Sunday, December 29, 2013

Fixing the buzz in my M-Audio AV-40 speakers

A couple of nights ago, I woke to the sound of my UPS going "EEEEEEEEEEEEEEE." I stumbled out of bed, shut down my computer, hit the reset button on the UPS, and went back to sleep. The next morning, I discovered evidence of gremlins. My computer was being weird instead of booting up ("whirrrrr ... whirrrrr ... whirrrr"), which was solved by a tip from Matt: unplug all the USB devices. I don't really understand the bug, but the fix worked. (Maybe I should have fewer than eleventy billion USB devices connected to my computer at all times? Nah.)

To my dismay, a secondary problem presented itself: my speakers were buzzing. They continued to buzz after switching them off and on again, removing the input, plugging them into another outlet, and smacking them around a few times. A quick Google pointed to a solution: replace four stupid bulging piece-of-shit capacitors.

How annoying. Lucky for me, I am really good at soldering. No, really, it's my superpower. Things I enjoy soldering include copper plumbing pipe and Theremins.

Here are the replacement capacitors, purchased from Mouser Electronics, which is a pretty great website where I could probably get very lost if I were a soldering Ph.D.:

I am kind of quirky when it comes to my soldering talent. I like to solder on the floor, and my favorite soldering iron is a desoldering iron, which I use to both desolder and solder. That little puff bladder gives me more control.

Here are some progress shots.

Matt's action shot. I can't take my own pictures of myself soldering because it requires both hands and sometimes my mouth.

The dumb capacitors have been desoldered, and I am inserting the new capacitors into the vacated holes.

Snipping the leads.

Applying the deadly flux.

When I built my Theremin, I gave myself a mild case of flux poisoning, so these days I am careful to breathe in as little of the delicious flux smoke as possible.

And hey, look at that, I fixed them. No more buzz. I've also headed off the possibility of any one of these capacitors randomly exploding and barfing all over the circuit board, ruining everything. That happens sometimes. Just ask Matt, who lost his AV-30s to exploding capacitors.


Jack Frost said...

I'm having a similar problem. Was your buzz intermittent? My problem is that I am not good at soldering lol.

Richard Thompson said...

Hi Melissa, i had to write and thank you for giving me back my
speakers. I own the exact same make and model of speakers which suffered from an extremely loud buzz, so much so that I couldn't use them for a few years. I decided a couple of month ago to do some research over the problem which when I found your blog post. I ordered the exact same capacitors from you're photos and to my amazement with my limited soldering knowledge I managed to repair them and they are working like new again. Thanks once again,
kind regards.
Richard .

Spin2Win said...

Just did my AV40, which started buzzing like crazy in the middle of watching a video.

My model looks a bit newer, with a slightly different board layout and wiring. I was able to unplug the connectors to the Aux In/Phones & volume control, unplug the speaker wires (note the polarity!), but unsoldered the wires to the right speaker connector. That, plus unscrewing the transformer and heat shield plate gave me enough slack on the wires to work with the board. One of the things that slowed me down was the volume of glue. Some of the caps were covered in silicone caulking, and some wires had a yellowy contact cement-like glue that looked a lot like electrolyte, but upon closer inspection seemed to be just to reinforce some components in case the speaker got bounced around. There is also a tonne of black urethane glue holding the heat sink and pcb to the back panel. Though I tried to remove it, it seemed like something would break first. In the end, the glue stayed, and I was able to work around it.

The 4700uf caps were bulging and leaking. One of the 220uf caps was also bulging. Used solder wick and my vacuum tube to get the caps out without incident.

I ordered replacements for the 2 4700's and 2 220's from Mouser. I tried to get as big a voltage rating as I could, while still fitting the big 4700's under the heat shield. But...I could only fit the same 35v rated cap, and even then, it was a bit taller. I was able to upgrade the 220's from 25v to 35v. We'll see if these last longer than the 5 years the previous caps lasted.

Resoldered the right speaker wires to their jack, used the long needle-nosed pliers to reattach the speaker wires, and got everything screwed back together.

Fired up the power, and everything worked like new!

Thanks for the info. You saved me buying a new set of speakers.