BIAS problem ???

Discussion in 'Hi-Fi and General Audio' started by melorib, Apr 24, 2007.

  1. melorib

    melorib Lowrider

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    My new amplifier came with 4 SED Winged C EL34, biased at 30mA by the seller, to extend tube life, 40mA is recommended by the manufacturer...

    Sunday I changed bias to 40mA, when I switched off the amplifier, the speakers made a loud noise, same noise Monday... :eek:

    So today I changed back to 30mA, switched off, no more strange noises... I saw people recommending 50mA, saying it sounds better...

    What could be the problem, tubes or amplifier... :rolleyes:
     
    melorib, Apr 24, 2007
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  2. melorib

    zanash

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    it will sound different ... but better ? its more a personal taste thing .

    Are you using a good multimeter to take the readings ?

    My old valve set up[dynavox vr70e] needed to be biased by hand ...not hard but tricky to get all of them identical ... but it was best measuring the biass voltage in mv but I can't recall the way you convert ...I settled on 300mv which was between the recomended 200-400mv for the el34's.
     
    zanash, Apr 24, 2007
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  3. melorib

    melorib Lowrider

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    The meter is built-in, and already in mA...

    The sound apparentely didnt change, when I changed to 40mA, only started making noise on switch off...


    [​IMG]
     
    melorib, Apr 24, 2007
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  4. melorib

    melorib Lowrider

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    Last night, after that suffering game, GO MANUTD, it made the noise again, now at 30mA... :(
     
    melorib, Apr 25, 2007
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  5. melorib

    Dev Moderator

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    Man U have that effect:D.

    FWIW, my speakers make a noise every time I switch off my valve power amp. Regarding the bias, I'd just follow the manufacturer's recommendation. I'm not a valve expert but by appying more bias than the recommended amount you could just be over-driving the valves and that will shorten their life. Unless of course you think that the sonic gains justfy it.
     
    Dev, Apr 25, 2007
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  6. melorib

    melorib Lowrider

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    The seller tells me the switch-off noise is normal in this amplifier, but then, why doesnt it do it every time... :rolleyes:

    The 40mA I tried, is the manufacturer recommended bias...
     
    melorib, Apr 25, 2007
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  7. melorib

    anubisgrau

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    i told you, mac 275
    but your speakers will bump like hell when switching off...
     
    anubisgrau, Apr 25, 2007
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  8. melorib

    melorib Lowrider

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    The speakers and me... :elephant:
     
    melorib, Apr 25, 2007
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  9. melorib

    melorib Lowrider

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    It is getting more interesting, it varies, this morning right speaker, last night left speaker, afternoon, none... :rolleyes:

    I guess I will have to live with it, now that I am pretty sure it is not a defective tube, am I really, I will test turning down the volume before I switch-off... :(
     
    melorib, Apr 26, 2007
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  10. melorib

    la toilette Downright stupid

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    I always turn the volume down before I turn my amp off - I just thought this was the thing to do, especially with a valve amp, although I'm not sure where I got that idea from! If I turn my (valve) amp off with the volume turned up I don't get a bump, but I do get a loud 'click'.


    (boo Chelsea, boo....)
     
    la toilette, Apr 26, 2007
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  11. melorib

    Dev Moderator

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    I also turn the volume down before switching off and still hear a loud "click" rather than a thump.
     
    Dev, Apr 26, 2007
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  12. melorib

    melorib Lowrider

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    Now that I know it is ot a tube problem, I will start doing that...

    Someone in AA mentioned bleed resistors, maybe the Classic is so purist that it doesnt have them, or they are faulty... :rolleyes:
     
    melorib, Apr 26, 2007
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  13. melorib

    lordsummit moderate mod

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    My Manley sometimes pops, sometimes doesn't. It's just life
     
    lordsummit, Apr 26, 2007
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  14. melorib

    melorib Lowrider

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    I just wanted to know if it is a feature or a problem, apparentely it is the first, as long as it sounds good and doesnt screw up the speakers, no problem... ;)
     
    melorib, Apr 26, 2007
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  15. melorib

    smegger68

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    It's not just valve amps, as legions of older Exposure owners will attest to. It's just a function of a particular way of designing output stages. Turning down the volume before you switch off will minimise the noise. And stop worrying about it - a brief thump wont damage your speakers at all.
     
    smegger68, Apr 26, 2007
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  16. melorib

    lordsummit moderate mod

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    It's also more noticeable with higher efficiency speakers, a little pop at 83dbw becomes a much bigger one when you get nearer 100!
     
    lordsummit, Apr 26, 2007
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  17. melorib

    Andy 831

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    I turn off the source, maybe wait 10 secs then turn the amps off and get not clicks pops or bangs
     
    Andy 831, Apr 26, 2007
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  18. melorib

    melorib Lowrider

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    Instead of turning down the volume, manual job, I just mute the pre on remote, yesterday no thumps... :D
     
    melorib, Apr 27, 2007
    #18
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