[Darvy]

Well I did another one cmoy and it seems to go well.

I'm using alligator clips now and I can definately hear the boost to the sound. Now here is the problem. The volume is definately LOUD and there is a gain sound in the background. Its the kind of sound you get when you turn your volume up all the way (mine was at 10 percent) or when you turn up the gain on a guitar amp.

I think the amp is just maxed out in terms of its gain. I mean if I even attempt it bump it up to 100 percent I would probably blow my ears away.

In terms of music, everything but guitar music seems to be fine. Clean guitar sounds fine but when it gets into distortion guitar music, the sound becomes a garbled mess.

Also I cleaned the pcb with the pcb cleaner from radioshack. I think its as clean as it can get.

How can I get rid of this background sound? Am I right to assume its the gain?

I also have a volume control knob that tangent recommended in the cmoy site but I'm not exactly sure how to put that in. Is this volume knob to control the gain?

Thanks!

 

[Darvy]

I looked at that "First DIY Amp works" thread and looks like mine has some problems.

Any ideas what it could be? what can I do to check?

 

[Megaptera]

A few quick questions to help guide the troubleshooting:

First off, what opamp are you using, and what kind of voltage are you feeding it? Also, what kind of headphones are you using?

How much gain did you set? The default 11, or did you choose a different gain? The sound you describe could easily be the amp clipping or the headphones just getting too much power, especially if you've got the gain set pretty high (which, in most cases, 11 is). I've got my amp at a gain of 5.5, and with my HD580s, the volume is comfortably loud at about 50%, for what that's worth. With my Grados and other low-impedence headphones, it's even less.

As for the volume, do you have a volume potentiometer, or just the knob? The pot is what will actually control the signal, and it goes basically between the input jack and the amplification circuit. The knob goes on the pot's shaft, to make it easier to grip, but if you've only got the knob, you won't be able to control the volume

The pot doesn't usually control the gain in a CMoy, it sort of deamplifies the audio signal before it goes to the amp circuit -- if you think of the signal as I(nput) X G(ain) = L(oud), the pot usually makes I smaller, which reduces L in turn. I have seen people set it up so you reduce G instead, like you ask, but I believe that it's a more technically difficult way of doing it. I'm not sure what the exact pros and cons of that are; you probably just want to use it in the standard fashion.

 

[mustang]

Thanks for the great explanation Megaptera---it cleared some stuff up for me.

Regarding your cmoy Darvy---I don't quite know what you mean by "gain sound"

Definetly decrease the gain as the default 11 is too high. Experiment with the R3 value until you find one that fits you the best. The next cmoy I plan to build will have a gain of around 4-5 so it can touch base with low impedence as well as with high impedence headphones. Also, it doesn't hurt (as far as I know) to have too low of a gain granted your comfortable volume level is attainable through the knob.

If you still have some background noise, try checking all your connections and make sure what's grounded is grounded. If you still have some humming and hissing, check all your clipping and make sure no one clip is touching the other.

Hope it helps.

 

[Darvy]

Quote:

Originally Posted by Megaptera A few quick questions to help guide the troubleshooting: First off, what opamp are you using, and what kind of voltage are you feeding it? Also, what kind of headphones are you using? How much gain did you set? The default 11, or did you choose a different gain? The sound you describe could easily be the amp clipping or the headphones just getting too much power, especially if you've got the gain set pretty high (which, in most cases, 11 is). I've got my amp at a gain of 5.5, and with my HD580s, the volume is comfortably loud at about 50%, for what that's worth. With my Grados and other low-impedence headphones, it's even less. As for the volume, do you have a volume potentiometer, or just the knob? The pot is what will actually control the signal, and it goes basically between the input jack and the amplification circuit. The knob goes on the pot's shaft, to make it easier to grip, but if you've only got the knob, you won't be able to control the volume The pot doesn't usually control the gain in a CMoy, it sort of deamplifies the audio signal before it goes to the amp circuit -- if you think of the signal as I(nput) X G(ain) = L(oud), the pot usually makes I smaller, which reduces L in turn. I have seen people set it up so you reduce G instead, like you ask, but I believe that it's a more technically difficult way of doing it. I'm not sure what the exact pros and cons of that are; you probably just want to use it in the standard fashion.

First my Opamp is OPA2132P. I'm feeding it with 9 volt battery and I'm using Sony MDR cd3000.

Yes I'm using the 11 gain. Looks like thats the problem since the headphones are low impedance. The volume is just too high. I'm running the controls from the computer and its both set at 10 percent and its about right. 10 percent volume my media player and 10 percent my windows's volume control. Looks like 1 percent of the total volume I could attain. And thats about right LOL.

Thanks for the GREAT answer. Lucky for me I bought the lowest gain resistor - the 3.1 gain. I will give that a try right now and let you guys know if that works out!!

thanks!!

 

[Anton]

For R3 if you want to reduce the gain, do you add a higher-valued resistor? I guess this makes sense, but within what range are you working; i.e. is there an upper limit?

I guess the real question is that I use etys and my Cmoy with 11 gain is so loud that I have the volume at about 1; how large a resistor should I use in R3 to get an appropriate gain? There must be a formula for this, right?

 

[Darvy]

Well after I put my 3.1 gain in.. it is definately better.

The hizz at the back is reduced but its still there. Kinda like a perfect face having a small pimple on the nose.

I guess I have some interferences. Looks like I'll check my crappy soldering job again.

I'm so close I can feel it.

 

[leftbldg]

Quote:

Originally Posted by Anton For R3 if you want to reduce the gain, do you add a higher-valued resistor? I guess this makes sense, but within what range are you working; i.e. is there an upper limit? I guess the real question is that I use etys and my Cmoy with 11 gain is so loud that I have the volume at about 1; how large a resistor should I use in R3 to get an appropriate gain? There must be a formula for this, right?

R4/R3 + 1. A 4.7K resistor in R3 will give you gain of a bit over 3. With higher values your gain becomes kinda negligible.

See tangent's guide (also the part selection chart under "Required parts"):
http://www.tangentsoft.net/audio/cmo...eaks.html#gain

 

[Earwax]

Quote:

Originally Posted by Darvy Well after I put my 3.1 gain in.. it is definately better. The hizz at the back is reduced but its still there. Kinda like a perfect face having a small pimple on the nose. I guess I have some interferences. Looks like I'll check my crappy soldering job again. I'm so close I can feel it.

Is the noise coming from your source? Put the player on pause and then listen.

Do you have the volume pot connected yet? If not, and your source is noisy the amp will increase the noise. For some reason that I don't understand yet, running the source at 80 or 90% volume results in a better signal to noise ratio than lower volumes.

If the noise IS from the amp, check and double check all the ground connections.

 

[Anton]

Thanks, leftbldg, I shoulda started with Tangent.

 

[jnewman]

What Earwax said - with a few exceptions, stock computer soundcards are AWFUL sources, especially laptops. Have a look and make sure you're not getting messed up there.

 

[Megaptera]

Quote:

Originally Posted by Darvy Well after I put my 3.1 gain in.. it is definately better. The hizz at the back is reduced but its still there. Kinda like a perfect face having a small pimple on the nose. I guess I have some interferences. Looks like I'll check my crappy soldering job again. I'm so close I can feel it.

Like Earwax said, it could easily be coming in from the source. The way I narrow it down is by listening to the amp with no source connected, at full volume -- if there's any problem causing hiss inside the amp, that's where it is. Otherwise, plug it in, pause the source, and check again.

If there's still no hiss from amp or source, it's probably the recording -- I have one of Andres Segovia's albums, and it has so much background hiss, I can't listen to it on anything remotely resembling a hi-fi setup.

 

[Darvy]

Quote:

Originally Posted by Earwax Is the noise coming from your source? Put the player on pause and then listen. Do you have the volume pot connected yet? If not, and your source is noisy the amp will increase the noise. For some reason that I don't understand yet, running the source at 80 or 90% volume results in a better signal to noise ratio than lower volumes. If the noise IS from the amp, check and double check all the ground connections.

My setup is quite different from everyone so I'll put it in better details.

First of all, I haven't connected anything yet. I'm still running everything on alligator clips.

this is the setup

via alligator via alligator
Sony MDR cd3000 ----------> Cmoy ----------> cable -----> Computer


Sony MDR cd3000 ------> computer [no disturbance - silence]

via alligator via alligator
Sony MDR cd3000 ----------> Cmoy ----------> cable [random sounds but its gone when I touch the ends - you can tell i'm a n00b]

via alligator
Sony MDR cd3000 ----------> Cmoy [ no disturbance - silence]


I'm thinking of just putting everything in the box (I got a plastic one) and just try it out on different things.

So deducting from what Megaptera and others say.

I have no disturbance when the headphone is directly connected to the PC which means my SOURCE is fine.

I have no disturbance when the headphone is connected just to the CMOY so the CMOY is fine.

So where the hell is the noise coming from??

 

[Megaptera]

Quote:

Originally Posted by Darvy So deducting from what Megaptera and others say. I have no disturbance when the headphone is directly connected to the PC which means my SOURCE is fine. I have no disturbance when the headphone is connected just to the CMOY so the CMOY is fine. So where the hell is the noise coming from??

It's probably the source, or possibly (but not likely) interference in your cable.
Your source could have a bit of background hiss, but in most cases, it's too quiet to hear -- the CMoy is amplifying everything that comes over the audio channels, not just the actual signal, so the hiss is easier to notice. That said, I don't know much about your headphones -- if they're really super-easy to drive, like a lot of low-Z phones, you'd probably be able to hear it there too.

Three things to try:
One, make sure you're plugging into the line-out on your sound card, not the headphone out. (The headphone out has an amp in the way, which will do nothing to improve the sound for you.) Make sure the volume on your pc is set to about 80%, since depending on your OS and audio software, some sound cards clip with the main volume above that. Then, with no music or audio playing, check the amp again for hiss, at all volume ranges.

A second thing to try (when all set up normally) is adjusting the volume up and down. Does the hiss go up and down with it?

Third, try moving the cable around (again, in your normal setup). If the hiss varies as you move it, or you hear a humming sound, that's interference.

 

[Darvy]

Quote:

Originally Posted by Megaptera It's probably the source, or possibly (but not likely) interference in your cable. Your source could have a bit of background hiss, but in most cases, it's too quiet to hear -- the CMoy is amplifying everything that comes over the audio channels, not just the actual signal, so the hiss is easier to notice. That said, I don't know much about your headphones -- if they're really super-easy to drive, like a lot of low-Z phones, you'd probably be able to hear it there too. Three things to try: One, make sure you're plugging into the line-out on your sound card, not the headphone out. (The headphone out has an amp in the way, which will do nothing to improve the sound for you.) Make sure the volume on your pc is set to about 80%, since depending on your OS and audio software, some sound cards clip with the main volume above that. Then, with no music or audio playing, check the amp again for hiss, at all volume ranges. A second thing to try (when all set up normally) is adjusting the volume up and down. Does the hiss go up and down with it? Third, try moving the cable around (again, in your normal setup). If the hiss varies as you move it, or you hear a humming sound, that's interference.

Thanks for your tremendous help. I think I'm getting close.

You're right about it not being the cable though. It's gold tip cable from radioshack. It should be good.

1.) I move the cable around and nothing happens so its not the cable.

2.) Now after making sure I was connected to the line out and doing exactly what you say, putting up volume up and down, I found out that the hiss DOES increase and decrease according to the volume.

So this means that the source is the problem? Is it amplifying the hiss from the computer sound card as you mentioned above?

This means I can go ahead and assemble the CMOY? and so I can try on other sources like cdplayers.

Oh this means my CMOY was a success??!