Ground buzzzzz

LMO said:
The issue is the integrity of the ground wire connection. If you have a failure that shorts AC directly to the case, then the ground leg has to be able to carry that current until the breaker trips.

A standard household circuit is usually 15 or 20 amps, plus whatever the tolerance is for the breaker.
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Ok, I understand that, but the only implication is the durability of the device itself, right? Not the harmful effects to the Axe-fx or the rest of your gear? Under what conditions would you pump more than 6 amps through that thing? Are you all worried about power spikes (lightning) or something else? If lightning stikes, your Hum-x (*and* your power conditioner) will be history, but the rest of your gear should be fine. And under normal operating conditions, both the Hum-x and your power conditioner should be fine.

I guess I still don't get it. If I buy a power conditioner, I'll get one that can handle more than the gear I intend to plug into it. I would approach the Hum-x the same way. And I figure I can plug my Axe, my power conditioner, my floor controller, and my two Verve 12mAs into the Hum-x without even approaching its 6 amp limit. So what's the issue again, and how is it different from anything else?
 
Dpoirier said:
Ok, I understand that, but the only implication is the durability of the device itself, right?
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The issue is safety (along with the side issues of legal liability and fire code). Spikes be damned; if there's an equipment failure and your Axe-FX (or power cord, or another connected piece of gear) develops a dead short to ground, but your ground connection isn't working because those 6-amp diodes fried, all that juice is going to go looking for the best path to ground it can find, and that best path could be you. Or it could be the sound guy 150 feet away in the booth. It's all a matter of what's closest to what when hell breaks loose. But it'll probably be you. You're touching Axe-FX wiring by way of your guitar strings, and you might also be kissing ground with your microphone.


Dpoirier said:
Are you all worried about power spikes (lightning) or something else? If lightning stikes, your Hum-x (*and* your power conditioner) will be history, but the rest of your gear should be fine.
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If lightning strikes, all bets are off. Your power conditioner may be able to handle the surge, but there's no guarantee that your other equipment — even stuff sitting in the corner that's not connected to anything — will survive the strike.
 
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Rex explained it well.

One further detail: a TVSS device (power conditioner) must be UL certified or it can't be labelled as a surge suppressor. The Hum X does not carry UL certification, so we don't know what, if any, safety testing has been done.
 
i have a ground loop as well, however i just ordered an active atomic wedge and an xlr cable so i'm hoping i can fix it via the ground lift switch on the axe or amp and hopefully this will replace my current solid state peavey amp setup right now.... i'm hoping i don't have to spend 80 bucks on something like the hum-x as well.....
 
If you run XLR, you may find that you have no ground loop, even without using the ground lift switch.
 
sounds good to me!!!! my question is why doesn't the axefx have xlr outputs on output 2? i would like to send output 1 to FOH and output 2 to my atomic wedge but what if i get a ground loop to my wedge or something via quarter inch cables.....? also, on output 2 do i send the left one to my wedge because that is mono, and if i get another wedge i send the right of output2 to that wedge? thanks guys, sorry i'm such a noob
 
mgavin said:
my question is why doesn't the axefx have xlr outputs on output 2?
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Dunno. I wasn't on the design team. :)


mgavin said:
also, on output 2 do i send the left one to my wedge because that is mono, and if i get another wedge i send the right of output2 to that wedge? thanks guys, sorry i'm such a noob
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You can do it that way if you're running mono. You have choices with either output. You can run them in mono or stereo; you can make Output 2 be a copy of Output 1; you can feed sound to Output 2 independent of Output 1. Read the section in the manual about I/O Configuration. It'll get you started.
 
If you look at the schematic for the '63 Fender Reverb you will also see parallel 6 amp diodes in parallel with a resistor, although this one is 10 Ohms. The Fender circuit is on the secondary side of the transformer, while the Hum X would be on the primary. I think I need to meditate on this a bit more--perhaps the Hum X design is not so bad?
 
Interesting. If the diodes failed open, the 1K resistor in the Hum-X would limit ground current, though it wouldn't necessarily result in a safe voltage on the shorted equipment. If the diodes failed closed, the resistor would be irrelevant. On the other hand, how much current can those diodes handle in the fail-closed state? 6 amps is the max operating current, not necessarily the max failed current.
 
Another thought: what do the regs say about a short to ground on the secondary side, given that it's already isolated from the primary?
 
I've been looking for more info while waiting for a EE/electrician friend to get back to me. The electrical codes generally require safety grounds to handle 25A (US) or 30A (Canada).

Here is an excerpt from an article on grounding audio equipment:
Elliott Sound Products said:
The loop breaker works by adding a resistance in the earth return circuit. This reduces circulating loop currents to a very small value, and thus breaks the loop. The capacitor in parallel ensures that the electronics are connected to the chassis for radio frequency signals, and helps to prevent radio frequency interference. Finally, the diode bridge provides the path for fault currents. The use of a large chassis mounting (35A) type is suggested, since this will be able to handle the possibly very high fault currents that may occur without becoming open circuit. Note the way the bridge is wired, with the two AC terminals shorted, and the two DC terminals shorted. Other connection possibilities are dangerous, and must be avoided.

In the event of a major fault, one (or more) of the diodes in the bridge will possibly fail. Semiconductors (nearly) always fail as short circuit, and only become open circuited if the fault current continues and 'blows' the interconnecting wires. High current bridge rectifiers have very solid conductors throughout, and open circuit diodes are very rare (I have never seen a high power bridge go open circuit - so far at least). Use of the bridge means that there are two diodes in parallel for fault current of either polarity, so the likelihood of failure (to protect) is very small indeed.
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Note the recommendation to use a 35A bridge (four diodes) as compared to what we believe are two parallel 6A diodes in the Hum X.
 
I'm a little baffled that the manufacturer (ebtech?) has not yet acknowledged this issue and updated their product to meet UL requirements (or whatever it is)...

Furthermore, Google searches for that product give nothing but praise, and no complaints (that I could find) related to safety. Adding the term "+safety" to the search, you still won't find any complaints... just references to the fact that using a hum-x is much safer than lifting ground on your power cord...

So again, why are folks on this forum more concerned about this safety issue (assuming there is one) than anyone else outside of this forum? Special needs? More tech-savvy user base? Anal retention?

I'm not arguing - just genuinely trying to find a reason *not* to use my hum-x once I receive it (placed the order at the beginning of this thread).
 
Dpoirier said:
I'm a little baffled that the manufacturer (ebtech?) has not yet acknowledged this issue and updated their product to meet UL requirements (or whatever it is)...
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I found a quote, purportedly from the director of Ebtech engineering, saying that Ebtech does the same testing that UL does. If that is true it begs the question of why it hasn't been UL listed.

Furthermore, Google searches for that product give nothing but praise, and no complaints (that I could find) related to safety. Adding the term "+safety" to the search, you still won't find any complaints... just references to the fact that using a hum-x is much safer than lifting ground on your power cord...
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I ran across a rant about the potential safety issue the first time I searched out info in the Hum X, which is why I started thinking about the 6A diodes.

So again, why are folks on this forum more concerned about this safety issue (assuming there is one) than anyone else outside of this forum? Special needs? More tech-savvy user base? Anal retention?
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Probably my fault. The Fender circuit with 6A diodes I referenced above is designed to handle potential current until the main fuse in the box--not the breaker on the AC line--opens, interrupting the current flow. This of course does not apply to the Hum X.

The question comes down to the failure mode of the 6A diodes in the Hum X when subjected to 25A of current for 1 minute (the US standard). Typical failure mode for diodes is to short out, which is good in this case... if the short doesn't burn through during that minute.

I'm not arguing - just genuinely trying to find a reason *not* to use my hum-x once I receive it (placed the order at the beginning of this thread).
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That's easy. The Hum X is $2 worth of parts that sell for $50 to $70.
 
LMO said:
That's easy. The Hum X is $2 worth of parts that sell for $50 to $70.
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Ah, ok, now we're getting somewhere.

So what would the schematic look like (including part numbers or at least values) especially if you wanted it to be worthy of UL listing? Apologies if this has been discussed already in this thread (or elsewhere)... I'm kind slow when it comes to electrical circuit, and a diagram helps a lot (even an ascii diagram).

I imagine it might be possible to "butcher" a power bar to add the necessary devices inside the power bar's housing (assuming enough room)? Any downsides to doing that? Or to using this circuitry in the first place?
 
I posted a link to an article with a schematic a few posts back.

As far as modifying a power bar, the only thing I know to watch out for is the type of sockets that automatically make a ground connection to the case. You would need isolated sockets.
 
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Dpoirier said:
Furthermore, Google searches for that product give nothing but praise, and no complaints (that I could find) related to safety. Adding the term "+safety" to the search, you still won't find any complaints... just references to the fact that using a hum-x is much safer than lifting ground on your power cord...

So again, why are folks on this forum more concerned about this safety issue (assuming there is one) than anyone else outside of this forum? Special needs? More tech-savvy user base? Anal retention?
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Your average consumer isn't concerned about safety until something goes wrong. They assume that if a product is on the market, it's safe. They figure there are agencies, trade associations and regulatory groups out there making sure things are safe for them. LMO and I have both spent at least part of our careers doing things that require us to be concerned about safety with regards to electrical power. We have either heard or witnessed the horror stories that happen when things go wrong, and we know some of the reasons behind the regulations. We look for these things out of habit. The user community in general won't complain about safety until they personally experience something going wrong.
 
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