Yamaha CA 800 right channel noise

Discussion in 'Yamaha' started by dbdb, Nov 7, 2017.

  1. dbdb

    dbdb New Member

    Messages:
    5
    Hey everyone.
    I'd like some help diagnosing a hum (sounds more like white noise) coming from the right channel of my CA 800. I didn't notice it when I purchased it months ago because when the amp is cold it isn't audible. Hoping there's an easy enough fix for it.

    Here's what I know:

    -isn't audible for the first couple of minutes after power up
    -right channel only
    -noise drops slightly when I switch the audio muting to -20db
    -noise gets way louder when I switch off the preamp coupler on the back
    -no other switches or knobs change the noise
    -I'm always running it in class A, but the noise is still there in class B

    Really appreciate any advice on this. This amp sounds fantastic, otherwise.
    Thanks!
     
  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    36,824
    Location:
    Fort Dodge, Iowa
    Do you hear any music from that channel ?
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    36,824
    Location:
    Fort Dodge, Iowa
    Or just "white noise "..
     
  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    36,824
    Location:
    Fort Dodge, Iowa
    Could be and transistor , diode or cold solder connection within the right amplifier assembly.
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    36,824
    Location:
    Fort Dodge, Iowa
    http://sportsbil.com/yamaha/ca-800-sm.pdf
    After the noise has started. On the right amplifier assembly.

    Page 6 , step A . Check the voltage and try to adjust if needed. (primary stage Differential amplifier circuit current adjustment.)
     
  6. dbdb

    dbdb New Member

    Messages:
    5
    Yes. It's not really noticeable at all when listening to most music. Quiet passages and silence are the only times I can hear it. I'm also not noticing any distortion at all in that channel. It's just noise at a low volume, and doesn't change volume when I turn the volume knob all the way up or down.
     
  7. dbdb

    dbdb New Member

    Messages:
    5
    I'll pick up a voltage meter sometime this week had one years ago and lost it in a move. Thanks for the link to the manual!
     
  8. dbdb

    dbdb New Member

    Messages:
    5
    But really I can only hear it when the room is silent. It doesn't really have any noticeable impact on the listening, I'd just like to fix it before it does, or potentially causes other problems
     
  9. mbz

    mbz AK Subscriber Subscriber

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    Location:
    Melbourne, Victoria
    Reading between the lines I think your about to jump on that poor C458 on the heatsink.
    Maybe measure dc offset (mV, between red/black speaker posts) as per sm.
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    36,824
    Location:
    Fort Dodge, Iowa
    Dc offset is not going to tell you squat about excessive floor noise in the amplifier assembly. I've never seen the thermal tracking C458 actually go bad in this model.I'm thinking a noisy transistor in the front end. Just wanted to see if the FET current was in the ballpark.
     
  11. mbz

    mbz AK Subscriber Subscriber

    Messages:
    1,136
    Location:
    Melbourne, Victoria
    I would have thought that 200-300mV would be audiable?
    Maybe time to buy that book and do some reading....
     

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