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  • Twin Reverb tremolo

    I notice on two twin reverbs I've had, I switch on the tremolo & a big volume drop happens: annoying/ I'd say maybe 2/3rds vol? (maybe as much as 1/2 I'd say). I recall a similar vol drop on a deluxe reverb I built too. Is it possible to adjust volume 'up'?

    Also the intensity I find not quite strong enough @ max: can this also be 'upped'? I have a vox AC15 TBX with a stronger tremolo & very small vol drop switched on.. I realise a totally different circuit, but even so..

    thx Sea Chief.

  • #2
    I think it’s mainly down to the particular characteristics of the light dependant resistor (LDR) used in the opto coupler (aka trem bug). They aren’t precision devices and as they use cadmium, a now banned substance, like tubes they’re a legacy product we should feel lucky is still available at all. All you can do really is buy a couple and use the better one.
    Occasionally too much ambient light can get past the bug sleeving and prevent the LDR ever properly reaching its ‘dark’ resistance. So try closing off the ends of the bug sleeving (where the neon and LDR legs emerge) with opaque tape, eg regular black insulation tape.

    If it’s still not acceptable after that, your best option may be to build / buy a trem fx pedal.
    My band:- http://www.youtube.com/user/RedwingBand

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    • #3
      Hi pdf.. I didn't know these bugs were so fallible as it were. Is your reply though answering the volume drop issue (my main thing annoying me), &/ or just the intensity thing?

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      • #4
        Originally posted by Sea Chief View Post
        Hi pdf.. I didn't know these bugs were so fallible as it were. Is your reply though answering the volume drop issue (my main thing annoying me), &/ or just the intensity thing?
        It could address both. The "bug" or "roach" is comprised of a LDR (light dependent resistor) and a lamp. The LDR changes resistance and variably grounds the audio signal (before the mixing stage for the two amp channels) relative to how much light falls on the resistor from the lamp (or any light source). The lamp is operated by the oscillator circuit so that it's intensity goes up and down.

        With this sort of tremolo the signal can only be made weaker. If some light other than the lamp is entering the bug that may serve to partly ground some signal even at it's highest intended output. I don't think this is the case though because I would expect that to affect the dry signal even with the oscillator switched off, which is the dry signal level. More likely to my mind is that the lamp in the bug is either not shutting off completely enough and/or quickly enough to allow the signal the reach it's maximum, not partially grounded condition between oscillator cycles.

        I've never played with one of these circuits but looking at their operation I would expect just the behavior you describe. Soooo...

        There are a couple of possible solutions. One is to buy a couple of bugs and see if you get better behavior from the new ones, They don't last forever and not all neon lamps are created equal. Since you have this trouble with all three of your bug system tremolo amps I don't think you would find enough satisfaction with this. Perhaps some improvement, but probably not enough for you.

        Get a pedal like pdf64 suggested and just accept that you don't care for the on board tremolo of these amps. No rule says that just because it's an on board effect that it has to be loved by everyone.

        Some builders have experimented with LED's for the bug circuit. LED's would be faster and more on/off than the neon bulb. This would probably cause less attenuation of the high volume sweep and a faster transition between high and low volume sweeps. More choppy? More on/off for the signal? This may be to your liking. Some players want a very smooth volume transition from low to high signal levels for their tremolo. Others prefer the more staccato on/off effect. I don't know if anyone is selling LED trem bugs but there are several threads about how to do it on the misc. forums if you search *trem roach LED*.

        Something to consider. Perhaps your oscillator is not allowing the bug lamp to reach an 'off enough' and 'on enough' state for best operation. Though I'm not sure how you should modify the circuit to achieve more of both states. So this may come up.

        Also worth considering is bias vary tremolo circuits. These circuit affect the bias of the power tubes or sometimes even a preamp stage by decreasing and increasing the bias, and therefor the amplification of the signal. These circuits have less of a tenancy to decrease overall volume because it doesn't strictly reduce signal. It also increases signal. You don't notice the increase as obvious because of the median between high and low levels. I expect this is how your Vox tremolo works, but I don't know. I think it would be prohibitive from a difficulty level standpoint to try to convert your bug circuit amps to this kind of circuit though. There's also the consideration that bias vary tremolo (applied to power tubes) is much better for amps that don't operate at higher plate voltages like your Twins.

        NOTE*** I used the word tremolo instead of vibrato even though some posters may use vibrato to refer to the Fender moniker for the circuit. And some may use the words tremolo and vibrato interchangeably. It does not matter for the purposes of this discussion since we all know circuits in question.
        "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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        • #5
          Tremolo is up/down change in volume, vibrato is up/down change in pitch. Leo had that wrong.
          It's weird, because it WAS working fine.....

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          • #6
            Originally posted by Randall View Post
            Tremolo is up/down change in volume, vibrato is up/down change in pitch. Leo had that wrong.
            Twice

            Attached Files
            "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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            • #7
              Yes but it doesn't matter.. he wasn't a guitar player after all (or a musician of any sort afaik) so its understood I think he just put a wrongly or oddly chosen word on channel 2.

              Surely just the US culture of just 'call X what the hell you want/ its a free country' so no-one mentioned to him at the time vibrato is actually the wrong word, I think.

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              • #8
                So its just a Q then (probably after the strat pic^) he just got the words swapped wrong.. vibrato should be on guitar tremolo on amp. Maybe fully aware, after s'one pointed it out maybe, & he thought it a marketing ditty to leave be who knows.

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                • #9
                  Yes, my previous post was in regard of both issues raised. There’s probably some degree of interrelation between them.
                  My band:- http://www.youtube.com/user/RedwingBand

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                  • #10
                    tremolo on amp.
                    Not generally. Some amp circuits achieve both, vibrato (pitch shift, FM) and tremolo (AM). E.g. Vibrasonic 5G13 (or Vox AC30).
                    Last edited by Helmholtz; 12-11-2019, 05:32 PM.
                    - Own Opinions Only -

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                    • #11
                      That effect of volume drop when activating the tremolo I have only found it with very old defective/degraded or poor quality optocouplers. The volume drop is usually also associated with the low intensity of the effect.
                      In USA you can find them in CEdist and in Europe, in Tubetown (Germany). I have used both and it is very possible that they have the same origin. Comparing them with the optocouplers that Fender has used in the reissues until six or seven years ago in Europe its maximum effect is slightly less (around 10-15%) but it is not relevant and goes unnoticed.
                      They are the ones I use for many years and I have never encountered different behaviors. Unlike reverb tanks...

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                      • #12
                        Originally posted by Helmholtz View Post
                        Not generally. Some amp circuits achieve both, vibrato (pitch shift, FM) and tremolo (AM). E.g. Vibrasonic 5G13 (or Vox AC30).
                        No, but my point was (& thread to do with only) twin reverbs: fender. I have a vox AC15 with tremolo written 'correctly' on its control panel & footswitch.

                        I was just considering why fender labelled it wrong.

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                        • #13
                          Originally posted by Pedro Vecino View Post
                          That effect of volume drop when activating the tremolo I have only found it with very old defective/degraded or poor quality optocouplers. The volume drop is usually also associated with the low intensity of the effect.
                          In USA you can find them in CEdist and in Europe, in Tubetown (Germany). I have used both and it is very possible that they have the same origin. Comparing them with the optocouplers that Fender has used in the reissues until six or seven years ago in Europe its maximum effect is slightly less (around 10-15%) but it is not relevant and goes unnoticed.
                          They are the ones I use for many years and I have never encountered different behaviors. Unlike reverb tanks...
                          That's interesting- would pro amp makers be able to test them somehow & choose what 2 out of 10 are vg, & discard the rest? or would they only buy 2 of the 10 I wonder.

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                          • #14
                            Originally posted by Sea Chief View Post
                            That's interesting- would pro amp makers be able to test them somehow & choose what 2 out of 10 are vg, & discard the rest? or would they only buy 2 of the 10 I wonder.
                            They'd just buy the two and then cuss and spit and send one or both back if they didn't work properly

                            I've been known to buy two reverb pans when I needed one just because I've had trouble in the past. In that event I actually DID end up with a third tank before it was over. But how much modern reverb tanks SUCK BALLS isn't the point of this thread

                            I suppose you've got very little to lose by buying a new trem roach just to see if it helps. Ten bucks plus shipping.
                            "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


                            • #15
                              Some amp circuits achieve both, vibrato (pitch shift, FM) and tremolo (AM). E.g. Vibrasonic 5G13
                              Does it really shift pitch? Seems to me it splits the audio into highs and lows and separately trems them. But I don't see any frequency change.
                              Education is what you're left with after you have forgotten what you have learned.

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