having problem with mint amp i built :(

[tobrien]

hey guys,

I am new to the whole DIY audio scene, and instead of building a Cmoy as my first amp, i decided to do a mint amp. anyways i bought the premade mint board from tangentsoft and used an AD8620AR chip and for the buffers i went with Burr-Brown BUF634Us. anyways it works fine on the right channel but doesnt work on the left channel, like (i know this is dumb) but when i touch the metal legs with my finger on either the right channel buffer or amp chip the sound goes kind of grainy and the volume lowers, but this does not happen with the left buffer chip. So i was wondering what might be wrong with it. i do not really know where to begin.

can any of you guys help me? it would be greatly appreciated as this is a belated fathers day gift for my dad

 

[ssmith187]

ics:

 

[tobrien]

Quote:

Originally Posted by ssmith187 ics:

 

[BlazerFRS]

Ideally we want close up pics of the top and bottom of the board so the resident gurus here can examine your work and give you some advice.

Most of the time someone will see the problem, and tell you how to fix it up.

It could be any number of things, so without pics we're kind of working blind.

 

[tobrien]

ok, pics in one moment

 

[tobrien]

here are the pics, note that my camera isnt that great

http://jtobrien.net/storage/amp/bottom.JPG

http://jtobrien.net/storage/amp/top%201.JPG

http://jtobrien.net/storage/amp/top2.JPG

http://jtobrien.net/storage/amp/top3.JPG

the pics are on a very fast host

edit: hold on my htaccess needs to be revised for this forum

edit2: works now

 

[Megaptera]

It's difficult to tell from the pictures but it looks like you have one of the buffers on the wrong way -- probably the left one, if that's the one not working. All the chips should be oriented so that pin 1 is closer to the big caps than to the bank of resistors (pin 1 should have a little dot next to it, or some other indicator). You can generally tell how to orient an IC on a PCB by looking at the solder pads -- if one of them is, say, square or otherwise different, it's usually pin 1.

Touching the pins isn't necessarily a good diagnostic tool. About half of them carry an electrical signal of some sort on the chips you're using, so touching more than one will short them together -- never a good thing, sometimes a very bad thing.

 

[MisterX]

Quote:

It's difficult to tell from the pictures but it looks like you have one of the buffers on the wrong way

It sure is.

 

[tobrien]

Quote:

Originally Posted by Megaptera It's difficult to tell from the pictures but it looks like you have one of the buffers on the wrong way -- probably the left one, if that's the one not working. All the chips should be oriented so that pin 1 is closer to the big caps than to the bank of resistors (pin 1 should have a little dot next to it, or some other indicator). You can generally tell how to orient an IC on a PCB by looking at the solder pads -- if one of them is, say, square or otherwise different, it's usually pin 1. Touching the pins isn't necessarily a good diagnostic tool. About half of them carry an electrical signal of some sort on the chips you're using, so touching more than one will short them together -- never a good thing, sometimes a very bad thing.

so, i should turn the buffer chip around basically? how would i go about getting the chip off? all i have is a solder sucker and a good Hakko 40w iron

edit: i do believe you are correct about the dot thing and the orientation, i see on the working one a black shiny dot closer to the caps, and on the not-working one i see a black shiny dot closest to the resistors

 

[MisterX]

Quote:

so, i should turn the buffer chip around basically? how would i go about getting the chip off? all i have is a solder sucker and a good Hakko 40w iron

I would use the big blob of solder method.....
Fill the leads on one side of the buffer with solder and gently lift it.
Repeat for the other side.
Be carefull not to oveheat it.


Dunno if this will help but this how the buffers should be placed

 

[tobrien]

Quote:

Originally Posted by MisterX I would use the big blob of solder method..... Fill the leads on one side of the buffer with solder and gently lift it. Repeat for the other side. Be carefull not to oveheat it. Dunno if this will help but this how the buffers should be placed [MG]http://photo.head-fi.org/data/500/4330board-med.JPG[/IMG]

ok, i'll give that a try, thank you!

 

[tobrien]

Quote:

Originally Posted by MisterX I would use the big blob of solder method..... Fill the leads on one side of the buffer with solder and gently lift it. Repeat for the other side. Be carefull not to oveheat it. Dunno if this will help but this how the buffers should be placed [MG]http://photo.head-fi.org/data/500/4330board-med.JPG[/IMG]

ok, i got the chip turned around, and i can hear music on the left channel (which was the buffer i turned around) but it's rather weak, the right is much strronger.

did i damage the chip or something?

 

[MisterX]

Could be.... they don't like being put in backwards.
Check everything else and make sure the problem is really the buffer.

 

[tobrien]

Quote:

Originally Posted by MisterX Could be.... they don't like being put in backwards. Check everything else and make sure the problem is really the buffer.

what do you mean they dont like being put in backwards? you mean like putting them in the wrong way the first time hurts them?

 

[Megaptera]

Basically, putting it in backwards means that you've connected the power rails (the pins marked V+ and V- in the datasheet) to pins that are not supposed to have a lot of power coming into them. Best case scenario is that the power rails were connected to non-connected pins (that aren't connected internally to anything) but I don't remember the BUF634's pinout off the top of my head and I wouldn't count on that happening. It's quite likely the chip was damaged, basically.

It's not the only thing to check, though: look for any solder bridges along the left channel, and double check your resistor values to make sure everything's in the right place.