Want to build speaker selector switch

Discussion in 'DIY' started by Nodnarb481, Mar 15, 2019.

  1. Nodnarb481

    Nodnarb481 New Member

    Messages:
    4
    Hey guys

    I've been doing some research on an idea I had. Basically want to sit a box between my guitar amp head (tube amp) and my 4x12 speaker cabinet (75w rms, 16 ohm speakers) that will let me select any combination of 1 to 4 speakers without blowing up my amp. Started reading about stereo selector switches and that is basically what I'm trying to do. However, I can't really find any that don't let everything dip below 8 ohms. Do you know what the circuitry inside one of these things looks like or how I may mod/build one to suit my application?

    Thanks!
     

     

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  2. Watthour

    Watthour Electron Rancher - JS3600

    Welcome Aboard!

    We would need to know the impedance of each speaker you are intending to connect. Adding speakers in parallel will halve their impedance, so a rather complex rotary switch will likely be needed to connect up to four speakers with the necessary parallel/series connections to prevent the overall impedance connected to the amp from dropping to a dangerous level.
     
  3. Binkman

    Binkman AK Subscriber Subscriber

    Messages:
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    Location:
    Chapel Hill, NC
    greetings;
    And a diagram of your speaker cab's wiring. Head amp. model's stated required or recommended speaker(s) ohms.
     
  4. Nodnarb481

    Nodnarb481 New Member

    Messages:
    4
    Thanks for the replies, guys. The amp head is a Hughes & Kettner Tubemeister 18. It is good for 8-16 ohms. The four speakers I'm going to be using would all be 16ohm speakers such as the one below. I'll be using the four different speakers. But they will all be of the same wattage and impedance.

    https://www.musiciansfriend.com/acc...tar-speaker?rNtt=celestion vintage 30&index=8

    The cab is just an empty box right now. I'm going to set up the wires however I'd like to. I assume all of the speakers will have to be in parallel or wired completely separate of each other to give me full control of what is on/off.
     
  5. Watthour

    Watthour Electron Rancher - JS3600

    Yes, it is probable that in order to maintain proper impedance, each speaker would have to be wired to a multi-pole switch to allow the switching to connect them in series, parallel/series pairs, and a combination of those depending upon the number of speakers selected. I can envision a 15-position switch to accomodate all possible combinations of four individual speakers.

    Pos 1 - Sp 1
    Pos 2 - Sp 2
    Pos 3 - Sp 3
    Pos 4 - Sp 4
    Pos 5 - Sp 1 + 2
    Pos 6 - Sp 1 + 3
    Pos 7 - Sp 1 + 4
    Pos 8 - Sp 2 + 3
    Pos 9 - Sp 2 + 4
    Pos 10 - Sp 3 + 4
    Pos 11 - Sp 1 + 2 + 3
    Pos 12 - Sp 1 + 2 + 4
    Pos 13 - Sp 1 + 3 + 4
    Pos 14 - Sp 2 + 3 + 4
    Pos 15 - Sp 1 + 2 + 3 + 4
    Pos 16 - Sp Off*
     
  6. Nodnarb481

    Nodnarb481 New Member

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  7. toxcrusadr

    toxcrusadr Omelette au Fromage Subscriber

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    Yes, that is another way to do it. If you have 4 speakers, you could connect each to one of the positions, and when you press more than one button at once, it will correct the impedance so it presents 8 ohms to the amp regardless.

    Only downside is that it will likely use resistors to accomplish this, wasting power, and as such you will not be able to take advantage of all the power your amp can supply. Which is, after all, the point. If you study powering multiple drivers a bit it becomes clear. Playing two drivers at 8 ohms in series for 16 ohm amp load will not give as much output as playing them in parallel for 4 ohms and 4 times the amp output. [As an example, I know your amp only goes to 8 ohms.]

    The more complicated DIY switch could place combinations in series or parallel with no resistors or loss of power.

    1 driver = 16 ohms
    2 drivers in parallel = 8 ohms
    3 drivers - not really a good way to do this - in series would be 32 ohms, parallel 5.33 ohms. The former does not get much output out of the drivers and more power could be had with 2 in parallel. 5.33 ohms is obviously too low for the amp. Suggest skipping the 3 drivers combo.
    4 drivers, two in series and those two series pairs in parallel with each other = 16 ohms.

    So, 4 of the 15 settings watthour posted above would be unnecessary, requiring only 11, probably a 12 position switch, unless you wanted to skip the 'off' position in which case a 10 position would be adequate.

    Now, how many gangs would it need? I was thinking one - this would work if all the negative leads could be common, but if some combos require series connection, some neg leads go to other driver positive leads so it is more complicated than that.

    I have some funky multi position switches and if this thing goes anywhere I will be glad to look and see if I have anything that will work.
     
  8. toxcrusadr

    toxcrusadr Omelette au Fromage Subscriber

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    It is definitely some work to design and put it together though. You may decide the ready made switch is a much easier way to go.
     
  9. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
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    Location:
    High Plains, Eastern Colorado
    Do you really want to use 3 speakers at one time? Doing this using 1, 2 or 4 speakers is easy with a 3 position switch, 4 DPDT relays, some diodes, and a small dc power supply. The load will be either 8 or 16 Ω. If you want 3 you will need another relay, a 4 position switch and a 2.7Ω power resistor, for an 8Ω load. The resistor may affect the frequency response.
    EDIT: more info
     
    Last edited: Mar 15, 2019
  10. Watthour

    Watthour Electron Rancher - JS3600

    ...Or a pair in series with a parallel single. And all wires would likely need to be switched.
     
  11. Nodnarb481

    Nodnarb481 New Member

    Messages:
    4
    For sake of building this and getting proof of concept done, I think Im okay with dropping the 3 speaker positions. So any 1 speaker on. And combination of two. And then 4 speakers. So basically 11 variations.

    If I went the simple route of modding the speaker switch, how much quieter would it make it? I'm not totally opposed to that because this is a studio project. Doesn't need to be loud, just produce great tones. I actually chose the head I did because it can be turned from 18w, to 5w, 1w or even direct input into my audio interface. Didn't take long for me to realize my 60w half stack was probably annoying my neighbors haha.
     

     

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  12. Binkman

    Binkman AK Subscriber Subscriber

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    Just observing; I don't see any potential advantage switching between speakers in one cabinet. I can see two cabinets or two heads in to one cab.
     
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  13. DeFriend

    DeFriend New Member

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    Location:
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    Dang, it may be easier to give each speaker its own power amp.
    From one input, feed the signal through a miniDSP to four different channels (4x10?)?
    This would allow mixing and level matching, if you want direct comparisons.
    You can have unused speakers and unused amplifiers, or that 15-pole switch that will likely be a source of noise.
     

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