Buffering explained

Discussion in 'Effects, Pedals, Strings & Things' started by tacoma5050, Oct 10, 2006.

  1. tacoma5050

    tacoma5050 Member

    Messages:
    88
    Joined:
    Sep 29, 2006
    I am confused :confused: about buffering, what it is ,what it does, why I may want it, why I may not want it, etc... Can some one explain it in a nutshell.

    Also, if my EFX loop specs are:
    Send:Impedance- 1K Ohm or greater.
    Nominal output level- -6 dbV, 0.5 V RMS

    Return: Impedance- 2 M Ohm.
    Designed input level- -6 dbV, 0.5 V RMS

    My EFX loop considered a high imped loop, right?

    As long as there are only high imped pedals in a high imped loop, then signal thru the loop remains a high imped signal, right?

    But if I had one low imped pedal in the loop, then the signal before the low imped pedal would be high imped, but the signal after the low imped pedal would becoame low imped and remain low impedence no matter what pedals followed that, right?

    I have a 2005 Gibson LP Studio with stock pickups, are those pickups high or low imped?
     
  2. drfrankencopter

    drfrankencopter Member

    Messages:
    1,338
    Joined:
    Feb 17, 2006
    Don't worry about keeping a high impedance path high impedance, or vice versa for low impedance. What you need to know is that for optimal frequency response, the input impedance of a device should be 10x or more the output impedance of the previous device in the chain. There are some exceptions (like power amps into speakers), but for modern line level gear this is pretty much the rule.

    A low output impedance means that the device can drive the next box in the chain easily, whereas a high output impedance may have a hard time driving a low impedance device (might get more distortion, and some change in frequency response).

    A buffer presents a high impedance input, and a low impedance output, and (ideally) no coloration or gain added to the signal. It makes it easier to drive difficult loads (including long cables).

    Your FX loop has a 1k output impedance, so it should be able drive pedals and most rack FX easily (some exceptions would be older pro-audio gear that uses 600 Ohm input impedance). With an input impedance of 2M the return is an easy load for devices in your loop to drive. In fact, you should be able to plug your guitar directly into the return and have good frequency response.

    Hope this helps....

    Cheers,

    Kris
     
  3. nashvillesteve

    nashvillesteve Member

    Messages:
    3,985
    Joined:
    Nov 22, 2005
    Location:
    Nashville, TN
    Does a booster pedal lower the impedance?
     
  4. drfrankencopter

    drfrankencopter Member

    Messages:
    1,338
    Joined:
    Feb 17, 2006
    Depends on what you mean by booster, and which impedance you mean, input or output.

    Something like an Eternity (which I just got) has a high input impedance (most if not all pedals will have a high input impedance so you can plug your guitar straight in), but it has a high output impedance, and suffers some low end and high end loss when driving a long cable (even 20 feet was enough to notice a difference to me). So, if you consider an Eternity to be a booster pedal, then I'd say the output is likely a higher impedance than is desireable. This is why the Eternity is best followed by a buffered pedal (or maybe an amp with a really high input impedance).

    The eternity is probably more the exception than the rule though, as most boost pedals will have a low-ish output impedance. I just saw a post saying that the Carl Martin pedals have a 200 ohm output impedance...they should be able to drive pretty much anything.

    Cheers

    K
     
  5. nashvillesteve

    nashvillesteve Member

    Messages:
    3,985
    Joined:
    Nov 22, 2005
    Location:
    Nashville, TN
    My Hotcake has a buffer, but if it's on most of the time as a clear, yet slightly gainy boost (gain at noon, but it cleans up easily since I play fingerstyle) , then there's no buffer in line, correct? I'm still short a buffer in the chain (though the outputs of my switching system have buffers with level control knobs, but it needs to be up front and not just at the end, no?)
     
  6. tacoma5050

    tacoma5050 Member

    Messages:
    88
    Joined:
    Sep 29, 2006
    I have a 2005 Gibson LP Studio with stock pickups, are those pickups high or low imped? What is there typical imped value?
     
  7. drfrankencopter

    drfrankencopter Member

    Messages:
    1,338
    Joined:
    Feb 17, 2006
    5-10k is normal for passive pickups....actives can be very low (150 ohm).

    Assuming your Les Paul Pups are passive it's safe to call them High Impedance.

    BTW, NashvilleSteve, your Hotcake can still act as a buffer even when the effect is on....what matters is the output impedance (which I don't know for a Hotcake).

    In my opinion it doesn't really matter where a buffer is placed (begining or end of the chain), what matters is that it go after any pedal that has a high output impedance or poor output drive capability.

    Cheers,

    Kris
     
  8. mild

    mild Member

    Messages:
    2,117
    Joined:
    May 11, 2006
    Location:
    Bottom of the World
    Kris,

    Are there any rules of thumb for the relation between effect types, and impedance values?

    Jono
     
  9. amz-fx

    amz-fx Supporting Member

    Messages:
    1,383
    Joined:
    Oct 18, 2005
    Location:
    USA
  10. Electric I

    Electric I Member

    Messages:
    3,070
    Joined:
    Sep 17, 2005
    Handy stuff to know. Thanks
     

Share This Page