CMOY Amp Troubleshoot Help

[duane]

Hello,

I'm building my first CMOY Pocket AMP via Tangents website and have gotten to the part in his instructions after you install the V+ and V- hookup wires to add a battery and test.

I borrowed a friends DMM and set it to DCV 200. I took the negative probe touching the ground jumper on the bottom of the board and the positive probe to the V+ wire and get a reading of 7.9 and then I touch the positive probe to the V- hookup wire and get a reading of -1.2. While the battery is attached the led is lit up.

All help greatly appreciated. Thanks.

 

[averydonovan]

I just built a CMOY using trial and error (more error than trial). Are you using one 9-volt? I would carefully check the solder connections in the power supply and make sure those resistors in there are of the same value (4.7K). Hope this helps.

 

[duane]

Ok, I'm not as far as you think. So I get some time to measure it tonight and the the V+ is measuring at 3.85 and the V- is measuring at 3.70. Is this fine or are the measurements too far off?

 

[s.c]

It is fine, keep check on the reading while you continue on the circut part.

 

[RockysDad]

If you have a setable range DMM, alway set it to the lowest range possible for the most accurate readings. For example, the most you are going to measure is 9V. The 2V scale is too small, so go to the next one which is 20V max. This is the one you need to use. You'll find that the measurements are closer to 9V total. Also, keep the black lead in the middle of the two 4.7k resistors and measure the + and - leads. You should get +4.5V and -4.5V +/- .2V if you battery is exactly 9V. The black lead now is on "virtual ground". This term will be important when you start troubleshooting for voltages around the op amp. Have fun!