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Old 14th October 2011, 01:48 AM   #1
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Join Date: Mar 2011
Location: Walnut Creek, CA
Default Need help troubleshooting PreAmp build

I'm having trouble with a v1.0 MadAboutSound Wallin preamp board I bought from the swap meet forum. I ordered all the parts from DigiKey, stuffed the board and soldered them in. This is only the 2nd pcb project I've built.

When I turn it on, the LED lights briefly, as it's supposed to. But I don't get any output to my sound card. I've tested the mic directly into the sound card, and they both work. The problem is definitely between the input on the card and the output.

Can some one give me suggestions for troubleshooting? What do I measure?
Attached Images
File Type: jpg PreAmp1.jpg (560.1 KB, 64 views)
File Type: jpg PreAmp2.jpg (562.9 KB, 54 views)
File Type: png PreAmpSchematic.png (18.8 KB, 56 views)

Last edited by Randallm; 14th October 2011 at 01:52 AM.
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Old 14th October 2011, 04:33 AM   #2
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I built the version 1.1 some time back. If I recall correctly there were a few mistakes in the v1.0 pcb. Check the board vs. the schematic to make sure it is correct. Also check with madaboutsound.
"We monitor many frequencies. We listen always. Came a voice, out of the babel of tongues, speaking to us. It played us a mighty dub… "
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Old 14th October 2011, 04:50 AM   #3
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Join Date: Mar 2011
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I forgot to mention that I'm aware of the problems with the v1.0 board, and have made the appropriate modifications.

What I'm really interested in is basic troubleshooting. I haven't a clue what to look for.
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Old 14th October 2011, 06:01 AM   #4
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I figured it out! I'm using 3.5mm STEREO jacks. I was using a MONO plug for the mic input, but a stereo plug for the output to the card. The jack out was wired to the LEFT output, the card was looking on the RIGHT input.

Shorting the left/right connectors on the jacks makes it work. I can't wait to test something!
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Old 14th October 2011, 06:14 AM   #5
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Next to a multimeter (and less $ than a decent o'scope), a good tool to have in your diy audio kit is a signal generator and a signal tracer. OK, that's really 2 tools. But both can be put together for cheap, for instance a 555 oscillator for a signal source and a LM386 amp for a tracer. I built my set using a LM3909 and a little, old active speaker unit with a 2" driver.
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
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