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cmoy amp. no sound out of right headphone

post #1 of 6
8/16/11 at 9:04pm
Thread Starter 

hi all, 

 

im new to DIY audio but i saw the cmoy amp through a friend and decided to make one. i have a pair of superlux HD 668B which im hoping to pair the amp with. so i got it built and i tested the V+ and V- to ground and it was split halfway. about 4.4 or 4.5 for both. the sound didnt work so i ran around on the forums and i resoldered everything and cleaned the flux with isopropyl alcohol and i got sound out of the left side of my test headphones. crappy headphones of course. so i resoldered anything that looked possibly like a dry joint and i cleaned again. still nothing so i looked on a thread which said to measure the resistance across pins 6 and 7 on my op amp. im using the one tangent suggested the OPA2132PA op amp. i got about 10k resistance (9.94k for both sides. i tested pins 1, 2 and 6, 7). at this point im thinking that my headphone jack is messed up ( i used the one tangent suggested as well)? is that a possibility? any advice would help greatly :)

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post #2 of 6
8/16/11 at 9:25pm

Have you posted pictures of the amp somewhere so that others can see that you have made the right connections? If not, that is the first thing I would do. You can check to see if the non working side of the connector is shorted to ground with your meter. The connectors are usually pretty resilient so that is not likely the case, but it is a possibility. This is a dual opamp. That channel may also be dead.

 

It is more likely you have made a connection error on that side of the circuit.

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post #3 of 6
8/17/11 at 12:05pm
Thread Starter 

i havent posted pics >< i just got a new phone so the camera is now working. here are pics of the front and back. the right headphone isnt working so i figured the problem was on the right side of the board too? IMAG0005.jpg

 

IMAG0006.jpg

 

hopefully these help. it would be awesome to get these headphones to work.

 

EDIT: i just measured the V- and V+ to ground using the op-amp data sheet. is that what i was supposed to do? they both came out as 4.45V. i also reversed my headphone jacks and the sound still came out so i know its not a defective jack. how would i know that the amp itself is fried?


Edited by pandamonium - 8/17/11 at 4:58pm
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post #4 of 6
8/18/11 at 2:45am

I cant see under the cap on the left in the top down photo but it looks otherwise correct. You could try another op amp. Before you do, check to make sure that you don't have a solder bridge somewhere. Something is probably shorted.

 

On the bottom pic check that there is no solder bridge on the right side between pins 2 and 3. Looks like a mass of solder there. Do you have any solder wick? There is really a lot on there. Try to clean up as much of those big globs as you can.


Edited by rembrant - 8/18/11 at 3:03am
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post #5 of 6
8/18/11 at 12:26pm
Quote:
Originally Posted by pandamonium View Post

hi all, 

 

im new to DIY audio but i saw the cmoy amp through a friend and decided to make one. i have a pair of superlux HD 668B which im hoping to pair the amp with. so i got it built and i tested the V+ and V- to ground and it was split halfway. about 4.4 or 4.5 for both. the sound didnt work so i ran around on the forums and i resoldered everything and cleaned the flux with isopropyl alcohol and i got sound out of the left side of my test headphones. crappy headphones of course. so i resoldered anything that looked possibly like a dry joint and i cleaned again. still nothing so i looked on a thread which said to measure the resistance across pins 6 and 7 on my op amp. im using the one tangent suggested the OPA2132PA op amp. i got about 10k resistance (9.94k for both sides. i tested pins 1, 2 and 6, 7). at this point im thinking that my headphone jack is messed up ( i used the one tangent suggested as well)? is that a possibility? any advice would help greatly :)

One of the points in ohming things out is to verify that the feedback loop is connected (on both sides). You don't specify whether or not you were ohming pins 1,2,6 and 7 out to ground or to each other. Both methods are valid, but tell you different things. 1 and 7 are the output pins; there should be a 10K resistor connected between these and the inverting input pins for each channel.

 

CMoy-Headphone-Amplifier-Schematic.png

 

The non-inverting (+) opamp inputs are pins 3 and 5, the inverting (-) inputs are pins 2 and 6, and the outputs are pins 1 and 7. Assuming you are using Tangent's part values, the feedback resistors for the stock gain of 11 would be 10K and 1K. These should be done with the opamp out of the socket. So from the schematic above with these values: 

 

ohming pins out to ground should give you

  • pins 1, 7: the feedback resistors in series, 10K and 1k, or 11K, + R5 if you have one in
  • pins 3 and 5: 100K ohms
  • pins 2 and 6: 1K

ohming adjacent pins out to each other:

  • pins 1-2, 7-6: the feedback resistor (10K)
  • pins 2-3, 6-5: open

 

If these all check out, then I would start ohming out the input and output connections, making sure the caps are connected, etc.


 

 

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post #6 of 6
8/18/11 at 2:28pm
Thread Starter 

thanks for the input guys. rembrant i check for solder bridges and i tok another look at under the left capacitor to see if there was anything there that was touching. i twisted it quite a bit to get it to fit right and everything there checked out. 

and pars i got those numbers when i was checking what you said to do. so thank you for clearing that up. 

strangest thing happened though. i was fiddling around with it and decided to try to connect the input and outputs straight to each other to see if my headphone jacks were working and i got sound from left when i connected the left audio and right when i connected the right audio. then when i disconnected it, both speakers started to work. so now my amp works and i have no idea how. i didnt do anything except check if my connections were faulty and i guess one of them was but it fixed itself? so i have no idea what happened there. 

anyhow my first cmoy amp and i think im addicted. im probably gonna try to build more in the future and ill definetley be back on these forums haha. 

thanks for your input and advice guys :)

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