[greatfool]

[/UR[/IMG]


I'm a noob building a cmoy based on tangent's website as my first diy amp. After frying one op-amp (TL082) by having in backwards in the socket, I think I have now gotten everything in the right place. When I power up the circuit on a 9v the power supply definitely works, the LED lights up and the + pad is about 4.4V and the - pad is about -4.4V so I think thats right, I know the chip is powered cause I fried one. My problem is there is zero sound, no hiss, no hum, no pops... I've tried testing the voltage on the input jack with a 1khz tone from my computer headphone jack at full volume and I get 0 or .1V for a second. I'm not totally sure Im measuring right (I put the red probe on the input lug on the jack and the black probe on the ground at the bottom of the board.) Also tried measuring the actual mini jack tip and ring voltage but again nothing, which can't be right cause the volume drives headphones very loudly. The pics are from after I removed the jacks cause they had no voltage. I'm about to rebuild this thing with all new components incase I fried something else with my backwards op-amp, but before I do that anything I could fix? Sorry I'm really lost but want to learn. Thanks.

 

[Pars]

You have to either put in the R5 resistors, or a jumper in their place to complete the feedback loop... pins 1 and 7 of the opamp out to the "M" jumpered pads.

 

[greatfool]

Ah thanks I missed that part. Its working great now , except for my crappy soldering making moise on the inputs.

 

[Samgotit]

What kind of solder is that?


Sam

 

[Porksoda]

I am a fan of the philosophy "If it ain't broke, don't fix it" but as a constructive criticism I WOULD recommend that you try re-flowing your soldering work. It looks like most of the joints are cold, as the solder isn't flowing nicely onto the copper strips on the board. It looks to me like you aren't using any flux. Try dabbing a bit on there and re-flowing the joints, giving the copper strips a chance to heat up so the solder flows all nice-like. These cold joints COULD be a source of the noise you were talkinga bout.

Also, it looks like you put the various components onto the board, and then bent the leads to where they are supposed to go rather than soldering them in place and using the strips to make connections. This makes it much harder to remove a component once it is in, and looks much less clean than properly soldered components.

I can't find a good example picture, but check out the videos on tangent's site for the best explanation I have seen so far:

http://www.tangentsoft.net/elec/movies/

cheers!

 

[greatfool]

Yeah my soldering is generally sub-par, also I wasn't aware that I needed to use flux or what it is, I'm going to watch those videos now. I'm planning on doing another board once my OPA134 op-amp gets here so this one can be a kind of practice amp. The heck of it is, the channel that is clear sounds awesome with 18V. I'm not sure I understand about the components though, I just bent the leads to try to get them into position like tangents though the power supply resistors I messed up by trying to get them to fit horizontally. Thank you for all your help!

Oh the solder is from radio shack 62/36/2 silver-bearing solder "for high tech" or something like that. I remembered reading that 60/40 wasn't the best to work with, seems to sound pretty good though.

 

[Samgotit]

Quote:

Originally Posted by greatfool Oh the solder is from radio shack 62/36/2 silver-bearing solder "for high tech" or something like that. I remembered reading that 60/40 wasn't the best to work with, seems to sound pretty good though.

Curious, that's what I use. It usually flows like the River Euphrates without added flux. Make sure it says "Rosin-Core".

I find that the blue painters masking tape works very well for holding components flush to the top of the board. No need to bend the leads, and the tape is easy to remove.

Practice on another board getting the solder to flow around the unbent leads. The solder should pool out on the copper pads surrounding the leads.

Sam

 

[camaronkazi]

Another thing - I usually prep the board by rubbing the copper tracks with a soft gum (pencil not ink) eraser then a quick clean with rubbing alcohol. Makes a big difference.

 

[[AK]Zip]

Looks like you have a bunch of cold joints. If it works great, but I suggest you go back and reheat the solder to the board itself. Either way. ENJOY!

-Alex-

 

[tomb]

Hey, guys - I'm just a noob to DIY, too - but I have done some soldering in my day. To be honest, most of those don't look like cold joints to me. On the contrary, the joints look smooth and shiny. There may be too much globbed on, but they don't look cold - except maybe for that bottom ground jumper. If anything, it looks like he's not heating the pads along with the wire/leads and solder.

That's a great tip about the tape, and about the eraser treatment on the board pads. I used to use a little fine grit sandpaper, but this stuff is way too small for that - and little bits of ground copper flying around would not be a good thing.

It sounds like the main problem was the omission of the R5 jumpers. Also, Tangent's tutorial specifically details bending the resistor leads in an elaborate fashion around the opamp, so I'm not quite sure what the perceived problem is with that.

You might check if you got some flux dripping into the pot or the jacks. I use more flux than solder

(Kester paste) and got a bunch dripped down into the Panasonic pot on mine, and had some scratchiness when I first turned it on. I poured a little Radio Shack tape head cleaner (recommended by Tangent) into the pot lead openings, and that cleaned it right up - scratchiness gone! If it's only one channel on yours it may be that happened to one of the jacks.

 

[greatfool]

I built another cmoy with new parts and somewhat better soldering after I learned from tangent's video to solder then clip leads, not clip leads then solder like I was doing

. The new one pretty much sounds great except for a slight hiss thats really only audible with no music playing, I am going to try putting in R5 resistors. Also on some headphones I get a lot of extra noise when the plug is all the way in the jack but a perfectly clean signal when I just insert the tip and hear the left channel. Im guessing that a problem with the ground wiring or right channel wiring on the output jack so I'm going to try redoing those. Thanks for the help, this DIY stuff is really fun.