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happyboy 23rd January 2006 02:42 PM

can someone help me on my first mosfet amp?
hello everybody, i am new here. first time dealing with mosfets. i recently built this circuit which can be found below. i tested only one channel of it and had problems. i tested it first without the mosfet load and the 7805 did manage to give me a 5V reading. but however, once i reconnected the mosfet load back, the 7805 ouput voltage jumps to around 11V. the rails voltage is around 16V. i tried hooking up a signal and a speaker but there was no sound. anyone got any idea what could be wrong? thanks in advance:)

lineup 23rd January 2006 03:07 PM

2 Attachment(s)
I recognize this circuit from
DIY Hi-Fi class A MOSFET amplifier

I do not know what can be problem.
Test that your 78L05 isnt broken.
Check that you have connected everything correct.

You have +16V and -16V ?

datasheet of IRF530

ilimzn 23rd January 2006 04:12 PM

This circuit will only work well if diodes D1, 2 and 3 are thermally coupled with the heatsink of M2. M2 and ancillaries are a current sink, and a rather convoluted one at that, look at some of N. Pass' designs for a simpler one. It is probably that the 78L05 is undercompensated, and it oscillates, since there is very little load. Put a 10uF electrolytic in parallel with C2, that should cure it.

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