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Advice needed for repaired 2 channel amp

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  • Advice needed for repaired 2 channel amp

    I have a six year old NAD 325 amp that has been repaired to an extent by a local tech that I don't entirely trust where his theoretical knowledge is concerned, hence this request.

    The amp works this way:
    When the mains power is turned on, it goes into standby mode, with an amber light. When the power on button is pressed on the amp, amber turns red for a few seconds and then turns green ready to work - this is speaker protection circuitry at work.

    The problem developed resulted in the amp sometimes going from green back to red, sometimes with a audible pop from the speakers even with volume at zero.

    From red, the power on button has to be pressed once, taking the amp back to standby/amber. Initially, a cycle or two of this kind resulted in it working. It had to go for repair when no amount of cycling would get it to start.

    The amp is back with me. The tech says that he has changed all the caps on the protection circuitry board, but there are also some on a surface mount type board in the output stage that are best dealt with by changing the board, an expensive repair, given the resale value of the amp.

    He also says - and this is all borne out by the amp behaviour - leave the amp permanently in mains powered standby state if you don't want to spend more money. Then it will work flawlessly, turning to green without any speaker pops. If the amp loses mains power, then the problem resurfaces, unless it is left with the mains powered on for about 15 minutes, in amber standby state.

    I plan to give the amp away to my daughter, it is surplus to my requirement. Leaving it with mains power on isn't a big deal - power consumption in standby mode is 1watt, and it does not heat up at all left that way. And then it works just the way it always has, in a few days of use at home.

    Questions I have are - What does this indicate about the remaining life of the amp? And as long as it is working fine used this way, is there any downside in doing so?Finally, what is the reason for this behaviour?

  • #2
    Should be OK?

    Is there a NAD service agent in India you could quiz? As long as the CD offsets (or other pre-settings) are within tolerance, I'm sure no harm would come.

    Having said that, after seeing what a brand new unboxed amp left powered up did to a precious pair of speakers in our dem room one morning (DC on the phono stage 'amplified' through to the speakers at 48V or so), I'd try to get this annoying fault fixed - and surface mount stuff CAN be repaired I believe, but you need the skill and/or training to do it.

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    • #3
      Demonstrably faulty

      Originally posted by DSRANCE View Post
      Is there a NAD service agent in India you could quiz? As long as the CD offsets (or other pre-settings) are within tolerance, I'm sure no harm would come.

      Having said that, after seeing what a brand new unboxed amp left powered up did to a precious pair of speakers in our dem room one morning (DC on the phono stage 'amplified' through to the speakers at 48V or so), I'd try to get this annoying fault fixed - and surface mount stuff CAN be repaired I believe, but you need the skill and/or training to do it.
      No, the sales distributors have little capability. The tech said that the surface mount board can be repaired, but he said it was easy to do more harm than good in trying to do that.

      There is one thing he showed me though. He connected a multimeter to the speaker terminals and at start up, the left speaker terminals had the needle move to about 12V before falling back to zero, while there was no movement when attached to the right terminals. He said both should show no movement.

      In its future use, the amp will be wired to a surplus pair of good but cheap speakers as well, so while it would be unpleasant, it would not be more than that if speaker damage was to occur.

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      • #4
        Try it with another pair of speakers.

        Originally posted by Kumar Kane View Post
        No, the sales distributors have little capability. The tech said that the surface mount board can be repaired, but he said it was easy to do more harm than good in trying to do that.

        There is one thing he showed me though. He connected a multimeter to the speaker terminals and at start up, the left speaker terminals had the needle move to about 12V before falling back to zero, while there was no movement when attached to the right terminals. He said both should show no movement.

        In its future use, the amp will be wired to a surplus pair of good but cheap speakers as well, so while it would be unpleasant, it would not be more than that if speaker damage was to occur.
        Maybe get any other pair of speakers , connect them to any other amp to check if they are OK. Then check if this phenomenon you described repeats again with this specific nad amplifier. If everything is OK it is very probable something happened to the cicuitry inside the left speaker (maybe some cold soldering? - I am guesssing only). And don't save money on the hi-fi for your daughter too much :)! I remember my daughter's face look after first listening to Rihanna's "Umbrella" hit via very good two cubic foot monitors in her teenager years (Dad it is THE MUSIC!).

        All the best.

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        • #5
          It's the amp, not speakers

          Originally posted by pkwba View Post
          Maybe get any other pair of speakers , connect them to any other amp to check if they are OK. Then check if this phenomenon you described repeats again with this specific nad amplifier. If everything is OK it is very probable something happened to the cicuitry inside the left speaker (maybe some cold soldering? - I am guesssing only). And don't save money on the hi-fi for your daughter too much :)! I remember my daughter's face look after first listening to Rihanna's "Umbrella" hit via very good two cubic foot monitors in her teenager years (Dad it is THE MUSIC!).
          I wasn't clear enough - the voltage was seen on the left speaker terminals of the amp when they were not connected to the speaker. The speakers themselves are fine.

          And as to not saving money - I would rather now spend it on her daughter, my first granddaughter! This is the second system I am passing along, one given a few years earlier is doing very well. And in her teen years, she had pretty much the same reaction to hifi kit - it was " I never knew that this track had these back up vocals, I can hear them clearly now".

          I installed the system at her place last night, and it is sounding very good - and no start up issues. As long as the amp is never deprived of mains power, it seems to work ok.

          Comment


          • #6
            Series fuse?

            You could put a small fuse in circuit with one or both speakers. A guess, but perhaps a 1A slow-blow type? It's just possible that it would minimise the damage caused by the amp finally failing, but if too low a value, would be liable to blow on loud music.
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK

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