Channel failure. One channel dead after 15 mins

Discussion in 'Hi-Fi Stereo Systems & Separates' started by iamian16, Aug 8, 2012.

  1. iamian16

    iamian16
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    Sorry, newbe here with a bizarre problem..

    I have a separates system and though some bits are ancient, like the PL12D deck it used to work fine.

    Recently after about 15 - 20 minutes the right channel will crackle and then go dead, intermittently breaking back to normal volume. This happens with tuner / CD / phono / aux. inputs. No difference.
    I've checked the usual suspects. The wiring to the speakers is fine, the plugs are soldered on and the connections are tight. If I swap round the speakers it is still the right channel one that fails.

    Now the odd thing is if I physically touch or tap the speaker cone it all comes back for a few moments.

    It almost seems as if a DC voltage is permanently polarizing that channel.

    It seems OK with headphones.

    Any thoughts please?
     
    Last edited: Aug 8, 2012
  2. RBZ5416

    RBZ5416
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    I would guess at a dry joint, possbily in the speaker switching relay. Does the amp have outputs for two sets of speakers with an A/B switch? If so, it may be worth trying connecting to the B terminals. Otherwise it will require someone handy with a soldering iron to track down the dodgy connection.
     
  3. iamian16

    iamian16
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    Thanks for that advice. The amp has only output for a single pair of speakers.
    Not sure I know what a switching relay is or where it might be.

    Where do I look for a dry joint?

    As I mentioned the fault occurs on the right channel irrespective of which speaker I use on it. The cable is intact and makes good contact at both ends, the plugs are soldered onto the cable and a good tight fit into each speaker.

    It is touching or lightly poking the speaker cone which restores things but as I can do this to either speaker I don't think it a fault with the speaker itself.
     
  4. BlueWizard

    BlueWizard
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    I would first make sure that there isn't a stray strand of speaker wire that is moving with the change in temperature and shorting out the sppeaker terminals.

    Short of that, it gets down to how skilled you are with electronics and how adventurous you are.

    As you say, the fault could be inside the speaker itself, but I would check the speaker wire connections first; both at the speaker and at the amp.

    Steve/bluewizard
     
  5. RBZ5416

    RBZ5416
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    It would be worth switching the speaker cables over as well, just to eliminate them.

    Relays are used to keep the speakers disconnected when the amp powers up to avoid the "thump" generated as the circuits initialise. They also (generally) are linked to a protection circuit so that they will cut the speaker if the amp develops a fault that could damage the speaker. their appearance can be quite varied from a clear plastic box where you can see the contacts & operating coil inside to a completely enclosed coloured plastic package. Best thing is probably to use Google images to search for your amp make/model & also search for a service manual.

    But you need to be careful as without knowing what you're doing, you could further damage the amp or yourself! It may be better to enquire locally for a repairer or some manufacturers offer fixed cost repair/servicing.
     
  6. reddish75

    reddish75
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    Odd fault, what amp is it?
     
  7. iamian16

    iamian16
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    Thanks for your replies.

    Having rechecked last evening for loose strands, broken wires etc I ended up with a bodge to the right channel using 2 core flex with exactly the same result. It works for 15-20 minutes, starts crackling and goes dead. If I then either

    1. temporarily disconnect the speaker
    2. tap the speaker cone

    it comes back to life but for decreasingly short spells.

    As it happens to the right channel rather than one individual speaker (KEF C3) I suspect the fault is with the amp:

    Acoustic Solutions SP100

    Which, reading Amazon reviews and a few other comments on it and the related
    Acoustic Solutions CAMP1-BLACK HiFi
    seems to explain it all!

    Basically it seems this budget amp is a budget too far.

    Oddly, two or three others describe the same problem and it's the right channel again.

    As it's now too late to take it back (It must be about 5-6 years old) can anyone suggest:

    1. What might need repairing?
    2. If it is worth repairing if I cannot see something obvious? (I can wield a soldering iron, can probably fix dry joints and broken wires) - I suspect the answer is no!
    3. What's recommended in the budget range. 2 x 30/35W, inputs for tuner, CD, aux and importantly PHONO. (I have loads of vinyl and that PL12D deck...)
    A link to a thread on this forum would be fine.

    I'm still puzzled though as to why pressing on the speaker cone makes it work again - it as if there were a DC voltage pushing the cone?


    Thanks
    I
     
    Last edited: Aug 9, 2012
  8. reddish75

    reddish75
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    Ok firstly the amp isn't worth spending any money on, it will cost more to repair than its worth, you could go poking around inside with the probably plug directly into the wall soldering iron you have (not recommended as these run at much higher temperatures than needed in electronics).
    The fault could be due to hot running parts in the right side of the amp damaging components I.e drying out capacitors, damaging transistors etc, or it could be a dry joint through heat exposure non of which are simple to diagnose.

    Someone will probably chime in with amplifier recommendations but for me the Cambridge azur range second hand (540a/640a) would probably meet your requirements and sound much much better than that acoustic solutions.

    Regards
    Chris.
     
  9. iamian16

    iamian16
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    Reddish 75 Thanks for that.

    And you are right, no real idea when poking around with the soldering iron though if it's for scrap anyway...

    Cambridge 540a / 640a - found a manual online - and a few on ebay - but these do not seem to have Phono input?
    I don't want to buy a pre-amp, I'm a bit pushed for space already.
     
  10. juggler

    juggler
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    I can think of only one mechanism which might be inducing a temporary fix but don't have a satisfactory explanation.

    Touching the cone must either be moving something in the speaker - but the speaker and cable swapping eliminates that - or earthing something through your body.

    That suggests a build up of charge somewhere there shouldn't be, whether due to static, faulty capacitor, bad earth somewhere in the amp I'm not qualified to say.

    I wonder whether touching the speaker terminals has the same effect?
    Though considering it may be an amp earthing fault, I'd be very reluctant to do so in case of a serious shock.
     
  11. iamian16

    iamian16
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    I have not tried just touching a speaker plug as opposed to removing it. Removing either plug certainly works for a minute or two.

    I think we have traced it to an amplifier problem and if it is putting a constant DC voltage down the speaker cable I'd be concerned about damaging the speakers. :(
     
  12. reddish75

    reddish75
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    Do not touch the speaker binding posts or any plug connected to then whilst the amplifier is on! Damage to you, speakers or amp will happen.
     
  13. reddish75

    reddish75
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    Rotels are generally good sounding and reliable, loads to choose from.
     
  14. MarkLG

    MarkLG
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    On an amp of that age and value as soon as a fault develops the best thing you can do is scrap it. It really isn't worth messing about with it, and it certainly isn't worth paying somebody else to fix it.
    Work out what you want pay to replace it and get on ebay. Anything from Rotel, NAD, Marantz, etc will sound pretty decent and be an upgrade on your current amp.
     
  15. sap81uk

    sap81uk
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    Get yourself a good Rotel amp.. Scrap your poor Acoustic Solutions amp. Do that and you'll be miffed why you didn't do it earlier!
     
  16. Wilseus

    Wilseus
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    Another thumbs up for Rotel here. And Arcam.
     

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