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Thread: Amplifier Control - Avoiding "Thump"

  1. #1
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    Post Amplifier Control - Avoiding "Thump"

    Hi,

    I have almost finished installing my MP3 player in my Honda CRX, and need a way of controlling my audio amp to avoid power-off thump from the speakers.

    At the moment, the amp's control wire is turned on along with the computer. The amp has a built in delay before it switches on, so no problems as the amp turns of a few secs after the computer.

    But when i go to switch off, the amp goes off the same time as the computer, (auto power down via ATX) and BANG - my windows almost blow out!!! I can't think of any way of solving this unless i can find a way of getting the PC (windows 2000) to toggle a parallel/serial port line or something as soon as the shutdown command is sent so just before it shuts down the amp is turned off.

    I am using a SB Live, and put some ground loop isolators between the SB Live and the amp which actually made the thump worse! I think i'll remove them!

    Thanks for the help!

    Mark

  2. #2
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    have you thought about using the ATX shutdown circuitry that they're offering around here? try here
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  3. #3
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    Thanks for the info!

    Looks like this idea would do the job, when i push the power button at the moment, my machine hibernates. I could always build a delay unit like this with a 555 timer or something to turn off the amp, then signal the computer to turn off after.

    Cheers,

  4. #4
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    Originally posted by marklamond:
    <STRONG>Thanks for the info!

    Looks like this idea would do the job, when i push the power button at the moment, my machine hibernates. I could always build a delay unit like this with a 555 timer or something to turn off the amp, then signal the computer to turn off after.

    Cheers, </STRONG>
    I hate to be over simplistic, but if you are signalling your machine to shutdown, why not put in a really long shutdown wav file?
    either silence/pink noise/ or the like....

  5. #5
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    Because he said "hibernate", not "shutdown". And I don't think that any sounds are played when you hibernate.

    But you do have a point... that is if he wants the computer to shut down *after* the amp does, but he asked about shutting down the computer before the amp, which I think would be very difficult.

    to marklamond: do you know that the computer is causing it? I know many amps that will thump themselves when turning off. if the audio is not connected to the computer, does it do it? if the computer stays on as the amp shuts off, does it still do it?
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  6. #6
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    Yeah, it is the computer turning off that causes the amp to thump. If you turn off the computer and leave the amp connected, it really thumps very loud. If you turn off the amp with the computer (with a relay) the thump is somewhat less.

    If you turn off the amp while the computer is on, it is completley silent.

    I want the folllowing to happen:

    <Press Power Button>
    Computer on
    Amp On

    (As the amp has it's own power-on protection, power can be applied to both at the same time.)

    <Press Power Button>
    Amp Off
    Computer off

    Thinking about it, i could make the circuit simpler by powering the amp off alongside the computer, as even though hibernate is quick, it's not as quick as the amp at turning off. That would be better than having to build an electronic delay.

    It's an interesting point about using a blank sound file, but i would like to not have to rely on the OS, and have a hardware solution which will be 100% reliable.

    BTW, the amp i have is a Denon DCA-800.

    Cheers,

  7. #7
    Oms
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    I have the amp's remote turn-on wired to the DTR line on a serial port. This allows me to turn the amp on or off in software. I use a trivial little program to raise DTR on boot, and to lower it before shutting down, thus avoiding the thump.

    I'm not sure about Windows hibernation -- it could even lower DTR automatically. Then all you'd need would be some program that keeps the serial port open.
    Custom Linux system on an '89 VW GTI 16V Edition One
    Jogdial volume control, Sony joystick, IR remote...
    Used to be the fastest Linux on the road, until all these NOS types came along...

  8. #8
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    I thought about that, but can't really afford a serial/parallel port for this function alone.

    Cheers,

  9. #9
    Oms
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    Don't most motherboards have 2 serial + 1 parallel ports anyway? Or are yours all in use? You know that you can still tap into DTR even if you're using the port for something else, right?
    Custom Linux system on an '89 VW GTI 16V Edition One
    Jogdial volume control, Sony joystick, IR remote...
    Used to be the fastest Linux on the road, until all these NOS types came along...

  10. #10
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    Yeah, suppose you could "hack" DTR somehow?
    I have one com port for the GPS, which only uses TX/RX and the Phone has another port, again only using TX/RX. I want one spare for the digital camera, programmable ecu, g-force meter, kitchen sink etc.

    I think i will use a little circuit in the end to solve this problem. I suppose i should use this problem to force myself to try out the PIC development kit i built over a year ago, but never used!

    Cheers,

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