Studiophile AV40: Bad capacitors causing hum/buzz
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Thread: Studiophile AV40: Bad capacitors causing hum/buzz

  1. #1
    Join Date
    Sep 2011
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    Default Studiophile AV40: Bad capacitors causing hum/buzz

    After approx 4 months of use, I just started noticing a distinct buzz or hum. It's in both speakers and isn't affected by the volume. It's there even if the input is unplugged.

    Out of curiosity I took the back off and it was easy to see the problem. Several of the electrolytic capacitors were bulging. I've seen that before on LCD monitors. Apparently, or perhaps I should say: according to folklore, it was caused by a rogue company in China supplying bad electrolyte. Lots of different companies and products were affected but luckily it's generally pretty easy to fix them just by replacing a few capacitors.

    The photo below shows the capacitors. They are bulging at the top of the cans where the 'X' is.

    AV40-badcaps.jpg

    Has anyone seen this before? The problem for me is that I'm in Finland but I bought the speakers in the US so shipping them back is going to be a major hassle. Does anyone have a schematic? I can see 4 of the caps will need replacing (you can see 3 in the photo) but I can't get a clear view of the rest of the board without a lot of effort so I don't know how many others are lurking in there.

    I have to say these speakers are pretty good. I had to put some foam in the reflex ports to tame the overblown bass but otherwise they've been superb.

    Rob.

  2. #2
    Join Date
    Sep 2011
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    4 capacitors replaced, including one that was put in the wrong way round. No hum, no popping when switching off and the sound is MUCH better.

    The capacitors I replace were:

    2 x 4700uF, 35V
    2 x 220uF 25V

    The only problem I had was that it was impossible to find 4700uF 35V capacitors that would fit in the available space and I'm actually quite suspicious that the originals were really rated at 35V. I measured the voltage and it was around 21 to 22V so I used 25V capacitors instead. Mains supply voltages vary quite a bit so it would be worth checking before anyone else does the same. Ours is nominally 220V but in theory it could go up to 250V which would take the voltage across the caps up near the limit.

  3. #3
    Join Date
    Nov 2008
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    Rob, i'm just curious if you have the old AV40 or the new version. The new version doesn't have the deep bass switch on the back. If you have the new revision and still there are problems with capacitor... M-audio is even crappier than i thought.

  4. #4
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    Sep 2011
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    The old version with the bass switch. IMO, the design and construction is a mix of good and bad. They obviously put a lot of effort into making the enclosure well damped and it's good to see that all the large components were glued as well as soldered to the board (although having the amplifier inside the enclosure is never going to be ideal). If they'd just spent another $10 on using better quality components and maybe a heatsink on the back to keep it a bit cooler it would have been a winner.

    The sound is now a lot better than any similar speakers I've tried. It's quite mellow and certainly doesn't have that 'electronic edge' you get with most computer speakers. I wouldn't call it true HiFi though. My 15 year old Audiolab + Epos system beats it by a mile (that's about $800 worth though).

  5. #5
    Join Date
    Jul 2012
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    2

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    I have some AV40 mkI (with the Bass Boost(!) switch) that have been buzzing for a long time. I had them plugged in at work and I just assumed it was really bad power causing the buzz, but now I have them home and hooked up to a decent power conditioner and the hum is just as strong as ever.

    I'm sure I'm out of warranty, so I'm tempted to try your capacitor fix, but I know nothing about capacitors. Are they just a dime a dozen, or should I buy some well made ones? As follow up, who makes well made ones?

  6. #6
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    Sep 2011
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    There are a few good brands. I've had good experience with Panasonic and Rubycon but there are others. The badcaps.net website has lots of info. I'd definitely recommend high temperature capacitors (105 C). Capacitor life is highly dependent on operating temperature and the AV40s run pretty hot inside. The quoted life in the datasheets will seem very low (1000-10000 hours) but that is only if you run them at the limit. The life increases exponentially if you run them at lower temperatures. You mustn't run them over the design voltage but it's ok if you are right up near the limit.

  7. #7
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    Jul 2012
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    Thanks Rob, that was my first visit to badcaps.net. I feel like I just took the red pill.

    Will post when I have updates.

  8. #8

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    Any update, mmdc? I'm curious because my AV40s recently started having similar hum issues (barely affected by changing the volume, hum without any inputs, etc).
    I opened it up and the capacitors are bulging – although not as bad as the picture Rob posted.

    Is replacing the capacitors the next step I should look at?

    I assume that they don't have a warranty past a year given I bought them at Best Buy..

    Any guidance either of you can give would be greatly appreciated. Thanks!

  9. #9

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    There are a few good brands. I'm sure I'm out of warranty, so I'm tempted to try your capacitor fix, but I know nothing about capacitors. Are they just a dime a dozen, or should I buy some well made ones? As follow up, who makes well made ones?

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