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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
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    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
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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
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    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.

  7. #6
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    Couldn't stand the degraded sound any longer.

    Pulled the case off and I'm going to guess these are the culprits....
    IMG_2537[1].jpg
    Franklin

  8. #7
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    Hopefully that is it. If not worth replacing anyway.

  9. #8
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    Yeah. Three caps on the power supply board. All different sizes, but I can't find them on the Jaycar website. I'll drop into a store to see if they can find them in their catalogue. Then time to dust off my soldering iron.
    Franklin

  10. #9
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    Hi Pete,

    I'm getting to my limit of knowledge here. The three caps that have peed on the power supply board are all 50V - 3300uF, 2200uF and 330uF. Jaycar stock the 2200 but not the others. The guy in the shop suggested I buy online from RS Components. When I go to their site and find the capacitors page there doesn't seem to be just a simple electrolytic capacitors category. The "Electric Double Layer" category looked promising, but there are no 50V caps there, the closest is 48.6V.

    Have you got any idea where I should be looking?

    Thanks,
    Franklin
    Franklin

  11. #10
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    The 48.6v caps are close enough. They are in the power supply so are not usually the ones that limit bass responce. The usual culprits are the ones in the audio chain. These are usually much smaller and may not exibit any visible fault. They tend to dry out and loose their capacitance, so replace any that you can find. Much quicker than removing them, testing them and finding that they are on the way out.

    Remember that as the volume is reduced your ears become less sensitive to bass and treble so most amps have a loudness compensating circuit to boost the bass and treble as the volume control is turned down. It may be capacitors in that circuit but they would be hard to identify so just replace them all.

  12. #11
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    There's like 50 caps on the main board. Not worth the effort I suspect.
    IMG_2548[1].jpg
    Franklin

  13. #12
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    Franklin, the category you should be looking at is "aluminium", the correct terminology for what are commonly referred to as "electros". You might also try Element 14 (formerly Farnall) as a source, they might be better for one-off orders.

    Chas.

  14. #13
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    Thanks Chas, the Element 14 site looks far easier for a novice to access. Still feeling now it might be a fools errand to go down this path though.....
    Franklin

  15. #14
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    Got a good deal apparently on a Pioneer SX-N30AE so I've decided to trash the NAD and move along with technology into the world of a networked receiver that plays audio from my home network as well as stream Internet Radio stations. Still staying with stereo only though.

    Anybody want a NAD refurb project before I dump it?
    Franklin

  16. #15
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    Default Stereo amplifier failing bass frequencies at low volume

    Quote Originally Posted by Fuzzie View Post
    Anybody want a NAD refurb project before I dump it?
    If no one else has taken it, I will have a go at bringing it back to life. Only issue is it will be a couple of weeks before I can get there (live on Brisbane north side).

    Thanks
    Peter

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