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Audio Switcher Help

Discussion in 'Electronic Design' started by Jon Slaughter, Nov 19, 2007.

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  1. I'm trying to use the MAX4571 essentially to mute some audio channels,

    http://www.maxim-ic.com/quick_view2.cfm?t=qv&qv_pk=1974#Applications/Uses

    I got the controller to work and it seems fine. My test was to put V+ on the
    input and scope the output(with a pull down to ground for when the switch is
    off). It seems to work fine. My code simply toggles the state the switches
    every 1s or so.

    But when I put an audio signal on the input instead I get the negative half
    clipped and it is extremely attentuated(About 1/10 or more). What I did was
    actually pass a sin wave generated by my computer which goes into a
    mixer(for easy volume control and other things that I tend to do) then from
    the mixer's headphone out into the input of the MAX4571.



    Audio+ --- MAX4571 NO1

    MAX4571 COM1 ---+--- Audio-
    R
    |
    GND

    (R anywhere from 500 to 3k but didn't help any and made it worse for lower
    and high values)

    With the scope connected to +.

    Any ideas why the signal would be clipped and severly attenuated?

    Its possible I ruined the device. For some reason my first PIC's I2C
    channels stopped working so I might have shorted something out when I was
    probing around. I replaced the pic and everything seemed to work but maybe I
    screwed up the MAX4571 although it will passes the constant voltage just
    fine.

    First thing I need to know is if it passes AC completely(the scope says no
     
  2. Eeyore

    Eeyore Guest

    Just using a series switch ?

    What 'controller' ?

    So what did you see ?

    Given an absence of a negative supply, I dare say it may have trouble passing AC
    signals. What did you expect ?

    The data sheet does not show any negative voltages allowable. You're using an
    inappropriate part.

    Graham
     
  3. It has only ground and +?
    Then you must likely bias your audio at 1/2Ub, else bottom get clipped.

    analog signal range is from 0 to +V!!
    +V
    |
    R
    |---------- chip input
    audio in --C---|
    |
    R
    |
    ///

    That chip sucks in my view,
    their 'no click' switching seems to be a slow 8 ms bump.

    The 74HC4053 rocks, has negative supply.

    Anyways, Maxim is hard to get sometimes.
     
  4. Some of there chips allow -V on the signal. I guess they use a charge pump
    to generate -V. Kinda sucsk that this one doesn't.
    I need a very large number of switches(about 80) that uses a small space as
    possible.

    Having to bias it really sucks but I guess I don't have much of a choice ;/
    For my application I guess the clickless switching is not all that
    important. (I suppose I could do the switching myself by monitoring the
    signal with the Pic and switch when needed using the high speed mode).
     
  5. It is an interesting subject.
    For some time I wanted to make an audio switch for on my desk, that
    connects all possible DVD outputs, recorder inputs, PC in and outputs,
    headphones, speakers, other stuff, in a crossbar way, that can be controlled
    by a simple small keyboard.
    So, autonomous, not PC controlled, as PCs may be off.

    I found one chip that did it all and it costs 135$.
    Doing it with 74HC4053 and the like, in DIL, takes 2 eurocards (100x160mm),

    Many years ago I did it for somebody else, controlled by a Z80 with CD22101
    4x4 crossbar switches, and it took half a 19inch rack... (needed logic level
    changes).
    Of course it can be done mechanically too.

    Oh, I am only talking about a say 16 * 16 crossbar, with headphone or line drive
    capability, in stereo.
    And perhaps one for video too....
    Maybe that is why I still switch connectors manually.

    An other thing with crossbars is that a not-connected bar will pick up noise,
    so you need to switch an unused bar to ground, requiring an extra bar.
    Using + and - supplies greatly simplifies things.

    crossbar, crosspoint, what is the difference?
    http://www.analog.com/en/prod/0,,768_832_AD8113,00.html
    Price about 45 USD
    http://www.digikey.com/scripts/DkSearch/dksus.dll?KeywordSearch

    Maybe one day :)
     

  6. http://pdfserv.maxim-ic.com/en/an/AN638.pdf

    The devices don't need any level shifting or anything. I'm going to have to
    troubleshoot and see whats wrong. As far as that app note is says, it should
    work the way I original thought. Might have screwed up chip(not sure how
    though but I'll try another one soon).
     
  7. YOU NEED 1/2 V BIAS FOR AUDIO.

    +
    |
    R
    |--------- chip
    audio -- C --|
    |
    R
    |
    ///
     
  8. lol, you didn't take a loot at that pdf did you?
     
  9. Actually I looked twice.
    Have you tried this?
    May solve your problem :)
     
  10. It won't solve my problem really. I guess it probably will work but
    ultimately its something I need to avoid(not only more components but more
    noise).


    Page 1,

    "Connecting an n-channel MOSFET in parallel with a p-channel MOSFET allows
    signals to pass in either direction

    with equal ease. Whether the n- or the p-channel device carries more signal
    current depends on the ratio of

    input to output voltage. Because the switch has no preferred direction for
    current flow, it has no preferred input

    or output.

    "


    Now thats telling me that it will take AC just fine such as an audio signal?
    I could be wrong in interpreting it though?

    On the data sheet for the 4610 it says

    "Each switch handles V+ to GND analog

    signal levels"



    Which says it doesn't take AC ;/ So I guess I'm wrong but I can't see how
    the first quote(from page 1) says AC won't work.



    Doesn't Figure 1 show a circuit that lets AC go through? Note it has -V so
    maybe -V = GND? But then that doesn't explain the quote that switch has no
    preferred directionf or current flow. This is telling me that I could treat
    the output as the input and vice versa but then that means that AC should
    flow?
     
  11. On a sunny day (Tue, 20 Nov 2007 19:23:22 GMT) it happened "Jon Slaughter"
    <KuG0j.23908$>:

    Look at it this way:
    It is a piece of silicon.
    If you have Vss grounded, then driving below Vss will see diodes.
    And on top of that, one of them chips has comparators that actually
    switch the thing off, if the voltage is close to Vdd or Vss.
     
  12. lmfao...somebody comes in here for help, somebody else gives him the right
    answer, and he comes back with a snappy retort like this.

    The fellow is correct; it needs vcc/2 bias for capacitively coupled audio.
    Swings above and below ground, don'cha know.

    Jim
     
  13. Um if you cared to read the entire thread or even the first you would have
    noticed that I never asked for a solution so the problem but asked why the
    device was behaving the way it was. Obviously you don't care about that
    though... I suppose your on PMS and have to find something to whine about.

    Also, the app note specifically say that current can go in both directions
    and my simulation of the circuit in the app note shows that it works that
    way too. Either the device I'm using doesn't work that way or there -V is
    ground. (there is no -V on the device though)

    In any case there are other methods that are potentially better than passing
    biasing... such as running a +- power supply so that I can avoid all all the
    resistors an caps(which introduce noise).

    Unfortunately your just a whinner that I guess has nothing better to do with
    your time?

    Again though, as I'm sure you completely miss what I'm saying(chances are
    you won't even read it but reply with the same BS). My first post was about
    the device itself and how it was described in the app notes and
    datasheet(i.e., no mention of biasing, example circuits not showing any
    biasing, app note specifically saying "both directions", etc...)

    Surely the biasing method would work but it would work even if AC could be
    passed... in that case it is far from the optimal solution. If the device
    I'm using will not pass AC(which it seems that way) then I need to know for
    sure.

    Theres a huge difference between using a method that works and a method that
    works optimally. I guess your one of those people that don't give a shit
    about that though?
     
  14. lol, you didn't take a loot at that pdf did you?

    Um, that would be look

    Ooookay, if we're going to play the horse's ass game, I can play as well as
    the next feller ...
    That would be Um, (comma).

    if you cared to read the entire thread or even the first you would have
    I've been reading the entire thread. I wanted to see how long you would
    rave on about your superior knowledge of data sheets until somebody showed
    you how the real world works.


    Obviously you don't care about that
    That would be "you're", and I'm way the hell too old for PMS.

    Yep, positive voltages at either end will be transmitted quite nicely.
    Negative voltages (below the Vss rail) will turn the parasitic diodes on and
    you will wind up with nothing.

    Oh, Christ, another "my simulator works just fine." Great. Pack your
    simulator into your product.



    Either the device I'm using doesn't work that way or there -V is
    That would be "their". You have no clue as to how CMOS devices work if you
    say there is no V-.

    You'd rather go to the expense of a +/- supply than use a voltage divider?
    Haven't marketed any products, have you? (And that would be "and".) Never
    seen a capacitor yet introduce noise. That's why we use 'em, don'cha know.

    That would be "whiner". I bided my time until somebody that knows what he
    is talking about told you what the problem was. No sense trying to teach my
    grandmother how to suck eggs.

    So do the Motorola data books. So do the National data books. Nobody
    bothers showing input biasing for an AC signal because that would defeat the
    specmanship of the part. You only have to mess with an experiment for about
    15 minutes and then look at the internal design of the part to figure out in
    a couple of seconds why you can't force AC through this sort of device
    without bias.


    That sentence fragment makes absolutely no English sense...


    in that case it is far from the optimal solution.

    You wouldn't know an optimal solution if it bit you in the butt.



    If the device
    Trust me, sonny, I've been using these things in real product design for
    almost thirty years. Jan told you an inconvenient truth and you seem
    unwilling to accept it.

    By the way, there are several ways of low noise biasing when you've got
    literally infinite input impedance but you apparently won't listen to folks
    that know how to do it, so go figure it for yourself.
    I've never known an optimal design to make it in the marketplace yet. A
    product is a bunch of engineering compromises flying in loose formation.


    I guess your one of those people that don't give a shit
    That would be "you're". I give a shit about a lot of things. One thing I
    do NOT do well is suffer fools graciously.

    Jim
     
  15. Lol, your dumber than I thought then. I would break it down for you but you
    already know everything about everything.
    Nope, sorry... are you a fucking priest or an engineer? If an engineer then
    start acting like it and show me the money instead of your "Trust me, sonny"
    BS.
    oh, infinite impedence huh? Sure.. I guess you think there is 0 capacitance
    in there too? I don't listen to people like you who are on an ego trip. You
    think just cause you've been around the block a few times that everyone is
    suppose to bow down and suck your cock. It ain't going to happen. Again,
    you totally missed the point of the original post and are trying to start
    something that is totally irrelevant to the original post.
    Sure, cause fuckers like you always bitch about it until you get your shitty
    design to replace it.
    Lovely... Keep trying to find my spelling and grammar mistakes instead of
    trying to solve the real problem. You call yourself an engineer? Is that
    what they taught you in schoo 140 years ago?

    Your just an old coot that can't get with the times. You rather force feed
    someone your puddin instead of showing them the proof. I'm sorry but like
    many instances I'm not going to accept your BS until you make it logical.

    Again, none of your fucking post has anythign to do with my original
    question, which had nothing to do with how to get the device to work but if
    the device supported ac or not. They are totaly different questions but I
    guess with your limited brain cells you fail to see that(I know a bunch of
    your buddies are going to jump on me and try to make it like its my fault
    cause birds of a feather flock together.

    Anyways, I got you on ignore now so feel free to reply ad nauseum. I'm sure
    you and your buddies can reforce your ego's all you want and feed each other
    ya'lls pudding.
     
  16. --
    "If you think you can, or think you can't, you're right."
    --Henry Ford
     
  17. Plonk.

    Jim
     
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