Hiss, hissing sound in speaker sets like the MegaWorks 550

Question

Over the years, I noticed that my MegaWorks 550 started hissing more and more. For anyone interested, i want to share my quest to find the cause.
First of all, i looked on this forums. There were several useful posts.
http://forums.creative.com/t5/Speake...ion/m-p/169575
http://forums.creative.com/t5/Speake...xed/m-p/184299
Based on these, I mailed customer service for some more information. Their mails were annoyingly useless. On top of that, they actually removed above mentioned posts from their forums! Here's a small summary of the mail conversation with customer support. It's so stupid, that it's actually fun to read:
ME:
Dear Creative, [...] my MegaWorks 550 [...] has a clearly audible hiss. [...] This hiss is also present when no inputs are connected and independent of volume level. The level of hiss is equal on all five sattelite speaker connections, even when objectively measured with an oscilloscope. [...] I know the MegaWorks 550 is farbeyond the warranty, but i am a trained technician and capable of replacing any part. Could you please give a hint as to what causes this hiss? Kind regards [...]
CREATIVE:
[...] To reduce static or buzzing noise from speakers, avoid placing speaker cables next to computer monitors, TV, an AC adapter, or any chargers for MP3 players or cell phones, etc. These devices have a strong field, which may interfere with speakers.
Hissing Sound http://support.creative.com/kb/showa...aspx?sid=64810 [...]
(duh, i already mentioned that it is independent of any inputs and also present with nothing connected)
ME:
[...]Dear Creative, Thank you for your answer. I read the support solution you pointed to, and i also read about eight different threads about this on your forum, suggesting several causes. I've tested the 550 in an electromagnetic Farady cage and with no inputs attached. The hiss remains constant on each of the five outputs and independent of the volume level.
It must be a problem in the electrical circuit. Since this is a very prevalent problem, I hope there's a technician at Creative who know the cause. It would be great if they could explain which capacitors or connections typically need to be replaced or resoldered to remove the hiss.
I'm, of course, very aware that the warranty of the 550 is expired, i would just really appreciate some hints on how to fix it myself. It would be friendly to the environment, to my wallet and to your reputation! [...]
CREATIVE:
If the issue persists after troubleshooting, please be informed that our product have 12 month warranty since the purchase date. Further information on product warranty can be found at:
http://uk.europe.creative.com/suppor...y/warranty.asp
Please note that with most out-of-warranty products, we do not keep stock of parts anymore. You may wish to check with customers on eBay or at other forum sites who may be selling used parts.
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Answer 1

ME:
Dear Creative,
I would expect a €450,- speaker set like the Megaworks 550 to last longer than the three years it did before it started hissing. However, it's beyond the warranty period, so i'm not asking for any official warranty. But surely the least Creative could do, is help me fix it myself.
I just need to know which capacitors to replace to fix it, probably somewhere in the power supply. I know that a lot of sets were sent back because of the issue, so surely there is a technician from Creative that can pinpoint the cause. PLEASE!
CREATIVE:
Thank you for getting back to us.
I'm really sorry but currently we don't provide any out of warranty repairment services.
We're unable to help you in this situation.
If you still require assistance, please reply to this email and include any previous correspondence to ensure a quick response.
ME:
Dear Creative,
I'm not asking for a repair service. I want to fix it myself. I know that a lot of people sent their Megaworks 550 back because of this issue, so there are people within creative who know what causes it. Please, I just need to know which capacitor to replace. I wont contact you after that, even if the repair goes wrong or anything.
CREATIVE:
Thank you for contacting Creative Labs.
We are sorry to inform you that we do not provide schematics, circuit boards, part details or pin-outs for all Creative products to customers. The information you are requesting is considered proprietary and are not allowed to share or release it to the general public, as it would be considered a breach or corporate trade secrets. For your reference every product information and its specification can all be found via the Creative website. http://uk.creative.com/
We apologize if this is not accommodating your need and your cooperation in this regard is appreciated.
So... i opened the case and did some more experiments. I used a variable voltage. The hiss was indeed dependent on the voltage. Since it was not dependent on inputs or volume level and present on all five speaker outputs, i came to the following
CONCLUSIONS:
- the hiss is most likely caused by the final stage of the power supply unit
- specifically: decay of one or more of the 10 capacitors in there
- this is caused by creative using capacitors of a barely sufficient capacity (too cheap). Once they decay the become insufficient.
- communicating with the customer service is a fun, but not very rational process
Perhaps i'll replace the capacitors. If i do, i might share pictures and keep you updated. Please respond if there's anyone out there who would appreciate that.
PS for search purposes: Cambridge SoundWorks megaworks 550 5.1 MegaWorks 550D THX 5.1