Distorted bass on vintage receivers

Discussion in 'Solid State' started by slateef, Dec 6, 2017.

  1. slateef

    slateef Active Member

    Messages:
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    I've noticed on several vintage receivers that I've bought and restored that the bass is somewhat distorted, especially at higher volumes - imagine listening through a blown speaker; that's the sound.

    What causes this? Would a complete replacement of the capacitors solve this issue? Or is it more an issue with the output transistors?

    Any guidance would be appreciated.
     
  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Possibly, if the receiver in question is over ~30 years old it is overdue for a refresh. I would start with a check and reset of the 'Bias' and 'DC' offset for a start - these settings should tell you a lot about the overall health of the unit in question.
    Highly unlikely.
     
  3. SaturationPt

    SaturationPt AK Subscriber Subscriber

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    What amplifier and what speakers? Sounds like clipping.
     
  4. w1jim

    w1jim I can fix it but good... Subscriber

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    I’d also think main PS caps.
    Hook up a volt meter to the DC power rails feeding the main amp and see how much the voltage dips during loud bass-heavy play
     
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  5. Powertech

    Powertech Member

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    Like he said.
    TIP: :angel: Use an analogue voltmeter and watch if the needle twitches downwards to the bass beat. It's easier than using a DVM.
     
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  6. SaturationPt

    SaturationPt AK Subscriber Subscriber

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    I was thinking that the OP having "restored" these units would have at least checked or replaced the caps and has brought them up to spec, ... but then "restored" is somewhat subjective here.

    If you can get a decent dual-trace scope you can track the rail voltage vs output, and also compare the input-output traces. Both very useful here.
     
    eiraved likes this.
  7. bberkom

    bberkom AK Subscriber Subscriber

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    Clipping is my first thought. Distortion at loud volumes on multiple different units? It's possible you simply don't have enough power to get the volume levels you desire with your speakers. Details on which receivers and speakers would help.
     
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  8. woodj

    woodj Super Member

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    How high?
     
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  9. slimecity

    slimecity Super Member

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    If its "soft/fuzzy" distortion in both channels that gets worse the louder you turn it up - I would first look at the large powersupply caps - chances are they have dried out.

    There are plenty of other issues that can cause distortion however.....
     
  10. Northwinds

    Northwinds Huh? Turn what down? Subscriber

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    Try moving your balance pot back and forth. I notice on Marantz receivers the same thing and moving the balance pot back and forth (work it good before you turn the unit on) and the distortion goes away. If this works for you, the balance pot needs to be cleaned
     
  11. eiraved

    eiraved AK Subscriber Subscriber

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    Your post is a bit confusing. Are you saying the bass is distorted after restoration or before? If it’s before restoration, then replacing those large PS caps would do the trick. They’re either dried up or leaking which is causing the bass issue. Because the receiver is old, a total recap is needed for it to shine.
     
  12. whoaru99

    whoaru99 Epic Member

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    I'm with this as most likely cause. Even more so if the bass cranked up in addition to higher volume.
     
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  13. Sriskie

    Sriskie AK Subscriber Subscriber

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    What are you using as a source? Some CD players can can have too high of output for some vintage amps.
     
  14. tom3

    tom3 Super Member

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    And around here the local radio station that plays current garbage really boosts the bass to the point of distortion, makes it seem stronger than it is on a bluetooth speaker I guess. But I'd suppose it's a power supply issue too. But I have wondered if the old TO3 outputs can lose hFE over the many years too?
     
  15. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    What speakers are you running?
     

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