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  1. #1
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    Default Stereo amplifier failing bass frequencies at low volume

    I've got a stereo receiver that's only about 15 years old that seems to have lost bass output at low volumes. The effect is similar on two different sets of speakers so I'm pretty sure it is the amp not the speakers.

    The receiver has always been much more powerful than needed and I don't think it has ever been turned up much over #2 out of 20 on the volume dial. I'm guessing some transistor or capacitor has popped, but the frequency range seems OK when the volume is turned up over the #2 setting.

    Is their anybody with electronics knowledge here that has any ideas on what might be going wrong? I suspect it will not be economic to find a service centre for stereo component gear to check it over.
    Franklin

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  3. #2
    Join Date
    Apr 2015
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    Default

    I used to be a technician many year ago so probably not good on something 15 year old.
    Being stereo would expect the problem to only effect 1 channel not both. What happens if you turn balance control hard to the left? Then repeat with balance hard to the right? Do they sound similar?

  4. #3
    Join Date
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    Alexandra Vic
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    What audio source are you using, and had you changed your input connections before you noticed this issue?

    If it is the receiver's FM tuner as the source, there could be a failing interstage coupling capacitor somewhere in the system. Similarly for the AM tuner, but the deep bass tends to be attenuated somewhat before the transmitter to avoid overmodulating and causing it to 'splatter', so it is harder to tell if it is a system problem or not.

    If it is an external source being used, eg tape machine, mobile phone with a music player, MP3 player etc, what is the external source and what inputs is it connected to?

    Does the receiver have a "bass cut" switch that has been accidentally moved at some stage, this filters deep bass if engaged. Does it have a "loudness" switch that has been moved, this boosts bass and treble at low volume control settings, but the boost tapers out as the volume increases. If it had been engaged until recently, but then turned off, this would appear to give a similar effect to what you are describing.

    If the unit is getting a little long in the tooth, it could be just a case of coupling caps drying out with age and reducing in value to the point where they limit the passage of bass signals through the system. There could be up to 5-6 of these coupling caps per channel, each having a slight but noticeable effect that become more obvious when all stages are combined.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  5. #4
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    Yes. by playing with the balance I found it is definitely a problem that is more pronounced on the right channel. Even with the fm mute/mono switch activated the right channel is at a lower volume. For the moment, using the balance knob to blend things might work but I guess it is a downhill slope. I might open the case up later and see if I can see any component that look suss.
    Franklin

  6. #5
    Join Date
    Apr 2015
    Location
    Brisbane
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    88

    Default Stereo amplifier failing bass frequencies at low volume

    Have a look for electrolytic capacitors with the insides trying to escape:
    https://www.google.com.au/search?q=f...npJ1_sqVHdR8M:
    The tops should be flat.

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