Fishman Loudbox 100 mute circuit

[nickb]

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

[Randall]

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.

[Randall]

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.

[nickb]

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