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Old 26th February 2011, 01:53 PM   #1
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Default Mono Aleph J's

Recently built one of two AJ mono-blocks and have a question for Mr. Pass or anybody about max temperature on the fets. I can hold my hand on the HS's indefinitely, but more concerned about temp of fets. What range in C should i be looking for? Much thanks to Bill who help me do something i could not have done by myself without either blowing something up or buying multiples of new parts.
Offset side to side is 30mV and offset at terminals is 2mV. Both after about an hour. Bias is a little over 1A. HS's can take more, but am more concerned with mosfets,
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Old 26th February 2011, 01:58 PM   #2
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Sorry, but this has been asked ad nauseum in this forum. Probably in four threads on the first page.

If you can't find it using the forum search function, use google and add site:diyaudio.com

50C max operating T.
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Old 26th February 2011, 02:15 PM   #3
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Quote:
Originally Posted by Nelson Pass View Post
The device is rated at 150 watts at a 25 deg C case temperature,
derate at 1.2 W per deg C.

I like to run them around 25 watts, and I have run them as
high as 50 watts without excessive failure rates, but this is
heat sink dependent.

I am running my fets @ 25W but the case temp is 40C. Heatsinks can be touched indefinitely. Measures at exposed metal cutout on side, fets are hotter than 50C.
De-rating them according to above figures drops max dissipation to 130W.

Am i getting poor heat transfer if HS's are at slightly different temp than fet case
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Old 26th February 2011, 03:21 PM   #4
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I have ground hum. Have xlr pin in 1 and 2. Shield wire from trafo, line filter ground and psu ground all tied to same spot on chassis.
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Old 26th February 2011, 05:29 PM   #5
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Got rid of ground hum by rotating trafo. Sounds stupid but my a wise old man told me to do it and I have always found wise old men worth listening to.
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Old 26th February 2011, 10:20 PM   #6
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Worried about turn off thump(push out). More severe than turn on. My driver is FR and has max x-max of 8mm which only 6mm should be used for peaks in response. Turn off looks to be 1/4" of travel. Any suggestions? Tried searching but no answers. Perhaps my wording is wrong. I will probably get speaker protection circuit, but while waiting, would like solution if possible.
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Old 26th February 2011, 10:55 PM   #7
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everything counts

give us proper schematics of amp an PSU , along with pictures

it's hard to use crystal balls , these winter days
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Old 26th February 2011, 11:03 PM   #8
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Quote:
Originally Posted by Zen Mod View Post
everything counts

give us proper schematics of amp an PSU , along with pictures

it's hard to use crystal balls , these winter days
Using Brian GT boards. Thump is not unusual, from what I have read, and has to do with uneven DC drain, I think. Amp is functioning great otherwise. Plus, you have been around the block enough to draw the schematic in your head
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Old 26th February 2011, 11:14 PM   #9
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yes - but I don't know are you using schematic from my head



if that's the case - that you're using generic A schematic , along with generic PSU , along with generic shaped wiring - there is no need to worry - ppl are using the same even with dreky Lowthers
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Old 26th February 2011, 11:33 PM   #10
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There are some changes in places, of course. Amp is working great with 30mV offset between + and -. About 1mV of offset at speaker terminals. Bias is 1A per fet +or-, and dissipation is about 25W.
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