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Old 1st January 2013, 03:05 PM   #751
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The bias is related to heat. The hotter they get, the less bias it takes for a given current. You decided you bias at operating temperature, which is correct. When you turn the amp off and it gets cold, the same Vgs produces les current. As it warms up, the temperature increase once again cause the bias to rise. I do wonder how hot they are running. Can you put you r hand on the sinks for 5 seconds? Maybe should back down to 3 pairs or consider monoblocks. Hope you enjoy.
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Old 1st January 2013, 03:14 PM   #752
anilva is offline anilva  India
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Thanks. I backed down my bias to 250mV as of now and it has climbed to 270mV ever since (30 minutes). The heatsinks are passing the 5 seconds touch test so far, but just about.
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Old 1st January 2013, 03:15 PM   #753
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hello. have you messured 47VDC rails with amp running at 2.4A bias? or is it only calculated? i would expect about 41-42VDC rails from 2x32V sec.
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Old 1st January 2013, 03:17 PM   #754
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Quote:
Originally Posted by anilva View Post
Thanks. I backed down my bias to 250mV as of now and it has climbed to 270mV ever since (30 minutes). The heatsinks are passing the 5 seconds touch test so far, but just about.
You have enough current that thermal stability has to be main issue unless you can do something about the heat. Consider that it may warm some playing into a load. IN truth, at those bias levels, the diodes are a non contender unless you are playing into brutally heavy load. In that case yo have a heat problem.
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Old 1st January 2013, 03:24 PM   #755
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Originally Posted by anilva View Post
Thanks. I backed down my bias to 250mV as of now and it has climbed to 270mV ever since (30 minutes). The heatsinks are passing the 5 seconds touch test so far, but just about.
i have always said that v3 stereo amp with one side heatsink and natrual cooling is just about impossible
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Old 1st January 2013, 03:59 PM   #756
anilva is offline anilva  India
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hello. have you messured 47VDC rails with amp running at 2.4A bias? or is it only calculated? i would expect about 41-42VDC rails from 2x32V sec.
At load the DC rails are at 43V each.
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Old 1st January 2013, 04:01 PM   #757
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i expected it would be at a bit lower then 47VDC
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Old 1st January 2013, 04:12 PM   #758
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At load the DC rails are at 43V each.
I advised the holed bottom and this cover (HIFI2000). A fan in the center of the lid on the inside will give much freshness. Congratulations for the work
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Old 1st January 2013, 04:13 PM   #759
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by anilva View Post
At load the DC rails are at 43V each.
Interesting. In NP's paper, the F5T V2 schematic specified a 32V rail voltage. However, in the V3, no numbers were given. I assumed (probably wrongly) that the required rail voltage is still 32 V. However, in the text of the paper, NP use an example of : 36 V secondary to give 48 V rail. However, in the PSU schematic, he still shows caps rated at 50V. So the question is, what should be the rail voltage be for V3? I suppose that higher the rail voltage, higher the output (provided the PSU can pump in more juice when needed).

Thanks!

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Old 1st January 2013, 04:15 PM   #760
anilva is offline anilva  India
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i expected it would be at a bit lower then 47VDC
I mentioned that it is 47V DC at no load earlier. Looks like I have to use a quite cooling fan mounted to the top cover to evacuate hot air from inside and also provide enough ventilation to the bottom cover to enable air flow.
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