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Post subject: Frontman 15G Aux-In Buzz
Posted: Sun Mar 08, 2015 11:59 am
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I'm getting a loud background buzzing sound when I use the aux in on my Frontman 15G to connect to my desktop PC. It also happens when I plug into the line out on a stereo system. I don't get the background buzz when I connect the aux in to a laptop or my phone running on batteries. For the record, I also don't get the buzz when using the aux on another company's amp of similar specs.

I checked for continuity between my computer chassis and the handle covers on the amp (which are connected to ground) using a multimeter. There seems to be good continuity, so as far as I can tell with a multimeter they're on a common ground. They're also plugged in to two different outlets but on the same wall. I even tried running a wire (with a 10 ohm resistor) between the computer chassis and the amp's ground, with no effect. Given that, is it still likely to be a ground loop problem?

Troubleshooting steps I may try next, based on what I've found poking around the web:
1. Plug the computer and amp into the same power bar.
2. Connect the computer chassis to the amp ground with straight hookup wire, without the resistor.
3. Wire a 10 or 100 ohm resistor into the signal ground on the aux cable between the computer and amp. I'm not really sure what the consequences of this one might be. I'd be really glad for any feedback on this one especially.
4. Buy a filtering power bar (this one doesn't seem promising, but I want one anyways for my computer).
5. Buy something like the Behringer HD400 ( http://www.youtube.com/watch?v=jSA2F1AwboU ) and use it between the computer and amp. I'd prefer not spending the money if I can avoid it.
6. Build a ground lift box for the amp using a pair of diodes. I'm also not sure what all the implications of this solution would be. (e.g. http://www.youtube.com/watch?v=CuvDMjxhE68 ) It all *seems* reasonable and a lot safer than just disconnecting the amp from ground, which is another solution I've read about but am *not* considering. My concern with this solution would be the case where there's a short in the box itself and the diodes blow out because of an excess of current.

I'd appreciate any thoughts, especially given the tendency of these amps to blow out when people are using the aux in.


edit: There's some info on the web about a similar problem with older Frontman 15G/R amps, in which the signal ground wasn't connected to the electrical ground. Those discussions often reference a schematic for the 15G/15R that's available online. My amp seems to be a newer design and doesn't have this problem. To confirm this with my newer amp, I checked for continuity between the sleeve of the aux in, the sleeve of the input jack, and the ground plug, and there's continuity between all of them.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Sun Mar 08, 2015 5:43 pm
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OK, I've tried numbers 1, 2, 3, and 4, no effect.

Please let me know if you have any thoughts.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Mon Mar 09, 2015 8:04 pm
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It sounds like a ground loop problem. Buy a few 3pin to 2pin AC adapters from your local hardware store.
Install them onto the AC cords to your computer. Tower, monitor and printer.
If that doesn't work, remove the adaptors from the computer system and put one of them on the amp cord. If that doesn't work, try novel combinations.
The only common ground should be through the audio cable.
To be safe, remove the adaptors when you don't need them.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Tue Mar 10, 2015 3:59 am
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TimsAudio wrote:
It sounds like a ground loop problem. Buy a few 3pin to 2pin AC adapters from your local hardware store.

Bad idea. See my and scott-uk's answer to your identical proposal in viewtopic.php?f=27&t=98375


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Tue Mar 10, 2015 7:45 pm
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I would love to reccommend a transformer to break the ground loop,
Impedance issues and signal degradation from poor quality transformers are only minor problems,
The major issue, in my experience, is that they are just not very effective in quieting the problem. The loops are in the multiple AC cords for the computer, not just between the computer and amp. I have chased many ground loops and transformers only worked in a few cases, so I use this method.

As far as safety, my post recommended removing the adaptors for normal computer use.
But...
The audio cable has sufficient current carrying capability to bleed off normal AC leakage. If a catastrophic failure occurs, a fuse will blow.

The AC adaptors are effective and safe. The EU may have banned them, but they apparently also banning inefficient and high power appliances. That means tube amps could be on the chopping block too..


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Tue Mar 10, 2015 11:20 pm
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TimsAudio wrote:
That means tube amps could be on the chopping block too..


That would be the BEST thing that could happen to Fender IMO. If they can't export amps across the pond they won't need to concern themselves with nebulous meddling by bureaucratic assholes and it'll be the end of latex nipples on power switches, hamster cages around power tubes, solid-state tremolo circuits, and last but not least, that GODDAMM RoHS-COMPLIANT SOLDER.

Good riddance!

:evil:

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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Wed Mar 11, 2015 2:41 am
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TimsAudio wrote:
As far as safety, my post recommended removing the adaptors for normal computer use.

Ah okay, so he'll only get electrocuted while playing guitar. That helps.
Even neglecting that risk, do you seriously expect people to install and remove five adapters every single time they want to use their guitar while their PC is on?

Quote:
If a catastrophic failure occurs, a fuse will blow.

Fuses are for preventing fire, not electric shock.

Quote:
The AC adaptors are effective and safe.

I don't know what to say. Removing a technical measure that was designed to save lives is not "safe", and - to put it politely - I can't take anyone seriously who would claim that.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Wed Mar 11, 2015 9:38 am
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This issue of safety vs performance has been going on since the 60s when U grounds first came out.
Back then, the solution was to just snap off the third pin with a pair of pliers. Polarity was a crap shoot.
The method of using an adaptor prevents the hot and ground from being reversed.
While the remote possibility of being shocked while playing guitar with adaptors is a consideration, playing guitar with a loud hum or squeal is very safe because it will just be turned off.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Wed Mar 11, 2015 12:48 pm
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ChrisH1 wrote:
designed to save lives

Any documented cases of death-by-ground-lift? :| Can't say I've ever heard of it, and the all-knowing google oracle doesn't seem to have any idea either.

I did find this though .....

If you were to AC ground the absolute minimal amount of things in your system it should be your stage console (FOH in one console systems) and backline power. I don’t want to get sidetracked into the various system grounding techniques but I will say that you can pretty much AC lift anything you want with minimal adverse effects as long as you ground the closest console to stage and backline power. This is not to say that AC lifting various pieces of gear will not present potential hazards and I am in no way recommending that you AC lift gear (at least in this article) but solving ground loops often presents a bit of a dilemma. You want the hum to go away, you know AC lifting is not the safest thing to do yet cutting pin 1 on every loom to a rack is not only impractical but may not even solve the particular problem. I realize there will be some AC ground lifting going on.

From: HOW TO NOT KILL A PERFORMER ON A STAGE BY ELECTROCUTION

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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Thu Mar 12, 2015 3:23 am
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strings10927 wrote:
Any documented cases of death-by-ground-lift?

No hard numbers, but a few minutes of googling found this:

http://www.hse.gov.uk/pubns/indg247.pdf
Quote:
Entertainers have been injured and even killed from electric shocks while performing or practising. Make sure your next performance is not your last.
Do NOT remove protective earth connections. Removal of earths is one of the common causes of entertainers receiving electric shocks, some of which have been fatal.


http://en.wikipedia.org/wiki/Cheater_plug
Quote:
Bill Whitlock, president of Jensen Transformers, writes, "never, ever use devices such as 3 to 2-prong AC plug adapters, a.k.a. 'ground lifters', to solve a noise problem!" Whitlock relates how an electrical fault in one device that is connected to its electricity source through an ungrounded cheater plug will result in dangerous, high current flowing through audio or video cables. Whitlock notes that in 1997, consumer audio and video equipment electrocuted nine people.
The cheater plug is also recognized as a safety hazard in laboratory settings. For example, in August 2005, Tarun Mal, an associate professor at Cleveland State University, was electrocuted when he plugged a defective fluorescent lamp into a time switch using a cheater plug. Subsequently, the state of Ohio issued seven citations to the university for unsafe electrical conditions.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Thu Mar 12, 2015 7:04 am
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ChrisH1 wrote:
strings10927 wrote:
Any documented cases of death-by-ground-lift?

No hard numbers, but a few minutes of googling found this:

No hard numbers? Or not a single documented case? Ground lifts are available all over the place in the US, they even have them at food stores. Can you imagine how many people per year plug guitar amplifiers into them? I'm not saying you can't get a shock, but if there is even a single documented case of someone dying that way, nobody seems to be talking about it.

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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Thu Mar 12, 2015 7:08 am
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strings10927 wrote:
No hard numbers? Or not a single documented case?

Did you read the Wikipedia article? I even quoted the part with a documented case.


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Thu Mar 12, 2015 7:23 am
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Electrocuted is commonly used to mean 'shocked'. But I see the guy died. Here's how:

Cleveland State University is not liable for the death of biology professor Tarun Mal, who was electrocuted in 2005 when he used a nongrounded electrical device that adapts a three-pronged plug for a two-pronged device to plug in a homemade grow lamp.

Home made grow lamp? :|

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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Thu Mar 12, 2015 7:33 am
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strings10927 wrote:
Home made grow lamp?

I didn't read that detail :)


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Post subject: Re: Frontman 15G Aux-In Buzz
Posted: Thu Mar 12, 2015 2:54 pm
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If you read Mr Whitlock's seminar it's an advert for his $200 ground loop isolator. So of course, an 89 cent adaptor would be evil...for his bottom line.
The CPSC article he cites is for radio, televisions and stereos.
Computers and amplifiers weren't mentioned.
His isolator looks like a good piece for stereo and video, but won't address computer loops or EMI/RFI problems common to high impedance guitar amplifiers


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