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Old 25th June 2002, 11:00 PM   #11
e96mlo is offline e96mlo  Sweden
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MRehorst:

The problem with higher currents is that losses in cables, PCB's etc becomes a lot higher. Also the inductances in the cables and speakers produces nasty voltage spikes at large current changes.

You need a certain rail voltage to produce a certain power at, say 8 ohms. Then you can parallel two speakers to increase the power but you can't use much less than 4 ohm loads or it will be cheaper to use two amps in redundancy than making the enormous output stage required.

There is also a problem with low Z speakers and that is that when too few turns of wire are used, the linearity suffers. That is probably why most speakers are 8 ohms. It's a good compromize.

/Marcus
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Old 26th June 2002, 01:19 AM   #12
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I imagine that if you had a 1 turn voice coil made of flat copper strip and it was an inch wide but with only 1/4 inch inside the magnetic gap at any one time maybe the linearity would be ok?

If you had an amp that would swing +/- 5 volts at 100 amps then you could use a step-up transformer between it and the speaker. For the amp itself there are some absolutely stunning low voltage fets available nowadays e.g. IRF3703 30v 210A 0.0028 ohms(!) TO-220 case.

Seeing you can only get N-channels this good, and you can have the two 5v rails floating WRT each other, the circlotron is the only topology worth considering

GP.
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Old 26th June 2002, 03:50 AM   #13
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Default high current output

oh me oh my, it seems we have to swim through a sea of caveats, to reach the promised land. to non swimmers can I introduce you to planet audio [www planetaudiousa.com] they sell 2 ohm speakers. e.g fu18-2. 3600w /1800w 15Hz-500Hz 87dBdual 2 ohm etc.
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Old 26th June 2002, 06:42 AM   #14
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Default hi power amps

Mr Feedback wrote:

"Hi again AudioFreak, My kids just asked me why I laughed out aloud when reading your reply.
I fear Mr slicemaster is a plain lost cause.
All his asking and no listening reminds me of a brat who thinks he knows it all and is likes to crow about it, but when pressed really does not know Jack.
Let me applaud if you can get through his thick skull !.
BTW being young is perfectly fine, I still think like I'm young too, and I knew about etiquette and respect when I was young - the above mentioned don't have a clue."

I have this sign on my desk:

"People who think they know it all are especially annoying to those of us who do"

Go figure

Jan Didden
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Old 26th June 2002, 06:47 AM   #15
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I'm only going to use 4 speakers in parallel/450W amp, you know, mrfeedback. Better than my older plan to use 12 in series-parallel/900W amp isn't it. See, I'm catching on, now don't you worry.

P.S. Audiobahn makes a 5000W RMS 34" sub with a dual 1 ohm voice coil. It costs about $2900 each though, I can't imagine anyone actually buying one, but by reputation, many of you probably think I would, and use 1600W IGBT's as output devices while I'm at it.
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Old 26th June 2002, 11:56 AM   #16
e96mlo is offline e96mlo  Sweden
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Circlotron:

The magnetic field starts bending quite early at the ends of a regular coil. With a one turn coil the field would be almost circular around the wire, which gives really poor linearity.

I don't think your idea is feasible. First of all you don't want an output transformer. They are hard to make and expensive, especially att the currents you are talking about. Secondly, the FETs that you refer to are probably designed for switching applications and in that case they are no good for linear amps.

If you still want to go through with it, let us know how it goes.

AMPMAN:

87 dB is probably the worst efficiency in a 18" driver that I have ever seen. No wonder that they have to be able to take thousands of watts.


/Marcus
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Old 26th June 2002, 12:15 PM   #17
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Hi Kilowatt. Nobody plans schemes as grand as yours! What other projects have you done to a completion that we may have confidence that this latest one of yours will come to be also?

GP.
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Old 26th June 2002, 05:01 PM   #18
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Default high current

the natural home of the transistor is the automobile they have only 12 volts to work with maybe we can learn from them
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Old 27th June 2002, 05:39 AM   #19
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Quote:
Originally posted by e96mlo
Circlotron:

The magnetic field starts bending quite early at the ends of a regular coil. With a one turn coil the field would be almost circular around the wire, which gives really poor linearity.

I don't think your idea is feasible. First of all you don't want an output transformer. They are hard to make and expensive, especially att the currents you are talking about. Secondly, the FETs that you refer to are probably designed for switching applications and in that case they are no good for linear amps.

If you still want to go through with it, let us know how it goes.

/Marcus
Nah, I wasn't being serious. As for the stepup transformer, I was illustrating the difficulties involved in using a + - 5v supply in a workable but probably impractical way. Better to put your money into a power tranny instead of an o/p tranny, hey?

Those fets are indeed meant primarily for switching, but is that not an open invitation for a diy'er to try then in a linear amp? I for one have had quite acceptable results using 500v n-channel-only switching fets in linear use.

Just for that, I know where to get my hands on a pair of IRF3703's. I'll put them in my bench testbed and show them who's boss! I'll report the results.

Thinking more about voicecoils, if you used copper strip I wonder how well it would work if you used multilple turns wound like a roll of tape? Not too thick though. Keep the magnet gap small.

GP.
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Old 27th June 2002, 07:14 AM   #20
e96mlo is offline e96mlo  Sweden
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Hard to know if you were serious or not, since I have equally crazy ideas myself from time to time.

Regarding the voice coils:
I think the problem remains as long as you don't have a voice coil that is much longer than the width if the magnet gap.

I have read though, that underhung voice coils (that is when the gap is wider than the coil is long) gives extreme linearity for the trade off of smaller Xmax and lower BL. But it still requires the coil to have enough turns to be resonably "ideal".

There is a thread around here somewhere about making your own drivers. I don't know what has been said there. It's probably worth checking out, though.

/Marcus
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