First CMOY and running into problems.

[snyper1982]

Okay, this is my first attempt at an amp, and this is starting to get frustrating. I have looked over all my solder connections, and I didnt see any bridges or anything. Anyways, on to the problem. When I try to listen to either left or right channels individualy I can still hear sound from the other channel. I have no idea what is causing this so any pointers are greatly appreciated. I checked out the DC offset, I think I did it right, go from the virtual ground to the left and right ouputs. Well anywasys, the measurement i got was like .175 volts and like .170 volts. Anyone have any ideas what the problem could be?


-edit-

Ok I tried the DC Offset thing again, and its wasnt nearly as high as it was before. Do you have to have something playing when you measure it, or can you just turn it on and measure it?

 

[Sinbios]

You're supposed to go from output ground to either of the output channels.

 

[nikongod]

how much sound do you hear between the chanels? if it is nearly nothing, it could be cross-talk between the chanels.

as far as the output offset, measure with the input grounded.

 

[snyper1982]

I hear enough to where it starts soundeing distorted. For the offset, I am supposed to connect left input to ground and measure the left offset, and same for the right channel?

 

[sbelyo]

without seeing a picture I would say that there is a solder joint problem or a ground fault.

If you could post a pic of the bottom of the board and let us know if you are using a pot for volume or not. Also what op amp and how many volts are you using to power it.

As for the offset check to see if your meter has a mVdc setting be cause 0.175 Vdc is pretty high.

 

[snyper1982]

OK, I will post a pic in a few minutes. I am using a single 9 volt at the moment. I was using a pot but I have desoldered it from the amp, as well as all the jacks.The opamp is the opa2132pa. I rechecked to offset, and set the DMM to mVolts and it read at .5 mvolt on the left and .9 on the right. I dont know why the reading was so freaking high before.

 

[Sinbios]

Quote:

Originally Posted by snyper1982 I hear enough to where it starts soundeing distorted. For the offset, I am supposed to connect left input to ground and measure the left offset, and same for the right channel?

No, measure from output ground to output left and output right

 

[snyper1982]

Quote:

Originally Posted by Sinbios No, measure from output ground to output left and output right

Well according to tangents layout, the output ground is the virtual ground.

Here is some pics of my board, and the tangent layout so you can see what i mean about where i am getting the ground for my output.

 

[snyper1982]

ok well after going over tangents diagram again. It turns out that I had the opamp power wires wired from the top row instead of the second row. Well it doesnt do the horrible distortion anymore, but it does start distorting when i turn the volume up a bit on my source. Its getting late so I will have to troubleshoot more tomorrow. I am thinking the distortion is now due to lack of power.

 

[amb]

One single 9V battery doesn't allow for a lot of output voltage swing. If you have high-impedance and/or low efficiency headphones then it's likely the amp is clipping. If the battery isn't new with full voltage, then it would be even worse.

 

[robzy]

Quote:

Originally Posted by amb One single 9V battery doesn't allow for a lot of output voltage swing. If you have high-impedance and/or low efficiency headphones then it's likely the amp is clipping. If the battery isn't new with full voltage, then it would be even worse.

As above, try more voltage.

Rob.

 

[The Monkey]

Quote:

Originally Posted by snyper1982 ok well after going over tangents diagram again. It turns out that I had the opamp power wires wired from the top row instead of the second row. Well it doesnt do the horrible distortion anymore, but it does start distorting when i turn the volume up a bit on my source. Its getting late so I will have to troubleshoot more tomorrow. I am thinking the distortion is now due to lack of power.

Also check your resistors to make sure they are the correct values. I dropped in a 100K instead of a 10K the other day by accident.

 

[snyper1982]

Thanks guys, I really appreciate your help. I will run another 9v in series when I get home from work. I will double check my resistors also. There is a way to check them without desoldering them right? I am fairly certain that I have all the resistors correct though, I tried to resistance match each side as tangent suggested as I was assembling the amp, but it wouldnt be the first time I overlooked something.....

Thanks again though, you guys are great.

 

[Pars]

Quote:

Originally Posted by snyper1982 Thanks guys, I really appreciate your help. I will run another 9v in series when I get home from work. I will double check my resistors also. There is a way to check them without desoldering them right? I am fairly certain that I have all the resistors correct though, I tried to resistance match each side as tangent suggested as I was assembling the amp, but it wouldnt be the first time I overlooked something..... Thanks again though, you guys are great.

As far as checking the resistor values and connections, get your schematic and DMM. Take a look at this post, and also use the search function, as there are a ton of CMoy troubleshooting threads. Basically, ohming out the opamp socket (opamp removed) to virtual ground should show you your entire feedback loop, etc. Since most of these resistors are to ground, you should read their value. If not, check the schematic (might be in parallel with something else, etc.)

 

[snyper1982]

Ok. Well it turns out that I was using a 100k resistor for R3, instead of the 1k. Anyways, I got that taken care of. Well my amp picks up a lot of noise when I am by my computer, is that normal? I was planning on using this on my computer at work and i would like to find a way to get rid of it, if at all possible.

BTW, this amp sounds great now. Getting the sound out of it like I was hoping I would. Can't wait for my HD580's to get here on monday.

Thanks again for all your help.