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Mixing 4 audio channels to 3?

Discussion in 'Electrical Engineering' started by DaveC, Oct 26, 2011.

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  1. DaveC

    DaveC Guest

    What is wrong with using an op-amp to "amplify" DC? Surely they are
    I think he means that better audio results can be achieved by providing true
    dual-voltage supplies and eliminating all coupling caps.

    The "DC amplifier" is a fine design, but will result in inferior audio
    performance due to the caps.

    Now, if someone would volunteer such a negative voltage generator circuit...
    ;-)

    Thanks.
     
  2. Guest

    It's not ground. It's Vcc/2. I generally call it Vref, or some such thing.
     
  3. Don Pearce

    Don Pearce Guest

    Exactly. Much easier than all these halved supplies, coupling caps and
    multiple grounds.

    d
     
  4. DaveC

    DaveC Guest

    Exactly. Much easier than all these halved supplies, coupling caps and
    So, how -- exactly -- would you create that negative voltage?

    Dave
     
  5. DaveC

    DaveC Guest

    Here's the whole thing; DC coupled mixer with a charge pump for a
    Thanks John. Nice design.

    What part is used for SW1-3? Purpose? If these are "anti-thump" turn-on
    suppression switches, I think the main amp is similarly turn-on delayed. Of
    course it's important to know the timing of these to avoid any window through
    which the sub's cone could launch (or lunch?)...

    Thanks,
    Dave
     
  6. DaveC

    DaveC Guest

    Here's the whole thing; DC coupled mixer with a charge pump for a
    John, what's the reason behind choosing 6.2K for the feedback R on U3 (sub op
    amp)? And if that is to be a pot (the original idea), is 10K appropriate?

    There should be some kind of sub volume control...

    Thanks,
    Dave
     
  7. DaveC

    DaveC Guest

    C2, C3 are polarized, so I presume electrolytic?

    What type should C1 be?

    Thanks.
     
  8. tuinkabouter

    tuinkabouter Guest

    Our hearing is more or less logarithmic, so it might be about right.

    Further more most volume pots in audio are logarithmic.
     
  9. DaveC

    DaveC Guest

    Here's the whole thing; DC coupled mixer with a charge pump for a
    "mF" means microfarad?

    Thanks.
     
  10. DaveC

    DaveC Guest

    Thanks for the great explanation JF.
    The link doesn't work, and my service doesn't carry binaries.

    How about putting it here? ::

    <http://www.tinypic.com>

    Thanks!
     
  11. DaveC

    DaveC Guest

    Here's the latest:
    Almost! :)

    I need some absolute attenuation for the sub's output and some relative to
    the input signal.

    In other words: I need to be able to change the input level to the mixer
    (each of the 2 sound card's level will remain most of the time at max) so I
    can change volume for each stereo input (from each sound card) and for the
    *relative* level of the sub. The way it is now, the sub is outputting full
    level (no pots in that circuit) and the L and R channels are variable.

    So, the input to the sub mixer circuit needs to come from the input pots'
    wipers, not directly from the input. And U3 needs variable gain.

    The power amp (that this mixer is supplying the audio to) has a mute pin that
    has a slow R-C tc on it, so we can eliminate S1-S3 and assoc. components, I
    think.

    Thanks!
     
  12. DaveC

    DaveC Guest

    With R12 cranked down to minimum R the output of U3 goes down to about
    Yeah, R12 needs to be a pot. That does it.

    Thanks!
     
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