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Viewing 8 posts - 1 through 8 (of 8 total)
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  • October 6, 2009 at 3:04 pm #79089
    Ashman
    Participant

    Hello,

    I purchased a second-hand Metal Muff on ebay a month ago and today started experiencing some difficulties which I hope someone reading this can help me with!
    The Setup:
    Ibanez JS guitar -> DS1, Metal Muff pedals -> Crate amp

    The Problem:
    The MM is outputting very low volume when in bypass, almost with no regard to how high the amp is turned. It sounds like the guitar and amp are turned to 1! When the Distortion is engaged it just sounds aweful, very tinny and thin even with all the knobs maxed out.

    Attempted solutions:
    The first thing I tried was to replace all the cables – no difference.
    I took the Metal Muff out of the chain and found the ds1 to be working properly – so the issue is obviously not with the guitar, amp, or cables.
    I normally operate my pedals with a 9V battery. Thinking it might be a battery problem I Opened the case and replaced the battery. While it was opened I checked for any obviously loose/burned soldering and found none.
    My final test was to remove the battery altogether and use an Ibanez power supply (minus in the center, Plus around). The MM is showing power but I’m still getting this weak, dead sound.

    Any help or suggestions greatly appreciated!
    Regards,
    Ash

    October 6, 2009 at 6:02 pm #102063
    The EH Man
    Moderator

    First off, excellent job with the troubleshooting. I think you pretty well covered everything you could do w/o being a tech.

    My initial thought is that an op-amp has gone bad in the unit. At this point it should be taken to a tech for repair unless you’ve got some more troubleshooting/repair skills.

    July 27, 2010 at 3:48 am #110500
    Turco
    Member

    Hi Ashman, maybe it´s a little too late for the response but I´ve received from a friend an MM with the same problem and I´ve found that was the Q7 transistor (I think this is the one that routes the signal in and out the effect, not sure because I have no schematic to check at, can´t find it all over the net) failing.
    If you open the MM backcover you will find this tiny SMT transistor near the input jack, almost sorrounded by R55, R57 and D3 (MMBD4148SE), all SMT´s. This transistor is a FET N Channel switch and you can repleace it with the same MMBF4393 (SMT), or an PN4393 (TO-92 packaging, bigger, you have to re arrange the leads to fit it).
    I was unable to find either the MMBF4393 nor PN4393 over here so I have repleaced it with an MPF102 (TO-92, fitting it and crossing 2 leads) and it works great.
    Hope this helps.

    Best Regards,
    Turco.

    July 27, 2010 at 10:01 am #110476
    Ashman
    Participant

    Hey Turco,

    Thanks for the detailed reply! I had given up on fixing this myself ages ago and sent it into EH for repair. The unit is working perfectly now.
    I hope your solution helps someone else with a similar problem!

    Ashman

    July 7, 2012 at 9:56 am #117856
    JaviCAP
    Member
    Quote:
    Hi Ashman, maybe it´s a little too late for the response but I´ve received from a friend an MM with the same problem and I´ve found that was the Q7 transistor (I think this is the one that routes the signal in and out the effect, not sure because I have no schematic to check at, can´t find it all over the net) failing.
    If you open the MM backcover you will find this tiny SMT transistor near the input jack, almost sorrounded by R55, R57 and D3 (MMBD4148SE), all SMT´s. This transistor is a FET N Channel switch and you can repleace it with the same MMBF4393 (SMT), or an PN4393 (TO-92 packaging, bigger, you have to re arrange the leads to fit it).
    I was unable to find either the MMBF4393 nor PN4393 over here so I have repleaced it with an MPF102 (TO-92, fitting it and crossing 2 leads) and it works great.
    Hope this helps.

    Best Regards,
    Turco.

    Hi Turco!

    Two years after your post, but I’d like to tell you that this answer has been of great help, as I had the same problem on my Metal Muff (extremely low output sound on bypass and not processed signal, just plain weak sound when switched on).

    I used a 2N3819 (TO-92) instead of the original MMBF4393 and now is working great.

    And you were right, this transistor is the one routing (JFET N channel) signal to the effect or bypassing it.

    Thank you very much! Repair cost was about 25 cents + 3 drops of solder!

    July 27, 2012 at 3:58 am #117935
    jjohnson
    Member

    Have the same problem with my Bass Big Muff. Do I have the same transistor? Haven’t worked up the courage to tear it apart yet. :)

    Thanks,

    Jeff

    August 5, 2012 at 10:13 pm #117982
    JaviCAP
    Member

    Hello,

    I have not the Bass Big Muff layout / schematics, just a few pics, but this problem (extremely low output on bypass and clean no processed signal when activated) is nearly always related to transistor problems.

    I would point my efforts to the 4 bc547c trannies. Luckily enough, in the bass muff, unlike the Metal Muff, are common TO92 trough hole ones, so you can replace all four in a matter of seconds.

    But, there’s always a “but”, the problem could be located too in the op amp IC, a tlc2264c smd, that is not.. lets say “easy” to remove / replace.

    If the pedal were mine, would replace the BC547C trannies one by one. If the problm is not solved, would replace the opamp, but if you’re not familiar with this kind of components and have a smd solder iron / station, would take it to the EHX service desk.

    Best regards and good luck

    August 15, 2012 at 12:23 am #118001
    jjohnson
    Member

    Thanks! I’ve decided to send it in for repair. Fingers crossed.

    Jeff

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