Development 500 W - 2 KW @ 2 OHM Amp only with Mosfet NPN Devices

[Dorian Gray]

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 ?

 

[richie00boy]

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.

 

[Dorian Gray]

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

 

[richie00boy]

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.

 

[longthrow]

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..

 

[Dorian Gray]

@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

 

[richie00boy]

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.

 

[Dorian Gray]

ok i see

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

What is your opinion ?

 

[richie00boy]

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.

 

[Don S]

+/-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?

Thanks, Don

 

[Dorian Gray]

Yes its PA Amp and i want improve the design

 

[retrosong]

y this schematic ist not very clear picture pliz the postet clear picture?

 

[Don S]

Yes its PA Amp and i want improve the design

The original design is solid? I am guessing you are not getting 1500W into a 2 ohm load. Is that correct?

Thanks, Don

 

[Leolabs]

Better go for BJT,easier to find those high power(for audio),esp from OnSemi.

 

[Dorian Gray]

@ Don s

The amplifier is working with 4 Ohms very good, i dont have test 2 Ohms with full output power, and before i make new pcb i want inform me.

Its better to do it with N devices because its easy to find High Power High Voltage N Mosfet devices.

@leolabs yes thats right with BJT. You can build with BJTs very cheap amplifier but the sound with BJT is not so good.

The Sound with Mosfet Devices is another, better like a tube amplifier so i need help to make changes in schematic for N Devices.

And amplifiers with BJTs you can find enough in the market from China build for the big companies in USA

@ retrosong .... here is new schematic


This Mosfet amp with IRFP 9240 and IRFP 240 in output stage is working good and stable with very low bias power.

I have removed in schematic output stage IRFP 9240 and replaced with N devices IRFP 240. Could this work ?

If not who can help me to drive only N devices in output stage?

regards from Germany

 

[AndrewT]

Go and look at Quasi's designs.

 

[richie00boy]

I have already told you why your amp will blow up if you do those modifications.

 

[Dorian Gray]

@ richie,...

I need more information from you to understand it, can you help me, because im not technican ?

The amp is working very stable, i cant understand this, i think its easy modificatian only with N devices and +/- 90 V

Sorry for this stupid questions, but i want learn it

 

[AndrewT]

Hi,
go and read how a quasi complementary amplifier works.
Then find how to make FETs work with this topology.
Finally find how to make Vfets work properly.
The last bit is in Quasi's threads.

 

[Dorian Gray]

I will do it