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  • Switch for output transformer

    Can anyone recommend an appropriate switch (type, name, brand etc.) to change back and forth from 8 ohm to 4 ohm
    taps on the output transformer of a Fender Princeton clone (22W)?

  • #2
    You want a DPDT (dual position, dual throw) "on/on" switch. The center lug goes to the "hot lead of the speaker. The end lugs go to each output tap of the output transformer. Ground goes straight to the speaker.

    The amount of power a speaker sees isn't huge but it's substantial. Don't get some mini toggle thing.
    "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

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    • #3
      I think you only need an SPDT switch because the transformer ground and frame ground will remain the same with no switching needed.

      Just be sure its a high current switch . This CARLING SPDT On/On should do the job fine. https://www.delcity.net/catalogdetails?item=27200033
      Last edited by WRGKMC; 02-08-2018, 06:22 AM.

      Comment


      • #4
        He's trying to make a toggle switch to select between the 4 ohm and 8 ohm tap on the output transformer. Both leads will have to enter the switch with one lead leaving to the speaker jack. Hence the need for a dual throw switch. The ground can connect to the speaker from anywhere grounded.

        I once wired a Magnatone amp so that when a second speaker was plugged into the external speaker jack, the tap on the output transformer was automatically switched to 4 ohms. I never liked how Fender amps used the same 8 ohm tap whether you used an external speaker jack or not.
        "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

        Comment


        • WRGKMC
          WRGKMC commented
          Editing a comment
          Many Fenders only use a single speaker tap and the transformer load is variable from 4 to 8.

        • guitarcapo
          guitarcapo commented
          Editing a comment
          Yes and that creates an impedance mismatch. Fender just was too lazy to do it right

      • #5
        Originally posted by guitarcapo View Post
        You want a DPDT (dual position, dual throw) "on/on" switch. The center lug goes to the "hot lead of the speaker. The end lugs go to each output tap of the output transformer. Ground goes straight to the speaker.

        The amount of power a speaker sees isn't huge but it's substantial. Don't get some mini toggle thing.
        I'd like to address two separate issues.

        First off, I can't for the life of me understand why the builder asked me if I wanted to have a Speaker Out Jack or Recording out jack.
        At the time I knew nothing about what I would use the Speaker Out jack for, but still opted for it. He didn't answer my question concerning it.
        The build was for a separate amp head + speaker cabinet.

        Well now I know that, given the parallel speaker wiring, having a separate Speaker Out jack is useless.
        If you want to use an 'external' speaker, you can simply unplug the main speaker out and plug in your 'external' speaker there.

        The External speaker jack is totally redundant as the amp is currently wired.


        About the switch...
        I was also thinking that a DPDT switch would be the one to get. But looking at wiring diagrams for them
        now I'm not so sure.

        It seems a SPDT switch might be the candidate I need?

        I'm looking at a SPDT (On-On) wiring diagram now. It has 3 connectors (1,2,3)
        Switch position 1 has connectors 1+2 tied together.
        Switch position 2 has connectors 2+3 tied together.

        So why not just connect the 4 ohm tap to connector 1 and the 8 ohm tap to connector 3
        and then connect the connector 2 to the external speaker out jack?

        Also which of these three would you lean towards:
        1. toggle
        2. rocker
        3. slide

        I think the lowest profile switch would be better to prevent accidentally hitting the switch.




        Comment


        • #6
          Originally posted by Jazzer2020 View Post

          So why not just connect the 4 ohm tap to connector 1 and the 8 ohm tap to connector 3
          and then connect the connector 2 to the external speaker out jack?

          Also which of these three would you lean towards:
          1. toggle
          2. rocker
          3. slide

          I think the lowest profile switch would be better to prevent accidentally hitting the switch.
          That's exactly how its done..

          As far as the type of switch, the Rocker and Slide require square holes. Ever cut through a chassis to install a switch before? Cutting a square hole requires drilling a round one then filing the sides flat. Messy business trying to get a proper fit and the metal dust can get in circuits and short out. Slider switches need a square hole plus two screw holes. Toggle and sliders both contain allot of plastic and tend to break more easily.

          Metal toggle is the way to go in a tube amp where there's allot of heat. They are proven to be most durable.

          If you're worried about accidental switching, instead of mounting it out the back, simply mount it facing the speaker like tubes and transformers do. So long as you can reach inside and flip it when needed you should be OK.

          Comment


          • Jazzer2020
            Jazzer2020 commented
            Editing a comment
            Thanks WRG, metal toggle it will be. And thanks for the tip about mounting it facing inside.

        • #7
          Somethng to be aware of:

          100 Watts into 4 Ohms is 5 Amps - be sure the switch can handle the current.
          "Our presence here is only for a short period of time.
          We do not have to shorten it by fighting each other"

          Comment


          • Jazzer2020
            Jazzer2020 commented
            Editing a comment
            Thanks onelife, I'll be sure to get at least a 5 Amp switch.

          • WRGKMC
            WRGKMC commented
            Editing a comment
            Its only a 22W amp but a higher amp switch will be more durable.

        • #8
          One more question on this upgrade.

          So far I just plugged in another 8 ohm speaker in the Speaker out jack.
          So I had the Main 8 ohm speaker + 2nd 8 ohm speaker (jacks wired in parallel) using the 8 ohm tap.

          It sounded good to me. Nice full sound, perhaps a tad louder than just the Main speaker (no changes to any of the dials).

          What should I expect after the switch is installed and I switch to the 4 ohm tap with the two speakers connected, in terms
          of:

          a) Sound?
          b) Volume?
          c) any other changes?

          this assumes I still make no changes to any of the dials.

          TIA



          Comment


          • #9
            Ok....all this being said, if you simply plug a second external speaker in parallel with the internal speaker, the output transformer will see a lower impedance load...but your amp isn't going to blow up or anything. That's how Fender has done it for a long time now with no problems. In my experience you might lose a bit of power and bottom end compared to having a perfect match...but all it does is effect frequency response a bit at most. For the better or not because it's subjective. Switches make more sense if the load is more off like 16 or 2 ohms.
            "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

            Comment


            • #10
              Originally posted by guitarcapo View Post
              Ok....all this being said, if you simply plug a second external speaker in parallel with the internal speaker, the output transformer will see a lower impedance load...but your amp isn't going to blow up or anything. That's how Fender has done it for a long time now with no problems. In my experience you might lose a bit of power and bottom end compared to having a perfect match...but all it does is effect frequency response a bit at most. For the better or not because it's subjective. Switches make more sense if the load is more off like 16 or 2 ohms.
              I hear ya' !
              It won't kill the amp and I could easily get by with two 8 ohm speakers (parallel) using the 8 ohm tap.
              And I wouldn't be using that setup a lot.

              But... theoretically and in practice, it would be better for the amp to use the 4 ohm tap with two 8's in parallel.

              I just took a look at the back of the amp. It's going to be a challenge to find a good spot for the switch.
              I bought one yesterday. Heavy duty. 20 amps. Gold-plated connectors with screws.

              If I go ahead installing the switch, can I just use the screws or would you apply solder to them too?


              Comment


              • daddymack
                daddymack commented
                Editing a comment
                if you use lugs, the screws should be fine. Stripped wires should be tinned and soldered to the switch.

              • Jazzer2020
                Jazzer2020 commented
                Editing a comment
                Thanks daddymack!

            • #11
              I'd likely remove the screws then solder the wires to the tabs. Reason being this is a combo amp the speaker vibrates the head like a SOB.
              Simply wanging the wires down with screws may wind up being fine but I'd be concerned with oxidation and the screws vibrating loose so I have a habit of making my work permanent. If you do solder be sure you use hemostat or alligator clip as a heat sink. If the switch has screws it likely made of plastics that shouldn't be over heated. Terminals overheated can destroy the switch internally.

              Comment


              • #12
                Originally posted by WRGKMC View Post
                I'd likely remove the screws then solder the wires to the tabs. Reason being this is a combo amp the speaker vibrates the head like a SOB.
                Thanks!

                Actually it was custom built as head + speaker cab, so vibrations aren't an issue here.

                One more question.
                What gauge wire would you recommend to make the connections?

                Comment


                • #13
                  OK I can really use your help now guys!
                  I did the installation.
                  Bought the switch GC Electronics No. 35-130 SPDT 10Amp toggle
                  You can see what it looks like in general at the link given (the link shows a DPDT, but the rest is the same)

                  Drilling the 1/2" hole in the chassis was a BIATCH!
                  If I knew it would be so much work I wouldn't have done it.

                  Wires are soldered and good to go. Tested the connections, works.

                  Here's the problem...
                  Drilled from outside to inside of chassis (on back, found a tight spot).

                  So the inside has burrs, it's not pretty!.
                  I can't file them because:
                  1. I don't want to!
                  2. I don't have the proper tools to do it
                  3. It would make a huge mess inside the circuitry, too risky
                  4. your choice....

                  I mounted the toggle through the hole and attached the two nuts supplied.
                  You can see them at the linked site.
                  First the hexagon nut and then the circular nut.

                  So what's the problem? I can't get the nuts to tighten properly!
                  I think it's because of the burrs inside.

                  It looks like it's tightened, but a few flips of the toggle and the switch
                  becomes loose. Won't do.

                  Any suggestions on how to get her tightened properly?


                  Comment


                  • onelife
                    onelife commented
                    Editing a comment
                    try putting one of the nuts on the inside of the chassis - it would also help if you put a knurled lock washer on the inside (like a volume pot is mounted in an electric guitar)

                • #14
                  Now you have an idea what techs do for a living.

                  De-burring is a problem. Next time you drill through a chassis use a wood block behind the steel. It will cut clean that way. The wood absorbs the heat when the metal gets thin and prevents it from bending over and creating burrs.

                  If you had a Dremil you could take care of that burr in seconds with an abrasive stone tip. If you had a larger but then the hold you could use it on the burred side to de-burr it too. Depending on how tight the hole is you may be able to get a mini file in there and make sure you get all the metal dust. In fact use masking tape and paper to seal off the area.



                  Comment


                  • #15
                    Onelife:
                    "try putting one of the nuts on the inside of the chassis - it would also help if you put a knurled lock washer on the inside (like a volume pot is mounted in an electric guitar)"

                    Thanks Onelife for the tip. I tried putting one of the nuts inside the chassis and it helped quite a bit. I don't have any knurled lock washers that fit.

                    This has been quite the learning experience, I must say!

                    This heavy duty switch that I bought (bigger than the two 1/2" SPST switches I have in the amp for power and standby)
                    exerts quite a force when the switch is toggled. A force much greater than the other two switches.
                    It is this force that is the problem.

                    So for the time being (if I can remember) I will carefully flip the switch so it doesn't hit the switch body.
                    This will prevent it from shaking the body and loosening the nuts.

                    I'll keep an eye out for a smaller SPDT switch, possibly 5 amp, and swap the switches later on down the road.


                    Comment

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