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adding line out to a speaker output

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  • #16
    Originally posted by vintagekiki View Post
    https://drtube.com/schematics/marshall/5213psu.gif

    It works convincingly the best.
    Insulated jack (JS3) and R27 (100 ohm) to avoid ground loops (ground loop buzzing)
    Instead of VR1, it can have a trimmer pot or a fixed resistor.
    And as you can see, the line out is wired with the standard series resistance and a dropper to 0V. The circuits already suggested will work like this. If the negative speaker terminal isn't at 0V then it can't be used as the 0V reference for a line out. That's why it didn't work.
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "If you're not interested in opinions and the experience of others, why even start a thread?
    You can't just expect consent." Helmholtz

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    • #17
      Originally posted by Chuck H View Post
      If the negative speaker terminal isn't at 0V then it can't be used as the 0V reference for a line out. That's why it didn't work.
      Yes. The problem with the Mustang amps is they used a bridged configuration. They also have a ground wire to the speaker frame so you run into big trouble if you ever replace the speaker with a type that has the negative lug connected to the frame.
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


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      • #18
        Originally posted by Randall View Post
        Well, I wired it up today, and the cold slap of reality hit me in the face. It doesn't work. It seems in this amp the speaker neg is not grounded, so the sound goes really low if the line out jack is touching the chassis, even with nothing plugged into it. Also, with the jack isolated the sound goes very weak if a cable is connected to a mixer. Clearly this is a problem. I thought this would be pretty straight ahead, but I'm stumped.
        Transformer. Mouser has fingertip size transformers that will sort this out, Xicon brand. Get a 600:600, use the primary instead of your smaller resistor. Secondary is "floating" iow doesn't care whether one lead is grounded or not. So you send the output to another unbalanced input, or send balanced to the input of a mixer or mic preamp.

        https://www.mouser.com/ProductDetail...%2FZ8KUebnk%3D

        2 bucks, ya can't go wrong! Don't worry much about the 300-3K bandwidth, that's at the power extreme. With a 10K-30K padding resistor, there's plenty of bandwidth. If that's still a worry, there are better transformers that cost only @ $15.
        This isn't the future I signed up for.

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        • #19
          With a SS power amp I wouldn't expect any benefit from taking the line out signal at the speaker out.
          - Own Opinions Only -

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          • #20
            Originally posted by Helmholtz View Post
            With a SS power amp I wouldn't expect any benefit from taking the line out signal at the speaker out.
            Yep, that too.
            This isn't the future I signed up for.

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            • #21
              If you can get to it, may have to be a member, take a look at Jensen AS045 or AS061. It is Jensen's design for guitar line out. Weber use to sell a xformer to do this. Don't know if they still do. Also you may want to do a search this forum for Slave line out, started by mac dillard. I have found that the transformer is critical.

              Doesn't appear that Weber sells this little xformer(WBALUN) any more...The spec. that I have says frequency responce +/- 2db 80hz to 20 khz,,,DC resistance 150 ohms Pri and Sec, Max Idc 80 ma., typical AC 1V RMS.

              I don't know how to post a schematic but they come off of the hot on the speaker jack to a 5K to 100K (select value for best range of output signal level ie: your voltage divider) to a 1KA pot. Wiper of pot is connected to the primary of the xformer...Secondary of the transformer to out put jack/XLR connector. You can put a low value cap in parallel with the 5K/100k resistor to peak the high end.
              Last edited by mac dillard; 08-09-2019, 08:27 PM.

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              • #22
                "With a SS power amp I wouldn't expect any benefit from taking the line out signal at the speaker out."

                Why not?
                It's weird, because it WAS working fine.....

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                • #23
                  Originally posted by Randall View Post
                  "With a SS power amp I wouldn't expect any benefit from taking the line out signal at the speaker out."

                  Why not?
                  There's not much interaction between the power amp & speaker the way tube amps do. SS amps more or less simply make the input larger and that's that. What you put into the input is what you get at the output, only bigger.
                  This isn't the future I signed up for.

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                  • #24
                    Originally posted by Helmholtz View Post
                    With a SS power amp I wouldn't expect any benefit from taking the line out signal at the speaker out.
                    Line out signal at the speaker out, uses instead microphone to connect amp to the sound system (PA system)
                    For the sound system, it doesn't matter, whether it's an SS or a tube amp.
                    It's All Over Now

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                    • #25
                      Originally posted by Randall View Post
                      "With a SS power amp I wouldn't expect any benefit from taking the line out signal at the speaker out."

                      Why not?
                      SS power amps (especially switched mode) typically don't have any (desirable) sound shaping properties.
                      If the power amp doesn't add anything but power, it makes no sense to use the power output for line out.
                      Last edited by Helmholtz; 08-10-2019, 01:08 PM.
                      - Own Opinions Only -

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                      • #26
                        "SS power amps (especially switched mode) typically don't have any (desirable) sound shaping properties.
                        If the power amp doesn't add anything but power, it makes no sense to use the power output for line out."

                        I would have to respectfully disagree here that it does in fact make plenty of sense to pick the signal off the power output if only as purely a matter of convenience dealing with a SMT board. It's a modeling amp, all the "sound shaping properties" are done on a computer. Who plays a shitbox amp like this and worries about if their line out to the mixer for sound reinforcement at a dinner club is having slight plus or minuses to their tone due to the signal being taken before or after their SS power amp? Certainly not me.

                        The amp is out the door, with the customer advised the simple solution to use the FX send as his line out, which works pre MAster Vol. I should have suggested this sooner, if I hadn't been too focused on what I was asked to do, add a line out.
                        It's weird, because it WAS working fine.....

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                        • #27
                          Indeed! Short of hacking into a crowded and complicated build topology it seems that the output is at least a convenient place to tap in. Plus there's the convenience of the outputs low impedance making the design of the line out a simple matter.

                          Randall, if the customer decides they REALLY want a line out after the master volume, or if it ever comes up again in the future, just take the dropping resistor of the circuit already discussed to 0V rather than the negative speaker terminal and it'll work fine.
                          "Take two placebos, works twice as well." Enzo

                          "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                          "If you're not interested in opinions and the experience of others, why even start a thread?
                          You can't just expect consent." Helmholtz

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                          • #28
                            DOH!!!
                            It's weird, because it WAS working fine.....

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                            • #29
                              I would have to respectfully disagree here that it does in fact make plenty of sense to pick the signal off the power output if only as purely a matter of convenience dealing with a SMT board. It's a modeling amp, all the "sound shaping properties" are done on a computer. Who plays a shitbox amp like this and worries about if their line out to the mixer for sound reinforcement at a dinner club is having slight plus or minuses to their tone due to the signal being taken before or after their SS power amp? Certainly not me.
                              Well you asked why and I gave you my reasoning.
                              Didn't say it's wrong or bad, just don't see any benefit over using the FX send or phones output.
                              The output impedance of op-amps is generally very low as they use heavy NFB, maybe lower than the source impedance of a voltage divider at the speaker out.

                              You could have avoided some trouble and discussion by providing a schematic from the start.
                              - Own Opinions Only -

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                              • #30
                                Originally posted by Randall View Post
                                DOH!!!
                                - - - is what I said after spending time offering solutions...

                                Oh well, on to better things! Gotta sort out my socks. They are in disarray, more than usual.
                                This isn't the future I signed up for.

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