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Fishman Loudbox 100 mute circuit

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  • #16
    You are welcome.

    They should be the same. From the specsheet:

    Nominal input level:
    Ch. 1 -20dBV/-10dBV with 10dB pad
    Ch. 2, ¼” Jack (Tip) -20dBV/-10dBV with 10dB pad
    Ch. 2, ¼” Jack (Ring) -20dBV/-10dBV with 10dB pad
    Ch. 2, XLR Input -40dBV/-30dBV with 10dB pad
    Aux Input (stereo) -10dBV

    At least you can compare the two channels. Here is the complete sch in case you don't have it. Enjoy

    Loudbox100_schematic_Rev4P4.zip
    Experience is something you get, just after you really needed it.

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    • #17
      I split my test signal and fed into both FX return jacks, channel 1 is louder. I activated the mute switch, and had a look at the FX return circuit. Good strong signals on U3 pin 7 on both boards, and good strong signal on U3 pin 8 on channel 1, but a weaker signal by about 1/3 on pin 8 channel 2. Again I briefly shorted C32 following U3 pin 7, and once again the volume increased. Sadly, I have used my last one, and must order more. I think these caps are definetly a common problem with these Loudboxes this is the 4th 10uF/16v one I have replaced.
      It's weird, because it WAS working fine.....

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      • #18
        Well, to sum this job up, I found yet a third bad 10uF/16v cap. So C9 was halting the signal in Channel 2, replaced it, but ch 2 wasn't as loud as ch 1. Found a bad C32, this increased the volume only slightly. Found a third bad C7, between the first and second stages of U1. Now Ch 2 barks every bit as loud as Ch 1.

        So, this is the second time I have replaced multiple 10uF/16v SMD capacitors in a Loudbox. I bought a strip of 10 to keep on hand. Seems these are prone to failure. Seems to me the signal must have been degraded before it finally cut out. Made it a bit tricky at the beginning trying to understand what I was seeing. But it's all good now.

        As always, thanks for your help guys! Especially when I was misleading.
        Last edited by Randall; 04-21-2020, 05:49 PM.
        It's weird, because it WAS working fine.....

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        • #19
          I'm sure your discovery will help many people. BTW you might want to edit your post the read 'SMD capacitors' instead of 'SMD resistors' to help searches to be more effective
          Experience is something you get, just after you really needed it.

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