Digi's GC not working.

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i built digi's boards as he posted, i have the reg's set 28.25V. I left out the input cap and output resistor. The first time i pluged it in for a test go with the inputs shorted. The + regulator blew, i noticed that the dc trim pot was at max after i read it with a dmm and it said it was at 200k. I thought it would not have mattered. I replace the reg that blew with a new one and it didnt blow. I never got a dc offset reading on digi's boards like i did on brain's boards that i got last week. Not sure what the problem was but when i did get a reading it said it was -25.4v. When i did a reading with out shorted inputs i got something around 25mv. I took so many readings i got lost. I have jumper wires where the input cap and output resistor goes. Pluged in the input from a cdplayer and no sound. Checked my board for anything shorting out nothing all the connections look good (soldered ones too). Im lost as to where to go next.

p.s. Digi's boards are inverted topology.
p.p.s. Brians boards work just fine with the regulater supply and i get sound. With didi's everthing looks good but no sound.
*give me a few and ill have pic of the board

thanks in advance for the help
 
I really cant tell by the picture but it look like the resistor is on the wrong pins. If it is an inverted amp,the feedback resistor should be on pin 3 and pin 9

Have you measured the resistance bewteen pins?

Is the power supply working properly without the amp connected?
 
jaudio said:
I really cant tell by the picture but it look like the resistor is on the wrong pins. If it is an inverted amp,the feedback resistor should be on pin 3 and pin 9

Have you measured the resistance bewteen pins?

Is the power supply working properly without the amp connected?

yes the psu works just fine with out anything connected and like i said above im using briangt's lm3886 boards on it. yes the resistance is 219k as my ratshack meter measured. and they are connected to pins 3 and 9.
 
Re: 3886 in 3875 boards?

Cobra2 said:
please show more pictures or links to the pcb-design
3886 will not work in 3875 board without mods.

Arne K

edit...I'm too slow in the morning...


all the links from digi's boards are here in this link...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=41746


@digi
the caps from brains boards were 47uf not 4.7uf so i might have to order some then...

*edit*
morning ? i havent been to bed yet... getting digi's board to work and going over stuff over and over is starting to bug the hell out of me. :hot:
 
Nordic said:
Can't see anything obvious, unless the chip is blown...
Have you tied removing the chip from the PCB and measuring the voltage at the pin's holes?


with the chip in place im getting
pin 10 -20v
pin 9 -20.8v

pin 1 28.2v
pin 4 -28.4v
pin 5 25.2v

*edit* i have no other boards to test. Since i only bought enough to build 2 of didi's amps, with some extra parts.
would a 47uf be that big of a difference vs the 4.7uf digi has listed to test?
 
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