rockola cd bubbler pop and distortion

Discussion in 'General Electronics Chat' started by lozza, Sep 24, 2009.

  1. lozza

    Thread Starter New Member

    Sep 24, 2009
    2
    0
    I have a Rockola Bubbler (orange amp and computer), 6-7 years old, that worked perfectly until last year when it blew the power supply pcb and a power amp after I switched it off and then on again.


    Cutting a long story short I have replaced the 58270-1A power supply pcb, and the entire amplifier i.e. 59132-1A preamp and 2 x 58440-A power amp boards. Despite this I have a fault on the Jukebox that I cannot understand nor correct.

    When playing a cd I hear a distortion/fuzz in the background more noticeable on quiet pasages of music and also an intermittent popping/low boom noise from the speakers. The latter sound is if an electronic component is periodically/sporadically cutting in and out causing a low frequency boom from the speakers.

    The cd mechanism is ground strapped and I have checked all the ground straps -all are tightly connected.

    I have also connected the cd player to an external amp and it plays perfectly i.e. no problem with cd output.

    The sound distortion/fuzz is not present on the BMG input when playing an ipod. In fact the ipod music played throught the BMG (aux) input has no background noise at all.

    If I play the ipod thru the cd input then there is a very slight distortion/fuzz on the ipod generated music but nothing like when the the cd player itself is connected.

    Given the ipod has 'perfect' sound when played thru the BMG (aux) input I have completely ruled out speaker problem.

    The problems described do not render the jukebox unlistenable but it does not have the sound clarity it used to have and the intermittent popping noise is a constant reminder of an undiagnosed fault.
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Have you added or moved any grounds from the original circuit layout - even using similar power connectors but on different PSU cables?

    That fault appears similar to a ground loop problem I had with some computers and internal amp add-ons (drive bay mounted stereo amps).
    The sizzle seemed to be the CPU current changing with load and the pops were the hard drive head actuator drawing pulses of current.

    In that case, the (add-on) amp modules had two ground paths, the audio cable and the PSU cable, both connecting back through the PSU and motherboard. The cure was to cut the ground wire in the amp power connection and link it back to the motherboard ground against the audio out connector, so the motherboard supply current did not modulate the amp ground.
     
  3. kkazem

    Active Member

    Jul 23, 2009
    160
    26
    Hi lozza,
    I have another idea. If you obtained these replacement boards from the factory, they likely need to be adjusted for optimum sound results. Most power amps do have internal adjustments needed. I recommend that you contact the manufacturer if they're still around and ask if there is a tuning procedure needed after replacing the board(s) that you replaced. If they are no longer in business, then you need to try to get a hold of a service manual for the item, if any exists. If not, try asking around or searching on the net for dealers of that item that may have experience in the matter and could possible help you by phone or by email.

    Good luck!

    Regards,
    Kamran Kazem
    kkazem
     
  4. lozza

    Thread Starter New Member

    Sep 24, 2009
    2
    0
    Kamran: Rockola Corp in Torrance who still make this Jukebox had the amp on test for two days before they sent it so I have to assume they tuned it properly.

    Robert: There is extensive ground cabling that is webbed through out all the components of the Jukebox all of which feeds back to the power supply tranformer unit (which is a separate unit to the amp). It occurred to me that the ECM/RFI filter unit in the power supply box may have got damaged when the power supply blew. However disconnecting ECM/RFI filter from the mains power supply made no difference.

    There is a sought of happy ending to date. The popping noise seems to have disappeared after I disconnected and then reconnected the ECM/RFI filter and reassembled the power supply unit. I also inserted a very large ferrite ground loop in the audio input connecting the cd player unit to the amp unit. I am currently leaving well enough alone!

    The fizz/distortion/scratchybackground I hear on quiet passages of songs played on the cd (but not ipod connected to the same amp) seems also to be less prominent although still there. But seems worse on some cd's songs than others. Again I have decided to accept the present situation. Jukebox engineers in the UK that have any experience the Rockola Bubbler are few and far between. Any further exploration of the issues described above would mean transporting the machine at great cost with no guarantee it could be further improved.

    Thanks for your helpful comments they were much appreciated.

    Laurence (Skipton North Yorkshire)
     
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