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Thread: PL400 Diodes on C6 to prevent latch up: how about on Series II (PL-36)?

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    PL400 Diodes on C6 to prevent latch up: how about on Series II (PL-36)?

    I have been reading about the PL400 latch up, and people say that putting back-to-back diodes across C6 can prevent it. And changing C6 to 470uF helps low end response.

    I have 3 PL400 Series II's with PL-36 kicking around. I am thinking that they all have the same latch up potential. Would these same changes to C6 correspond to C111/C211 on the PL-36? If anyone can confirm this, I will toss some caps and diodes at them right away without further ado.

    I know that the right thing to do is to get 3 White Oak upgrades and add speaker protection. I definitely want that but right now at this moment that is not in the budget.

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    Forum Veteran Fishoz's Avatar
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    Unfotrtunately you have been replied to by one of the least tech savvy members of our group...me! The east coasters are just rolling out of their coffins, one of the aces will be along soon and will more than likely be very happy to give their input.

    Good thought on the White Oak future. This is the place to be.
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    He's wrong of course, but I can guess good.
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    Would love to hear your "guess" orange.

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    Thanks Gepetto! I will make those changes.

    2 of these PL400s are my dad's (his original one and the 2nd one I got for him) and I just talked mom into buying him a white oak kit. Will be assembling the kit carefully, test it in mine, once it works, sneak it into his and do this cap/diode mod on his 2nd one and on my original PL-36. Wish me luck! We'll see if he goes for a 2nd white oak and/or returns the favor.

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    Quote Originally Posted by spmac View Post
    Thanks Gepetto! I will make those changes.

    2 of these PL400s are my dad's (his original one and the 2nd one I got for him) and I just talked mom into buying him a white oak kit. Will be assembling the kit carefully, test it in mine, once it works, sneak it into his and do this cap/diode mod on his 2nd one and on my original PL-36. Wish me luck! We'll see if he goes for a 2nd white oak and/or returns the favor.
    I appreciate the responses here but looking back now, I did not read the responses very carefully. I don't want to mislead anyone else to think that the diodes are necessary or correct on the PL-36 board. From my small amount of testing with the diodes installed, everything did seem fine. I did not observe any ill effects or distortion. However, I think I will remove the diodes from my board for now until we can understand more about it. From all other sources, I only see mention of the latch-up issue occurring on the original PL400 (without the input op-amp). Phase Linear may have fixed the issue when they changed to using an input op-amp.

    My advice for others at this point: unless someone steps in and definitively helps us understand the implications of adding these diodes on the PL-36, I think that we should err on the side of caution and not put them on there.

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    Administrator Gepetto's Avatar
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    Quote Originally Posted by spmac View Post
    I appreciate the responses here but looking back now, I did not read the responses very carefully. I don't want to mislead anyone else to think that the diodes are necessary or correct on the PL-36 board. From my small amount of testing with the diodes installed, everything did seem fine. I did not observe any ill effects or distortion. However, I think I will remove the diodes from my board for now until we can understand more about it. From all other sources, I only see mention of the latch-up issue occurring on the original PL400 (without the input op-amp). Phase Linear may have fixed the issue when they changed to using an input op-amp.

    My advice for others at this point: unless someone steps in and definitively helps us understand the implications of adding these diodes on the PL-36, I think that we should err on the side of caution and not put them on there.
    They do no harm in any of the PL control board generations. Hopefully they NEVER do anything and you never experience a latch-up. If you experience the amp attempting to latch-up, you will be glad they are in there.

    ALL White Oak Audio board generations have these despite the fact that the theoretical ability for the amp to latch up has been designed out.

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    Okay, thanks guys, I will leave them in there.

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