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Damaged NCC200-Left

Discussion in 'd.i.y.' started by allen6266, May 7, 2014.

  1. allen6266

    allen6266 pfm Member

    Hi All,

    By looking at below picture, can anyone tell what possibily cause the damage?

    Measure at speaker terminal, I got -51v. This happened in the afternoon when I am listening at normal level, the amp was switched on in the morning.

    I have not remove the board yet for further investigation, probably drivers and output transistor are gone too?

    Your input please. Thanks.

    allen.

    [​IMG]
     
  2. Drzoigberg

    Drzoigberg pfm Member

    Hi,

    Looks the same as happened to mine (same resistors burnt out), hopefully you have speaker protection !!!

    Les told me that it was probably my signal earth dropping out.

    Les helped me fix mine have a chat with him.

    Regards

    Jim
     
  3. Col

    Col pfm Member

    Ho Hang on is this A common fault with this NCC200 v1.3 as I am about to order the parts for the boards I just got
    I don’t want to built into problems I hope :( is there something I should know about with this amp
     
  4. martin clark

    martin clark pinko bodger

    NO, it's not a common fault.
    Ampsl like this really blow only if (1) the output is accidentally shorted (2) inadequate heatsinking is added (especially important if you run at high voltage rails)

    The second is especially important because the NCC and Hackernap omit all forms of DC -offset and transistor SOA protection in pursuit of audio quality.

    If you want to add a relay-based speaker protection from both these potential faults, use Velleman kit 4700 in your build also.
     
  5. Col

    Col pfm Member

    Thanks Martin
    Good to Know

    I did not want to built into a problem I will be building mono blocks using 0.25.0.25v 300VA Transformers about 35v rails

    My Heatsinks should be ok cool rail 200mm 40 X 100mm Heat Sink 0.7C/W and thanks for the tip on Velleman kit 4700
     
  6. 337alant

    337alant Negatively Biased

    Col
    No, this is not a common fault, and this amp is very stable. As Martin has said these are very reliable amplifiers, but as with any amp take the precautions that Martin has outlined.
    Also make sure all your crimped connections are sound if a power rail connection becomes detached intermittently it could blow the amp if speaker are attached, same goes for the signal ground if that is dropped or comes detached you will get that loud squeal you get if you are trying to hot connect a phono lead
    I note that your signal in loops in and then out?, why is that.
    Alan
     
  7. allen6266

    allen6266 pfm Member

    Jim,
    No, I don't have speaker protection, actually I have vellemen 4700 lying around, reserved for hackernap. Signal earth? I played with swapping pre-amps recently. After this incident, I plugged my pre 42.5 (modded, with diy local regs inside) into nap110, discovered that one of the channel got intermittent sound, probably loosen pin at din socket. Is this the culprit?

    Martin,
    Output accidenlty shorted? connection between speaker and amp are secured with quite tight banana plugs along naca5 cable. I will check possible short on the amp board iself, and possible short in speaker box. About heatsink, do you mean for drivers or output transistors? Are my heatsinks look OK as seen in the picture? Heaksink for output are fasten onto metal case chasis, with heat sink compound.

    Alan,
    Signal loops as you can see there, I have RCA & DIN socket for amp inputs, but I only use one at a time. I will check on crimp terminals for power supply rails. Seems like you also mentioned signal ground..hmm. I did not know and aware of importance of signal ground, that can cause this disaster.


    I took out my speakers, the 6 1/2inch mid/woofer has got mild smokey smell, the voice coil still looks like copper, instead of charcoal. Measured the VC resistance, within spec 6.5 ohm. Same to the tweeter. So my speakers are safed from this disaster, probably I was quick enough to switch off the amp? The amp was switched off immediately after I heard no sound from left speaker.


    Here aother picture:
    [​IMG]

    [​IMG]
     

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