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Screaming Bright Switch Cap??? - 1974 Fender SF Twin Reverb Master Volume Push Pull Switch

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  • I found that there is actually no convention/standard regarding speaker phasing (electrical/acoustical). Some speaker cones move outward when applying a positive voltage to the + terminal and some move inward even within the same brand. Speaker phase probably only matters if you add an extension cabinet.

    But I would reverse the speaker wiring to avoid guesswork and because the old solder joints don't look very reliable.
    - Own Opinions Only -

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    • thank you, man!
      I’m re-wiring for all the reasons above + these connections are clearly not original (plug has been changed and soldering does not look great as you’ve indicated)

      Comment


      • It seems both speakers are in phase with each other and that's the most important thing. As Helmholtz noted, there is no standard for speaker phase. But though he mentions that sometimes same brand speakers exhibit different phase, I haven't seen this. At least not the way I read it. That is, same speaker from the same company, but inverse phase to others of it's type. BUT!.. There is one exception, and that would be Jensen. Helmholtz will correct me if I'm wrong, but I've read in many places that older Jensen speakers were inverse phase compared to their contemporaries as well as what is the modern standard. So perhaps even the modern standard for modern Jensen models. So a P12R from 1965 might be in opposite phase from a P12R manufactured today. And...

        This could have been the motivation for how your amp was wired. Because there are some mojo hunters out there that believe recreating the "original" phase by wiring the non inverse phase speakers in inverse phase might buy them the missing tone link.
        "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

        Comment


        • Originally posted by Chuck H View Post
          As Helmholtz noted, there is no standard for speaker phase. But though he mentions that sometimes same brand speakers exhibit different phase, I haven't seen this. At least not the way I read it. That is, same speaker from the same company, but inverse phase to others of it's type. BUT!.. There is one exception, and that would be Jensen.
          There was a brief period early 2000's when the "new" Jensen / Recoton speakers had polarity indicators reversed. Positive voltage to the + terminal sucked the cone into the frame. They got over that quickly, but some are out there.

          Also, JBL for many years had red terminal negative. One fellow I knew called 'em up @ 1980 and asked "WHY?" Answer "We've always done it that way." Curiously, not too long afterwards, they reversed and black terminal was negative. Grrr... I lost track since then, and polarity test every JBL I run across. As one should with Recoton Jensens.

          I'm sure there are other aberrations out there.
          This isn't the future I signed up for.

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          • thanks guys, this is quite an interesting fact. I have never actually investigated this subject in the past and didn’t know there were other options. every time i would hook a speaker to an amp i would (in case of doubt) test the speaker with a battery to confirm outward cone movement and connecting the identified (+) speaker terminal with the TIP of the speaker plug.

            what surprised me is that the tip of my speaker plug was connected to the (-) speaker terminal. as it’s clear these connections are not original i am reversing them back to (what at least i consider) standard

            i have checked with a battery that the (+) and (-) terminals of the speakers move the cones in the way i expected (outwards with battery positive pole connected to positive speaker terminal)

            if it is of any interest my speakers are:
            Jensen
            12”
            1974
            ceramic magnet
            alnico / ceramic voice coil
            made in italy

            (C12N 2200430)

            Comment


            • That is, same speaker from the same company, but inverse phase to others of it's type.
              I actually found this with Vox Celestion Silver Alnicos from the 60s. Four of them (2 reconed, 2 original) had inverse phase and magnet polarity (being the reason for inverse phase) w.r.t. the majority.

              Also saw inverse phase with some JBL and Kendrick speakers. Jensens I don't remember (did the tests around 20 years ago).

              The more common or "normal" phase seems to be positive voltage to + makes cone move outward. Maybe there is actually some standard meanwhile.
              - Own Opinions Only -

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              • it might be a standard, word of mouth or a psychological effect
                in any case, my logic is that if I hit the speakers with a guitar chord I want the air to be pushed towards me instead of being sucked in
                what could also make sense is that if the speaker cones are pushed inwards there could be more chances of some physical friction within the speaker components
                I remember the anomaly being called “farty speaker” at some point
                in any case, I have reverted the speakers polarity to the “standard” and will be reverting the voltage divider to the sole 1 M resistor and removing the 560 pF + 5 K resistor altogether. will give the amp a good push after this and let you know.

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                • in any case, my logic is that if I hit the speakers with a guitar chord I want the air to be pushed towards me instead of being sucked in
                  what could also make sense is that if the speaker cones are pushed inwards there could be more chances of some physical friction within the speaker components
                  As guitar signals are AC not DC, polarity is reversing at least 80 times per second. It hardly makes a difference if the cone moves out or in for the first few milliseconds. If so, guitar PUs with different phase/polarity would sound different. There is no standard for PU phase either.

                  I built a speaker phase reversal switch box and couldn't hear any difference.
                  Last edited by Helmholtz; 10-06-2019, 05:32 PM.
                  - Own Opinions Only -

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                  • A speaker cone is driven both directions by applied AC. It's alternating current. That's why the DC battery test will move a cone forward OR backward depending on the polarity of the test. That is to say that a speaker wired one way or the other doesn't push air toward you or suck air away from you. Either wiring does both in equal measure. However...

                    Your playing circumstances can be sensitive to phase. Sitting in front of an amp is different from facing away from the amp when it's on stage. Ever notice how players chasing feedback and acoustic interaction turn and move to get the affect they're after? I encourage anyone here to try this for themselves. Hook up a switch to invert speaker phase, set up your amp and A/B the two polarity options (EDIT: As per Helmoltz post, do this at some volume level that imparts physical interaction between the instrument and the amp). That isn't to say that one way will be better for everything, but one way might be better for, say, just sitting in front of the amp and noodling rather than playing live.
                    "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

                    Comment


                    • Originally posted by Helmholtz View Post
                      The more common or "normal" phase seems to be positive voltage to + makes cone move outward. Maybe there is actually some standard meanwhile.
                      That's supposed to be the standard, quoted in several texts like Sound System Engineering by Don & Carolyn Davis. However, as we have found out, there are those who "dare to be different." Or make a misteak in manufacturing - or sometimes reconing - charging magnets backwards or using reverse wound voice coils. Maybe even mis printing the connector tab. It happens.
                      This isn't the future I signed up for.

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                      • duly noted!

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                        • Originally posted by Chuck H View Post
                          Your playing circumstances can be sensitive to phase. Sitting in front of an amp is different from facing away from the amp when it's on stage. Ever notice how players chasing feedback and acoustic interaction turn and move to get the affect they're after? I encourage anyone here to try this for themselves. Hook up a switch to invert speaker phase, set up your amp and A/B the two polarity options (EDIT: As per Helmoltz post, do this at some volume level that imparts physical interaction between the instrument and the amp). That isn't to say that one way will be better for everything, but one way might be better for, say, just sitting in front of the amp and noodling rather than playing live.
                          Facing towards or away from the speaker has nothing to do with speaker polarity, and everything to do with the human ear being more sensitive to sounds coming from in front of the head as opposed to sounds coming from behind. The typical stage "back line" volume level is - almost always - loud & obnoxious to the audience, plus the FOH mixer who's trying his best to get vocals heard over that blare. (A perpetual problem I've had to face zillions of times.) In situations where there's enough space and equipment and personnel to mix back line speakers into wedge monitors, or even better, in-ear monitors, there's a much better chance of coming up with an overall quieter AND well balanced mix.

                          With the guitar feedback trick, just like a microphone, many guitars will start up a howl, often involving the strings, when pointed at the speaker from only a couple feet away. A phenomenon, when it's kept under control, sometimes used to good effect by the guitarist, but when it's unexpected - not. Whereas, with the player's body between the guitar and speaker, and pickups pointed away from the amp, less chance of setting up that feedback loop. Polarity of the speaker or pickup again has little to nothing to do with the fb loop. Instead proximity, directionality and frequency response are the guiding factors.
                          This isn't the future I signed up for.

                          Comment


                          • Carlos Santana use to have places marked on stage that gave him his famous sustain during sound check. Every working guitarist has done gigs where they just couldn't get their sustain and feedback mojo working (with much stomping and gnashing of teeth). I'm sensitive to your perspective as a sound guy, but any unexpected feedback for guitarists is most often due to an equipment failure. Microphonic pickups. Otherwise I don't hear guitarists complaining too much about their guitar communicating with their amp in a more musical, sympathetic way. Acoustic guitars being an exception. I've had 'em almost shake apart when some noob walks away from their instrument without turning it down. Anyway...

                            I've done the same test as Helmholtz with a speaker polarity switch. At harmonic feedback levels of gain and/or acoustic interaction levels of volume it absolutely made a difference in my tests. Since this was my experience it's impossible for me to dismiss. Being as I know it actually happened and all.
                            "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

                            Comment


                            • At harmonic feedback levels of gain and/or acoustic interaction levels of volume it absolutely made a difference in my tests.
                              I have no reason to doubt your results (didn't perform this experiment myself). The desirable(?) positive feedback requires to the PU signal to be/oscillate in phase with the sound.
                              But...

                              Carlos Santana used to have places marked on stage that gave him his famous sustain during sound check.
                              ...with a sound wave phase not only changes over time but also with distance from the source (speaker). E.g. for a 1kHz soundwave phase reverses about every foot distance from the speaker, thus turning positive into negative feedback at this frequency. So changing the players position determines if sustain of the note played will increase or decrease.

                              In other words, with reversed speaker polarity, the places of constructive feedback will be at different locations.
                              The same holds for PUs having reversed signal polarity.
                              Last edited by Helmholtz; 10-07-2019, 03:39 PM.
                              - Own Opinions Only -

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                              • Hello guys, I'm sorry if I sometimes derail the conversation and we end up chatting about "mojo hunters" and Santana feedback / sustain spots but I also find that part of the conversation interesting. Thank all for you input.

                                Now, back to the subject of the problem here (let's call it "farty noise in loud passages with reverb tank connected") I decided to take a step back reversing the circuit to a previous known as faulty state (reproducing the anomaly) before starting the mods proposed. And... I could not reproduce the failure. This is good news, but also bad news as I cannot understand why. Let me list all the variables.

                                1) Speakers rewired (white cable is now + to + terminals and black is - to -)
                                2) Polarity reversed (+ DC applied to + plug terminal moves speaker cones outwards)
                                3) New Speaker Plug and cable (needed a longer cable to hook the cabinet to the amp head)
                                4) Eliminated voltage divider and reverted it to the 1 M Ohm resistor (see image below)
                                5) eliminated the 5,000 Ohm + 560 pF between V3 1-6 and point "A" (red Reverb transformer primary) - see image below



                                6) the Reverb tank is out of the enclosure (something that was also done in the past)



                                The current layout is shown below (distance from the enclosure to the amp head is about 50 cm / 2 ft, reverb tank is partially below the amp head).

                                I've tried different guitars (humbucker, single coils), going to 10 with the CHANNEL VOLUME, TONE and MASTER VOLUME settings.
                                Connected and re-connected the Reverb tank several times.

                                I was not able to reproduce the failure.

                                Decided to reverse the speakers polarity again and still no failure reproduction.

                                I'm starting to think this is pure witchcraft... :/

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