IRFP250N - how to check input impedents and input db becs

[prabanjas]

IRFP250N

I have IRFP250N mosfet power amp(200w rms output with 35-0-35 rail) and want to know the input impedents and input db becs I am not getting output in driver even i am giving 20 db input. Its better If I get a good preamp circuit for this..

Thx in adv..

 

[Audioguru]

IRFP250N

Your amplifier cannot have 200W output with a supply that is only 70V total unless the amp is bridged or the speaker is less than 3 ohms.
Maybe its output is 200 Whats.

We don't know the amplifier's input impedance. it could be anything.
We also don't know how much gain the amplifier has. It could be anything.

 

[pranam77]

IRFP250N

If you dont mind uploading, may we have a look at your schematic which gives 200 watts?

 

[prabanjas]

Re: IRFP250N

no probs

but I dont have scematic becs I got this board from one of my friend. I am novice and dont hav much exp on mosfet power boards..

only stk and tda stuff i hav and not in mosfet and transistors..

I attached the image pls refer..

 

[Audioguru]

IRFP250N

The Mosfets have a high voltage drop when used in an amplifier. Then the "200 Whats" amplifier will produce only 45 watts at clipping into 8 ohms or maybe 80 Watts into 4 ohms.

Some of the old driver transistors are available only in India.

 

[prabanjas]

Re: IRFP250N

Thanx for ur reply..

The problem is input millivolt which I given is not matching and no output. Thats why I am asking a preamp which can produce enough power to buffer the input. Attached the BUFFER circuit which I used for this..

Kindly suggest me if any modification which I can do for this...(including may I change the OLD DRIVER TRANSISTERS)

 

[prabanjas]

Re: IRFP250N

Thanx for ur reply..

The problem is input millivolt which I given is not matching and no output. Thats why I am asking a preamp which can produce enough power to buffer the input. Attached the BUFFER circuit which I used for this..

Kindly suggest me if any modification which I can do for this...(including may I change the OLD DRIVER TRANSISTERS)

 

[Audioguru]

Re: IRFP250N

Your sub-woofer controller circuit cuts high frequencies above 8Hz.
It also cuts low frequencies below 25.2Hz.
The result is a peak at 18Hz with higher and lower frequencies rolled-off at 12dB/octave.
The sub-woofer is operated in a small sealed enclosure below its resonant frequency.

Nothing can be changed on the Mosfet power amplifier without seeing its schematic. Maybe the amplifier does not work.

 

[prabanjas]

Re: IRFP250N - how to check input impedents and input db bec

I left the Idea to do more research on IRFP 250.. becs its gone.( I given 5 mv input)

Can u suggest me a hi-fi subwoofer amplifier circuit which can work with 35-0-35 5A rail and reliable( with short circuit and thermal protection). I have only 10" 8ohm and 250w subwoofer and its should be enough to drive it.

 

[Audioguru]

With a total of only 70V, the output of the amplifier is about 64V peak-to-peak (or less) at clipping into 8 ohms if the amplifier uses normal transistors. Its output voltage and power are much less if the amplifier uses Mosfets.
64V p-p is 22.6V RMS. Then the power at clipping into 8 ohms is only 64W, not 250W.

There are millions of 64W amplifier circuits on the internet. The site where you found the sub-woofer control circuit has plenty of amplifier circuits.

 

[prabanjas]

Re: IRFP250N - how to check input impedents and input db bec

may I use LM3886 for this..

I thing its enough to drive 64w but want to know whether it will withstand 70v ??

If u have a suitable good scematic for lm3886 kindly help me..

thx.

 

[Audioguru]

The manufacturer's recommended schematic for an LM3886 amplifier is on its datasheet. It says with a plus and minus 35V supply, its power at clipping into 8 ohms is 50 watts.

Its max operating voltage is 84V but then its output power and dissipation power are much more and it gets too hot.