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Sound only on one channel

post #1 of 16
2/20/10 at 7:21pm
Thread Starter 
Hi All,

I recently built my second Cmoy amp and everything was fine. I slept woke up and now one channel is working. I have checked all my soldering joints, swapped the amp chip from my last Cmoy and replaced the right output wire. I was wondering if anyone had any suggestions. The sound is perfect in the one ear, but as you could imagine it isn't what I am looking for. Any help would be greatly appreciated. Thank you and take care
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post #2 of 16
2/20/10 at 7:57pm
Thread Starter 
Ok, I now have the problem in both amps. I tested headphones and the male to male cable. This problem is driving me nuts. Do you think the amps are damaged? I made sure to use a socket. Thank you
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post #3 of 16
2/21/10 at 5:28am
Thread Starter 
I'm hoping it is the amps that maybe were messed up? I know it is a weird situation, but if you have anything to check that I may have missed I would greatly appreciate it. In the mean time I await mouser.com's response to a possible exchange/return of the amp. I may pick up a cheap one at radioshack for a quick test. Thanks for any help. Take care.
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post #4 of 16
2/21/10 at 6:07am
Have you checked your source? Could be that there is only one channel from the source.

If the amp chip is bad, something in your CMOY is burning them out.
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post #5 of 16
2/21/10 at 6:10am
Thread Starter 
Would it be odd if the chip was being burnt out to only kill one channel? Looking at the input soldering from the input to the potentiometer and then the board looks good. Would you recommend swapping out all the cable on the problematic line? I used the one working channel on the output and touched it to either left and right channel to make sure that my output jack wasn't at least broken. Thanks for the write back.
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post #6 of 16
2/21/10 at 8:40am
Quote:
Originally Posted by Syntax010011 View Post
Would it be odd if the chip was being burnt out to only kill one channel?
Not really. My best guess is there is a wiring problem in the 2nd CMOY that burned out one channel in both amp chips. -- Moving the chip into the 2nd amp killed one channel.


Can you post some close up photos? I'd look for something like output shorted to gnd or V+
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post #7 of 16
2/23/10 at 3:20am
Thread Starter 

The image

Hi,

Thank you for the replies. I recently got a chance to remove the potentiometer to see if it was the issue, also swapping the inout jack and the input wires. No luck with any of that. Could a capacitor be an issue? I have taken a picture. My soldering job is embarassing and was made difficult on my newbie choice in cheaping out on a lower priced weller (15$.) I did make sure to run an xacto knife over any areas that looked like a bridge to me. I may just have to rebuild the amp on a new board. Do you think any of these parts are salvageable? Thank you and take care.

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post #8 of 16
2/23/10 at 12:36pm
Pull the opamp from the socket, and with the power off, ohm out (DMM ohms mode) every pin to virtual ground. Note same pins per channel (pin 1 and pin 7 should be approx. the same, etc... use the schematic). If those all look fine, then ohm out adjacent pins (this will show your feedback loop), again looking at the schematic.

A problem I have had with the first couple of Cmoys I made was the wires or leads were not thru the PCB all the way. It would work fine for awhile, and then just quite working if I moved the board around. I fixed this problem by making sure that leads were thru the board far enough, and making sure I filled the ring all around the lead with solder.
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post #9 of 16
2/24/10 at 3:58am
Looks like there might be solder bridges between the power buss and a couple of the op-amp pins. Best to follow Pars suggestion for testing.


Quote:
Do you think any of these parts are salvageable?
Are you thinking about taking the parts off this board and starting over?

I'd say the op-amp is toast. You should be able to re-use the parts that are off the board easily. The volume control is worth the effort to re-use.
You could buy some solder wick and maybe save the parts on the strip board, but I wouldn't bother. Resistors are cheap unless you went overboard.
If you bought caps that cost > $1.00 each, you could try and save them.


If you do build another board, try using a little less solder. A better soldering iron would make it easier but isn't essential. If you do decide to get a better iron, save up for a Weller WTCPT (my fav) or the Hakko everyone else recommends. Sometimes you can find a good deal on a used Weller on eBay. If you buy new, buy from a reputable dealer like HMC. Watch out for the cheap poorly made clones on eBay.
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post #10 of 16
2/24/10 at 9:14am
Forgot to add --

Are you using RadioShack solder? Multicore or Kester in one of the smaller diameters makes it easier to get the right amount of solder on a connection. You don't have buy the expensive botique solder.
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post #11 of 16
2/25/10 at 2:08am
Thread Starter 
Hey,

Thanks for staying on top of this for me. I greatly appreciate it. I am currently in the process of getting any parts that would be difficult to salvage from mouser. I am probably gonna get another board and redo it. I also got helping hands. I think not having something holding it really messes it up. I often had to find elaborate things to lean on or solder at awkward or look up angles. I am hoping helping hands will help. No joke intended there :-p As for the solder I am using the .032 diameter 60/40 radioshack. I probably should have bought their lead free version, but I didn't see it at first and don't want to spend more right now. Thanks again for the help. Here's hoping the next go will be the perfect one.

P.s. I stripped an old USB cable for wire, do you think that is fine? Seems to conduct sound just fine. Thanks
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post #12 of 16
2/25/10 at 2:52am
Don't get lead free solder... pita to work with. You should have gotten their 63/37 or the silver bearing stuff
Silver-Bearing Solder (1 Oz.) - RadioShack.com

It is eutectic, meaning it solidifies faster... less chance of a cold joint from moving while it is changing state.
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post #13 of 16
2/25/10 at 2:55am
Thread Starter 
I gotcha. If/when I run out it will be the first on the list. Thanks Pars. I assumed lead free was good for the health and retained quality, but I see a warning on that label anyhow. Good to know. Thanks again
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post #14 of 16
3/18/10 at 6:00pm
Thread Starter 

Thanks!

Hey Everybody,

I just wanted to say thanks for everyones help. The new build went swimmingly. I put together this time lapse of the build:

[IMG][/IMG]

(Click it to launch the video from my smugmug page)
All the best!

P.s. getting a 'helping hands' really helped a huge amount to get better soldering points. Before it was a balancing act :-p
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post #15 of 16
3/18/10 at 11:39pm
Wow Syntax010011, thanks for the video. Did you have the casework done before you started the board, because I did'nt remember seeing you work on it in the video, and the casing went really fast. Maybe you holepunched it?

In any case, great work. I've got to get one of those "helping hands" Last time I made a cable, I screwed the jack into a vice, which helped way much over the alternative, and it looks like those things are really helpful.

What's the total time?
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