1kW MOSFET amplifier

[Kilowatt]

No, that's just the Darwin Awards version of the story. In it, someone did this on the highway and crashed into a hillside. That is only a myth. In truth, that hillside was an abandoned mine shaft that the craft, which ran on rails crashed into and it collapsed, the guys sped off in their pickup, leaving skid marks that happened to point toward the rubble, makeing it look like someone was driving the rocket car on the highway and crashed into the hill and was killed. In truth no one was hurt or killed, but it looked like there was, and so the famous Darwin Awards story was born. See for yourself.
http://www.bored.com/rocketcar/

Anyway, enough of that, yeah, I agree with your statement "Whether Kilowatt builds this thing or not, it could be an interesting design to follow. I'm not sure why you folks are so upset he's considering this. We've cautioned him about the safety issue." But if people still think I'm doing something dangerous, they will often continue to warn me. Also, it's not all about the safety, some people think it's rediculous and pointless too. I might even be considering this possibility myself, but you still seem to think I'm stubborn as well as doomed. At least that's how it seems to me, maybe you think otherwise.

Anyway, if you have a huge area (I don't know for sure where this would be, but there are such places) that you want to fill with full, really loud hifi sound, what could be more cost effective than my design. It's much cheaper than even a bunch of Crowns, sounds way better, and power is always cheaper than speaker sensitivity. Maybe you're right though that I don't need quite 7200W, but I can always just use fewer 900W channels. Can anyone honestly think of a scenerio where my amp would be more dangerous than any other PA?

[mrfeedback]

Hi KIlo, multiple 900W amplifiers is a whole different thing to a single 7200W amp.
Indeed multiple amplifiers is the only correct way really.
Running multiple woofers in series parallel connection at high power is asking (begging ) for all kinds of damping/resonance related problems, however multiple amplifiers driving parallel loads is perfectly fine.
Indeed 12 woofers will give you all the SPL you could ever want - witness the big Genesis 1 system.
This has 12 carbon fibre 12" woofers and 4000W total between 16Hz and 120Hz.
I have spent a whole day with such a system, setting up and then listening, and that system is SERIOUSLY impressive.
Capable of causing structural damage if you were to resonate a room/structure with it, though.
Remember this would be for bass only, and if you want very high power full range system, it MUST be active crossover/multiple amp channels because passive crossover at 7200W is just not feasible.
Nobody is knocking you down, we are just trying to tell you the facts and it seems like you are not listening.
You have been told !.

Regards, Eric.

[Kilowatt]

Yeah, my plan has been to use 8 completely independent (except for chassis and highly reliable cooling system) 900W channels. 2 for bass, 4 for midrange, and 2 for trebble. I don't really see a difference between 8 amps and 8 amps in one chassis. One chassis was my originall plan, I don't see why I shouldn't do that. I will give each one their own supply with their own switches though for better reliability. I haven't ever thought of using a passive crossover, at least not since I've been on the forums, completely unfeasible, as you said. I once calculated the frequency/power curves that one would have, it was really bad, and the components would have to be huge and waste a lot of my precious power.

There would be 6 Eminence Delta 15" subs for each bass channel, 6 EV EVM10 10" midwoofers for each mid channel, and 6 horns (of unknown name brand) for each trebble channel. All the drivers would be horn loaded, and Xover frequencies would be 80Hz and 3,000Hz. But there are problems with series drivers? How severe? Is this just when you have like 3 or more in series (i.e. some of them are floating) or is it also when you have 2 in series. I wanted to use 3 in series, 2 in parallel. Any other way and I'd need a transformer in my power supply (wouldn't break too many of your hearts, just mine). What if the 3 are in the same box? Isn't there anything I can do for series drivers?

You know what would be really, really cool is if I could have an adjustable switching power supply for each amp that could go from +/-60 to +/-160V, but it would be way too hard to design and is almost unfeasible, unless some manufacturer already makes such a thing. It would give that isolation you're all so worried about, give me an excuse to make the high voltage amp, and allow me to run only one driver in series. The voltage could be raised for use with ESL's or if high transmission efficiency is needed (i.e. really, really long cables). What a compromise!

[SteveG]

Sounds like you are at least considering your many options, which is good.
As far as PA systems are concerned- they always do it with multiple arrays of drivers AND amps. It is a much better way to go.
Here's my advice to you- take it as you wish:
build your 8-900 watt amps, with isolation transformers, but build them two at a time in your chassis. I think you will be impressed the first time you put 1800 watts to your subs! I once rented a PA for my band for a medium-sized hall. It came in at 2000 watts total, and was really clean- plenty of headroom.
Why 12 ohms? I get the number, as it occurs often in dealing with speaker impedances, but you are making the solution more difficult than it has to be. To drive that kind of power into 12 ohms means your amp has to swing mega voltage, which will result in a compromised design (getting into slewing problems- adds so much circuit complexity to the front end). Remember- less is usually more, as far as devices in the signal path. In my opinion (of course) you would be much better off going into a 2 ohm load. I have also read that you really should never wire woofers in series. It dosen't make sense really, when you consider that you get nothing but power handling out of it. With a parallel connection, you get a 6db increase. Less voltage swing required, easier to design a good front end, etc. The only thing that will be a problem will be the number of outputs, but it sounds like you can handle that. With this kind of a design, a step down transformer will benefit, as you won't need the voltage, and it will up your current (assuming a BIG transformer is used). Look at the specs on the PA amps- they are all voltage limited- they push the big power into a 2 ohm load! Also, consider that no one builds an off line amp commercially... obviously the risk to consumers is too great. Sure, you can reason that you will be careful, but there is a reason no one is doing it- it really is unsafe. All it takes is one slip to end you, right now. If I remember correctly, all it takes is 2mA to stop your heart.
I don't want to come across as a jerk, but I have to say that your design is not synergetic. Your trying to justify building this off-line beast, when it is only messing up the design in general- just for this one purpose (getting rid of the power transformer). Look at that schematic, and consider the complexity to drive that impedance to that power level. Consider how much simpler the front end will be if you would only drive it into a 2 ohm load (and all the efficiency you will gain with your speakers). I think you will come to a similar conclusion if you really consider it all.
By all means, build your awesome system! Just make it a system with synergy, and the results will be all that much more impressive. Do more with less!

[AudioFreak]

6ma @ 240V across the chest is quoted quite commonly as that which is required to stop the heart but of course, this will depend on many factors....

[SteveG]

I knew I was close... Like you said, a lot depends on the situation.

[AudioFreak]

Extremely High Current output designs are not synergistic either because distortion rises rapidly with current output.

[SteveG]

Kilowatt,
By the way, your choice of drivers probably couldn't be considered "hi-fidelity"
You are going to get into serious lobing issues with the 10's- they're running way too high. The horns will give the same problem, unless you have some kind of an arrangement in mind. The 10's will also not disperse at the frequencies you will be running them to- they are going to beam like a flashlight, which will not sound natural. Also, 900 watts into a horn is WAY overkill! I have seen guys run PA outdoors and use 1/2 that!
Pro sound and hi-fi are two very different animals.
Your woofers are going to be loud, but they will most likely not have good extension. PA speakers are designed not to produce a lot of energy below about 50 hz, generally speaking. It causes too much of a problem with "rumble", such as mic stands moving, etc.
Of course it's perfectly ok if that is what you want- a PA system. I just want you to know that this system is a far cry from being considered hi-fi, with these components.
How about a line array with some good 6-1/2" mid woofers (with 600 watts to each array) crossed over at about 2K or less, and one big mother JBL horn with a 400 watt amp per side? Back that up with even 4 12" titanic woofers per side with a couple 1000 watt amps per side, and you would have a serious system that would most likely sound pretty decent too!
Food for thought- I put my MTM's outside in my back yard (which has a 100 acre field behind it) with my cheapy 100 watt/channel amp, and I had it less than 1/4 way up, and it carried for a LONG way. Of course, the bass is where you need the power outside, but you know my thoughts on how to do that. You also may be surprised that 80Hz crossover point outside is not always the best solution- the midbass may get lost. I've had good luck with 120hz or even higher.
More food for thought-
I once gigged out of town with my band, and the place we were playing (a large to medium sized church) supplied the PA, which turned out to be a home-made system. It was a four way system with 1- 18" EV, 1- 15" EV 1- 10" EV, and one large horn per side, all quadamped (mono). The system kicked!! It kicked major butt! It was SOOOO clean. I could feel my kick drum in my chest! We were running 2000 watts max. with 100 of the watts on the horns.

[SteveG]

Extremely High Current output designs are not synergistic either because distortion rises rapidly with current output.

That's a given, but at the levels Kilowatt is talking about he will not only be driving a heck of a lot of voltage into his woofers, he will also be dumping some current too. I think the benefits of going lower in impedance far outweigh the problems. Of course there is a tradeoff with any design, and that may be the downfall.
BTW, is this problem as pronounced in MOSFET output stages as it is in bipolar stages?

[Kilowatt]

Well, some interesting ideas. I once heard that driving into higher impedances gave better sound than into low impedances. Of course I've seen sales brochures for amps that can do 1 ohm or so say just the opposite, but you know how sales propaganda is. If I lowered it to, say, 900W into 8 ohms, I'd be stuck in some sort of in-between voltage range where 1 MOSFET in series isn't quite enough for comfort, but 2 is overkill. I'd also need a transformer or transformers. Please keep in mind that what I have right now of this amp weighs about 65lbs when full of coolant, and measures 24"W, 22"D, 16"H. It would be maybe 8" deeper after the direct line PSU was attached and be heavier too. My 4 channel Leach amp won't be much smaller, but maybe half as high. With transformers, it would add, just an edgucated guess, 250lbs to my amp. Can you lift 315lbs? Maybe if it's in a backpack, but I'd be too worn out after hauling it to do anything else. Time to get a forklift. This was my main insentive to make it direct line powered.

Maybe I can use a switching supply (or switching supplies), if I can find such a thing. That would be fine. I might also need to find a little higher voltage devices, so I can run up to maybe +/-120V. I guess wht I thought was this: Anthony uses +/-110V, but he pushes his devices to the limit, Glen (project 20kW) uses +/-115V. 160V isn't a whole lot higher than 110V. However, after reading your ideas, I would like to build maybe only 4 900W channels, I would be better off breaking up the rest of my 7200W even further, continuing with maybe a couple of 450W channels and some 225W channels too. For these, obviously, +/-160V is out of the question. Try +/-60V, also, +/-120V is what I'd need to get 900W into 8 ohms for the big ones. I can't have those heavy, bulky, expensive, power transformers, so I need switching regs with plenty of headroom. They'd also help me do away with those huge filter caps. Do you know of any 1500W +/-120V switching regs? I can't see myself making them.

What drivers do you think I should use? Xover freqs? Maybe 4 way? I've looked all over for speakers and couldn't find much better than those EV 10's.