Sony STR-DB780 Receiver Logo
Posted on May 22, 2008
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Protection Problem with Sony STR-DB780 AV Amp / Sony SA-VE535HS speakers

Hi, I have just bought a Sony STR-DB780 AV Amp paired with Sony SA-VE535HS speakers. I upgraded the speaker wire on the fronts centre and rear to 79 strand to replace the supplied wires. But I had a poblem in that the amp kept going into protect mode. Having checked and double checked the connections for shorts without any joy in solving the problem I resorted to the supplied wires which I had had working previously. Problem solved ... The only thing I can think that maybe an issue but being new to this I am not sure if I am totaly off track is that by connecting thicker wires it alters the ohms of the speakers and may be should set the switch on the back of the amp to 4 ohms instead of theh current 8 ohms.( Don't want to flick the switch without advise .. ) Can anyone please point me in the right direction or has anyone come across the problem themselves. Thanks When in TV/SAT mode it cycles through PCM 4B and Unlock before going back to TV/SAT. The sound remains as it cycles through PCM 4B but disappears as it goes through Unlock. This can happen once an hour or every few seconds. I am told the Unlock means it is confused (Sony solution) and the solution is to disconnect it from the mains and reconnect but this does not affect anything. It is only on TV/SAT that it happens not on disc, tape or receiver.

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Dean Joly

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  • Posted on May 22, 2008
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How have you checked for shorts in your wires? Did you use a multimeter? Test the resistance of your new wires compared to the old wire, should be close to the same and next to nil on the same wire but if you don't get infinity between pairs then you have a short.

About your second problem, what kind of connection are you using for your TV sound? Sounds like it's a digital connection but is it coax or optical? Sounds as if it loses sync with your signal and has to resync. If you are using optical you may have a bad cable if you are using coax the cable may be picking up interference from something or the cable may be bad.

Benjamin Patri

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  • Posted on May 22, 2008
Benjamin Patri
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Hi keith

The thicker wire will reduce the resistance and thus have more power running through it which no doubt tripped the protection mode.

For the unlock, it will do this when it is set to AFD auto format decoding, and is just looking for the best audio to play.


:Let me know if you have any other questions

  • Benjamin Patri
    Benjamin Patri May 22, 2008

    here is a great resource for determining how to wire your speakers

    http://www.crutchfieldadvisor.com/S-yJDh...


    Have a Great Day and if you need anything else, I am here to help


  • Benjamin Patri
    Benjamin Patri May 27, 2008

    Were you able to fix this, if so then please give me some feedback by
    rating my solution. If you need any more help, I would be glad to
    assist you, just ask.

    thanks and Have a Great Day!

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  • Posted on May 22, 2008
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What you are talking about is impedance matching... it is done to avoid reflection... reflection causes noisy output due to distortion so only wires of specified thickness is being used... you can achieve the desired result by changing the length of the new wire you tried...

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