So... if a pedal is "true bypass" does it still drain the battery when not in use?

Discussion in 'Effects, Pedals, Strings & Things' started by m@2, Jul 18, 2008.

  1. m@2

    m@2 Member

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    I'm hoping I don't need to unplug my pedals to save the 9V batteries... talk to me TGP. Can I leave my pedal board alone between sessions? (example: MXR CC, or phase 90 type pedals)
     
  2. dividedsky

    dividedsky Member

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    Sorry, it still drains the battery as long as there is a plug connected to the "input".
     
  3. pbone

    pbone Member

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    That's true of any pedal, true-bypass or not.
     
  4. m@2

    m@2 Member

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    aw, bummer. the pedal board is so clean without all the adapter cords

    oh well... looks like i gotta buy a couple more adapters : (

    thanks for the info
     
  5. neil99

    neil99 Member

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    yup, what he said. You could get some dummy plugs and put them in the 9v input while not in use, kind of a pita though. This will break the connection to the battery.
     
  6. todaystomorrow

    todaystomorrow Member

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    +1... not nearly as much as a PITA as unplugging them though. I used to do that with a fuzz of mine.
     
  7. Waxhead

    Waxhead Member

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    I wish you guys would stop polluting the environment with batteries.
    There's no need to use them. Get a power brick and you'll never have to plug and unplug stuff everytime you wanna play. Plus, within a year you'll be saving money too :AOK
     
  8. StompBoxBlues

    StompBoxBlues Member

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    And you won't have to mess around with wondering which ones are going bad, etc. have them drop out in the middle of a song, etc. The only think I tend to use batteries for now are fuzzes (especially reverse polarity ones).

    The dummy plug works well, but how much easier just to have a power supply.
     
  9. dancehall

    dancehall Member

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    Can someone explain why this would be? I thought the whole point of true bypass was a direct physical connection from the input jack to the output jack without any connection to the circuitry of the effect. Why would that drain the battery?
     
  10. rollo greb

    rollo greb Member

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    It's my understanding that most pedals use a stereo jack for the input, so as long as you unplug the cord from the input, it won't drain the battery.

    Edit: Oops, reread the post. Yeah, it can be a pain having to unplug the cords.
     
  11. amp_surgeon

    amp_surgeon Member

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    Yes, true bypass does provide a direct connection between the input and output, and there is no SIGNAL connection to the effects circuit on either end.

    Most pedals don't have an on/off switch to turn off the juice to the effects circuit. In most cases, you DON'T want the juice removed from the effects circuit when the pedal is in bypass mode. If the effects circuit had to be powered up every time you switched from bypass to effect then there would be a noticeable delay while the effects circuit powered up. Most effects circuits will also make some noise when they're powering up. You don't want either of these things happening during a performance, so the vast majority of effects keep the power on even in bypass mode.

    Of course, you don't want the effects circuit powered on when you're not using your gear, so most pedal makers provide an interlock circuit that will remove power from the effects circuit when it's disconnected. They do this by using a tip-ring-sleeve jack on the input (a regular stereo type jack). They connect the ring to the negative side of the battery. When you put a mono plug into the jack it shorts the ring to the sleeve, thereby grounding the negative side of the battery terminal and powering up the effects circuit. If the pedal has an external power jack then the positive side of the battery will be switched through the power jack. You can disconnect the battery by either pulling the plug from the input jack, or inserting a plug into the power jack.
     
  12. yeahyeahyeah

    yeahyeahyeah Supporting Member

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    :agree

    Most pedals will sound better when used with a power supply. Only fuzz face style pedals will sound better with a battery because the circuit is so bad (in a good way) that the battery becomes part of the sound. Most effects however, are designed to run on at least 9 volts. When you loose voltage, you loose headroom and that can make good pedals sound really crappy.

    Imagine your signal as a pure sine wave. In the middle of the wave where the peaks cross over and become the troughs there is a line called the normal. The normal is 0 volts, when the signal is below the normal it is negative, when it is above the normal it is positive. The signal is AC.

    The power supply is DC and if we only have 9 volts to work with that means that the signal can only go +/- 4.5 volts away from the normal. So 4.5 volts is what we call the power supply rails, because any signal that goes above 4.5 is exceeding the power supply and therefore won't be reproduced. in other words that is HARD clipping.

    When your voltage drops below 9 volts, your power supply rails are also dropped, meaning that the pedal will not have as much headroom before the signal is squashed.

    Power adapters on the other hand, they regulate your power and give you a consistent voltage every time. Consistent voltage, consistent sound quality. No hassle.

    So now that I've explained myself let me repeat, there is no advantage to using batteries.
     
  13. m@2

    m@2 Member

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    bought a power supply today. no more batteries
     
  14. Waxhead

    Waxhead Member

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    Good work mate :banana

    - now the rest of guys. Time to get with the program eh !!!!!!!!
     
  15. amp_surgeon

    amp_surgeon Member

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    This is all basically correct, except for the +/- 4.5V stuff. That would only be true if the input power were being split into bipolar power. In most pedals this isn't the case. The components don't operate on +/- 4.5V. They operate on 0 to +9V. This means that the signal has to alternate around some voltage above 0 volts if the negative half cycles aren't going to be clipped.

    There is usually a resistive ladder circuit on the input of each stage that sets a DC offset voltage for the AC signal. If the top of the ladder is connected to +9V, the bottom to 0 volts (usually ground), and both resistors are the same value, then the AC signal would alternate above and below +4.5V. In other words, a 2V peak-to-peak signal would alternate between +2.5V and +6.5V.

    Designers also have to consider the operating point for each stage. They select the amount of DC offset needed according to the point on each stage's response curve where they want the signal to alternate without clipping (or perhaps WITH clipping, if that's the intention of the effect).

    The DC offset coming out of one stage may not be the DC offset needed for the input of the next stage. For this reason a capacitor will usually be inserted to block the DC offset from the previous stage, and allow the AC signal to get through, and the input of the next stage will have it's own ladder circuit.

    The signal coming in and going out of an effect unit IS supposed to alternate equally above and below 0 volts, so there is usually a DC blocking capacitor on both ends.

    About the headroom - it's impossible to get a full 9 volts of AC swing out of any circuit operating on 9VDC. Every PN junction and resistor in the current path of the final stage is going to drop some voltage. Even if the final output stage were a single transistor with the emitter and collector connected to +9V and ground (assuming a common emitter configuration) it would still drop about a volt and a half, giving a maximum voltage swing of 7.5 volts peak-to-peak. Very few effects pedals drive any stage all the way to the power supply rails. It just isn't necessary. The input and output signals are generally less than 1 volt peak-to-peak. However, reducing the power supply voltage CAN reduce the gain and increase distortion.

    Also, while it's true that all pedals will perform more consistently with a stable power supply, some people just like the sound a pedal makes when the voltage sags like it would do with a weak battery. This doesn't just apply to Fuzz Face type circuits. Some pedal power supplies have a sag control for this reason.
     
  16. StompBoxBlues

    StompBoxBlues Member

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    Well put, and what some people (even that talk about biasing an amp) may not know is it is the same thing there.

    Meaning...the tubes aren't running AC, biasing is also setting that midway to the top point, where the signal can fluctuate above and below some set point, then the DC component is removed to become true AC at the output. Tubes only "flow" in one direction also...going from zero (but not minus) to more flow of current...

    I think the water model works great to explain it. A faucet can control a much larger flow of water, so if you wanted to play something with a faucet...you can't make the water go BACK up, you would have to have some point of flow you could agree is zero, then add or subtract water flow to make it "seem" to go positive and negative.

    which could be attached to a big clapper......:eek: or something that would just react to changes in flow...okay, it falls a little apart at the end..
     

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