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700mv ripple on Akai Sampler linear supply

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    700mv ripple on Akai Sampler linear supply

    Hi fellow troubleshooters. This is my first post on badcaps. I've recently setup an electronics workbench. i'm also building a studio with old equipment bought faulty at low cost.
    I've been into electronics since the mid 80's and particularly in the last few years though only getting hands on with repairs now. My knowledge gaps are significant so I'll be posting here to seek guidance advice and general practical applied learning.

    On my bench today is an old ca. 1993-95 Akai hardware sampler. This runs on both a linear and Smps supply. Both are getting on in age and ripple seems fairly high. The smps gives me some 150mv on average but rather alarmingly the supply feeding the sensitive DAC output stage is fed from the unregulated linear supply. This goes to two LDO + - -15v regs that in turn feed the dac through a couple of 78/7905 By this point ripple is down to 34mv but I'd. like to minimise what the main supply feeds and get on top of this rather loud ripple.

    The sampler isn't playing well. I see ringing peaks on square and saw waves so there are other issues but i figure start with the supply.

    I've attached a shot of the psu board. this is fed by a separate smps which appears ok given its age. These were expensive devices back in the day and Akai specced them quite well.

    I've done a quick in circuit cap esr test with a ‘peak' meter and most including the main filter caps look good. The only suspect is the small .47 next to the rectifier which I'll desolder for test later today.

    I'll also measure all voltages under load and update the image with these printed in case that helps the process.

    So I'd be most grateful for suggestions on what could be amiss here. Is 700mv ripple normal ?

    Thanks in advance
    Attached Files

    #2
    Re: 700mv ripple on Akai Sampler linear supply

    Yes that ripple would be normal for a linear power supply.
    They probably do this to get less noise to the ADC or DAC:
    A switching power supply might have allot more high frequency noise that is hard to filter out...
    "The one who says it cannot be done should never interrupt the one who is doing it."

    Comment


      #3
      Re: 700mv ripple on Akai Sampler linear supply

      i would re-cap the power section,
      those caps are so old i cant find a datasheet!
      they have a 1000hour rating and are 85' listed.

      also, they are "audio grade" and shouldnt be in the power section to begin with.

      Comment


        #4
        Re: 700mv ripple on Akai Sampler linear supply

        Thanks for your answers. I have ordered replacement caps, mostly panasonic FC for the the recap.

        This was an expensive device new aimed at recording studio racks.
        In 94 these cost nearly £3K new so i expect Akai probably used audio caps in line with what some audio people seem to do. I agree psu needs low esr low ripple first. I've ordered Panasonic FC. Do you guys recommend a specific cap for Linear supplies. I'm also recapping the supply in an Emu sampler that is SMPS. What caps would you guys use for switchmode.

        Thanks

        Comment


          #5
          Re: 700mv ripple on Akai Sampler linear supply

          for switchmode i like panasonic FR,
          for linear you just want long life and high ripple handling and 105' is nice.
          so you have a good choice there.
          panasonic F-something, or rubycon ZL / ZL-something all fit that description

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