1st time cmoy trouble.....
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coperam

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Hi all,

I've recently tried to build a stock cmoy amp following tangent's online tutorial. However, I seem to have produced a 1lb solder weight.....

Anyhow, the problem is that I get very faint music for output. Unless I attach both alligator clips to the input post(i.e. capacitor post) then I get very loud sound equivalent to the pcdp. HA.

I checked voltages for the power supply and they came to 3.73 on both sides. So I assumed that is not the problem.

I double checked the resistors with my meter and they are fine and matched.

Also, the sound will stay on even with the battery unplugged so I assume the circuit is ok but the opamp isn't getting any juice??

Please help. I sure would appreciate any further troubleshooting advice so that my 2days haven't been in vain. I've attached two pictures to try to show what it looks like....thanks again.

 
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post-190393
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HD-5000

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Nobody will help the poor guy?
 
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puppyslugg

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OK, HD-5000 I'll give it a try.

Quote:

Unless I attach both alligator clips to the input post(i.e. capacitor post) then I get very loud sound equivalent to the pcdp.


That is the input cap? How did you connect the alligator clips?
 
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coperam

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Thanks for the replies guys.

I soldered the one post of the capacitor to the board and didn't trim it. I attached two alligator clips, one from vol. out and one from the headphone. I think this just caused a short...ie. connected the headphones to the pcdp just to make sure the testing equipment was working.

I've played with it some more and now the op amp is getting hot and there i no sound.

thanks again.
 
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puppyslugg

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If the opamp is getting hot, it is probably oscillating. However you had it connected before was probably more correct. But...
I think you should look at the schematic and start from the beginning. Start with the input and work your way thru the circuit. Such as, 'the one end of the input cap is connected to the input jack, the other end is connected to...and so on and so on. It's rather a simple ciruit and it shouldn't take you that long.

Good luck.
 
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JMT

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You say that you have checked your resistors values to your meter, I would also suggest that you check your resistor values to the schematic. You first symptom sounded to me like the value of R2 (100K) was incorrect. Then recheck all of your solder joints. Either re-heat them or use some desoldering braid, suck out the old solder, and re-solder the joint completely. Also, take puppy's suggestion and systematically work your way through the circuit.

Troubleshooting is a bitch, but sometimes a necessary evil. You'll figure it out.
 
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coperam

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Thanks guys for the replies.

I took the circuit apart and resoldered on a new board. I double checked the resistors and they seem fine. The results were the same. I either get very very faint sound or no sound at all. The amp doesn't get hot now, however.

I'm wondering if I'm connecting the cd player and the headphones correctly to the amp. I just connect the left channel. I clip an alligator clip to the tip of the headphone plug and clip the other end to the left line-out post on top of the board. I take another alligator clip and put that on the tip of the plug coming from the headphone jack of the cdplayer and the other end is connected to the input capacitor post. I then connect the ground of the plugs on the headphones and the cdplayer to each other. Is this correct?

I also am wondering if there should be a voltage reading from the v+ or v- from the wires at the op amp to the ground? I don't get a reading here....Is this right? I do get a reading of 4.7v at the v+ and v- at the power supply circuit and the ground.

I must be missing something. I'm not good at reading schematics. But I think everything is connected correctly. Please keep the suggestions coming, thanks.
 
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coperam

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Yep. Oh well. I've spent enough time on it and without further help there is nothing else I know how to do. Thank you for your help.

Maybe I will look at it some more later or just burn it! lol.
 
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JMT

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coperam, it's just tough to troubleshoot via the forums. All we can do is read your description of the problem, and take a best guess based on what we have experienced in the past. Have you searched the archives over at HeadWize? Since Chu designed the original amp, and many have been built and troubles diagnosed there, it might be worth it to look around.
 
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Quote:

Originally posted by coperam


I also am wondering if there should be a voltage reading from the v+ or v- from the wires at the op amp to the ground? I don't get a reading here....Is this right? I do get a reading of 4.7v at the v+ and v- at the power supply circuit and the ground.


You're supposed to get a reading of 4.7v (+ or - doesn't matter) between the V+ and ground pair or V- and ground pair. Between the V+ and V-, you should get a PD of 9.4v.

Did you connect the virtual ground to the ground on your amp? You should do that to get a +/- 4.5v relative to ground. The op-amp doesn't care for absolute voltages.
 
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