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Help needed with beta22

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  1. pianola
    I have a problem with my just-finished beta22. It is a three channel configuration with the sigma22 acting as power supply. I did all the initial checks and everything was fine. I connected a headphone while the amp was off, then switched it on and turned up the volume. Everything seemed to be normal and I could listen to the music.

    But then I disconnected the headphones while the amp was operating and this seems to have burned both the left and right channel [​IMG]. As far as I can tell, all four MOSFETs of the right channel are blown, as well as Q24 of the left channel. Everything else seems to be fine, at least as far as I can tell from the readings of my multimeter, but I guess some more parts might have been destroyed.

    My question is if anyone can tell me what caused this. I guess it is because the left and right channel were shortened during disconnecting the headphone, but I read that this is normal for phone jacks. Is the amp not constructed for that or is there something else wrong with my amp?

    Any help is appreciated.
     
  2. johnwmclean
    I've read a couple of threads that have dicussed this, the 1/4" plug causes a momentary short when unplugging. The recommendation is to always have the amp turned all the way down when unplugging.
     
  3. El_Doug Contributor
    sorry to hear that your careful work got destroyed [​IMG]

    perhaps this will be a good opportunity to join team 4-pin?
     
  4. MoodySteve
    Quote:

    Originally Posted by pianola /img/forum/go_quote.gif
    My question is if anyone can tell me what caused this. I guess it is because the left and right channel were shortened during disconnecting the headphone, but I read that this is normal for phone jacks. Is the amp not constructed for that or is there something else wrong with my amp?

    Any help is appreciated.




    As others have mentioned - there's a momentary short when you pull headphones out of a TRS jack that can cause precisely the problem you encountered. I think someone's ß22 got zapped at a meet in this fashion.

    I hope your problem can be fixed by replacing parts (i.e. I hope you didn't burn any traces - those can be :ahem: 'difficult' to find).

    PS - Welcome to Head-Fi!

    Quote:

    Originally Posted by El_Doug /img/forum/go_quote.gif
    perhaps this will be a good opportunity to join team 4-pin?



    3-channel ß22 is actually an unbalanced config with an active ground channel - he'd need to add another board to go balanced.
     
  5. Bojamijams
    So the epsilon12 wouldn't protect again this either?
     
  6. johnwmclean
  7. n_maher Contributor
    Quote:

    Originally Posted by MoodySteve /img/forum/go_quote.gif
    3-channel ß22 is actually an unbalanced config with an active ground channel - he'd need to add another board to go balanced.



    What difference does balanced vs. unbalanced make? You can still use the 4-pin XLR jack just fine, I use one on my primary headphone amp and it's only a 2-channel design. [​IMG]
     
  8. aloksatoor
  9. wolf18t
    Quote:

    Originally Posted by Bojamijams /img/forum/go_quote.gif
    So the epsilon12 wouldn't protect again this either?



    Nope. The Epsilon12 was made to protect headphones drivers from DC offset and turn-on thump from some amplifiers.
     
  10. JamesL
    Can someone explain to me the circumstances in which an output short will cause damage to the amplifier?
    Is this risk present in amplifiers such as the soha, millet, etc.. and how can I tell?

    I'm not sure if its detrimental to the longevity of a product, but an output short obviously doesn't pose a major threat to most mainstream/commercial products such as an ipod or a computer.

    I think tangent suggested using output transistors with higher current ratings to lower the risk in case of a output short (at least, in case of the PPAv2).
    Turning the attenuator down is easy enough to remember, but you never know when somebody else will .. (hold on.. wait for the bad pun)... pull the plug on your amp.
     
  11. El_Doug Contributor
    Quote:

    Originally Posted by MoodySteve /img/forum/go_quote.gif
    3-channel ß22 is actually an unbalanced config with an active ground channel - he'd need to add another board to go balanced.



    clearly

    however, you don't necessarily need 4 channels to use a 4-pin connector [​IMG] someday all headphones will use a 4-pin xlr, and there will be peace in the middle east
     
  12. pianola
    Quote:

    Originally Posted by johnwmclean /img/forum/go_quote.gif
    http://www.head-fi.org/forums/f6/let...beta22-375627/

    ouch!




    I'd say, my problem is nothing compared to that. Nothing did actually burn. There was just a short hiss and a loud crack in the headphones (glad to have used cheap ones for testing).

    Quote:

    Originally Posted by JamesL /img/forum/go_quote.gif
    I'm not sure if its detrimental to the longevity of a product, but an output short obviously doesn't pose a major threat to most mainstream/commercial products such as an ipod or a computer.



    That was also my thinking. I guess you cannot tell an ipod user to switch it off before connecting/disconnecing the phones. Maybe it would be a good idea to write it somewhere on the official page of the beta22 that at least volume should be completely turned down before you plug in or out any headphones.


    Well, I'll replace the destroyed parts then. Luckily I have some spars. It's just a [​IMG] feeling if you have your just finished amp running and a couple of seconds later it ceases to work.
     
  13. amb
    Quote:

    Originally Posted by JamesL /img/forum/go_quote.gif
    I'm not sure if its detrimental to the longevity of a product, but an output short obviously doesn't pose a major threat to most mainstream/commercial products such as an ipod or a computer.



    True, but none of those devices are capable of the large amount of current that a β22 could produce. Also, many commercial designs utilize output current limiting circuitry or have output resistors to limit current, at the detriment to performance. The β22 (and σ22) do not have any current-limiting, so a little extra care is needed. Turning the volume down to minimum before removing or inserting a TRS headphone plug is good habit to develop no matter what amp you're using, anyway.
     
  14. FallenAngel Contributor
    Yep, easily done and a good habit to have (as is making sure you power up/down equipment in sequence).

    Most commercial designs are made "idiot-proof" and obviously cater to the "ease of use" crowd over the "audiophile" crowd.

    If you are worried about such thing, either do not use such an amplifier or install protection for it (which would make it perform worse). Or, follow basic rules and enjoy the best. [​IMG]
     
  15. Iniamyen
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