Announcement

Collapse
No announcement yet.

OT-Speaking of Old Audio Stuff

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • OT-Speaking of Old Audio Stuff

    I have a Harmon Kardon receiver, dual amp, it was top rated at the time (late 70s). I use it in my shop now, but have an issue. Some time ago, it had what sounds like static "pops" mostly when I would turn it off. It would scratch and pop a few times before going quiet. I found a guy who used to run an audio repair shop, no longer in business, but asked him if he would clean it, said that would cure it. It did for a while, but it's back. So rather than taking it back to him, the is there something I can do? Vacuuming maybe? Is there some kind of anti-static spray I could use on various parts?

  • #2
    Originally posted by rws View Post
    I have a Harmon Kardon receiver, dual amp, it was top rated at the time (late 70s). I use it in my shop now, but have an issue. Some time ago, it had what sounds like static "pops" mostly when I would turn it off. It would scratch and pop a few times before going quiet. I found a guy who used to run an audio repair shop, no longer in business, but asked him if he would clean it, said that would cure it. It did for a while, but it's back. So rather than taking it back to him, the is there something I can do? Vacuuming maybe? Is there some kind of anti-static spray I could use on various parts?
    I can't answer your question but I'm thinking if you check out Audio Karma's website you'll probably have much better luck. Been a while since I was playing with older audio, but that's the go-to website for this stuff. http://audiokarma.org/forums/index.php

    Comment


    • #3
      Most likely the power supply capacitors have dried out and need replacing. That should do wonders.

      metalmagpie

      Comment


      • #4
        There is a HK vacuum tube preamp repair posted here: https://www.youtube.com/watch?v=E_5cVxeoG7U
        While not your exact model might give a few general pointers.

        Comment


        • #5
          If only "MOSTLY" when you turn it off, but would do it other times as well, it may be a combination of several things. Some do more when the unit is just "ON", and some when it is turned off (or on).

          When turned off (or on), the DC voltages are changing, and capacitors are charging or discharging, which means there is DC current flow where there usually is no DC when the unit is just "on". If there are bad connections, they may cause pops or noise, even if they normally do not cause noises.

          Charging of capacitors associated with volume control, or EQ pots, can cause noise if the pot is "dirty". Pots normally do not have DC in them for audio applications (the noise is more associated with adjusting the pot, but can occur even if the control is not being turned).

          Noises in use can be bad connections, or semiconductors that are starting to go bad. It is not uncommon for the noise level to increase before the part actually fails. Often that is a type of noise that is a burst of noise, or an actual pop.

          Leaky capacitors (usually coupling capacitors) can cause noises. Resistors of certain types cause noises as they begin to fail.

          A late 70s unit is not likely to be tube-type.
          Last edited by J Tiers; 02-26-2018, 11:05 PM.
          1601

          Keep eye on ball.
          Hashim Khan

          Comment


          • #6
            Degraded capacitors are a common source of problems. Switches and controls are prone to developing bad contacts, and some types are hard to clean. I've actually had to drill into some types in order to get a cleaning spray into them. Drilling creates debris which could interfere with contacts as well, plus you could drill into the inside mechanisms and destroy a switch in no time, so that's not a sure process- but it may save you from having to replace parts which you either may not be able to get anymore, or can't justify the cost of. A lot of the older gear was quite good, and HK did make some very good stuff.

            To get into it and replace capacitors effectively means knowing which ones to replace. Where the unit has overlapping circuit boards and where you can't access both sides of the boards easily this will be an almost herculean task. The chances of breaking a wire connection are high, and it's not always easy to see where the wire has come from. Going in there and trying to do it yourself can easily result in losing the use of the unit entirely. Trusting it to a technician is no guarantee either, and if he or she does a thorough job it will be costly. Not trying to be a downer, but this is the reality of it. I've had to scrap a lot of components because the cost of bringing them back to decent life is too high.

            You could get lucky by replacing the main power supply capacitors, but if that doesn't fix it you are out that money and time. From my experience they don't fail that often- coupling caps are more likely to be failing, and there are a lot of them in the typical amp or receiver. Also, the output relay is bound to have poor contacts by now, and while this won't cause the symptoms you are having, it's something that should be dealt with to help prevent dropouts of the signal to the speakers.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

            Comment

            Working...
            X