Phantom powering a Liquid Foot 12+ (WARNING)

greiswig

Power User
As a PSA, let me tell you about a lesson learned the hard way. Nowhere on either manufacturer site will you find this, but if you attempt to power a LF 12+ through the MIDI cable in an AxeFX II, you will burn up a component in your AxeFX, and phantom will no longer be an option. The AxeFX can't support the amount of current the 12+ requires, but that's not noted anywhere in either manufacturers' documentation.

Jeff at Liquid Foot has a hidden option (on the order page, look under "Special Notes") for an external unit that will prevent this from happening. But if you're going to use phantom power, this is NOT an option, it's a requirement.

I have a support email in to FA, because I'd really like to not have to send the AxeFX back in for a repair.
 
Interesting.
I downloaded the manual and looked all over the site, but I also could not find the power specs. I DID get from the website "Power In AC or DC (9-12v)"
But I still don't know the current draw or even the power drawn by the unit.

It would have to be quite a bit to burn anything in the axe - as far as I know it's just wires going to the 7 pin (phantom power), so the current required by the unit would have to be substantially more than the wires are rated for. I'd tend to believe that something in the LF would fry instead, unless the power was put on one of the 5 pins used by the axe for actual midi, which would prob fry something.

Is the LF powering up with an external supply? Does the axe still work?

Not dismissing your claims, just trying to seek as much info as possible. I was looking to get a 12+ myself, but as I can't find the info I need from the site or manual red flags are popping up in my head already lol
 
[caveat] I'm no expert, but...
This doesn't make sense... IF you were phantom powering an LF 12+ unit that requires 9-12v and doing that via 7-pin midi from the Axe, there's nothing (AFAIK) in the Axe that generates powers. The *Phantom* power comes from the adapter unit supplying power to the 2.5mm jack on the back of the Axe then down the midi cable in pins 6+7. If the Axe got fried, then something was not correct - bad midi cable or the power adapter was beyond max supported current (IOW - AC current perhaps) for Axe wiring.

IOW - phantom power is a pass-thru from the wal-wart adapter.
 
IOW - phantom power is a pass-thru from the wal-wart adapter.
Yea, that was my understanding as well. I suppose it's possible the wires can't handle anything above a certain current draw but...it'd have to be one hell of a current draw. The wire gauge in those 7-pin MIDI cables isn't exactly hefty. Can't imagine the internal connection between the adapter jack and pins 6/7 on the MIDI IN jack on the Axe-Fx are much thinner than what's in the cable.
 
Is it a home made midi cable? In such a case the 7+5 pins could have been inverted. Not a problem though if the foot controller run on ac like the mfc.
 
[caveat] I'm no expert, but...
This doesn't make sense... IF you were phantom powering an LF 12+ unit that requires 9-12v and doing that via 7-pin midi from the Axe, there's nothing (AFAIK) in the Axe that generates powers. The *Phantom* power comes from the adapter unit supplying power to the 2.5mm jack on the back of the Axe then down the midi cable in pins 6+7. If the Axe got fried, then something was not correct - bad midi cable or the power adapter was beyond max supported current (IOW - AC current perhaps) for Axe wiring.

IOW - phantom power is a pass-thru from the wal-wart adapter.

even better said than I was trying to :D
If I had to guess, I'd guess that the wires would be able to take at least 1-2A, most midi controllers draw less than 1A.

Is it a home made midi cable? In such a case the 7+5 pins could have been inverted. Not a problem though if the foot controller run on ac like the mfc.

I was alluding to this as well...but when we get a reply as to what works and what doesn't/what happened it might be easier to guess what went wrong.
 
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Okay, just to be clear, I do actually know what I'm doing. ;-) But I know it's hard to tell if somebody's a newb or not.

The cable is a Rocktron 7-pin MIDI cable. The wall wart being hooked up to the phantom power "in" jack on the back of the AxeFX II is the stock Liquid Foot power adapter. Yes, the LF unit still powers up if that same wall wart is directly connected to the LF. But when I measure voltage across the 2 extra pins of the MIDI in jack at the AxeFX, I get 9VAC (instead of the 13.4VAC open-circuit voltage that the power supply measures at the jack itself). And clearly it isn't passing enough voltage or current to power the LF 12+.

I cobbled together an adapter using a 7-pin DIN connector that I had that let me hook the power supply directly to the pins of the cable, outside the AxeFX. The LF works fine using this, so the problem is not at the LF end of things, or the cable, or the power supply.

The AxeFX and the 12+ both work fine other than being able to supply phantom power through the 7-pin MIDI connection. So there is clearly something wrong between the phantom power input jack and the relevant pins on the MIDI in jack within the AxeFX II.

The Liquid Foot 12+ pulls something 1A, but that fact is only locatable by looking on page 9 of the draft manual. Neither manufacturer mentions a limit in what the AxeFXII can take, or that this is a known issue, but it apparently was known. It would not surprise me if similar foot controllers coming out (e.g. the RJM Mastermind) have similarly high current draws because of the lighted displays. So this may be an issue for more controllers than just the Liquid Foot 12+.
 
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Nah, it actually sounded like you knew what you were doing ;) Just didn't have much info.

If it IS that you are getting 9V, that changes everything.

I'd prob guess that the current heated up the ferrite shunt, causing it to fuse to the wire itself (burning scent), possibly causing an unintentional load on the power supply.

That's 100% speculation though. I suppose it's best to shoot FAS support an email?
 
Sounds more like normal voltage drop over a long cable run. 1A is pobably on the high side for an MFC, but I factor in a 1V drop over the cable for my own (homemade) MFC which draws about 350mA - so losing 3V seems about right. I'd be surprised if any damage has been done.
 
I've sent 24V over hundreds of feet and got only a couple volts lost - 22.5V or so. Depends on cable type of course, so I can agree with you there too.

Doesn't explain the burning scent he mentioned tho
 
I've sent 24V over hundreds of feet and got only a couple volts lost - 22.5V or so. Depends on cable type of course, so I can agree with you there too.

Doesn't explain the burning scent he mentioned tho
Yeah - the smell is a worry. I expect you already know, but voltage drop is proportional to both current (high in this case) as well as resistance, and resistance is proportional to cable length in this case.
 
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But when I measure voltage across the 2 extra pins of the MIDI in jack at the AxeFX, I get 9VAC (instead of the 13.4VAC open-circuit voltage that the power supply measures at the jack itself). And clearly it isn't passing enough voltage or current to power the LF 12+.
Did you just stick your meter on each pin and measure?

That's not how you measure the potential energy of an unregulated, AC power supply like a wall wart.

If you want to make a proper measurement you need a load between the two points. And you measure across the load. Measuring two points in an open circuit, especially an unregulated, AC circuit, doesn't tell you the proper potential delivered by your power source. You need a load.

Back to your problem: the burning smell does sound suspect. Like perhaps you had a short or an arc on the MIDI jack that's caused the terminal to char and has made it resistant. So you're losing potential, it's being converted to heat. I would open it up and check that terminal.
 
GMArts/iaresee, I think you're misreading my 9VAC reading: this was a reading without anything attached to the MIDI in port on the AxeFX. And I can simultaneously measure the voltage at the phantom input jack, which measured the same as the power supply measures without being connected to anything: 13.4VAC. So both of these are, in essence, open circuit (zero load) voltages...I'm not trying to measure the "potential energy" of the transformer; I'm using this as a diagnostic to find whether there is a connection between the phantom input and pins 6&7 of the MIDI in jack, so this is a basic but diagnostic test. The input impedance on my Fluke is 10M, so there is virtually no load coming even from that either. Given that these are zero load measurements, a voltage drop of over 4 volts is very high, and indicates pretty clearly that something has opened (burned open) to the point of having many megohms of resistance.

I've never heard of a ferrite shunt, Jon. I don't know what component has failed. Jeff at Liquid Foot says this is a known issue, but not with the Ultra or Standard, and that he's asked FAS to put in something with more than a 1A rating. He's the one who told me it was "a ferrite." I did put in a support email to FAS, but have not heard back from them. But then I don't expect them to work weekends for little ol' me.
 
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Another possibility

Just reading through the posts I noticed one thing in the manuals that hasn't been mentioned.

The midi power pass through is designed for the MFC-101 or pedals that run on the same power. I noticed when checking the MFC manual that it is designed to run on 9 volts. I powered my Ground Control through it before I got my MFC, which is also 9 volt. If I am understanding the post correctly, when the original poster connects his higher power transformer, he still gets 9 volts out.

Is it possible there is a component inserted between the power input and the midi pins that limits voltage to 9 volts to protect the MFC from higher voltage transformers? I haven't torn my Axe II apart to check, but this seems to be a logical conclusion based on the information here. Perhaps the burning smell noted is that component getting hot from clamping voltage and dissipating the heat created from that process.

As an aside, I've used the Rocktron cables for years without a failure. I have never been impressed with the lightweight appearance of the cable, so I wouldn't be at all shocked that others haven't had the same luck, but they've been problem-free in my experience. With the MFC, I use the CAT5 cable, so maybe I got out before the roof caved in, cable-wise!
 
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(SNIP) I noticed when checking the MFC manual that it is designed to run on 9 volts. (SNIP)
Is it possible there is a component inserted between the power input and the midi pins that limits voltage to 9 volts to protect the MFC from higher voltage transformers? I haven't torn my Axe II apart to check, but this seems to be a logical conclusion based on the information here. Perhaps the burning smell noted is that component getting hot from clamping voltage and dissipating the heat created from that process.

It is possible, but if this were the case, I would expect to see it power my old Ground Control, which ran at 9VDC. It does not pass sufficient current. Voltage drops to nil. It sure acts like an "open."
 
i can verify this.. I had an ultra for a long time many years (since v4 firmware) in same rack with the same custom patch panel, same adapter. Powered my fx1 for years, then when i got the Liquidfoot, it powered it fine as well, no problems.

pulled out the axe 1, swapped it out for the axe2, plugged everything back up and my power adapter lasted about 15 minutes, then burned out, tried another adapter... same thing. totally rewired from scratch with brand new cables, burned out yet another adapter. Finally gave up, and wired the adapter to the patch panel, no problems since. I can verify that the axe is not supplying power through the midi cable, nothing comes out. No fancy adapters, just a 9v ac adapter i've used to power my fx1 for ages.
 
...plugged everything back up and my power adapter lasted about 15 minutes, then burned out, tried another adapter... same thing.

Interesting, but this actually sounds very different. The component that Liquid Foot says burned out is something inside the AxeFX II itself, not the external adapter powering the MIDI foot controller. But maybe they are related.
 
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