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Onix OA21 BIAS current

Discussion in 'd.i.y.' started by flo27fp, Sep 27, 2011.

  1. Bad Parameter

    Bad Parameter New Member

    hmm, I kind of liked it better at -18mV/@ :D

    I knew to bias quiescent when hot and recheck a few times but why no load? Because that is how bias is properly done with solid state, or to keep my tweeters from flying across the room if a probe slips?

    Thanks, for the fast reply too, I was worried I might be cooking something and kept feeling for temperature. I know my way a bit around hollow state, not much around ss. Higher bias V usually means colder operation, but I'm not sure what I'm measuring here exactly.

    It is indeed a nice amp, not as musical as older Naim, but transparent and involving nonetheless. To others out there, spray out the switcher, I did it because (I thought) I was having relay trouble and a savvy friend said it's more likely the selector. He was right and the sound improved, tiny touch of hum vanished too. I don't think audio even goes through the switcher, go figure.
     
  2. James Evans

    James Evans Bedroom Bodger

    Don't think so, the connector is just supplying voltage and connecting audio channels, so as long as the MM card worked ok the MC should too.
     
  3. Elephantears

    Elephantears Trunkated Aesthete

    Yes, it's working fine in fact. I'm only on the first side of an album, but it sounds great so far.
     
  4. martin clark

    martin clark pinko bodger

    Exactly that! stops the bass cones setting fire to the sofa on their bid to ecape this world. You can have a dummy load connected if you like - it will (should!) make no difference.

    Effectively, you are measuring the idle current through the output stage. watching the voltage across the known emitter resistor is a convenient proxy. The ideal amount varies with output stage design (complementary; quasi-comp; emitter-follower, darlington or complentary-feedback-pair a.k.a Sziklai pair, or mosfet (and if so, which kind... a whole other game!) - and a whole other bunch of considerations. In any case - if some is good, more is not always better - unless you go the whole hog and full Class-A; which isnt a matter of turning the wick right up, needing to engineer for from the outset (PSU, heat management, yes, bias control also; all that stuff)

    As a bit of light reading to illustrate - here's the effect of varying it in a Nait2 - note, has different output stage architecture, hence much lower optimal bias from the Onix:
    https://www.pinkfishmedia.net/forum/threads/naim-amps-bias-current-setting-and-distortion.36057/

    HTH.
     
  5. Bad Parameter

    Bad Parameter New Member

    Y/B, E/D - I can confirm.

    Pretty much factory fresh now :) Don't recall but I think it was like $695 back around 1990, not a bad investment for 28 years service and 28 more to come.

    Oh, and a few years back I gave it an Alps Blue pot, that made a notable improvement too, enough actually that when I have $90 to throw around I think it might merit a TKD. Maybe for its 30th birthday.
     

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