Having an issue with a MOSFET in my Blue Hawaii - diyAudio
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Old 20th April 2011, 04:33 AM   #1
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Default Having an issue with a MOSFET in my Blue Hawaii

I have just purchased a Blue Hawaii headphone amplifier (HeadWize - Project: Blue Hawaii Hybrid Electrostatic Amplifier for Stax Omega II Headphones by Kevin Gilmore) I'm a novice with electronics, having built a few solid state amplifiers. What I am finding is that I have a power supply MOSFET that is currently running ~20c higher than the other. I disconnected each channel of the amplifier and noticed that the MOSFET still ran considerably hotter, so I do not think it is an amp channel drawing far more current. That leaves bad component(s) in the supply I think. Any ideas on where I should start? This is the supply schematic: http://gilmore2.chem.northwestern.ed...gilmore4_2.png This is a picture of what the amplifier looks like: http://gilmore2.chem.northwestern.ed...gilmore4_4.jpg

Thanks!
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Old 20th April 2011, 06:58 AM   #2
singa is offline singa  Singapore
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Hi, the mosfet power supply looks simple enough...Try measuring voltage
across the 3 zener diodes they should be the same for the good channel.
You could swap the mosfets or replace with another if you've got a spare.
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Old 20th April 2011, 01:33 PM   #3
grawk is offline grawk  United States
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He's gotten this answer elsewhere, but when it came out that he used to go by the handle "trevornetwork", selling other gilmore amplifier designs that were poorly built and dangerous, he was banned.
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Old 20th April 2011, 02:34 PM   #4
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Ok 'Grawk'. I am not sure what your issue is, but just because I made a poorly built amplifier -SIX- years ago and was banned on A DIFFERENT FORUM does not mean that I cannot solicit the opinion of a more competent forum regarding an amplifier that is obviously not performing as it should. Putting it simply, kindly go away unless you have something useful to contribute.
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Old 20th April 2011, 02:41 PM   #5
SY is offline SY  United States
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Gentlemen, keep to the topic. Personal attacks are against forum rules.
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Old 20th April 2011, 06:20 PM   #6
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Ok. I've performed the measurements.

For the hot MOSFET. The series zeners measure at: 154V, 153.6V, 50.1V. For the other MOSFET the measurements are: 156.9, 158.1, 52.3.
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Old 20th April 2011, 10:38 PM   #7
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Do you mean one channel is hotter than the other (same device), or one heat sink is hotter than the other heat sink on that same channel?
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Old 20th April 2011, 10:40 PM   #8
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^ Good question!
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Old 20th April 2011, 10:43 PM   #9
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One MOSFET's heatsink on what I think is the negative rail is 20c+ hotter than the one on the positive rail. The reason why I disconnected each amp board was to check if one of the amp boards was causing additional load on the power MOSFETs. Since that did not seem to be the case as the same MOSFET heated up whether the left or right amp board was connected I suspected a component(s) on the supply board.

I hope I am answering this question correctly. Please let me know if I can clarify.
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Old 20th April 2011, 10:54 PM   #10
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why is it hard to believe that one rail would have a larger current draw than another? Do you understand what grounded grid means?

I'd focus in understanding how basic circuit elements work, like resistors and diodes and then coming back to this "perceived problem" when you have gained a bit more understanding. It seems that you are not even sure which components form the "positive rail" and which are the "negative rail". Also, identify which componets are BJTs. Figure this out first and we can go from there.
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