Guide to fix up a Cmoy 2

[neutralzz 0]

this might make a difference.. but its dam big..

[squalle 0]

LOL

 

that's called killing an ant with elephant rifle

 

with that kinda s ize, I gotta hunch telling me that somehow it'll give some problems too

 

[jasonhanjk 0]

Ouch. Very BIG!!!

 

Digital pot is another study and is used differently from standard pot. You must only use them for single supply only (unless they are design to use dual supply). Which one sound better, I don't know.

 

If you have an analog pot that is 50k but min resistance is 100 ohm. In terms of dB is -0.017. You won't hear any difference.

[kross 0]

hi guys, you guys experience any popping sound when u on/off the cmoy? i have this problem so dunno how to get rid of it.

[matt.pimm 0]

Hi,

I think on-off popping might just be a feature of the amp. There is no output isolation to stop this effect. I think it is assumed by most to disconnect your cans whilst switching on and off with the volume at minimum, then connect cans.

 

Hope this helps

 

 

Matt

[squalle 0]

it might be due to the op-amps being on/off or vice versa

 

or might be the DC offset causing it

 

have u measured for DC offset at the output?

[kross 0]

din measure. will measure when my multimeter is ok. i'm using batteries.

[jasonhanjk 0]

It's always best to plug in your headphone when the unit is on and plug out before off.

[klernie0521 0]

Newbie question here.

I have completed my cmoy2 amps but the right side doesnt have signal.

I thought the problem came on the op amp for ground so i by pass it but no luck

Any ideas what is the cause of this problem and how i can make it function?

 

btw i used 0.1uf 63v cap rather than 1.0uf 63v.

 

http://img494.imageshack.us/my.php?image=front5jw.jpg

 

http://img494.imageshack.us/img494/9052/back5hb.jpg

Edited November 26, 2005 by klernie0521

[neutralzz 0]

your soldering's in big blops.. try to check whether any points have been shorted

[heady 0]

Did you clean the flux off the board before testing? And what op-amps are you using?

[klernie0521 0]

op amp used opa2314 and LT1077CN8

 

Haven't clean the flux before testing. Newbie question, what do i use in cleaning the flux?

This is my first time assembling electronic parts (particular soldering)

 

Thank you very much for bearing with me

[1bit 0]

hi klernie, welcome to sgheadphone!

to troubleshoot the no signal problem on the right channel, the first thing come to mind is to check the connection for the right channel as also suggested by neutralzz.

there are two possibilities: one or more component of the right channel is shorted to ground, or some where along the right signal path there's a poor soldering. check for these problems using continuity tester on your multimeter.

i can't see clearly from the picture but the soldering on the pot looks suspicious to me, check for short from the wiper to the ground pin for the right channel.

 

if the connections in the right signal path is ok, check the soldering for the power and ground pin for the right channel opamp ic (but it looks alright from the picture)

 

if the connections on the pcb are fine, check the connection off-board i.e. the soldering on the input/output jack. the right channel could be shorted to ground there.

 

if there's no connection problem, the components might be faulty. check the opa2134 by interchanging it.

 

if the problem only persist on the right channel, the ground opamp should be okay as if it has gone kaput the left channel won't be working as well.

 

but i think the ground opamp that you use (lt1077) is not suitable as it can only source/sink 5mA

 

for the input capacitors (C1 and C2), i'd recommend you upgrade them to higher capacitances. with 0.1uF for C1 and C2 and 10kohm for R4 and R8, the cut-off frequency is around 150 Hz. you'll be missing all the bass like this.

 

0.1uF for the bypass capacitors (C3,C4,C5) would probably be enough

 

btw heady, how do you clean the flux off the pcb? where can you buy flux cleaner?

[1bit 0]

forgot to add: be careful if you want to change the input caps, the soldering pad on the pcb could fall off

 

[heady 0]

All solders I have used deposit this greasy oil on the PCB. I am told this is flux and is conductive, so it can short the solder points. I use surgical alcohol to clean the PCB after soldering. I pour some into a small dish and use a toothbrush to scrub the PCB. You can get the alcohol from pharmacies, chinese medical halls etc.

 

Actually the recommended alcohol is supposed to be purer than this commonly available surgical alcohol but that is hard to get. I have used the 75% alcohol (25% water) commonly available as surgical alcohol and have had no problems so far.

 

After cleaning, you need to dry the PCB. I sponge off the excess with paper towels and then use a bulb blower to blow the alcohol from under components. Then I use a hair dryer on low setting to dry the PCB. Note that alcohol is flammable and if not careful, using a hairdryer may set it aflame. Skip the hairdryer if you are worried.

Edited November 27, 2005 by heady