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Help me design this switching system

Discussion in 'Electronic Repair Modifications DIY' started by Guitarfreak, Aug 10, 2010.

  1. Guitarfreak

    Guitarfreak Well-Known Member

    I want to create a switching system for my monitors with a three position switch so that I can instantaneously switch to L speaker only, R speaker only, or both. I have scratched out a drawing using a DPDT switch but come to the problem of having a mono output using this setup. I am assuming this system would require the use of a 4PDT switch because of this. Am I on the right path?
  2. Boswell

    Boswell Moderator Distinguished Member

    I wired up a mono version of one of these once in my youth before I knew any better. I connected the loudspeakers in series, and attached the switch centre pin to the the join of the speakers and the outer pins to the two ends of the speakers. The switch in either of the two end positions shorted out a set of speakers, and the centre "off" position left both speakers in circuit. Not pretty, but it worked for what was required at the time.

    Are you powering these from a stereo amp so that when you have both speakers on, they operate as stereo? If so, what do you want to happen when you select one side only?
  3. MrEase

    MrEase Active Member

    It would not be wise (without a lot of care) to do this at speaker power levels as you could easily fry your PA. You would be far better switching at low levels which will be necessary in any case if you have powered monitors. Having said that, this is not just a function of getting all the signals where they need to be as you will also have to consider both crosstalk within the switch (been there, done that) and switching clicks and pops. Neither of these is trivial to deal with properly and there are commercial systems available for doing this.

    To paraphrase your Bob Rogers quote, "The rich man buys once what the poor man tries to make himself again and again."
  4. Guitarfreak

    Guitarfreak Well-Known Member

    Good advice guys. My speakers are active so there is no power amp involved. I don't think that there would be any crosstalk between the speakers if I wired it using a 4PDT switch like it is set up on my paper. Something I didn't think about before is loading the speaker when it is disabled. I'm not sure how to do this, it's a good point. Is this necessary with active speakers?

    Boswell, my circuit would have the speakers running in parallel. I am planning on using either 14 or 12 guage shielded insulated wire for the inside contacts.
  5. Guitarfreak

    Guitarfreak Well-Known Member

    If anyone is curious, this is how I have the switch wired.

    Attached Files:

  6. MrEase

    MrEase Active Member

    Your diagram does not show how you intend to wire the switch very clearly but I suspect the problem with your circuit is that in the centre position, none of the switches are on, so it will be both speakers off, not on.

    Why on earth do you think there will be no crosstalk? Have you found a switch with no capacitance or inductance?
  7. Guitarfreak

    Guitarfreak Well-Known Member

    Garr, I thought the middle position was all terminals active. I knew that didn't make sense. They don't sell 4PDT switches where all terminals are active in the center position? Like a guitar switch does but in 4PDT version?

    I have some good ideas, but I don't know $*^t about shingles, that's the problem.
  8. Link555

    Link555 Well-Known Member

    Just to echo everyone else, me no likey the clicky and popy. Best to learn how make a popless switch from a fet or jfet first....

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