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FBV pedal causes hum with Amplifi 150

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I have bought an Amplifi 150 from eBay and all works great, but when I connect my FBV pedal it causes a pulsing humming sound. The pedal functions fine, but the hum doesn't go away. I tried the FBV pedal through my friends Amplifi 150 he bought new 2 months ago and it all works fine with no hum. From this I think it's a ground problem with the pedal connection / circuitry and it only occurs on older versions of the amps / internal PCBs or components. I've seen this mentioned twice in other threads but I didn't see a solution. I'm an electronic engineer and I'd rather fix this myself as I have no warranty than have to go through the hassle of finding a music shop to take it in & try to fix it. Did anyone manage to figure out what modification was required to stop the hum when the FBV pedal is connected? Any help would be greatly appreciated.

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When the FBV Pedal is plugged into the amp the patch settings remain unchanged, therefore a gate setting should not require to be altered.  The fact that hum is introduced to the patch when the FBV pedal is connected should be sufficient to demonstrate the hardware is introducing hum.  The same patch settings are on my firends Amplifi 150 and when the FBV pedal is connected there is no hum.  I am confident this is related to hardware introducing noise into the circuit on my Amplifi 150.

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When the FBV Pedal is plugged into the amp the patch settings remain unchanged, therefore a gate setting should not require to be altered.  The fact that hum is introduced to the patch when the FBV pedal is connected should be sufficient to demonstrate the hardware is introducing hum.  The same patch settings are on my firends Amplifi 150 and when the FBV pedal is connected there is no hum.  I am confident this is related to hardware introducing noise into the circuit on my Amplifi 150.

Maybe you already tried this... New patch cable? You did not say which FBV pedal you have, but I am assuming it is one that is tested by Line 6 to work with the AmpliFi (FBV3, Shortboard MKII or FBV Express MKII?). I am using a standard CAT5 ethernet cable between the amp and the FBV (3 or Shortboard MKII - I have both) on my AmpliFi 30 and I do not have any hum. If your cable has any of the internal wires loose or broken it will likely introduce hum (especially if it is a ground wire obviously, but I think it might potentially happen with any other wire). Make sure it's a straight patch cable, do not use a crossover cable or you could potentially fry the Amp, FBV pedal or both.

 

If that doesn't work, the ground issue could be in the amp RJ-45 jack itself maybe? Tons of things could cause ground noise, like loose wire in the jack, cracked cold solder joint, damage to the jack itself or loose jack, etc.

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Maybe you already tried this... New patch cable? You did not say which FBV pedal you have, but I am assuming it is one that is tested by Line 6 to work with the AmpliFi (FBV3, Shortboard MKII or FBV Express MKII?). I am using a standard CAT5 ethernet cable between the amp and the FBV (3 or Shortboard MKII - I have both) on my AmpliFi 30 and I do not have any hum. If your cable has any of the internal wires loose or broken it will likely introduce hum (especially if it is a ground wire obviously, but I think it might potentially happen with any other wire). Make sure it's a straight patch cable, do not use a crossover cable or you could potentially fry the Amp, FBV pedal or both.

 

If that doesn't work, the ground issue could be in the amp RJ-45 jack itself maybe? Tons of things could cause ground noise, like loose wire in the jack, cracked cold solder joint, damage to the jack itself or loose jack, etc.

 

It is an FBV Shortboard MkII.  I have tried different patch cables, but as the pedal & cable worked on the other amp this rules them out.  The FBV is not in the signal path & I would expect this to purely be for control, so it would need to introduce noise to the internals but without looking at the circuitry it's all just assumptions.  If the PCB with the RJ45 is on the same PCB as the midi connector I could understand this, but it's not worth thinking about too much as like you say there could be many scenarios which introduce noise.

 

As expected Line 6 advised not to open up or attempt any mods and to try a firmware upgrade and factory reset.  The firmware was already at v2.5 and I'd already tried a factory reset...this didn't change anything.  Only other option now would be to check the amp in to a Line 6 approved service centre, which I don't want to have to do with a second hand amp I've just bought which was meant to be working.

 

I have managed to arrange a return through eBay, so I've sent the Amp back (InterParcel & UPS Premium works like a charm!) and bought a brand new one from Andertons in Guildford.  Arrived in Edinburgh on Monday and everything works perfectly.  No hum at all and sounds great....shame about all the unnecessary postage costs but that's the risk with buying 2nd hand goods I guess.

 

Thanks to the people who replied.

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Glad you got it sorted out. Yes, it is always a gamble when you get anything from Flea-Bay, but it pays to read the fine print to make sure you can return DOA or otherwise defective goods without penalty (other than being out of pocket for S&H expenses).

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