Simon E Posted May 16, 2006 Share Posted May 16, 2006 Ok here’s my problem, I’m helping to spec. a new amp for a rig, and space is a serious issue, so I’m looking at the Powersoft Digam K series. I really want to drive 4x Nexo Alpha Bass cabs (B1-15) on one channel. This means I require 3.6 to 4.8kw (according to the Nexo manual). Now the Digam K8 has an output of 4.8kw’s at 2ohms, the problem is the Nexo drivers are apparently 6ohms each, meaning that if they are run in parallel they would be 1.5 ohms. The other option would be to run them as two pairs in series, giving 6 ohms, but even the biggest amp (the K10) can only output 3kw at 6 ohms, leaving the output 600w under the lowest recommended. Hmm… Is there some clever series / parallel combination I can use? Is there something I could do with resistors (I’m guessing not as a .5ohm 4.8kw wire-wound resister if available (which I doubt) would be a fair size! –see the previous comment about space) Can the Digam amps run at 1.5 ohms anyway? The manual for the existing one (K6) doesn’t say you can’t run them below 2 ohms, it just doesn’t list an output below 2ohms. It does mention that can run it in bridged mode at 2 ohms, but that extra cooling might be necessary. Do the standard rules apply to digital amps? What is it with Nexo and 3 / 6 / 12 ohm drivers anyway why cant they use 2 / 4 / 8 / 16 like everybody else!?! Just thought I ask before having to give up and think of another solution to the problem! :huh: Link to comment Share on other sites More sharing options...
Shaggy Posted May 16, 2006 Share Posted May 16, 2006 As far as I'm aware Digam Amps are unsuitable for use with Alpha as the latency of the amp confuses the controller. Is this not the case? Link to comment Share on other sites More sharing options...
Rob_Beech Posted May 16, 2006 Share Posted May 16, 2006 6 ohms you can put 3 on an amp rated for 2 ohms.thats agaisnt 4 ohms where you can only put 2 12 ohms you can put 6 on an amp instead of 4 from 8 ohms Rob Link to comment Share on other sites More sharing options...
Simon Lewis Posted May 17, 2006 Share Posted May 17, 2006 Is there some clever series / parallel combination I can use? Yes, but you wouldn't really want to. Running two devices in series and then parallelling a pair of them will bring you back to 6 Ohms. However, you'd need an amp that can deliver 3.6kW to 4.8kW into 6 Ohms, and few will achieve this on a single channel. Bridging the amp may achieve this. Is there something I could do with resistors (I’m guessing not as a .5ohm 4.8kw wire-wound resister if available (which I doubt) would be a fair size! –see the previous comment about space) I can make you a 4.8kW non inductive load resistor quite easily. However, you will simply dissipate all the power realised across that load as heat. This means less sound;-) Size isn't the main issue, getting rid of the heat is.... Can the Digam amps run at 1.5 ohms anyway? The manual for the existing one (K6) doesn’t say you can’t run them below 2 ohms, it just doesn’t list an output below 2ohms. It does mention that can run it in bridged mode at 2 ohms, but that extra cooling might be necessary. Do the standard rules apply to digital amps? The digital amp is "sort of" an audio controlled switch mode power supply. If you exceed the voltage/current characteristics of the power devices, it will still fail. I would be very surprised if this (or any other amp) can reliably bridge into 2Ohms for extended periods maintaining good broadband THD figures and standard thermal management. What is it with Nexo and 3 / 6 / 12 ohm drivers anyway why cant they use 2 / 4 / 8 / 16 like everybody else!?! Actually, Nexo are doing you a favour. The "8 Ohm" loudspeaker does not exist! It might measure at 8 Ohms for part of its frequency v. impedance curve, but depending upon the specific driver (i.e. the mechanical parameters) the specific amp/crossover system (i.e. the electrical parameters) and the enclosure loading (i.e. the acoustical parameters) the overall impedance will change. Nexo state that the minimum impedance is 5.2 Ohms. This is fairly well controlled, and shows that for your intended system, your minimum load will be 1.3 Ohms. This is pretty low for any amp to deal with, and you'd need very heavy duty loudspeaker cables (preferably dipped in liquid helium!) to avoid serious problems with poor damping factor and power dissipation in the cable. Just thought I ask before having to give up and think of another solution to the problem! :huh: I'd prefer to run a 1200W amp channel into a single box, find an amp that can deliver 2.4kW into 4Ohms into two boxes, or bridge an amp into two boxes. This reduces the likelihood of thrashing your amps, and also allows some degree of failsafe operation should one amp go down. It doesn't solve your space problem through! Simon Link to comment Share on other sites More sharing options...
Simon E Posted May 22, 2006 Author Share Posted May 22, 2006 Thanks for your replies, I believe some of the earlier digams had problems with the nexo controller, but that they have now patched up their differences and K series should work (I aught to spend some time with the K6 and check for myself however!) Losing power isn’t necessarily a problem as it would be possible to spec a bigger amp to compensate, but how much heat would be generated? Would it be better to use 2ohm resistors in series with each driver, or one 0.5ohm inline with the amps output? Would the additional resistor affect the clarity of the sound in any way? :D What I’d really LIKE however is enough space for a nice rack of Camco’s like everyone else :P Thanks!Simon Link to comment Share on other sites More sharing options...
mackerr Posted May 22, 2006 Share Posted May 22, 2006 Losing power isn’t necessarily a problem as it would be possible to spec a bigger amp to compensate, but how much heat would be generated? Would it be better to use 2ohm resistors in series with each driver, or one 0.5ohm inline with the amps output? Would the additional resistor affect the clarity of the sound in any way? :DAs pointed out earlier, a resistor will just divide up the power between itself and the speaker. You will get less power out of the amplifier, and some of that remaining power will be disapated as heat in the resistor. There should be no loss of quality, only quantity, and a lot of heat. Mac Link to comment Share on other sites More sharing options...
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