Ahahahh! you are right. sorry for "heart", i mean earth. not only bug english...i have brain that go..in automatic and joke
i thought so mate, no problem at all, but when talking of such important subject matter we have to make sure we are clear, so i asked for clarification.
haha, at least you make it obvious when you are in joke mode, most people take me far too seriously
i have brain that go..in automatic and joke
haha, at least you make it obvious when you are in joke mode, most people take me far too seriously
I agree on some important things. these effects are when they are concentrated in the software I'm developing (firmware). after 4 hours.
..Luckily you have a good sense of humor..eheh
Hi Back,
Red means that your output devices will melt if you run them under these conditions. The power envelope for a single pair of output devices really should be more like 350 watts, and I'll be updating the worksheet to fix a few small discrepancies around this.
If you setup conditions to drive 350 watts into 8 ohms, and then connect a 4 ohm load, you'll be asking a single pair of mosfets to deliver 700 watts and they won't last long under that kind of abuse.
If you want that much power, you'll need to start looking at more output devices. For 800W into 4 ohms you really should have 3 pairs of dual die lateral fets, and a whole lot of heatsink!
Cheers,
Owen
Red means that your output devices will melt if you run them under these conditions. The power envelope for a single pair of output devices really should be more like 350 watts, and I'll be updating the worksheet to fix a few small discrepancies around this.
If you setup conditions to drive 350 watts into 8 ohms, and then connect a 4 ohm load, you'll be asking a single pair of mosfets to deliver 700 watts and they won't last long under that kind of abuse.
If you want that much power, you'll need to start looking at more output devices. For 800W into 4 ohms you really should have 3 pairs of dual die lateral fets, and a whole lot of heatsink!
Cheers,
Owen
ok i understand all this and i am going two use to pairs of mosfets.
but what i don`t understand is this.
let`s say that i use two pair are capable of 700watt/4ohm
ok it`s plenty of power.
but my speaker drop lower than 4ohm around 3ohms actually.
i know i could lower the rails a little and go for 700watt/3ohm but since
i already have psu 75volt i wonder keeping the volume lower will i
take the 700watt or i have to go for lower rails or 3 pairs of output
devices because of current limit?
i would like to avoid both because i already have the psu and the output
devices will need matching and it` easier to match 2 than 3 pairs.
Hi back,
Keep in mind that regardless of the potential power output of the amplifier and the impedance of your speakers, the actual power produced and delivered to the speakers is a function of the amplitude of the signal. For example, most background listening uses somewhere around 1-10 watts. That means that a 700W amp would only be putting out 1-10W and the speakers would be absorbing 1-10W.
It sounds like the real issue is that you have a great power supply that you would like to use, but don’t really need as much power as it can put out. One simple option for using your brute of a power supply without burning out the output devices (one pair in this example) is to use a separate power supply for the LME at +/- 40 or 45 volts. Using the 75V power supply only for the output stage. This would prevent the output stage from ever attempting to deliver more than 312-378W into a 4 ohm load.
Regards,
Neel
Keep in mind that regardless of the potential power output of the amplifier and the impedance of your speakers, the actual power produced and delivered to the speakers is a function of the amplitude of the signal. For example, most background listening uses somewhere around 1-10 watts. That means that a 700W amp would only be putting out 1-10W and the speakers would be absorbing 1-10W.
It sounds like the real issue is that you have a great power supply that you would like to use, but don’t really need as much power as it can put out. One simple option for using your brute of a power supply without burning out the output devices (one pair in this example) is to use a separate power supply for the LME at +/- 40 or 45 volts. Using the 75V power supply only for the output stage. This would prevent the output stage from ever attempting to deliver more than 312-378W into a 4 ohm load.
Regards,
Neel
Would also mean the input stage clips first and that can be very nasty delivering DC into your voice coils and melting them within a few seconds.
And you'll be using expensive large heat sinks wasting heat for nothing.
In the grand scheme of things a lower voltage transformer is not all that expensive.
How sensitive are the speakers? Very sensitive ones will only require a lowish power, even though they may be 3 Ohms. If they are low sensitivity and you need to play them loud then another pair of mosfets is not all that expensive compared to the larger heat sink(s) you'll need.
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I question if that is a good idea.
With that power supply you might provide the output stage with a clipped signal.
The output stage (in general) should clip first; that is why the LME49830 runs on a higher supply voltage than the output stage.
By the way you hardly can have "too much" power as long as it is undistorted; most loudspeakers get damaged because of a distorting (clipping) amplifier, not because of (clean) high power when amplifying music.
Do you need the power of three output pairs?
When not, there is nothing wrong with a big supply for a single output pair, that is with the current capability. It would be nice however if you could cut the voltage down a bit.
How is the power supply; has it a toroidal transformer?