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Old 22nd June 2002, 05:12 AM   #1
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Lightbulb Super-power amps - higher current better than higher voltage

I've been reading here and there in this list about different people wanting to build absolute gigapower amplifiers and invariably two difficulties (will) come to light. 1/ The output devices are going to need simply enormous safe-operating-area to be able to drive a reactive speaker load given the high dc rail voltage that will be needed. 2/ That same high rail voltage and the power it will produce means that the speakers are gunna have to be wired in series-parallel or something ugly like that.

The way I see it is this: lets assume that your choice of a good solid speaker driver will take 250 watts rms and is 8 ohms impedance. Work out how many volts rms that is across 8 ohms. mulitply by 1.414 to get the peak voltage. Add ~5 to 10 volts and this gives you the total rail voltage your amp needs, half above zero and half below zero.

Now the next bit is my whole point - if you want more power, stick on another loudspeaker and another pair of output transistors (psu suitably rate of course). Ten times the power? Ten times the transistor capacity and ten times the speakers *all in parallel*. What's the point of building an amp that can swing absolutely whopping peak to peak voltages with the ridiculous demands that makes on transistors, and then find that most speakers won't handle that amount of drive voltage anyway? Just decide the maximum drive voltage that your favourite loudspeaker can handle and design your amp for this o/p voltage capability. More power = proportionally more transistors and more speakers all in parallel, the maximum output voltage always remains the same, only the current goes up.

GP.

GP.
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Old 22nd June 2002, 06:08 AM   #2
paulb is offline paulb  Canada
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Hm, so where do you take the feedback from?
How about just more amplifiers?
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Old 22nd June 2002, 06:44 AM   #3
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All the top and bottom emitter resistors go to the one line that feeds the speaker, so you take it from there the same as usual. I wasn't meaning that each extra set of transistors was independently feeding it's own speaker, rather that as you add another speaker in parallel with the rest on the rhs, you add another pair of transistors or more transistor muscle on the lhs, all feeding the same line.

GP.
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Old 22nd June 2002, 07:23 AM   #4
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1 amp per speaker or 2 is the only pro way to go .... redundancy rules!
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Old 22nd June 2002, 11:32 AM   #5
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Default Deafness

Hi AudioFreak, please explain this to young Kilowatt for us will you - it seems he still can't grasp this concept.
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Old 22nd June 2002, 11:41 AM   #6
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I know the feeling Mr. Feedback, but it appears that he is SLOWLY agreeing to listen. Next on the hit list is SliceMaster :O

p.s. I am not that much older than Kilowatt myself actually.
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Old 22nd June 2002, 11:51 AM   #7
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Default More horse power.

Hello Graham, this is indeed the technique used in pro-sound amplifiers suitable for driving low impedence loads.
For given power rails, adding extra output pairs will allow low impedence load operation without exceeding ouput transistor SOAR limits.
The caveats to this is that a stronger driver stage is required, and output transistor emitter resistors to ensure current sharing.
For best performance matched output transistors are needed.
For example my Jands JC-1000 amplifier has 12 MJ-15003/4 To-3 devices per channel.
2 are drivers, and 10 are outputs.
The pre-drivers are MJE 340/350 from memory.
These are used as drivers in lesser amplifers.
This monster (50 kG +) is rated 500+500 into 4 ohms and won't blow up if driving 3 by 8 ohm loads (2.66 ohms) per channel.
Serious power and very clean, and for home purposes infinite.
Perreaux 8000 is rated to drive 2 ohms via a weeks salary worth of To-3 mosfet outputs, and do this all day, and reliably.
I agree that if bothering to build an amplifier, it must be designed for performance and reliability into low impedence loads.

Regards, Eric.
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Old 22nd June 2002, 12:03 PM   #8
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Default Blockheads !

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.

Regards, Eric.
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Old 25th June 2002, 08:19 PM   #9
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Default amp power

transistors are current devices as opposed to tubes which are voltage devices, so it only makes sense to use more output transistors and lower impedance speakers
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Old 25th June 2002, 09:46 PM   #10
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Default Super Low Z speakers

I've been seeing a lot of 5V 100A+ switching power supplies at flea markets and swap meets in the last couple years. I have been thinking about how to make real low Z speakers so these super cheap (usually <$20), ultra high current supplies could be used.

Ribbons come to mind- maybe something like Apogees... Or maybe rewind the voice coil in a bass driver with just a couple turns of wide, flat aluminum or copper strap.

Maybe a class D or Tripath type amp- low voltage output transistors would be no trouble at all to find...
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