how to get started tracing down a hum in old H/K receiver

Discussion in 'Archived Threads 2001-2004' started by peter_anderson, Jan 29, 2002.

  1. peter_anderson

    peter_anderson Stunt Coordinator

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    I recently bought the H/K AVR 320, so my old H/K AVR 20II is no longer in use. Over the years, the AVR 20II acquired a constant white noise, audible regardless of volume, both in the speakers and especially in the headphone jack. With the speakers, it is generally not noticeable after 3.5 meters, but I can't stand to plug headphones into it anymore. The noise is kind of a hybrid between white noise and a really high-pitched (like >15,000Hz) hum.

    I have no fear of the soldering iron or of killing the unit.

    Somebody suggested to me that the transformer needs to be replaced with a higher quality unit. I think it might need some kind of beefy ground. What do you all think?
     
  2. Jeff Rosz

    Jeff Rosz Second Unit

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    hello peter,

    you wouldnt happen to have the schematics for it would you?probably not, huh? do you have any experience in signal tracing? is the noise coming from both L+R sides? since the noise is coming from the headphone jack too, i think we can rule out the power amp stage/s. you wouldnt have access to an oscilloscope would ya?

     
  3. peter_anderson

    peter_anderson Stunt Coordinator

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    noise comes from both sides, but the high stuff is only on the left (!). if i set the balance to right, all of the noise from the left disappears completely, and vice versa. i have the "ground" connection on the back connected to a coax grounding block which is in turn connected to the building ground via some coax. this connection makes no difference, though. i don't know exactly what 60Hz hum sounds like (except that it is very low) but i am pretty sure if it is there, it is being beaten out by the hissing.

    no schematics or oscilloscope.

    i wish somebody else with one of these older models could hear what i was hearing and let me know if it is normal; i honestly can't remember if it was this bad when it was new (5 years ago).
     
  4. Ron Shaw

    Ron Shaw Stunt Coordinator

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    Replace the transformer??? No, that isnt the problem. Most likely it is a leaky capacitor or a marginal transistor. Electrolytics are known to dry out and cause problems with age (but 5 years isnt really that old), and I bet that unit is full of electrolytics! A scope would be the best way to track it down. By the way you describe the effects of the balance control, I can tell you the noise originates before the balance control (somewhere early in the preamp stages). Other than that, I cant be of any use.
     
  5. peter_anderson

    peter_anderson Stunt Coordinator

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    no, that is great help! i don't think this is a good time to shell out for a good oscilloscope, so maybe this project isn't worth the time and money.

    thanks anyway!
     

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