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Post by floriangerard51 on Mar 12, 2012 17:42:33 GMT
hello, I'm currently buidling a linear PSU unit based on a LT1083CP. And i have some problems....it does work with the amp. I explain me. First thing is to test how much current is drawn by the amp with all the mods i did. Test gives me 1.4A and 23.95V with the stock SMPS PSU. Si built my PSU with a dual rail PCB as shown on the pictures. I did some tests and if i use some 20W resistors i can find some current and voltages... Without any charge: Voutputtransffo = 28.1VAC VinputLT1083 = 37.7VDC Voutput LT1083 = 27.6VDC IoutputLT = nothing connected With a 20ohms 20W resistor: Voutputtransffo = 27.6VAC VinputLT1083 = 31.4VDC VoutputLT1083 = 26.5VDC IoutputLT1083 = 1.32A With the amp connected: Voutputtransffo = 27VAC VinputLT1083 = 33.4VDC Voutput LT1083 = 6.2VDC Ioutput = 0.8A I can't understand why the PSU can't get to the voltage?! Any change in the output voltage of the PSU from 22V to 28V when i connected the amp it scale down to 6.3V.... I did a test of the PSU with 3 resistors in parallel 3X39ohms to get even much more current to test the PSU and it works with 27.6V and 1.96A....which is more than enough if i'm based on the first measurement... here the link of the pictures of the PSU and the schematics of the PCB. schematic: www.mediafire.com/?a2r69wcbu08yp67picts: www.mediafire.com/?0sxrhdveavi7619www.mediafire.com/?diy6j4adi808rsvwww.mediafire.com/?dajw3wgpy561k6xwww.mediafire.com/?tq1apesmfkk7u6hwww.mediafire.com/?7bbfrngbhq7tb97www.mediafire.com/?br5g07x2wjt59jfwww.mediafire.com/?z2cbt5ccwdisty3
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Post by floriangerard51 on Mar 17, 2012 16:29:29 GMT
Here is a solving of the problem,
Thanks to Frans (alias Solderdude) i made some troubleshooting and it can be useful for everyone using a Power Supply design like the JLH PSU Board or the PMILLET DC power supply board.
It seems that if you are using after the Vout of the LT108X any caps higher than 1000uF then the LT place itself in a safety mode delivering only 6.3V....
I do recommend then to place a small resistor (1ohms) with the input orignals caps (mine is a 3300uF 35V on the Bravo V2) or the other option is to replace the input cap with a smaller one like 470uF....
i'll post later the finished PSU inside and outside pictures and the effect if there is any on the amp.
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Post by pandapops on Mar 18, 2012 4:34:27 GMT
With a high current like that having 2 stage regulation using IC regulators will give very low noise levels, pretty much like premium super regulators, also droppng the voltage more gradually means that each reg will individually give off less heat, you've got 5W there to disipate and without a really big heatsink that will be seriously hot.
You can always blag IC regs as samples.
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Post by floriangerard51 on Mar 18, 2012 15:20:05 GMT
well the LT1083 is mounted for test purpose on a very small heatsink and it doesn't heat anything ;-)
For final enclosure i have a 20x10x4mm backplate where the LT is mounted and a big heatsink! So no problems for the future.
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