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
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
also forgot to metion that on the second go around the trimmer was set to 6ohms or as close as i could get to zero. i even tried both inputs with no luck
An externally hosted image should be here but it was not working when we last tested it.
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.
hmm 80 views and no one can help?
also tried a second board i have setup same thing no sound coming out. I did install a new lm3886 on the other board ... how possible would it be to get bad chips?
got them from here
http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=320670
also tried a second board i have setup same thing no sound coming out. I did install a new lm3886 on the other board ... how possible would it be to get bad chips?
got them from here
http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=320670
digi01 said:try to add input caps.
P.S.
have you setup the mute resistors?its on the bottom layer...
good luck
Z
yes i do have the mute resistors... i thought the input caps were optinal... i do have 2 4.7's from brains boards i wound up not using... ill go find them and try then...
Re: 3886 in 3875 boards?
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.
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.
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?
had to do some digging but here is digi's work.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=33802&highlight=digi01
and just in case for further looking
http://www.diyaudio.com/forums/showthread.php?s=&threadid=46609
digi has his working and i just dont know where i went wrong or if something is dead/wrong.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=33802&highlight=digi01
and just in case for further looking
http://www.diyaudio.com/forums/showthread.php?s=&threadid=46609
digi has his working and i just dont know where i went wrong or if something is dead/wrong.
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