[mojo]

I finished building a Cmoy, but I am getting some distortion. It sounds like the higher frequencies only - lower pitch guitars sound ok but voices are distorted. Source is an iPod or PC.

I have attached two photos. I checked all the resistor and cap values, they seem OK. R5 is jumpered... Any ideas?

 

[FallenAngel]

1) Get some rubbing alcohol and clean the flux off the board.
2) What power supply are you using? If its purely battery, then it's fine, if not, I hope you have a nice power regulator there.

 

[ozshadow]

Sounds like you have a solder bridge on the opamp pins. Sound like music in a tin can ?

 

[aderici]

does the flux on the board have any effect on circuit?
if yes what type of effect?
and what is the right way of removing it?

thanks,

 

[tomb]

For most purposes, we tell someone to clean the flux in order to better see the solder bridges. Otherwise, it is not conductive. There are some rarer types that are conductive, but it's unusual, and is almost never the type in solder cores. If left on for a number of months/years, rosin flux can become contaminated enough to conduct. So, it's always a good practice to clean it off.

Rubbing alcohol is sufficient and probably cheapest, although the 91% is better and tape head cleaner or specific flux cleaner is best. Several rinses along with some scrubbing with an old toothbrush works well.

Distortion is caused by some other problem in this case. I can't see any solder bridges to be honest. So, there are 4 or 5 things it could be:
1. bad battery
2. incorrect resistor or cap somewhere, or bad component (opamp)
3. flux in the pot, although this would be scratching, not really distortion
4. incorrectly wired input/output sockets
5. could still be a solder bridge we can't see.

 

[mojo]

Many thanks for the quick replies!

I will clean things up ASAP, but I have checked visually and with a multimeter and can't find any bridges.

Quote:

Originally Posted by tomb 1. bad battery 2. incorrect resistor or cap somewhere, or bad component (opamp) 3. flux in the pot, although this would be scratching, not really distortion 4. incorrectly wired input/output sockets 5. could still be a solder bridge we can't see.

Okay... I have tried another set of batteries. I should have mentioned that I measured 18.8V over one set and 18.0V over the other. I checked the supply to the op-amp and it seems nicely balanced.

I have not tried another op-amp yet, must give that a go.

In response to ozshadow, the sound is OK apart from the distortion at the top end. It doesn't sound like a can or anything, in fact it sounds good except for the vocals and drums.

Actually, if I had to drescribe it, I'd say it seemed like clipping distortion. It's the same at any volume level though, or at any input level, and on both channels.

 

[Ikrit42]

I had what sounds like the same problem with my first cmoy last night. It turns out, with mine, that I was bridging the left and right on either the input or output jack, I can't remember which.

Are you sure that you're getting channel separation?

 

[mojo]

Sorry it's taken so long to reply. I have been really busy...

After much much pratting about I fixed it! I have no idea how... basically, I was swapping op-amps around (I have two). In frustration, I accidentally connected one backwards and smoked it... feeling like a fool, I put the original one back in and it works great. Maybe the heat fixed a dry joint or something?

Oh well... all I can say is that it sounds damn good. My iPod can finally drive my Sennies! Yay!