847 True bypass questions

Discussion in 'Effects, Pedals, Strings & Things' started by slegros, Mar 2, 2008.

  1. slegros

    slegros Member

    Sep 9, 2007
    I'm considering doing the true bypass mod to my 847, but have read conflicting info on whether or not its necessary to swap one of the resistors on the board to balance the on/off volumes. Is it necessary to swap the resistor? How far off are the on/off volumes when the DPDT switch are installed and the resistor isn't changed? Thanks in advance!
  2. guitbeef

    guitbeef Member

    Apr 10, 2007
    Different pedal of course, but I just true-bypassed an early 90's Crybaby, and I felt it was necessary in my case to swap the resistor. My suggestion would be "first things first", and mod it for TB first, then plug it back in to double check your work and also to let your ears be your guide as to whether you need to make up the difference in overall volume.

    Edit: to answer one of your questions FWIW in my case with the Crybaby the volume drop wasn't drastic enough that I absolutely couldn't deal with it, but then again I'm a "volume pedal as master volume, post dirt pedals" kind of guy and the way I run my stuff I can make up the gain, but I felt it would be good for me to go the extra step, plus it's kind of awkward for me to deal with two of those pedals at once.
  3. dk123123dk

    dk123123dk Member

    Sep 15, 2007
    I did the mod to a 847, and I find there is no difference when the wah is on. When the wah is off it is MUCH better. I highly recommend this mod.

  4. walterw

    walterw Gold Supporting Member

    Oct 16, 2006
    did the TB mod years ago (big improvement), and never noticed any volume drop. recently became aware of, and did, the resistor swap, and noticed a slight increase in volume. not a big difference either way.
  5. mistercoffee1

    mistercoffee1 Member

    Apr 19, 2007
    Orange County, CA
    Use your ears as a guide. The difference isn't that drastic.
    If your pedal sounds a little quieter when engaged (prior to true-bypassing), then it's probably a candidate for that mod. Some need it, some don't.
  6. stinkfoot

    stinkfoot Member

    Jun 20, 2004
    Uppsala, Sweden
    The level of the effect itself doesn't change at all when modding to TB. What happens is that the TB mod removes the signal loading in bypass mode, making the bypass signal stronger (which makes the effect appear to have lost signal level). In the GCB-95 (and V847-A), the input to the circuit is buffered, so the bypass signal doesn't lose as much as with the V847 (and pre-1990 GCB-95) and the effect level in them is therefore slightly raised from the factory.

    This means that if you mod a V847, you may want find you want to raise the output level slightly. If you mod a GCB-95, it will probably not be as much of an issue (as that model already has a slightly higher output level). I agree with the earlier posters - do the TB mod first, try it and then see if and how much you want to adjust the signal level.


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