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Old 8th September 2002, 09:24 PM   #1
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Unhappy A sad Story

I have just completed my Alpha Current source Zen amp. Had it up and running and tested with an scope. Everything was fine.
Took it home and hooked it up to a tuner and a speaker for testing, decided to experiment with the pot to see what effect it had on gain. Fuse blows and signal dies. It wasnt the only thing that had died. I am using TO3 IRF044's and the Q1 on one channel had fried.
I suspect I know exactly what has happened. I have made a few parts substitutions, ie the dc drain resistor is 150ohm instead of 100ohm and the feedback resistor is 2.7k instead of 3k. I am also running the supply at about 43volts. I believe this combination was enough to build up the dc in the feedback loop to over 20volts, which would be enough to fry the gate.
The unfortunate thing is that the Mosfets have to be mail ordered and there is a minimum order value. They cost about $20 a piece so I would have to order a further 2 to get the minimum order. I have just been stung for a new car so this at the moment isnt good news. Wife tolerence is low.

Someone sujested using some standard transistors for the current source, any sujestions as to the effect this would have and what modifications I would have to make. Do I need to incorperate zeners to protecty the Mosfets in future.

Thanks for any advise.
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Old 8th September 2002, 10:13 PM   #2
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Try to find IRFP044 IRFP140/240 instead of the TO3, they will cost about 1,5Euro / Dollar. I use IRFP150 for my ZEN V2, and just bought 40 IRFP240 for about 1,3 Euro each foe the next amps.
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Old 8th September 2002, 11:52 PM   #3
skaara is offline skaara  Slovenia
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1,3 eu for irf240, thats chep, where did you bought them? are they from international rectifier?
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Old 9th September 2002, 12:56 AM   #4
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i wrote IRFP240 not IRF240.
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Old 9th September 2002, 06:36 PM   #5
skaara is offline skaara  Slovenia
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sorry, I meant irfp240..
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Old 9th September 2002, 08:13 PM   #6
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I doubt that the parts substitutions caused the
problem. More likely there is an error.
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Old 9th September 2002, 09:22 PM   #7
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skaara: http://www.reichelt.de/,

its 1,40 at the moment, if you by a lot a little bit cheaper. And it IR
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Old 9th September 2002, 11:02 PM   #8
skaara is offline skaara  Slovenia
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Thank you
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Old 10th September 2002, 05:58 PM   #9
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Default Your right Mr Pass

Something is very wrong with the circuit setup at the moment. I cannot work it out myself so will ask a friend to have a look. It didnt just take down Q1 it also took down Q2.
I suspect that it was a power surge that might have done it from a lose connection to the big filtering caps, but I cannot be certain.
Having been stung so badly I am giving it a bit of a rest for the moment. I have to admit my electronics experience has been outstripped by my enthusiasm.
I will get things going with IRFP044's next time. Pity as my heatsinks are setup beautifully for TO3's.
I will keep you posted when I have a result.
Shoog
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Old 10th September 2002, 06:25 PM   #10
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Shoog, where did you get the IRFP044's?

My set of Zen v4's still needs 2 of those (plus some spare if needed)
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