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(Topic ID: 273249)

Stern SB-300 Sound board oddities..


By Coyote

3 months ago



Topic Stats

  • 6 posts
  • 3 Pinsiders participating
  • Latest reply 3 months ago by barakandl
  • No one calls this topic a favorite

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    #1 3 months ago

    Hey guys -
    So I have a Meteor in my lineup, and recently due to issues, I re-capped my SB300 audio board. This included replacing the amp.

    For the last year, I've had a feeling that I was missing a 'voice', but I never really looked into it until now.

    A local pinsider (completist ) happened to have a couple spares, and I decided to try them out.

    One was missing a voice as well - but in Meteor, apparently it's the 'primary' voice, as it sounded horrid. The other seemed to have everything.

    But both of them seemed to have a low-pass filter on them. That's the best way I can explain it. Compared to my board, they were very tinny and missing bass.

    Since I don't have any other boards to test, I was wondering what part of the circuit would have the effect of a high-pass or low-pass filter, so I can at least look at my board - perhaps I missed a cap.

    Also wondering where the softer, under-voice would be generated, so I can look at why mine's failing. Is this one of the signals coming from the timer?

    #2 3 months ago
    Quoted from Coyote:

    Hey guys -
    So I have a Meteor in my lineup, and recently due to issues, I re-capped my SB300 audio board. This included replacing the amp.
    For the last year, I've had a feeling that I was missing a 'voice', but I never really looked into it until now.
    A local pinsider (completist ) happened to have a couple spares, and I decided to try them out.
    One was missing a voice as well - but in Meteor, apparently it's the 'primary' voice, as it sounded horrid. The other seemed to have everything.
    But both of them seemed to have a low-pass filter on them. That's the best way I can explain it. Compared to my board, they were very tinny and missing bass.
    Since I don't have any other boards to test, I was wondering what part of the circuit would have the effect of a high-pass or low-pass filter, so I can at least look at my board - perhaps I missed a cap.
    Also wondering where the softer, under-voice would be generated, so I can look at why mine's failing. Is this one of the signals coming from the timer?

    When the zener diode in the 10v circuit drifts sound quality gets pretty bad. I forget if it is over or under 10v, but not much variation and it gets a really "tinny".

    #3 3 months ago
    Quoted from barakandl:

    When the zener diode in the 10v circuit drifts sound quality gets pretty bad. I forget if it is over or under 10v, but not much variation and it gets a really "tinny".

    Okay - it's possible both of these test boards had bad diodes. I am 99% sure I replaced mine. Thanks.

    #4 3 months ago

    Interesting. I have one which sounds like an old AM/MW radiostation. It is missing everything above appr 2kHz and sounds very dull. Replaced the caps, tried another amplifier, replaced the 6840 timer, and tried another MC3340 but that didn't change anything. The voltage over the zenerdiode seems okay, I never replaced that one but I will do that on my next attempt; didn't know that one is critical. This board has a sticker marked "B" and seems to be a bit older as other boards with a "C" marked sticker. Are there different revisions with changes?

    #5 3 months ago
    Quoted from MarAlb:

    Interesting. I have one which sounds like an old AM/MW radiostation. It is missing everything above appr 2kHz and sounds very dull. Replaced the caps, tried another amplifier, replaced the 6840 timer, and tried another MC3340 but that didn't change anything. The voltage over the zenerdiode seems okay, I never replaced that one but I will do that on my next attempt; didn't know that one is critical. This board has a sticker marked "B" and seems to be a bit older as other boards with a "C" marked sticker. Are there different revisions with changes?

    I believe the only major change was the on-board connection for the Voice board, so the voice (speech?) board could send audio. I think the earlier revisions had a factory-soldered wire, whereas laster revisions had a trace in the PCB.

    I could be wrong, though. I'm NOT an expert at this board.

    #6 3 months ago

    Measure the +10vdc. I have seriously improved a bunch of boards sound quality by replacing the diode. More than a quarter volt drift and sound quality tanks where it sounds like some frequency is filtered out or muddled. Hard to describe but tin can speaker sound is good description.

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