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Old 10th March 2012, 01:31 PM   #351
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by solviken View Post
Thanks for answer But if i Bridge L15 would it be stable in 4 and 2 ohm? Was thinkin of using it as subwoofer amp!
The Reference Design shows the bridged rating for 8 ohms only.. so I would suspect no.. (4 and 2 are probably too low, something is going to loose its magic smoke..
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Old 10th March 2012, 01:47 PM   #352
alkasar is offline alkasar  France
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Quote:
Originally Posted by solviken View Post
But if i Bridge L15 would it be stable in 4 and 2 ohm? Was thinking of using it as subwoofer amp!
Remember that in a bridged amp, it is as if each half-bridge "sees" half of the load. Bridged amps usually target 8ohm and more loads. They rarely support 4ohms or you would have to drastically limit the power. Opposite to your goal.
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Old 10th March 2012, 01:53 PM   #353
alkasar is offline alkasar  France
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Originally Posted by MrSlim View Post
the L25D is even higher power than it (a variant not discussed in the Ref Doc).
isn't L25D an exact implementation of IRAUDAMP7S as in page 30 of the ref doc with two fets per channel ?

http://www.inductor.com/irf/iraudamp7s.pdf
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Old 10th March 2012, 04:32 PM   #354
alkasar is offline alkasar  France
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re-read my sentance above. really unclear

to make it simple, it seems to me that 2xIRFB4020 mosfets are functionnally equivalent to 1xIRFI4020 half-bridge integrated package.
Do I miss something ?
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Old 10th March 2012, 06:57 PM   #355
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Originally Posted by alkasar View Post
re-read my sentance above. really unclear

to make it simple, it seems to me that 2xIRFB4020 mosfets are functionnally equivalent to 1xIRFI4020 half-bridge integrated package.
Do I miss something ?

Yes functionally the same, however you missed something

IRF4020H-117P = Id at 100 deg C = 5.7 Amps Cont.
http://www.irf.com/product-info/data...4020h-117p.pdf

IRFB4020PBF = Id at 100 deg C = 13 Amps Cont.
http://www.irf.com/product-info/data...rfb4020pbf.pdf
You should see the Pd numbers, its almost shocking to see the difference between the two.

This is why I am a fan of the L25D from LJM and the L25DE from hien.t.nguyen for use with 8 Ohm speakers

Last edited by NissanSR20Man; 10th March 2012 at 07:11 PM.
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Old 11th March 2012, 01:12 PM   #356
alkasar is offline alkasar  France
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yes, seems that two single mosfets are more efficient than a couple

makes me believe that L25D is better suited for 4ohms than L15D.
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Old 11th March 2012, 02:15 PM   #357
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I believe the THD and noise floor is better with the L15 per LJM, you can get more power from L25 into 4 ohms, you better have a larger heatsink or a fan. I think you could blow away the power nameplate rating with proper cooling. The only drawback I see to the IRS designs is the heatsink is central to the board, menaing when really pushing it for long periods a fan is necessary. I am going to do a multichannel IRS amp using one of the two design mentioned above, my hangup is the fets not being moved to the perimeter like the LM3886/4780 kits
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Old 12th March 2012, 06:09 AM   #358
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I finally got around to building my L25D boards and linear power supply... One board works fine but for some reason the other one has a very loud hum. All of the solder joints seem alright. I'm not sure where to begin troubleshooting... Anyone have any ideas?
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Old 13th March 2012, 02:20 PM   #359
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No suggestions? I figured this would be the best place to ask
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Old 13th March 2012, 02:25 PM   #360
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DarpMalone, show some pics of your setup.
"hum" tests should be done with shortened inputs. Each input to it's ground.
If the hum stays, it means the amp is the source of it. Therefore we can start troubleshooting the amp, and not it's surrounding.
"hum" is 60-120Hz? Or noise?
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