MOSFET Amplifier IRFP240/IRFP9240

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#961
AndrewT said:
3pair output stage equals 6 source resistors.
Set the bias voltage low to start with, maybe 10.0mVdc across Rs1 and measuure all 6 after they have reached equilibrium.
Then increase in 10.0mV increments allowing time to resettle and re-measure.
By the time you get to 50mV (100mA) you have a table of measurements for all 6 Rs
You will see if they all remain very similar, or some wander off a little, or a lot. This will really show how well you selected for Vgs.

It was a test like this that showed how much better a thin mica is at transferring heat compared to a good quality low thermal resistance soft thermal washer. I had used my last three Thermal washers for all the upper devices and reverted to mica for the opposite side.
Click to expand...

Hi AndrewT, thanks a lot for your advice again. So, it`s time to work, soon I gona say something.

Regards
 
#962
Hi AndrewT, the amplifier is working good the powers are more or less in balance the sound is charming, but I had to run a little beat because heat sink is only for test, is not enough. I put 47mV in S resistors because they are R47. Thanks for your suport and thanks to Mr. Mile also.

Regards and Pozdrav
 

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#965
Hi Mr. Mile, I would like to hear something from you. I put 1Khz and 8R resistive load and I got this. The positive side almost clip and de negative side is as you can see in the photo (20V per divsion). I replace the drivers by 2SC4793 NPN positive side and 2SA1837 PNP negative side. Thanks in advance.

Pozdrav
 

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#966
kandimba said:
Hi Mr. Mile, I would like to hear something from you. I put 1Khz and 8R resistive load and I got this. The positive side almost clip and de negative side is as you can see in the photo (20V per divsion). I replace the drivers by 2SC4793 NPN positive side and 2SA1837 PNP negative side. Thanks in advance.

Pozdrav
Click to expand...

Bias circuit is in positive side and clip is unsimetrical... it is ok.
Regards
 
#977
The TL071 (and similar older FET opamps) will suffer from latch-up to the negative rail during clipping.

Even the lowly NE5532 sounds better, and does not latch-up.

I designed a commercial amplifier about 20 years ago similar to this with the TL072. The customer and I were auditioning it while being overdriven. He asked 'what is that horrible sound'. 'Latch-up' I replied. After substituting the NE5532 (with no other changes), the amp sounded much better at low volume levels, and did not latch-up when driven into clipping. We actually burned up a power transformer after driving into sustained clipping for over an hour. In the final design we ended up doubling the VA rating on the transformer.
 
#979
Hi, for the F100 amplifier, is it possible to use a short circuit protect circuit. Like, as in apex PA protect circuit...The amp works very well for most applications and in a PA kind of situation, it needs a short circuit protection.
 
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