Development 500 W - 2 KW @ 2 OHM Amp only with Mosfet NPN Devices - diyAudio
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Old 14th October 2007, 08:55 AM   #1
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Default Development 500 W - 2 KW @ 2 OHM Amp only with Mosfet NPN Devices

Hello

For long time i have designed with a friend Mosfet amp, the amp is working very stable with natural sound, railvoltage is +/- 90 V

I have see the N Channel schematic from QUASI and want modify my Mosfet Amp.

Id like to replace IRFP 9240 with IRFP 240 to quasi complementary output stage

I have replace IRFP 9240 with IRFP 240 in schematic , could this work only with N Devices ?

If not what is important to change or to add for stable working ?
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Old 14th October 2007, 09:03 AM   #2
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If you have to ask I have to say that you aren't qualified/experienced enough to make the changes to such a powerful amp.

The schematic you posted is barely readable, from what little I can make out it looks like it will immediately set on fire when you apply power, with the modifications you have made. As the whole bottom bank of MOSFETs goes into saturation.

Why modify the amp if it's working fine? You will not gain any benefit whatsoever simply by using all n-channel devices.
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Old 14th October 2007, 09:55 AM   #3
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The Problem is the P Channel Mosfet, its not possibile to get High Power high Voltage P Mosfet equal. to N Channel Mosfet for good results in an audio amplifier.

First I want replace P Channel Mosfets with N Devices in the schematic.

If its working (stable) with N Devices i want upgrade the N Channel Mosfet amp for high Voltage > 100 V and high power.


Can you help me
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Old 14th October 2007, 10:14 AM   #4
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The complementary amp in the schematic before you modified it will do at least 1500W into 2 ohms if you double the number of MOSFETs.
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Old 14th October 2007, 11:27 AM   #5
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you'll have to add a driver stage after the VAS for you to do a quasi complementary....the case of your VAS topology does not allow you to directly do this..
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Old 14th October 2007, 05:04 PM   #6
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@richie00boy ....1500W into 2 ohms if you double the number of MOSFETs.

ok but i think i need much higher Rail Voltage > +/- 90 V for 1500W into 2 Ohms and some people told me more than +/- 100 V Rail Voltage and the Mosfets will destroyed. How much could be the Rail Voltage with mosfets IRFP 9240 and IRFP 240 to upgrade this amp 1500W 2 ohms?

@ongthrow.... to add a driver stage after the VAS the case of your VAS topology does not allow

Can you help me and add the important driverstage after the VAS for quasi complementary into schematic because i am not qualified/experienced enough to make working changes

Thank you
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Old 14th October 2007, 05:38 PM   #7
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The modifications required are beyond your ability I'm sorry to say, the PCB will not accommodate them without fairly major work. You are much better building a correct design in the first place.
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Old 14th October 2007, 06:15 PM   #8
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ok i see

but I think about +/- 120V for 1500W 2 ohms with IRFP 9240 and IRFP 240 Mosfets

What is your opinion ?
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Old 14th October 2007, 06:49 PM   #9
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They are 200V rated so the highest rails you can use is +/- 100V.

Why do you need 2kW? Can you not use several amps rather than one big one? Surely you must be powering more than one speaker with that kind of power.
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Old 14th October 2007, 06:52 PM   #10
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+/-90 Volts will easily give you 1500 Watts into 2 ohms. Even accounting for circuit losses.

In order to do this though you will need a 3kW to 4kW transformer and plenty of filter capacitance. Maybe about 400,000uF. That is per channel! If you want to be able to do this on a steady basis, you would probably need 30+ pairs of output devices. Again per channel. Also a very big soft start circuit with a very large relay! Also even if you did build it this way you would need a 3.2kW circuit to power it!! That's a 30Amp circuit at 110V and 15Amp at 220V!!!!!!!!

Why do you need 1500W into 2 ohms? Is this a PA amp?

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