Amp 6 Basic has subtle constant static

[thejuddernaut]

Hey.
I built an Amp 6 Basic about 6 months ago and just now am getting around to powering it with a proper transformer and power supply rather than the smps that I was using. Ever since I first completed the project, there has been an audible white noise in the background. It all but disappears during loud passages, but is just audible enough in the quiet parts to cause me some serious stress. I thought powering it properly would help to eliminate this noise, but it actually seems to have gotten worse. Does anyone have any ideas about how to solve this problem?
Thanks a bunch,
Jud.

[krilli]

These amps are usually pretty quiet. And usually when there is noise, it's a simple fix - the amp is 99.9% working, there's just a small crack in the dam that's letting noise in, so to speak.

I would check the output filter soldering.

Do you have a reasonably good camera? - Could you maybe post a picture of the board? There are some eagle-eyed people on this forum!

[gnome]

I'd start by isolating the noise by hooking it up to a 12v battery, if the noise is still there then it is the amp, if it goes away then you know it is the power supply.
"usually pretty quiet" is a bit of an insult :P, the thing is jaw droopingly quiet. Hooking it up to 106dB speakers, there was just nothing.
Could also be your source, try different ones.

[thejuddernaut]

Alright Guys.
I tried some different power supplies with no real change. It very well could be my soldering. This was my first time with surface mounted parts and although I feel like I did pretty well, I could have made a minor slip or something. Here are some pics. Please let me know if anything seems obvious.
Thanks for all the help thus far,
Jud.DSC01152.jpgDSC01153.jpgDSC01154.jpg

[tuo]

It seems that you have used too much solder with your SMD components. And the output filter inductors does not seem the be in level with the PCB, which means there's solder under them and that might lead to a cold joint. Best way to solder those components is to add a little bit of solder on one pad, heat it up and place the component tightly on the board. When the first pad has cooled, the component will stay there and it is easy to solder the other pad(s) as well.

Now for removing the excess solder you can use solder wick.

Here are some pictures for reference: http://www.41hz.com/forums/entry.php...6-BASIC-SNEAKY

HTH

[krilli]

Couple of points - Leaded solder is good, lead-free bad ... 50W+ iron good, 30W pretty bad. I had to get a new iron the other day when my 50W died, I went for a 30W one to see what it was like, and it's way more difficult to get good joints! The warnings about the thick copper plane in 41hz gear are there for a reason. Ended up getting a 60W iron for the bigger joints, of which there would be a few on the AMp6.

So check your tools - The joints here could stand a little improvement overall, and the tools do make a great difference!

Sorry if I?m saying stuff you know ... It's just that as I learn more about soldering, the more I see how easy it actually is and i'd have liked to know that sooner!

[thejuddernaut]

Thanks for the help guys. I am using a 45 Watt soldering iron and flux on the surface mount components but I could have done better and will remove and resolder these components. I appreciate the time you guys took in helping me. Thank you much.
Jud.

[gnome]

I can see some dark areas around some solder joints which look like solder flux, which tells me that you haven't cleaned the board?

[krilli]

45W should be good! You're in much the same place soldering wise as I was a while ago. There's just a little bit of technique that needs to click into place I believe. It comes naturally with practice.

I emphatically recommend you get your hands on some liquid solder flux! It's the magic sauce that makes soldering much easier. Get "No-clean RMA" type flux or similar. Feel free to ask if you don't find anything that's obviously the right stuff. There's lots of flux types around, and only some of them make life easier

Desoldering tip - When desoldering, add LOTS of solder. As much solder as will reliably blob onto the joint area. The increased thermal mass will stay molten for longer, and allow parts to be easily removed. Small parts flick right off, and larger parts fall away And I'd avoid removing/resoldering through-hole stuff, the electrical connection there isn't as dependent on the physical positioning of the parts as in surface-mount. That is to say, the pin is already in the hole, so orientation doesn't matter, so reflowing should be enough if things aren't 100%.

What I would do is first get some liquid flux, and re-melt any joint that looks suspicious. I.e. not remove/resolder anything yet. Give special care to the small yellow decoupling caps - it comes to mind that those can be the culprits when there is slight hiss. With the surface-mount parts, it may be enough to just reflow them. If you add solder and reflow both sides at once, the surface action in the solder will most likely pull the part to a better position. Then you can remove the extra solder with soldering wick if it's blobby-seeming. And after letting the parts cool off for a couple seconds, perhaps add flux and re-melt the joint again if it's a little uneven from the wick. (Wick tends to "eat" the solder bump mostly where they touch, leaving an uneven joint.) ... edit - Actually, try resoldering one or two surface-mount components, and try removing/resoldering one or two. See which gives you the best results for the least pain. It kind of depends on the tools you have and how the parts and board react to heat which method will actually give better results in the end.

If that still doesn't work after a little experimentation, only then would I remove/resolder things. And then start only with iffy surface-mount components. Probably the through-hole won't need to be removed completely, which is unpleasant to do and risky anyway.

The thing is that if the amp is actually working, but with slight hiss, then it's not unlikely that it's only ONE joint somewhere that's less than good.

-- edit: +1 on cleaning the board before anything else. When it works, it's a big gain for little effort!