Trying to find a switch

Discussion in 'General Electronics Chat' started by roweder, Oct 8, 2017.

  1. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
    I am having trouble searching for a switch on Digikey. I'm not sure what parameters to set in the filtering boxes. I am open to other retailers, I was looking on digikey because I'm familiar with them. I've been searching google and eBay and digikey for ~1.5hr and I've come up empty. I'm pretty bad at searching for stuff so I decided to post here because I figured someone on here would know right away the proper terms for me to use when searching to have results related to what I'm describing.

    Here is what I need the switch to do:

    Switch 4 speakers (8 wires) between being powered by my car's radio and being powered by an alpine audio amplifier.


    I currently have my amplifier's RCA inputs going to a 3.5mm cable that I plug into my iphone. The alpine amplifiers have inputs designed for the speaker outputs of a car's stock amplifier, but I'm trying to move away from using this input because it's very finicky. My gain dials are set below nominal because the amps have more power than I need, but the gain seems to only affect the RCA inputs, and the gain of the input designed to take another amplifier's output doesn't seem to be adjustable, but it seems to change if I plug my iPhone into the amplifier's RCA inputs but do not play any music through it. So, that input seems a little unpredictable/unstable/weird, and I want to set it up differently.


    I am hoping to find a switch that rotates with two positions and functions like a single 2-position 3-pin switch, but basically with 8 of those switches inside of it. I'd connect the speakers to the center pin, the amplifier to one pin, and the car's radio outputs to the other pin (that x8 basically).

    The speakers are 4-ohm and can handle 100W. I'd like the switch to be able to handle the same power levels. I'm not exactly sure what voltage it needs to handle but I think it would need to handle 5A AC through each pin.

    Thanks in advance!
     
    Last edited: Oct 8, 2017
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    8,302
    2,003
    Draw a diagram showing how you want the speakers switched.
     
  3. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
    I'm on my phone but see if this helps
    69945C0B-1796-4B45-8BD5-B829E7A0CA9F.jpeg
     
  4. dl324

    AAC Fanatic!

    Mar 30, 2015
    8,302
    2,003
  5. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
  6. crutschow

    Expert

    Mar 14, 2008
    22,201
    6,465
    If you wanted to control all the speakers with one switch, you could use four DPDT relays or two 4PDT relays energized by that switch.
    Here's an example 12Vdc, 4PDT relay that should work.
     
  7. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    3,223
    822
    We're assuming the common wire (ground wire) is isolated one from the other. And in some amps that's the case. But where one line is common we only need to switch (for instance) the positive side.

    OK, I bet I just confused you. In many stereo's (two speaker systems) there's a common wire that is common to the amp and to all the speakers Only the left and right outputs are isolated from each other. No need to switch ANY common lines, since they're all - um - common potential. This is why your headphones has only a 3 wire connector. One probe (usually the tip) is for the (lets say) the left channel and the second is for the right channel whereas the main body of the probe is common to both speakers. So there should be no need to switch out the common line because it's basically a return path for the audio.

    If your amplifiers are wired with a common (negative) lead that is common to all speakers then you only need to switch four wires. Since you want to choose one amp or the other, you should only need a DPDT switch.

    Give me twelve min's and I'll draw a diagram.
     
    Last edited: Nov 5, 2017
  8. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    3,223
    822
    No need to switch 8 wires. That is IF your (black) wires are common.

    Amp Switch.jpg
     
  9. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
    That makes sense, but I'm not sure if the negatives are a common ground/potential. I suppose I could do some poking around with a connectivity indicator, but the amp's instructions say repeatedly and in bold that the negative leads should not be grounded.

    That is a very well drawn diagram.

    I'll mess around with the connectivity option on my multimeter and get back to you!
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
    7,983
    6,779
    If you have a "class D" amplifier, or an amplifier described as a "bridged" Amplifier, then you will NOT have common grounds to your speakers. If this is a car amplifier, then it is almost certain that you do not have common ground.
     
  11. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
    Ok, it is class D and a car amplifier. It is also capable of being bridged by connecting the negative terminals of channels 1 & 3 and 2 & 4.
     
  12. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    3,223
    822
    In that case then you need a 4PDT switch (or relay). Everything I did with the red wires needs to be done with the black wires as well.

    So to answer your question about what kind of switch you need, you're looking for a 4PDT switch. (four pole double throw) Or a relay 4PDT. But with a relay you'll still need a switch to turn it on and off. You'll also need to pay attention to what voltage you're using to switch it.

    Here's a 4PDT switch with a center off position: https://www.amazon.com/uxcell-Screw...pID=41KHnReuWZL&preST=_SX342_QL70_&dpSrc=srch

    Here's one rated for about 5 amps without a center off position: https://www.amazon.com/uxcell-Posit...91639&sr=8-2-spons&keywords=4pdt+switch&psc=1

    Here's one rated for 15 amps at 240 V (your amp isn't going to have that much voltage output at the speakers) and it does not have a center off position: https://www.amazon.com/Uxcell-Screw...F8&qid=1509891639&sr=8-6&keywords=4pdt+switch
     
  13. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    3,223
    822
    Here's the modified drawing: (BTW; the blue dotted line between the switches indicates a mechanical connection. Flip one they all flip)

    Amp Switch.jpg
     
  14. joewales44

    Member

    Oct 8, 2017
    150
    4
    i'm confused again. i thought ground was always ground? or is that not really a ground, but a return to the amp?
     
  15. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    3,223
    822
    Ground can be confusing. There are different types of ground. Earth ground is where the circuit is connected to ground via a grounding rod or a cold water pipe. There's a floating ground which is NOT grounded to earth ground. It's a common point in a part of a circuit. There's a chassis ground that may or may not be earth grounded.

    In your amplifier (guessing here - I'm not the expert) your - um - black wires (per my first drawing) was assumed to be common ground, meaning they shared a common potential. Apparently in a class D amp that can be bridged each output is a separate entity that can be thought of as a battery. With an audio sine wave you have current that moves in one direction then the other. As it changes direction it moves the speaker back and forth creating pressure waves we hear as sound. If we consider a single instance when current is in one direction we can consider one potential positive and the other negative. Where amps are common potential it's usually the negative side that shares a common point. But with your amps they don't share a common potential meaning each is its own power source for the speaker attached. Just like batteries, if you bridge them (in series) their voltages add up. Red to a speaker, black to the other red and the other black to the speaker will double the voltage applied to that speaker (assuming the sine waves are in sync.) Connecting all negatives together might not be advisable, though I don't see why not. Like batteries, if you tie all the negatives together you don't get higher voltages you get more current capability.

    But for the sake of not blowing up your amps, use the 4PDT switch as shown and you'll not have to concern yourself with this ground issue (as confusing as ground can be). (and believe me, opening that can of worms - well, it's a pretty big can; everybody will start an argument over what it means. Happened many times before and bound to happen again.)
     
  16. KeepItSimpleStupid

    AAC Fanatic!

    Mar 4, 2014
    3,336
    606
  17. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
    To add to Tonyr1084, I think that it is possible that for this type of amp the negative wire isn't always negative/chassis ground. Because the amp is only powered by 12v, it might be able to create more power easier if the negative wire is capable of oscillating between 0v (common ground) and -12v (or -28v, I think the amp is capable of doubling the voltage and the cars running voltage is ~14.4v).

    If the negative is a neutral, and the positive wire goes from -28 to +28, that would have a lower power output than if the negative is also capable of switching between -28 and +28. I'm hesitant to conclude that the black wire could ever have a positive bias though, because the speakers are made by the same company as the amplifier and they have capacitors on them that have a designated negative side.

    This is why I wanted an oscilloscope!!! I just couldn't justify it haha. You know what, I'm going to go grab a diode and try to measure a DC voltage from the negative terminal to the chassis ground while playing music. Give me 20 minutes.
     
  18. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
  19. roweder

    Thread Starter New Member

    Feb 2, 2017
    28
    0
    Oh, I should mention, thank you for finding switches for me!

    Unfortunately last night I ordered the DPDT switches I posted a link to. I chose ones with solder tabs instead of screw tabs, and I think that 4 DPDT switches will be a little easier to solder than 2 4PDT switches.
     
  20. Tonyr1084

    Distinguished Member

    Sep 24, 2015
    3,223
    822
    You don't need four of them. My illustration can be considered 4 SPDT (single pole) or 2 DPDT (double pole) [double throw] switches. The problem with having four switches is that you can switch them in the wrong order and end up shorting two outputs together. That's why I'd opt for a 4PDT switch. Screw terminals allow for you to create the wire termination and then install it without having to apply heat to anything. OR perhaps you can find a 4PDT switch with spade lugs (lugs like what are most likely on your speakers).

    Even having two DPDT switches you still run the risk of not switching things at the right time. Unless you plan on turning both amps off before you select which amp plays to the speakers.

    And there's one more concern I have regarding the amp that is NOT connected to the speakers - isn't it hard on an amp when it has no load on it? This I don't know - I raise this question so that someone with more experience can answer it.
     
Loading...