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Mixer problem.

Discussion in 'Electronic Basics' started by Anders N. Vinje, Feb 11, 2004.

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  1. Hey.
    I have this old Samic SM-810 Mixer that generates alot of hum. And somtimes
    there is a short burst of current that passes trough making a loud pop!.
    This is really annoying when making music.

    I have replaced the Opams that where inside with Burr Brown OPA1342. It
    helped alot against the humming and noise it was generating. The old Opams
    where ST TL072CN type. One Channel even had a Philips NE5532. Well i bought
    i used. So i guess the guy who had it before made som changes. well anyway
    this part goes into my old parts container. But here is still alot of hum.
    But i am wondering what generates that pop somtimes. Bad capacitator
    somewhere, maybe? I was thinking of replacing the the electrolytic mains
    filtring capacitators. With som lager ones. Something like 10000uf. There
    are there are two SMC 25V 2200uf on the + to gnd And two at the - to gnd. I
    only have a multimeter or else i would have seen how much ripple its
    generating in none use mode. The OPA 1342 uses a couple of mA more then the
    TL072. But i have heard the NE5532 is a sucker on quicent current. Maybe it
    sucking to much current allready?. I dont know. I have been looking for the
    schematic for this mixer, but i seems that Samick dosent exits anymore.
    Anyone know where to get it?

    Any suggestions on this mixer especially the poping would have been much
    helpfull.

    Anders.

    PS. After i have been posting on this newsgroup. I get those irretaing MS
    advise or something mail with a virus. I should never have used my own mail
    address.
     
  2. The filter caps may be the trouble, but only if the original ones were
    quite bad. Any of the opamps you list should have enough power supply
    ripple rejection to not respond audibly to any reasonable supply
    ripple. I suspect something else. Perhaps a bad ground on some
    shielding, or a piece of shielding missing. The pops might also be
    electrostatic pick up from things on the AC line turning on and off.
    You might pass a desk lamp near the unit, while turning the light on
    and off to see if you are getting this kind of interference that
    indicates poor shielding.
     
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