamps
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Re: 2 small amps or one big one?

#7 Post by djamps » Wed Aug 23, 2017 6:27 pm

Personally I would choose the two amp option even if only for the redundancy. Better to lose half your herd than all of it at once if an amp blows up or voice coil / wiring short circuits.

CoronaOperator
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Re: 2 small amps or one big one?

#8 Post by CoronaOperator » Thu Aug 24, 2017 12:29 am

djamps wrote:Personally I would choose the two amp option even if only for the redundancy. Better to lose half your herd than all of it at once if an amp blows up or voice coil / wiring short circuits.
+1. You can also source more than one circuit with 2 amps.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

CoronaOperator
Posts: 1446
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: 2 small amps or one big one?

#9 Post by CoronaOperator » Thu Aug 24, 2017 1:51 am

monekh wrote: Limited at 55V, 2 ohms... bit dangerous.
Are these Lab12's? They should be limited to 50v or less, Lab 15's you are okay.

How wide are your cabs and do you encounter stairs?
Gluing 2 cabs together making them dually's (and series wiring them for 16 ohms) could save setup time and the extra wiring.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

monekh
Posts: 61
Joined: Mon Mar 31, 2014 5:56 pm
Location: London / York, UK

Re: 2 small amps or one big one?

#10 Post by monekh » Thu Aug 24, 2017 10:42 am

CoronaOperator wrote:
Usually I run their mixer outputs into my mixer off to the side and then into the driverack. It gives you executive control over the output level and you can make adjustments without having to run up and interrupt his set while he is rocking out.
seems wise, will think about doing this.
djamps wrote:chances are it was not a faulty limiter -- you were running so much current the fuses were already baking hot -- sitting on the limiter at the end pushed them over.
hadn't considered this, thanks for explaining.
Grant Bunter wrote: Have a read of this excellent post:
http://billfitzmaurice.info/forum/viewt ... 45#p266748

There's two ways to solve 2 ohm loads.
The first is as you say, get another amp and run 2 cabs per channel to raise impedance into more like 4 ohms.

Or, if it has to be 1 amp, get one with sufficient power to serial wire pairs of cabs (using a breakout box), with the breakout box having a parallel feed to another serial out. Not sure what drivers you're using, but this will bring amp output impedance closer to 8 ohms than 2. The amp will run cooler, as the power supply will not be as taxed, and there will be less amperes in the speaker leads...
thanks Grant... a whole new terrifying phase of reading! kinda looking forward to getting to grips with it.
djamps wrote:Personally I would choose the two amp option even if only for the redundancy. Better to lose half your herd than all of it at once if an amp blows up or voice coil / wiring short circuits.
another good point, thanks.
CoronaOperator wrote:
Are these Lab12's? They should be limited to 50v or less, Lab 15's you are okay.

How wide are your cabs and do you encounter stairs?
Gluing 2 cabs together making them dually's (and series wiring them for 16 ohms) could save setup time and the extra wiring.
Lab 15s, 27" wide.. and we do encounter stairs. gonna read up on serial wiring and 16 ohms though.

Thanks all, will be on the lookout for another 3600 I think then!

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J_Dunavin
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Re: 2 small amps or one big one?

#11 Post by J_Dunavin » Thu Aug 24, 2017 11:03 pm

Eight T60s :shock:
How'd it sound???

I also vote for two amps or even more, it just gives you more flexibility in the end. At the very least a back up amp just in case one goes.
6 - DR200
2 - DR250
9 - T24
6 - T45
1 - Auto Tuba

monekh
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Re: 2 small amps or one big one?

#12 Post by monekh » Fri Aug 25, 2017 8:51 am

J_Dunavin wrote:Eight T60s :shock:
How'd it sound???
kind of lost track of how it was sounding in the end but lots of positive feedback ... it was nice to use them outdoors (it was a street party event) - had quite a few london sound system heads scrutinising them very closely! no one can believe they have 15s in them. props to Bill!

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