DJ, you will try to draw more power than the transformer can deliver: 1250 Wrms @ 4 Ohm. This is a theoretical figure and will be less in practice.
May I also point out that it is ridiculous of you to expect an answer within the hour!
HDTVman, it is true that an entirely accurate figure cannot be obtained but a maximum theoretical figure can.
/Marcus
May I also point out that it is ridiculous of you to expect an answer within the hour!
HDTVman, it is true that an entirely accurate figure cannot be obtained but a maximum theoretical figure can.
/Marcus
Check out www.sound.au.com where the articles for beginners probably would suite you. They are well written and are primarily covering audio.
Otherwise borrow a book on basic electronics from your school.
/Marcus
Otherwise borrow a book on basic electronics from your school.
/Marcus
DJ, it's required to know Ohm's law. This is your homework. I learnt this in school when I was 13-14 and I guess that even you have read something about electricity in school.
You are asking all the time about power, time to learn it! This is for your own good and for our patience.
You are asking all the time about power, time to learn it! This is for your own good and for our patience.
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Hi DJ,
Determining the max power that a transformer can deliver through an amp is a little more complicated than just Ohm's law although you do use Ohm's law on the way to the solution.
There are two limiting cases. How high a voltage the amp can deliver and how much current the amp can deliver. You have to calculate the max power each way for each load resistance and then use the smaller of the two figures for each load resistance.
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I am assuming you have a dual 50 V secondary transformer at 1200 VA and want to know how much power it will deliver into a 2 ohm and a 4 ohm load. Correct? I am also assuming you are using a torroidal transformer with a simple power supply design (a bridge rectifier and a pair of caps) and MOSFET output devices.
VDC = VAC x sgrt(2) ... 50 VAC x sgrt(2) = 70.7 VDC.
You will lose 2 volts in the bridge rectifer plus at full load your transformer voltage will typically sag about 4% so that means you will end up with rail voltages around +/- 66 VDC at full load.
If you are using MOSFET output devices (which I expect for an amp of this size) then you will probably lose another 5 VDC of the rail voltage in the output devices which means you will end up being able to deliver a peak output voltage swing of about +/- 61 VDC to the speaker.
VAC = Vpeak / sqrt(2) .. Max sine wave output signal = 43 VAC
Power from voltage into a given load is calculated as follows:
P = V x V / R
R = 4. P = 43 x 43 / 4 = 470 W
R = 2, P = 43 x 43 /2 = 940 W.
That is not the entire story however. Your 1200 VA transformer is able to deliver a max of 12 amps RMS at 100 V (dual 50 V secondaries. 1200 VA / 100 V = 12 A
Power from current into a given load is calculated as follows:
P = I x I x R.
For 4 Ohms: P = 12 x 12 x 4 = 576 W. This is higher than the voltage limit into 4 ohms so the voltage limit of 470 W into a 4 ohm load is OK.
For 2 ohms: P = 12 x 12 x 2 = 288 W. This is the lower than the voltage limit into 2 ohms so the max power your amp can deliver into a 2 ohm load without exceeding the power rating of the transformer is 288 W.
WARNING: You will easily be able overheat this transformer driving 2 ohm loads. I suggest you not use loads below 4 ohms with this amp and I would not use loads below 8 ohms in the bridged mode.
Note: The voltage limit calculations assume the transformer is outputting the nominal rated voltage. If the AC line voltage to the amp drops, then the max output power into 4 ohms will drop with it. Be sure to use large gauge extension cords to avoid voltage drops to the amp and also avoid putting too many amps on the same power outlet or you will lose max power capability.
DJ: Since you are so interested in High Power amps there is a very good book you should read. "High-Power Audio Amplifier Construction Manual" by Randy Slone. This is a good resource on building high power audio amps. His book includes an amp design (with PCB layout) for a MOSFET amp that delivers 550W into a 4 ohm load. This amp would be just about perfect for the transformer you have. Plus I believe you can purchase a double sided, circuit board with plated through holes from him to make that amp.
Here is Sloan's website
http://www.sealelectronics.com/
Final comment: If you are looking for max power into 2 ohm laod then you need a much larger transformer. Example: A 2500 VA transformer with dual 55 V secondaries is capable of delivering 1033 W into a 2 ohm load with MOSFET output devices.
May I suggest you also take a look at the QSC RMX-1850HD power amp. This is a two channel amp that will deliver 900 W per channel into 2 ohms loads or 1850 W bridged into a 4 ohm load. This amp is specifically designed for the thermal stress of driving subs which is what I expect you are trying to do. I can buy them here in the USA for about $450 each.
Phil
Determining the max power that a transformer can deliver through an amp is a little more complicated than just Ohm's law although you do use Ohm's law on the way to the solution.
There are two limiting cases. How high a voltage the amp can deliver and how much current the amp can deliver. You have to calculate the max power each way for each load resistance and then use the smaller of the two figures for each load resistance.
--------------------------------------------------------------------------------
I am assuming you have a dual 50 V secondary transformer at 1200 VA and want to know how much power it will deliver into a 2 ohm and a 4 ohm load. Correct? I am also assuming you are using a torroidal transformer with a simple power supply design (a bridge rectifier and a pair of caps) and MOSFET output devices.
VDC = VAC x sgrt(2) ... 50 VAC x sgrt(2) = 70.7 VDC.
You will lose 2 volts in the bridge rectifer plus at full load your transformer voltage will typically sag about 4% so that means you will end up with rail voltages around +/- 66 VDC at full load.
If you are using MOSFET output devices (which I expect for an amp of this size) then you will probably lose another 5 VDC of the rail voltage in the output devices which means you will end up being able to deliver a peak output voltage swing of about +/- 61 VDC to the speaker.
VAC = Vpeak / sqrt(2) .. Max sine wave output signal = 43 VAC
Power from voltage into a given load is calculated as follows:
P = V x V / R
R = 4. P = 43 x 43 / 4 = 470 W
R = 2, P = 43 x 43 /2 = 940 W.
That is not the entire story however. Your 1200 VA transformer is able to deliver a max of 12 amps RMS at 100 V (dual 50 V secondaries. 1200 VA / 100 V = 12 A
Power from current into a given load is calculated as follows:
P = I x I x R.
For 4 Ohms: P = 12 x 12 x 4 = 576 W. This is higher than the voltage limit into 4 ohms so the voltage limit of 470 W into a 4 ohm load is OK.
For 2 ohms: P = 12 x 12 x 2 = 288 W. This is the lower than the voltage limit into 2 ohms so the max power your amp can deliver into a 2 ohm load without exceeding the power rating of the transformer is 288 W.
WARNING: You will easily be able overheat this transformer driving 2 ohm loads. I suggest you not use loads below 4 ohms with this amp and I would not use loads below 8 ohms in the bridged mode.
Note: The voltage limit calculations assume the transformer is outputting the nominal rated voltage. If the AC line voltage to the amp drops, then the max output power into 4 ohms will drop with it. Be sure to use large gauge extension cords to avoid voltage drops to the amp and also avoid putting too many amps on the same power outlet or you will lose max power capability.
DJ: Since you are so interested in High Power amps there is a very good book you should read. "High-Power Audio Amplifier Construction Manual" by Randy Slone. This is a good resource on building high power audio amps. His book includes an amp design (with PCB layout) for a MOSFET amp that delivers 550W into a 4 ohm load. This amp would be just about perfect for the transformer you have. Plus I believe you can purchase a double sided, circuit board with plated through holes from him to make that amp.
Here is Sloan's website
http://www.sealelectronics.com/
Final comment: If you are looking for max power into 2 ohm laod then you need a much larger transformer. Example: A 2500 VA transformer with dual 55 V secondaries is capable of delivering 1033 W into a 2 ohm load with MOSFET output devices.
May I suggest you also take a look at the QSC RMX-1850HD power amp. This is a two channel amp that will deliver 900 W per channel into 2 ohms loads or 1850 W bridged into a 4 ohm load. This amp is specifically designed for the thermal stress of driving subs which is what I expect you are trying to do. I can buy them here in the USA for about $450 each.
Phil
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