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Old 1st December 2005, 12:57 AM   #1
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Default Digi's GC not working.

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
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Old 1st December 2005, 01:05 AM   #2
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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

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Old 1st December 2005, 02:09 AM   #3
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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?
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Old 1st December 2005, 02:23 AM   #4
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Quote:
Originally posted by jaudio
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.
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Old 1st December 2005, 06:45 AM   #5
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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/sto...oductId=320670
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Old 1st December 2005, 08:18 AM   #6
digi01 is offline digi01  China
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try to add input caps.

P.S.
have you setup the mute resistors?its on the bottom layer...

good luck
Z
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Old 1st December 2005, 08:23 AM   #7
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Quote:
Originally posted by digi01
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...
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Old 1st December 2005, 08:33 AM   #8
Cobra2 is offline Cobra2  Norway
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Default 3886 in 3875 boards?

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...
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Old 1st December 2005, 08:37 AM   #9
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Default Re: 3886 in 3875 boards?

Quote:
Originally posted by Cobra2
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...
3886inv gainclone PCB,group buy


@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.
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Old 1st December 2005, 08:47 AM   #10
Nordic is offline Nordic  South Africa
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Lol I built a stereo, dual rectified veroboard clone, burned out a resistor, traced the fault and repaired it, since you posted... will have some coffee, and then come and look through here to see if I can spot anything.
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