Expression Pedal 'midi zip' sound

spikeymcspikeface

Active Member
Hi, I've more-or-less finished building my new rig around my GT-16 and MEGX, but have one last niggling problem I can't seem to fix ...

Whenever I move the expression pedal (Mission RJM SP-1) I get 'MIDI zipping' sound - a buzz that happens only as I move the pedal. The volume of the buzz seems to be roughly in proportion with how fast I move the pedal (faster equals louder).

I've tried disconnecting each bit of kit in the rig (other than the amps, MEGX or GT-16, naturally), but can't zero in on a single culprit device that's causing the problem - it seems to be something systemic, it doesn't matter what particular things are connected / turned on / etc. The GT-16 is powered by the MEGX via a 7-pin MIDI (professionally made), and all MIDI connections run via two MIDI Solutions 'Quadra Thru' boxes, each of which get their power straight from the MEGX.

What should I be doing that I'm not ...?

Thanks.
 
It sounds like an improperly shielded MIDI cable. Also, some pedals are noisy when they receive MIDI data, that could be it as well.

What do you have the GT's MIDI output connected to? (List everything in the MIDI chain). What is the expression pedal controlling?
 
Thanks Ron ...

So this is the MIDI path:


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- The SP-1 is also controlling external function switch #1 on the GT-16 (so has two TRS connections with the GT-16)
- The GT-16 is phantom powered by the MEGX (via 7-pin MIDI cable)
- The two Quadra Thru's are phantom powered by the MEGX (via standard 5-pin MIDI cables)
- A Gigrig Power Generator supplies all 9v DC devices (MEGX, H90, EQ and Strymon), and each unit receives its power via an isolator (zero ground-loops)
- The Prostage has a separate 9v AC supply (but it's wired into the same power distribution as the Gigrig)
- The pre-amp has its own separate mains supply (but again, it's wired into the same power distribution as the rest of the rig)

I've tried disconnecting (physically and turning off) the H90, Prostage, EQ and Strymon, but it made no difference to the buzz when moving the pedal. The rig is incredibly quiet (other than when using the expression pedal), and all MIDI is working perfectly - it's just the buzzing / MIDI zip sound when the pedal is moved.

Any advice gratefully received ...!

As ever, huge thanks for all your incredible & generous support.
 
Turning off devices isn't going to be enough. I recommend starting at the right side of your diagram and unplugging MIDI cables, testing after each disconnection, until the noise stops.
 
Thanks Ron ...

And the good news is it was the very first MIDI cable I unplugged that showed the cause of the problem (!).

But the bad news was it's not the MIDI cable that's actually causing the problem - it's the MIDI connection between the Egnater IE-4 pre-amp and the rest of the MIDI chain (MIDI cable used makes no difference).

However, the great news is I've now been able to suss out that the problem is the Midi Solutions Quadra Thru.

I'd previously been using a Kento Thr-5, which never let me down (I only switched to the Quadra's because I was trying to simplify my new rig as much as possible, and they don't need a 9V DC supply). But if I put the Kenton between the Egnater and the rest of the MIDI path, the expression pedal buzz goes away. So out goes one of the Quadra's, and back in comes the Kenton.

Thanks again Ron, I know this must seem so darn obvious to you, but I'd been going round the houses for days and couldn't see the wood for the trees.

All sorted and happy.

Best.
 
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I'm glad you found the solution! I know how to deal with this kind of situation because I've had this same conversation dozens of times. MIDI is very noisy, electrically speaking, and you can't let it get out and into your audio path.
 
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