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Old 6th January 2013, 04:53 PM   #111
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Found 0.047, 0.1, and 0.22 in the parts bin. But I have to place an order for the rectifiers anyway so I guess I might as well get some others too.
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Old 10th January 2013, 07:42 AM   #112
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She lives! I get about 21VDC under load measuring 18mv of AC ripple with my fluke 45 bench top DMM. I started with the 0.1uF film caps across the rectifier AC tabs. Will try other values once my other rectifiers come in.

Not sure if its working correctly yet but I do get music out the end. I might try eliminating the input caps as well. Need to measure my preamp to see if there's DC there.

Click the image to open in full size.
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Old 10th January 2013, 11:02 PM   #113
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I've noticed the heat from the output MOSFETs is much different from the current source mosfets. Is that normal?
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Old 10th January 2013, 11:03 PM   #114
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something is wrong

either with amp , or with your noticing

choose

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Old 10th January 2013, 11:21 PM   #115
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must be the amp... My noticing is flawless. :P

I thought I measured the bias across the resistors to be the same across all of them... but I could be mistaken. What else can I measure to help trouble shoot?
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Old 10th January 2013, 11:25 PM   #116
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with signal , or without ?

what's physical layout , meaning - how you grouped mosfet banks ?

maybe hotter ones are just on naturally hotter area of hsink

dunno , without pics
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Old 11th January 2013, 12:29 AM   #117
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Physical layout is the same across all four banks. Each bank has four mosfets each. They are on their own heat sink (you can see from post #112 above that the four heat sinks are 2x2 front to back.)

This is likely with signal and without signal. I noticed it initially without signal but it's still happened with signal. Although I didn't let it go very long.

I'll take some pics and some more thorough measurements tonight.
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Old 12th January 2013, 01:49 AM   #118
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Well, the pics aren't going to do much good. They all look exactly the same... 4 MOSFETs per heat sink. I measured all 16 resistors (0.47R) and they are all at 450-460mV and thus, biased at about 1A. Does that not indicate they are all biased the same? Or am I missing something entirely?

Also, for what it's worth, I'm drawing about 1.75V across each of my 1R resistors in my CRC (5 per rail) so if V=IR, I'm drawing about 8.75A per rail which seems about right.

And still, the heat across the CS and output MOSFETs is significantly different.

It plays music... but not that well based on my ears but it's only one speaker so a bit hard to tell for sure. My guess is that something is wrong, but there's also the 4.7uF input caps that may be causing an issue. I'm going to try bypassing them to see if there's a difference... my source doesn't have more than a couple hundredths of a mV of DC so I'm not worried at all.
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Old 12th January 2013, 02:46 PM   #119
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ok - I presume that DC offset between outputs ( + and - ) is near zero ;

what's offset between outputs and gnd ?
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Old 12th January 2013, 05:46 PM   #120
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Yes, near zero. Output to ground was about 10V at startup but I haven't let it warm up fully before taking measurement. I'll try that today and also play with the vr2.

On a separate topic, is there a guide somewhere as to what conditions to do function generator testing? I hope to have one soon so just wanted to see what freq and amplitude scenarios I should plan on measuring with the scope.
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