LM3886 Chipamp problems...

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FenderBender11

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Joined 2011
Right-o. The preamp is on the LM3886 board...

However, I believe I found the solution. It may have been a combination of a few things...though I'm uncertain as to why they would all suddenly go wrong.

Anyway- I pulled out the Texas Instruments NE5532 op-amp that was on the faulty channel, as the amp was working...just there wasn't much power behind it. I just happened to have an prehistoric Signetics NE5532 in my parts bin so I put that one in. It was socketed.

And what do you know...it's back to normal. However, funny thing is that I also had to replace the pot because it was very very noisy and scratchy. Just plain weird. I was loosing my mind so I just put in an old Bourns one that I had and I knew how to wire. Sounds great now.

Still confused about the fuse blowing extravaganza, but for now, I'm going to accredit that to inrush current. Perhaps I should get some larger value fuses, maybe 5A+.

I still am uncertain as to why the op-amp suddenly stopped working though I guess I should just forget about it now.
 
GloBug

GloBug

Banned
Joined 2011
Sounds like you have a handle on it now. My bread board amp started up dozens of times with a 3 amp fast blo, although I knew I needed a bigger one. (4~5amp)

As far as the rest just sounds like cheesy or fake parts. Its nice to have a junk pile to salvage parts from.
 
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bcmbob

Member
Joined 2009
I'm not an expert in such things, but I've built four different LM3886 based amp designs and the process is always the same. I use a dim bulb tester at first power-up to determine if there are any shorts or transformer problems. Next is reading DC offsets and if the result is higher than a few mV, I stop there before attaching either a source or speakers. Full volt readings would push me to search for a serious problem.

I would suggest you post your situation to other threads where there is lots of activity - such as - http://www.diyaudio.com/forums/chip-amps/207971-bought-xy-lm3886-kit.html#post2930771

Good luck..:)
 
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gootee

Member
Joined 2006
fullnet.com/~tomg/index.html
FenderBender11 said:
I did. My mistake. I just got the board. No parts. Yeah I'm confused as to why the op-amp died, but I won't question it further. I've been testing it and it seems fine.

Thanks for all the help/interest.
Click to expand...

For future reference:

Usually, after a thorough visual inspection, the first thing to check is the DC power supply voltages, at the points where they get used.

When you have two identical channels and one works fine and one has a problem, you have one of the best situations for troubleshooting, because you can compare measurements at corresponding points, in the two channels, find where they differ, and thereby home in on the problem.

The measurements I'm talking about are resistances and DC voltages, if all you have is a multimeter.

The way you would usually do those would be with your "negative" multimeter probe clipped onto the main ground point. Then you just test coresponding points in the two channels, alternately, with your positive probe.

Resistance measurements must be done with the unit unpowered and unplugged, with caps discharged.

DC voltage measurements would obviously need to be done with the unit powered on. Usually, you would probably want the inputs shorted.

Once you find a significant difference between channels, you might have to give some thought to what could be causing it. Then you might need to remove a suspected component for out-of-circuit testing, or to simply replace it.

Cheers,

Tom
 
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