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AOTC DVD killed my Sony STR-VA555ES!!!

Discussion in 'AV Receivers & Amplifiers' started by Mattk, Apr 10, 2003.

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  1. Mattk

    Mattk
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    I was watching AOTC and the bass level was a bit OTT and then the worst happened, the amp went silent! Upon investagation there was no output at all from anything although the amp had power and all the display was correct and working. I opened up the amp and found two 10amp 125Volt fuses had blown near to the audio transformer! Hope that it was was just a case of me drawing too much power and the fuses went before any damage happened!

    I'm not running a sub and using full size speakers set up to 'large' and have the speaker setting to 4 ohms as my speakers vary from 4 - 8 ohms.

    Should this have happened at all or is it common to draw too much power when using lower ohm speakers?

    After spending that kind of money on this amp I wasn't very impressed if it can't handle running at -43db when watching films with lots of LFE!!:(

    BTW I've just realised my speakers are wired in parallel as I have 2 sets for the front and 2 sets on the rears so this would make the ohms less? Should they be wired in series to obtain a higher ohms to help with overloading the amp? Just a thought:)
     
  2. Steve.EX

    Steve.EX
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    Mattk
    I would wire them in series if i were you.
    Can i say that with all due respect if you are fortunate enough to get away with merely replacing the fuses then Sony must be commended for producing such a unit that is capable of such "dummy" loads - (joking)
    It would seem that you have loaded the unit so that it "see's" nominal loads of 2 ohms for front AND back pairs!!!!! Factor in the impedance dips present on all speakers - although some dip hugely and some hardly any, with a 2 ohm starting point any dip is seriously going to stress the amp.
    I will expect the Sony service engineer to be similarly "unimpressed" if you tell him what happened.
    I wonder what the temperature of the output devices was just before shut-down????
    Could you not smell them????

    Regards

    Steve.
     
  3. iwatkins

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    ... add to that I think it is recommended that with speakers ranging from 4-8 Ohms that the Ohms selector on the back of the 555 should be set to 8 Ohms.

    Silly boy ;)

    Cheers

    Ian
     
  4. Mattk

    Mattk
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    The amp was and always has run very cool and never gets even warm? It was only on for about 5 mins and it has been running like this for months now!


    As I understood it you set the switch to 4ohms if you are running 4 ohms speakers?????

    I have:

    Fronts: Jamo's rated at 4-8 ohms and smaller Jamos rated at 8ohms

    Center: Kef TDM23C (The only decent speaker I have :D )
    rated at 4ohms

    Surrounds: Jamo's rated at 6ohms and pioneers at 8ohms

    Surround back : Pioneer rated at 8ohms


    I guess at this point I need some serious advice on how to wire up and setup the amp to cope with what I have!!! Save me wrecking my poor amp:blush:
     
  5. bob1

    bob1
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    It should be set at 4ohms if the speakers are less than 8Ohms 4-8ohms means they go below 8ohms so is settings where right just his wireing was wrong.
     
  6. dunkyboy

    dunkyboy
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    What do you need all the extra speakers for anyway? If you really want lots of extra speakers I would recommend getting yourself some external power amplification...

    Dunc
     
  7. sounddog

    sounddog
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    If you want to run the extra speakers more safely, grab yourself a couple of 2channel power amps - should be able to pick up somthing suitable for less than £100 each.

    Running extra speakers like that will put lots of load on your amp. Alternatively if you only need to usually run one set at once, look at QEDs line of speaker switch boxes.

    Vikki
     
  8. wookie

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    :laugh:

    The attached is usefull.

    Impedance Selector Switches

    This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation.
     
  9. wookie

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    You could connect 4ohm resistors in line with each speaker, but this would limit power and performance below 100Hz
     
  10. Mattk

    Mattk
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    Thanks for all the advice people:) I feel kinda silly really but I have learnt. I'll wire up my speakers in series and switch the amp to 8ohms to make sure there are no low impedance loads.

    Would it be ok to higher the impedance to about 12ohms? running two sets on the front or maybe I should buy some decent fronts and do away with having to run a pair to get decent sound!

    Anyway hopefully the amp will be ok after the fuses are replaced, in the meantime I'm back to my old 830!
     
  11. sounddog

    sounddog
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    I would get a decent single pair ... will sound a lot better than using 2 pairs ... lot more consistant sound field. Maybe then use on of the old front pairs for the rears instead of the 2 pairs you currently use.
     

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