Still need help with my amp design

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Hi.
I was wondering if I should (or even could) modify this design
http://sound.westhost.com/project03.htm
by changing transistors and other component values, using huge output banks of 18 x 2N3055's and 15 x MJ2955's in series-parallel (3 in series), maybe adding a few transistors in darlington arrangement with the outputs, and raising the supply voltage to about +/- 150V to produce 1800W RMS into 6 ohms. This design might have a little too much quiescent current for such high power use, so maybe there's another simple design I could improve in a similar way.
I would appeciate any advice about doing so if it is possible.
I have used this design pretty much as is to get 150W RMS and it seemed to work.

Thanks.

[Edited by Kilowatt on 11-18-2001 at 02:13 AM]
 
The fog is starting to clear, 2 bridged 1800W/4ohms amps bridged should equal 7200w/8ohms right?
The bad news is it usually doesn't, even if that’s what everyone says. I suspect that Pass amps may, (as well as other esoteric manufacturers) he doesn't seem to muck about with his power supplies.
The trouble is that most 1800W amps have 1800W power supplies, often less! If they were built with 3600W supplies, (and few are) the cost and weight makes them unattractive, (but that’s how I like to build them).
Second point is that the output transistors mightn't cope, try the ESP site, http://sound.westhost.com.

I don't want to rain on your parade but the path you seem to be taking is fraught with many pot holes, go slow, read lots.

Regards WALKER

PS The Audiobahns are car speakers aren't they? With car audio installations the rules are totally different! Help me out here, what are you doing?

[Edited by walker on 11-18-2001 at 04:49 AM]
 
walker, the link is http://www.audiobahninc.com/prod/woofers/ALUM12.htm

walker you are also wrong about the mathematics of bridged amps ..... given your example.....
2 amps capable of 1800W/4ohm bridged into an 8 ohm load
each amp sees half the load, therefore, each amp drives 4ohms.... therefore you will get 1800w x 2 = 3600W into the 8ohm load.

The ALUM12X have an impedance of 3ohm or 12ohm .... funnily enough, kilowatt mentions 6ohms for the amps ..... well 12ohms bridged is 6ohms and he wants amps good for 1800W in 6ohms .... therefore, he wants 3600w running thru each channel of this rig.

These speakers have an efficiency of better than 96dB .... @7200W, SPL is gonna be ~140-150dB either this is for competition or sound reinforcement or kilowatt needs his head screwed back on .....

[Edited by AudioFreak on 11-18-2001 at 05:25 AM]
 
AudioFreak, you're exactly right!
I want 3600 Watts/channel into 12 ohms. I an using bridged mode so I can utilize both sides of my simple transformerless +/-150V power supply which runs from a range plug simultaneously. This system is to be used outside in the open so that it's sound can carry over some distance. It may be used for competition, or just to show off, and maybe I do need my head screwed back on. I suppose this system would also be convenient for a band.
 
But what will you do when it rains?
Keep in mind that power supplies capable of this kind of output are seriously heavy--couple hundred pounds for a finished amp.
Just wondering from the model number, but is an ALUM12X a 12" driver? If so, you're going to find that 500 Hz is an awfully high crossover point for a 12". Far better to crossover at 200 Hz or less.

Grey
 
Obviously, I would not use this thing in the rain, but Geoff is right. There is no transformer unless you would count the distribution transformer up on the power pole. The power supply is just rectified and filtered 240V mains power.
In reply to GRollins:
500Hz is indeed about the highest the ALUM12X drivers go (they're 12's). I want to keep the crossover freq. as high a possible so I won't have to have as much trebble power.
Now, back to the point:
Should I use the simple dedign given in my first post for this amp? What should I do?

[Edited by Kilowatt on 11-18-2001 at 02:28 PM]
 
Audiofreak, I'm often wrong, it’s the nature of the beast, but this time maybe not? Kilowatt was talking about using 1800W amps to produce 7200W with bridged amps, he didn’t mention how many. It is possible (theoretically, P=Vsquared x R) to get 7200W from two 1800W amps if the power supplies and output devices are up to it. In practice most amps will soft clip (the supply rails collapse) or just let the smoke out first. The output that you do get, when you bridge amps varies greatly and should not be assumed. If I have tripped up there please let me know.
Kilowatt if you want these levels of sound pressure level the best way is to copy professional sound re-enforcement systems. They use more, smaller amps generally 100/200W, OK some times a little larger. This isn’t the cheapest way but it has many benefits.
The drivers that you are using are very efficient! Unfortunately, efficiency and quality tend not to go hand in hand, in fact you generally have to choose one or the other, (multiple drivers, possibly, being an exception). I would recommend that they be directly connected to the amps to keep them under control. Most people don’t realize that the frequency response plots that manufacturers publish are direct amped and if you use a passive crossover you won’t get these responses. Unless I’ve miss understood you, this is what your planning to do.
Finally, not using a transformer in your power supply is LETHAL and definitely not he way to go. The power supply should filter out mains noise, (unless you have a switch mode supply), the transformer/capacitor circuit performs this function. A line filter to do this job will be large and expensive, sorry you rarely get a free lunch even when you think you do.

Regards WALKER

Havagooday fellow forum fanatics.
 
Walker,

Lets start again,
2 amps capable of 1800W/4ohm bridged into an 8 ohm load
each amp sees half the load, therefore, each amp drives 4ohms.... therefore you will get 1800w x 2 = 3600W into the 8ohm load. Using 2 amps in bridged mode, into that 8ohm load, you cannot get more than this outta this configuration (it is mathematically and electrically impossible)... if however, you were driving a 4ohm load then each of the amps would see 2ohms and give twice the power (then you would get 7200W) .... but we are talking about 8ohms, not 4 and anyway are the amps stable into 2ohms continuous? :)

To get greater than 3600W, would need to lower the impedance that the amps are driving.

Kilowatt is using 4 drivers (12ohms each) per channel in series/parellel configuration giving 12ohms......

Also, Kilowatt did mention 2amps per channel.

I didnt mean to offend in anyway .... just stating the facts and hopefully helping other people out.

[Edited by AudioFreak on 11-19-2001 at 06:10 AM]
 
Kilowatt,

I think that reasonnable way to obtain such very high power levels, with electrical safety and no excessive weight, is the use of switching amplifiers.

Such amplifiers are available for professionnal public adress systems, with poor high frequency response, but this is not a problem in your case. Switching amplifiers are also used for large broadcast AM radio transmitters, up to 100 kW and more. But I don't know where (if) you can obtain circuits diagrams and other details in order to build such appliance.

Also, I must insist on the fact that use of such very high power amplifiers, even isolated from the mains, is very dangerous : output audio voltage can be as high as 220 V RMS or more, which is lethal voltage.

Regards, Pierre Lacombe.
 
Ok, here's the deal:
I won't be using switchers in any way, except maybe for some PWM for the power supply because of expense and difficulty. I have my heart set on using cheap 2N3055/MJ2955 series-parallel banks for output, and a transformerless power supply because with this I could make the whole amp for only around $500. Also a power supply transformer for this thing would probably be as big as the box that I already have made for the amp. With my current design, it will fit in the box, just barely. I hope it doesn't start on fire. Each channel will indeed supply 3600W RMS into 12 ohms for the bass. The amp in question will be bi-amped with another amp for trebble. I plan to use two 1800W 6 ohm amp sections per channel bridged to produce 3600W into 12 ohms. 7200W total power. This 7200W RMS is only for bass, there is no passive crossover. For trebble, there will be another system with several horms and another large amp. I am hoping to use 1800 Watts into 4 or 6 ohms per channel (3600W total) for this so I can use the same or at least almost the same design for that.
Also, Geoff, isn't 300VDC w/ several 1000 mF just as dangerous wether it is off the mains or from a transformer that can supply almost as much power? A 1:1 isolating transformer would only add weight, cost, and heat production. As for filtering, The filter section will be just like any other, the only difference being that the transformer is up on a utility pole rather than in the box.
Now, no matter how cheap I make this, it couldn't possibly sound worse than some systems I've heard where there's one badly overdriven sub sitting in a rattley old pickup that vibrates so bad from the bass that you hear that more than the music can it? :)

[Edited by Kilowatt on 11-18-2001 at 11:01 PM]
 
Kilowatt, if you don't use a transformer the amount of switching noise that makes its way into the amp could easily degrade the sound. Would you allow your next door neighbour to run his air conditioner off your amp’s supply rails? It’s nice to have a transformer between your output transistors and the rest of the street, particularly one with a faraday shield.
I'll state for the record that I have never attempted what you are suggesting and that some of the comments made are therefore only speculation.

Regards WALKER
 
Sorry, missed the part about transformerless. Yes, without a transformer, the weight would be more manageable.
I must agree with Geoff, direct rectification of mains voltage, regardless of whether it's 120V or 240V, is a bad idea.
The reason I'm skeptical of running a 12" driver up to 500Hz isn't frequency response (although I could make a case that the quality of the 500Hz would be pretty low, too), it's dispersion. And if you're planning on PA usage, rather than hi-fi, dispersion is even more important. A single listener can always sit in the magic spot. Two or sometimes three can get by. But PA useage, where you're trying to reach hundreds or even thousands of people? No way. At 500 Hz a 12" driver is beginning to lobe strongly to the front with a few pronounced side lobes. Between the maxima, you're going to be dropping probably 6 to 12dB at a guess. This is not a good recipe for a happy audience.
If you're planning on going into the PA business, I'd recommend that you read up on the basics first, then back up and start planning hardware. If nothing else, the old maxim,"The show must go on," is more than just a phrase. If you use one or two really big amps, you're putting all your eggs in one basket. Pop an amp and the sound system is useless.
Bands tend to sue for breach of contract when the PA system drops and leaves them with an angry audience demanding refunds.

Grey
 
Maybe it wouldn't be an ideal PA system, but assuming there is little or no noise on the line and you are in the "magic spot" mentioned by GRollins, it would work wouldn't it? I think I will lower the crossover frequency to 300Hz and slit the SPL 50/50 with 8 seperate 100W amp, 106dB/W@1m horn sets for trebble. Now just how should I build my big amp? Is there any schematics for 1800W RMS into 6 ohms? Should I use a design like I mentioned in my first post with different transistors and my +/- 150V line powered power supply?
 
I like what you are doing, and I am also constructing a trafoless amp. Rectified 230V with 4*2200uF + 4*60uF caps.
I've mesured the DC voltage at 320 volt. This will drop during load offcourse. 1 question: How do you get the splitt DC voltage?? The output stage off this amp is a class D. The amp i realized, and works perfectly up to 2 kHz. Its using 6 volt supply, so whats left is to coustruct an output stage for 320 volt. For that i'm gonna use a H-bridge, to get +/- 320 volt: Giving 10kW in a 4 ohm load!

I am also coustructing a class AB amp with 32 motorola MJ15004/5 outputs, and a 12kVA trafo. total weight is 90 kg.
power: 2kW @ 2 ohm bridge. (Now trying to double it in 1 ohm!!).

Tip: Look in, http://www.aussieamplifiers.com to get a descent schematics...
 
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