41hz Amp4 - Telling MOSFETS apart, and measuring Inductance without a metre

Peteruk · 27th July 2007, 12:35 PM

Hey all!

I've nearly finished a 41hz amp4 kit, but I've come across a pair of issues I could do with some advice on, and I can't seem to get the 41hz site to work for me.

If anyone can lend any advice, it would be greatly appreciated!

Firstly, how do you tell the difference between the N-channel and the P-channel Mosfets? They both appear to be in the same bag, and I can't tell the two apart

Secondly, is there any way you can measure an inductance without an inductance meter? Can you apply a signal with a signal generator and then measure the resistance with an ohm-metre, then do some formula work?

Thanks to all who can help!
peter

Conrad Hoffman · 27th July 2007, 01:31 PM

For the inductors, you can apply a signal through a resistor then measure the applied voltage, and the voltage across the resistor, and calculate, or if you have a known capacitor, resonate the inductor with the capacitor in series or parallel, and use the standard resonance formula to determine the inductance, IMO the better way. Not sure of any easy way for the MOSFETS, other than to apply a very limited DC supply and experiment with driving the gate to see which way it turns on and off. There will be a diode seen between the source and drain, so that's one clue as to the direction. The pinouts are usually pretty standard, so I'd start there.

Nordic · 27th July 2007, 01:58 PM

I can recommend the following project...
Pretty easy, although , you will also have to build a pic programmer (or get one from e-bay - like me)..

It is accurate to +-1%.. and can also be used to measure capacitors.

http://www.janson-soft.de/lcmeter/lcmeter.htm
Use google translate from german...

I also saw a new project like this... which sems to have a nicer PCB

http://tk5ep.free.fr/tech/lcmeter/fr/lcmetre_f.php
Use google translate from french

27th July 2007, 12:35 PM	#1
Peteruk diyAudio Member Join Date: Sep 2006	41hz Amp4 - Telling MOSFETS apart, and measuring Inductance without a metre Hey all! I've nearly finished a 41hz amp4 kit, but I've come across a pair of issues I could do with some advice on, and I can't seem to get the 41hz site to work for me. If anyone can lend any advice, it would be greatly appreciated! Firstly, how do you tell the difference between the N-channel and the P-channel Mosfets? They both appear to be in the same bag, and I can't tell the two apart Secondly, is there any way you can measure an inductance without an inductance meter? Can you apply a signal with a signal generator and then measure the resistance with an ohm-metre, then do some formula work? Thanks to all who can help! peter

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27th July 2007, 01:31 PM	#2
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	For the inductors, you can apply a signal through a resistor then measure the applied voltage, and the voltage across the resistor, and calculate, or if you have a known capacitor, resonate the inductor with the capacitor in series or parallel, and use the standard resonance formula to determine the inductance, IMO the better way. Not sure of any easy way for the MOSFETS, other than to apply a very limited DC supply and experiment with driving the gate to see which way it turns on and off. There will be a diode seen between the source and drain, so that's one clue as to the direction. The pinouts are usually pretty standard, so I'd start there.

27th July 2007, 01:58 PM	#3
Nordic diyAudio Member Join Date: Sep 2005	I can recommend the following project... Pretty easy, although , you will also have to build a pic programmer (or get one from e-bay - like me).. It is accurate to +-1%.. and can also be used to measure capacitors. http://www.janson-soft.de/lcmeter/lcmeter.htm Use google translate from german... I also saw a new project like this... which sems to have a nicer PCB http://tk5ep.free.fr/tech/lcmeter/fr/lcmetre_f.php Use google translate from french

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