white noise, almost no mic signal

[jdier]

Bought from someone else fully assembled but with white noise. it is rev 1.9.1 board. been checking it out this morning. All tests from assembly instruction work perfect.

R9 and R8 measured low at 12.2V.

U1 trimmed to exactly +18V - 18V (and holds constant)

close to 0V at the junction of R29 and R30.

J3 measures 30, 30 and then 48 (but only measures 48 when switch is flipped)

L3 and L4 measured super low.

I checked all of the resister codes and part placements and everything looks good, but it provides just a loud white noise. There is a very light mic signal under the white noise, but it is mostly white noise.

I get noise at all positions on the input and the gain, with and without a mic plugged in.

three N72's, 1 A12 and a T15 all working fine.

I tested U1 as instructed, wondering if there is a test for the other IC's...

any other suggestions for what I can do at this point.

[jdier]

Tim and I exchanged some emails as I was working to diagnose this C84 that was just barely passing sound, mainly making white noise.

Basically, the solution to my problem was here:
http://www.seventhcircleaudio.com/trouble.htm

After verifying all the components were populated on the board correctly and the initial power up tests worked right, I tested the other two IC/Opamps, which tested fine, then I started looking at each solder joint under a ring and found a trace that the original builder must have messed up.

One jumper, retest, and everything is working great.

Thanks again for the help Tim!

[valencyna]

What is the best microphone to use for speech recognition? I'm hoping that by purchasing a better microphone, that my speech recognition program will work more accurately! Right now i am using the microphone that's attached to my web cam, it doesn't seem to be working very well, i am using the speech recognition program that came with windows vista! Thanx for your input.
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