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Old 1st June 2012, 01:17 AM   #1
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Default Problem with CMOY Headphone Amp

Hey Im super new to circuitry, this is actually my first soldering attempt. There is sound going through my headphone amplifier but no boost in volume at all. I bought the single hole perf board cause i couldnt find the radioshack board they are using in the tutorial. Can anybody help me get this thing boostin levels? Sorry the picture of the soldering is pretty blurry.

This is the layout I am following http://tangentsoft.net/audio/cmoy-tu...ayout-0150.pdf

This is the schematic (don't quite know how to read em yet) http://tangentsoft.net/audio/cmoy-tu...angent-sch.pdf

and this is the tutorial Assembling the Amplifier

Thanks a bunch, I really wanna get this thing goin!!
Attached Images
File Type: jpg cmoyamp1.JPG (292.5 KB, 77 views)
File Type: jpg cmoyamp2.JPG (279.3 KB, 71 views)
File Type: jpg cmoyamp6.JPG (503.6 KB, 68 views)
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Old 1st June 2012, 01:36 AM   #2
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These are great projects.

I notice you have a volume pot, do you really need that?

Try it without the volume pot and double check your resistor values.
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Old 1st June 2012, 02:36 AM   #3
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Do you have a multimeter? If so, you can start by checking the power in. Put your positive probe on the V+ (pin 8--upper right) and the negative probe to ground. Then take a reading with the positive probe on the V- (pin 4--lower left). With only one battery, you should show approximately +4.5V and -4.5V coming into the op amp. If the power is good, then you can start troubleshooting the signal.
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Old 1st June 2012, 02:41 AM   #4
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Took out the volume pot and its still the same, checked all the resistors and they seem to be fine. Signal is going 4.41 in pin-4 and 4.41 thru + side of battery
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Old 1st June 2012, 05:05 AM   #5
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Okay, that's good. Now you can try to figure out what's wrong with the signal. If you're using a computer or iPod as a source you can download a test tone to check your signal voltage. (Get a steady tone; don't use a sweep.) Play the test tone recording through your CMOY with the multimeter clipped to the each of the input leads. You've got two signal wires and one common ground soldered to the 1/8-inch jack. Measure the AC voltage on each channel (left is the tip, right is the sleeve), and write them down. Don't change the volume settings.

Now clip your multimeter negative lead to ground and clip or hold the positive probe on pin 1 (upper left). Write down the output voltage. Repeat the process for pin 7 (second from the top on the right). Write down the second output voltage. Now compare the input and the output. You should be getting gain of about 11X on each channel.
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Old 1st June 2012, 11:04 AM   #6
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I can't tell 100% from the picture,but it looks like you have solder bridging across the op-amp input +/- and output pins? (along the outer left and right sides of the board,in the third picture.) If that's the case,then you won't have any gain,and might even lose some.
You'll need to double check the connections,and clean up any solder bridges,etc.
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Old 2nd June 2012, 08:30 AM   #7
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Did a quick rebuild of the whole thing using a similar board to the one in the tutorial and its all workin now!! Sounds great! A lil bit of a hiss, so i might put a resistor into R5.

Thansk so much for the help..now to learn guitar pedals
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Old 2nd June 2012, 10:19 AM   #8
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Cool, pretty exciting eh?

I like how the little cMoy brings out the bass and detail, even at the same listening levels as before.
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