MXR M87 Compressor Input / Output Controls

Discussion in 'Effects [BG]' started by CPplaysBASS, Apr 22, 2012.

  1. CPplaysBASS


    Mar 17, 2007
    Hi all,
    Hope some other M87 owners can help me figure out something here.

    Based mostly on my positive experience with the 5 other MXR pedals on my large board, I bought not one, but two M87 Bass Compressors (also have a smaller board).

    Now when I first got them, I could have sworn the the input worked similar to the compression or threshold knob on a BBE OptoStomp ... that is, as you turn the input on the M87 clockwise, you have to increase the output to compensate for the compression effect and maintain unity.

    Yesterday, on the small board (powered by One Spot), I noticed the input actually increases the output volume as I turn it clockwise. It's like it's an input and output all in one?!

    More of "gain reduction" LEDS light up as they should, and all the other controls are behaving as they should.

    I just thought increasing the "input" would impact the compression threshold only with a perceived volume loss ... not actually increase total volume similar to what the output volume is doing.

    When the input is completely counter clockwise, there is no output at all ... no signal. I would have expected that having the input totally counter clockwise would be the same as just having the pedal off in bypass mode ... there would still be a signal, just not compressed at all.

    The one on my large board (Voodoo PPII) is the exact same so I'm thinking maybe it's not a fault, but since I bought both at the same time and they are from the same batch, I'm unsure and a bit paranoid since new products by any company always seem to have bugs that need to be worked out.

    In a nutshell, my question to other M87 owners is, does your overall volume increase as you turn your INPUT clockwise??

    Many thanks in advance!! Cheers!!
  2. The input means actual input gain, so it acts just like the preamp volume on an amp. You could think of it as the opposite of threshold as far as compression settings go.
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    +1 the MXR comp has all the knobs needed to set compression levels, as well as input, (or make-up_ gain. Set it to unity, with your comp levels set, so the pedal is the same volume on or off.
  4. CPplaysBASS


    Mar 17, 2007
    Many thanks!! That explanation makes a lot more sense to me than how it's stated in the manual ("INPUT adjusts the input signal level relative compression threshold and sets the amount of gain reduction").

    A bit of a learning curve with it compared to the OptoStomp, but really happy with the M87 .. especially now that I know all controls are working as they should!:smug:
  5. CPplaysBASS


    Mar 17, 2007
    Thanks for the reply.

    I've been using the input to control the gain reduction, as noted in the LED display, and using the output to set for unity. That works for me, but do understand there is a balance between "input" and "output".