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Author Topic: Heavy EMI interference in the studio with my peavy studio pro 112  (Read 3603 times)

Duojet

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Heavy EMI interference in the studio with my peavy studio pro 112
« on: September 12, 2012, 01:40:38 PM »
So, because people here have been so good to me, I thought I'd pose another riddle. I have a silver stripe era peavey studio pro 112. It mostly sounds great, but I have a small problem. In my lessons studio it seems to pick up a lot of interference. My previous amps in that space, a crate gx40c and g60 picked up some, but not this badly.

There's some 60 cycle hum and a bit of noise from fluorescent lighting, but that's not the worst of it. My cell phone (the fruit brand) drives it nuts. Turning up the reverb is like turning up the hum. Can I add shielding to the enclosure? Maybe shield the reverb cables or tank as well? What are the risks? Thermal issues? Microphonics?

Also, for bonus points, a previous owner removed the handle on top. Something else leaked through the hole and so now a jumper wire and a transistor(?) next to the main heatsink are corroded. They seem to work, and if sometimes the dirt channel doesn't work, a swift blow to the chassis brings it back in line. I'm inclined to leave it alone. What are the chances that's contributing?

Enzo

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #1 on: September 12, 2012, 06:26:49 PM »
Corroded part?  Not likely the cause.

Cell phone makes it crazy?   No offense, but turn the phone off when teaching?  Or set it across the room or in the hallway?

Get one of those cheap outlet testers - the kind with the three lights.


And make sure the outlets in the room are correctly wired and have a working ground.

Unplug this amp, and use an ohm meter to measure resistance from the ground pin on the power cord plug to the chassis.  It ought to be about zero ohms - in other words continuity.

How much of this noise occurs with NOTHING plugged into the amp?  How about with the guitar plugged in but its volume control at zero?

Duojet

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #2 on: September 25, 2012, 04:58:45 PM »
So it took me a while, but I got an outlet tester. And of course it reads open ground.

I never turn the volume or post gain past 2, and only to 2 when I'm the last one here. Clean channel with no verb is tolerable. Dirt channel with gain to about 3 and no verb is also tolerable. Past that it gets progressively worse, but I'd expect that.

Turning up the reverb on any channel is dicey. At any volume level. Hums like mad when it's set to 10. This stinks as my favorite sounds are drenched in reverb and delay. I can live without it but, still, that's a disappointment.

As far as the cell phone, I should be more specific. I use it as a tuner, recording machine, tab encyclopedia and so forth. So when I get the interference, it's cellular data. I'm using edge network, which seems to be the issue. The music store recently fixed their wifi, so when I switch to airplane mode, I don't seem to have any problem there.

I'm guessing with an open ground every cable I have is now an antenna. Boo. I'm wondering what the wiring looks like behind the outlet, but I need to ask the management before I attempt to fix it. Anyone have any ideas about remedies that don't involve modifying the building?

J M Fahey

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #3 on: September 25, 2012, 08:39:44 PM »
No, they *really* need to wire the buildiong following State or City norms or they will be into deep *s!!t*, no kidding.
Not because of interference but because of safety and danger to life, no less.
Tell them what you found, and "suggest" they'd better fix it *now*, quietly, before an Inspector finds it.
Mention them Murphy's Law, which makes such problems happen at the most inconvenient moments.
"Nothing happened during the last 40 years" is *not* an excuse.

Roly

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #4 on: September 26, 2012, 01:54:51 PM »
+10  :dbtu:

Can't say for anywhere else (and America seems a bit dodgy about earth wiring generally) but in Australia an open earth is a serious business, can get you disconnected until it's fixed, and getting a 'lecco in yourself is generally cheaper than the fine tooth comb treatment that a formal complaint generally causes.  Open earths are not uncommon here in older venues and quite a few musicians have stories to tell of getting "tings" from mikes and the like.  Agree 100% with JM, this is a serious and urgent matter before someone gets electroluxed.  >:(
If you say theory and practice don't agree you haven't applied enough theory.

Enzo

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #5 on: September 26, 2012, 06:58:40 PM »
I can't speak to the specific instance, but we have a lot of "grandfather clauses" in our codes.   All NEW construction must meet the present codes, but we usually don;t require older buildings be brought back up to code retroactively.  SO the old two-wire electrics in my 100 year old house can legally stay that way.   I did have a new main electrical service installed a while back, and THAT had to be modern,   but they were allowed to connect the same old 2-wire feeds from the walls into the new grounded service panel.   

Just like new codes require public buildings to have wheelchair accessible bathroom doors and ramp access to the entrance, but old buildings are exempt from the requirement.  Old buildings are then said to be "grandfathered in."

You can sure ask your landlord to upgrade, but he MAY be under no legal obligation to do so.

J M Fahey

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #6 on: September 26, 2012, 08:30:44 PM »
Can't speak for USA or Australia, but in Argentina we have an intermediate situation, trying to find a reasonable compromise.
Although the electrical code of '94 is strict, "they" won't go hunting millions of households for two very good reasons; sheer size of the task compared to available manpower, and knowledge that a proper electrical upgrade can be expensive and even unaffordable for a lot of people = it would be a *very* impopular decision.
Now, no "grandfathering" exemption is contemplated in the Law, if an Electrical Inspector gets into your home and sees the old electrical installation, he has the power to cut you off until normalized.
As I said, it's only a manpower problem and once the "man" is there, they have the "power".
As of any shop which applies for a licence (including Clubs, Lawyer Offices, stores of any kind, service shops, etc.) they need Fire Dept. approval, which, besides other stuff, checks for proper Electrical wiring.
No matter if the building was wired by Alessandro Volta himself 200 years ago.
*And* all licences perish between 2 and 10 years, so they have to be renewed ... which implies getting a City Registered Electrician signing the papers, risking his licence plus heavy fines and even Penal liability if he cheats, so he does not.

Duojet

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #7 on: September 27, 2012, 12:53:58 PM »
Wow, I knew it was bad, but I had no idea it was that way. I mentioned it to the owner of the school (we rent the building) yesterday, and he seemed surprised that I had even mentioned it. He said "how did you figure that out, what happened?"  He has a more that healthy fear of regulations, so I'm hoping it's fixed soon.

 Right now all the outlets on one side of the building are correct (next to the front desk and the waiting area) and all the other outlets (in the actual studios) are open ground, or open neutral. All the ones on my side of the hall are open ground, so I'm hoping it's one outlet upstream that needs to be fixed. I'll post about this again if I take the amp home and test it if they , I mean WHEN they fix the building

J M Fahey

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #8 on: September 27, 2012, 01:42:33 PM »
Really it's both easy to fix and not expensive.
Besides, he fixes it once and that's it, no monthly or yearly expense.
Living in a trigger happy Country such as USA I would not risk it, probably the building owner thinks the same.
Good for him.

Enzo

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Re: Heavy EMI interference in the studio with my peavy studio pro 112
« Reply #9 on: September 27, 2012, 04:31:13 PM »
If the building is already wired for three-wire, then yes, it is simple to repair problems.   What is problematic is trying to add a third ground wire to an older two-wire building.