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speaker protection

Discussion in 'd.i.y.' started by say it as it is, Mar 16, 2021.

  1. say it as it is

    say it as it is pfm Member

    hi all ok still trying to find my way about the DIY world been advised any amp build should have speaker protection fitted and my existing avondale amp.

    I bought these cheap as chips ones as told anyone I could need upgrading so what needs doing to use this type needs a 12v supply so need to get a small transformer any recommendations for a small 12v tx to feed a speaker protection board?

    so on the boards itself what do I need to change to either not degrade the sound or fail in short time.M!

    thanks


    https://www.ebay.co.uk/itm/300W-Dig...d=link&campid=5338728743&toolid=20001&mkevt=1
     
  2. Mike Hanson

    Mike Hanson Lovely!

    I've used similar boards myself.
    • I've had some units arrive DOA, and some seemed to work just fine.
    • @Arkless Electronics has commented that the relays alone should cost more than these complete units do, so perhaps the constituent parts are clones and/or substandard.
    • I've also been told by a respected authority (not here) that the electrolytic caps are very dodgy, and should be replaced. Otherwise, he thinks they're usable. (I've started to heed his advice, replacing the caps with more respected ones.)
    I've come to the point where I don't trust them 100%, but I've got a bunch of them that I'll use them for amps that are nearby. For amps going to friends further afield, I'm using the much more expensive ones from XRK.
     
  3. Gervais Cote

    Gervais Cote Predator

  4. Vinny

    Vinny pfm Member

    Les fitted Chinese units to my mono-blocks, straight off EPay. Presumably he tested them.....

    They have a modest current draw so don't go for a minute VA transformer. Most have crude onboard power regulation so accept a wide range of voltages AC or DC supply. I'd have to have the lid off here to check, but something like 6VA (????) torroidals are fitted here - around 6cm across, 2cm thick - ish. If really stuck. let me know and I'll open one up or look out the order or whatever.
     
  5. say it as it is

    say it as it is pfm Member

    Cheers will have a look later I get the concerns over Chinese stuff so should I bite the bullet replace the caps and relays?
     
  6. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Or just buy the one Gervais cote linked to?

    No additional transformer need
    Better quality

    What's not to like?
     
  7. OldSkool

    OldSkool pfm Member

    It looks like a good unit but you need two of them for a stereo amp...

    I'm doing an amp build at the moment and already built a Velleman board ready to go in it, but must admit I'd be happier with a higher quality unit from a SQ point of view if nothing else. So far my speakers have stood up to a couple of previous amp failures but I must be using up my luck. I may give these a go!
     
  8. Mike Hanson

    Mike Hanson Lovely!

    The Velleman's are perfectly fine in the sound quality department. I've got one each in my mono Voyagers.
     
    Marra and Operajulian like this.
  9. Vinny

    Vinny pfm Member

    Four times the price and double the volume?

    SQ is down entirely to the relay contacts.
     
  10. S-Man

    S-Man Kinkless Tetrode Admirer

  11. davidsrsb

    davidsrsb pfm Member

    Electronic mosfet switching is the way to go.
    Not many mechanical relays are intended for the combination of breaking ~ 50 V dc, currents of several amps and USUALLY switching dry.
     
  12. Vinny

    Vinny pfm Member

    Just a tad misleading :)

    The relay should, ideally, never switch anything. If it dies the first time that it does, the cost is peanuts compared to the saving.
     
  13. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    The Amplimo relay pretty much gets around most of the valid objections raised by davidsrsb, leaving the issue of breaking capacity and arcing but this is more of a problem in very high power amplifiers.

    IIRC did @davidsrsb not design a solid state unit with PCB layout for DIY use after we discussed this last time?

    I also designed, purely as an exercise etc, it was only in simulation, an SS unit but with a relay with gold plated contacts in use as well. The idea is that after power on delay and checking for DC offset the SS relay shuts first, followed by the relay contacts closing "to make sure there is a gold to gold metal contact being made and so eliminate any possibility of sound quality reduction due to passing the signal through a SS switch" (" " to indicate that we don't really know whether the SS switch does effect SQ). On detection of a DC fault the idea is that the relay opens first to avoid it having to handle switching huge currents at DC followed a few mS later by the SS switch opening. The relay then never has to handle high power or break large DC currents and so should avoid issues such as contact pitting and degradation. The Amplimo relay does the same thing mechanically by having tungsten and gold contacts which are mechanically timed to do the same but it doesn't get around "the problem of relays"... huge fault currents being able to basically weld the contacts together... defeating the object of having protection and leaving the speaker to fry anyway.
     
  14. grahamdocman

    grahamdocman pfm Member

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