Meta42 Problems

[damonpip]

Ok, I've already made a Meta with a OPA2132, now I'm trtrying to make one with a AD8620. I made an entire new Meta with the 8620, but the left channel didn't work at all. Next I used another 8620 and installed in in my original amp, after removing the OPA2132. Again, the left channel didn't work. I checked all the connections on both boards and found no problems. I soldered the chips directly on the SOIC pads, I didn't use an adapter. Any idea what the problem is? Also with the 8620 chip, it ocassionaly just clicks instead of playing the music. I was powering it wth a 12v wall wart, could low power be the problem?

 

[Arzela]

My ad8620 meta42 works fine off a 9v battery.

Maybe its a bad opamp you have. Tangent's web site has a simple op-amp testing circuit:

http://tangentsoft.net/audio/opamp-tester.html

 

[JMT]

I would suggest resoldering the chip to the board. Just heat up the joints again, maybe add just a touch of solder. Your symptom sounds like a cold joint.

 

[damonpip]

WOW it seems to have worked! Can't imagine the odds in that, soldering a chip badly in two boards on the same channel

 

[damonpip]

Or not, the left channel DOES work now, but it often starts sounding as though fireworks are going off in the left channel. Also, the left channel is much weaker than the right, could I have fried the chip? I do have a great soldering iron and I'm good at soldering so I would doubt that I fried it, but it is possible.

 

[Arzela]

I would try wiring the op amp so that
its 2 channels are reversed with respect to the board. This would show if its the
left channel of the op-amp that's bad,
or if there something wrong with the
left channel of the rest of the circuit.

However, it does seem that you have 2 bad ad chips....does your opa work in the new meta?

 

[tangent]

I have overheated that chip with a soldering iron before. If you aren't doing each joint in a few seconds, you're in danger of overheating it. The datasheet says a max of 10 seconds at 300C. This is probably somewhat cumulative: realize that in commercial board houses they stick the chip on the board with solder paste on each chip leg, stick it in a soldering oven and pull it out finished a few seconds later. That is, the entire process is completed in under 10 seconds. When you solder the chip by hand, you're likely to have the iron on the chip for more than 10 seconds total, so to compensate you have to let it cool down between joints. One way to do that is to just pause frequently, such as by cleaning your iron. Also, alterate side to side when soldering the pins, don't just run down one side heating that side up.

I've soldered well over a hundred of these chips now, and have only killed one due to heat. That one died because I spent too long getting the joints done, I'm sure of it.

 

[damonpip]

OK well, I didn't overheat the chip, I managed to get it off the board and put it on another board tha had worked fine before with the opa2132, and it works fine. The newer boards I made used different gain resistors, so is there SOME way that gain resistors could screw up the out put that much. I made two of the boards and checked them very well for soldering problems, so I really can't imagine what the problem is.

 

[tangent]

It may simply be that your surface-mount soldering technique is improving.