CMoy Distortion
Mar 19, 2006 at 8:22 PM Thread Starter Post #1 of 22

hembergler

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First off, I apologize for yet another CMoy-problem topic. I used the search function and wasn't able to find a solution to my problem.

Since I thought I had set up the amplifier circuit, I decided to test it before I put it in a case. I hooked up everything by having a Mini->Mini cable coming from my CD Player's Line-Out. Then, I used alligator clips to connect the proper parts of the amplifier to the tip/ring/ground of the Mini->Mini cable. Then, I took three more alligator clips and connected the Tip/Ring/Ground of a pair of KSC75's (great cheap headphones, by the way) to the outputs/ground on the amplifier. I put the headphones on, and voila! Distortion beyond belief. It was terrible, you could barely make out what song was being played.

I then tried disconnecting one channel, to see if either side was worse than the other. With only one channel working, the sound cleared up a lot, to the point where you could tell what song was being played. In general, most of the distortion was gone. But, there was absolutely no bass whatsoever. It was completely gone. The other thing, is if you touch any of the resistors, you can hear a definite buzz in the headphones. I'm guessing there's a grounding problem, that I don't know how to fix.

I've been attempting to follow Tangent's instructions thus far, so the configuration for all the resistors is the same as what's on his website. Probably worth noting, I'm using an OPA2132 op-amp.

Here are some photos of the amp so far...

Top View(s)
top1.jpg

top2.jpg


Bottom View(s)
bottom1.jpg

bottom2.jpg

bottom3.jpg
 
Mar 19, 2006 at 8:42 PM Post #2 of 22

The Monkey

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2 very quick troubleshooting steps:

1) check all resistor values to make sure you haven't dropped in something wrong accidentally, i.e. a 100k for a 10k.

2) It looks like you could have some cold joints. Try reflowing some of the joints and then use some alcohol to deflux the bottom of the board.
 
Mar 19, 2006 at 8:54 PM Post #3 of 22

diredesire

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I also noticed you didn't socket your op-amp. It appears to me (no offense) from the pictures that your you lack much experience soldering, or have less-than stellar equipment (again, no offense, the soldering is a bit globby and the joints look a little less than shiny)

This to me, sets off a few red flags. If you hold the iron on the op-amp too long it could have gotten damaged. I can't see anything immediately wrong with the amp, so this would be my guess.

The angle of the picture are a little weird, could you get them at perpendicular?
 
Mar 19, 2006 at 9:11 PM Post #4 of 22

Paragon

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Is it me or is there something weird about the capacitor on teh left? Almost looks like it is leaking.. or is it glare?
 
Mar 19, 2006 at 9:20 PM Post #5 of 22

rickcr42

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Hold it up to a bright light source with the lighting behind it and look for any connections (solder bridges) that should nt be there.Sometimes real hard to see with the unassisted eye but ready apparent when you hold the pcb up to a bright window or lamp
 
Mar 19, 2006 at 9:46 PM Post #6 of 22

hembergler

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What exactly is a cold joint? As a newbie solderer, I'm still, well, new to all of this.
rolleyes.gif


I'll get some more photos and check all the resistors later when I have time. Thanks for the help so far.
 
Mar 19, 2006 at 9:56 PM Post #7 of 22

Paragon

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Bad solder joint where the solder doesn't flow properly and does not have good conductance.

What composition solder are you using? 60/40 or 63/37?
 
Mar 19, 2006 at 10:01 PM Post #8 of 22

The Monkey

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A bad/cold solder joint sometimes looks like a blob or a dome instead of the convex ideal. Also if the join is very dull, not shiny, that could be an indication of a bad joint.
 
Mar 19, 2006 at 10:02 PM Post #9 of 22

rickcr42

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usually if the solder joint has a nice shiny appearance it is a good one but if that surface is dull could be an indication of a "cold" joint which is called what it is because the heat was not applied long enough to allow the solder to flow over and around the parts (or the part was moved before it cooled !) and because of this the solder crstallized instead of becoming a solid mass.

Crystallised means pockets and cavities where there should be "fill' so a good connection is not made.

hope this helps
 
Mar 19, 2006 at 10:55 PM Post #10 of 22

tomb

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I've seen lots worse - like my own CMoy!
rolleyes.gif
Yet, it worked perfectly following Tangent's instructions.

The solder joints look good to me - just maybe a little too much in places. (Heck, I burned the pads off in couple of places on mine!) Even then, Hembergler's looks great for a first time. It's hard to pinpoint the problem with interim test jumpers, though. There's no way to verify from these photos and description that the connections were made properly.

If that's not it, I agree with Diredesire - the opamp should've been socketed. I have always heard that a little too much heat would burn them up.

I would go ahead and finish it, while double-checking every single connection to make sure it's in the right place. If it still doesn't work with the completed pot, jack, and battery connections, then I'd unsolder the opamp, throw it away, and put in another one after soldering in a socket. You can get sockets at any Radio Shack. They're nice because as long as you don't totally melt the socket plastic beyond recognition, the opamp will work because it's never been touched.
icon10.gif


just a suggestion from one newbie to another ...

P.S. I'd get rid of that solid wire, too. It's great for the jumpers on the bottom of the board, but it sucks for anything else. I started that way, and saw real quickly that it was going to be a #$@%!! Even changing to flexible, I broke the pot leads two or three times trying to bend the wire while packing it in the Altoids tin.
 
Mar 19, 2006 at 11:32 PM Post #11 of 22

hembergler

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Quote:

Originally Posted by Paragon
Bad solder joint where the solder doesn't flow properly and does not have good conductance.

What composition solder are you using? 60/40 or 63/37?



I'm using 60/40 to solder since it's thinner, and 63/37 to tin the soldering iron.

I might just get a socket and buy a new op-amp if all the resistors check out. I've really looked over everything else and cleared away most of the flux to no avail, and I'm really not very good at soldering so I could definately have damaged the op-amp itself.
 
Mar 20, 2006 at 1:25 AM Post #12 of 22

Paragon

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I wouldn't use 60/40. One look at the pics and I was almost certain you were using that. A eutectic 63/37 is much better for joints. That would be my first suggestion. I will not touch a non-eutectic blend. The pasty state is horrible and has a tendency to leave unsightly solder joints.

http://www.tangentsoft.net/elec/movies/ -Take a look at #2 for basic soldering tips. It is long but good on the basics.

What's the word on that capacitor? Is it leaking on the top or is it just the way the picture looks?
 
Mar 20, 2006 at 1:48 AM Post #13 of 22

hembergler

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It's just the photo... I hope
biggrin.gif


Oh, and thanks for the video, I wish I had seen that tangent had videos before. That really helped to understand how to actually solder. You can only get so far reading guides without actually seeing it in action.
 
Mar 21, 2006 at 10:07 PM Post #14 of 22

hembergler

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Oh, and I forgot to mention, that I've tried putting the LED into the circuit, and it just doesn't work. It did work briefly, but no longer. At first I thought it was due to sloppy soldering, but I resoldered the connections and it still doesn't work. Is it possible that if a resistor is wrong, you can "blow out" an LED? Are there any other ways the LED could not be working? I measured the output to the LED, and it's getting the full 9volts from the battery, which seems a bit too high. (I think the LED is set for 3 volts or something of that sort)

I'll try to get some better photos by tomorrow
 

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