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MXR M87 Bass Compressor Issue

Discussion in 'Effects [BG]' started by Cameron storey, Nov 8, 2018.

  1. Cameron storey

    Cameron storey

    Nov 8, 2018
    Hello. I've recently been having issues with my pedal in regards to not getting any gain reduction showing up on the LED's or if they do illuminate (usually half way in the green) the reduction does not vary as you'd expect . The pedal is active with the blue led showing up on 9v battery, mains supply and dc power bank.

    My set up atm is Yamaha TRBX504 (active/passive) ---> Boss TU-3 ---> MXR M87 ---> Green rhino ---> Boss Geb7 ---> fender rumble 200.

    I have changed cables countless times and had the pedal direct to the bass and amp along with trying every possible setting on the pedal but nothing changes.

    I have read plenty of forums on here saying to have the input at max on the pedal and bass with the output on low, this also does not help.

    I noticed there is a small on/off switch on the circuit board but it doesn't seem to affect anything? What is this?

    Any one got any ideas on how to sort this without spending mad money on repairs? I'm assuming it's my error as the guy I bought it off claims it worked fine for him last week.

  2. geolikezik


    Mar 13, 2016
    I had both MXR M76 and M87 and the leds always responded as expected with the input knob between 60 and 100% depending on the bass passive/active.

    If you already tried the bass straight into the M87 powered from main and with the input knob fully clockwise and the leds still misbehaved then either you got an amazingly low-output bass or the pedal is defective.

    Easy to check, use another bass or guitar or even a keyboard to check whether the leds behave differently, that should tell you who the culprit is...

    Hope it helps
    bongomania likes this.
  3. morse


    May 27, 2011
    Mine had completely gone haywire. Led light at full without the pedal engaged. Volume slowly drops by itself when pedal was engaged. At max input and output, volume was low. Contacted MXR, told me to work with local dealer (Singapore). The local dealer was very helpful but could not resolve the issue, and my sense is that MXR was not very supportive. Seems no response from them. So, my pedal is a piece of junk. Read and heard that there are problems with this pedal - led light not working as intended, volume was erratic. Think mine has got the worst. Has another problem with another MXR pedal too. Will post separately. Staying away fm MXR.
    Last edited: Mar 20, 2019

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