can someone help me on my first mosfet amp?

happyboy · 23rd January 2006, 02:42 PM

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

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
http://www.bmm-electronics.nl/docume...ild/IRF530.pdf

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.

23rd January 2006, 02:42 PM	#1
happyboy diyAudio Member Join Date: Jul 2004 Location: -	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

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23rd January 2006, 04:12 PM	#3
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	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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