v69 transmitting unwanted classic rock...

K

k bucks

New member
hello

i just moved into a new apartment a couple weeks ago. i do a lot of recording for my own amusement but was distressed to find that my entire system was picking up static and radio signals. And yes, I do have a lot of crappy mic leads. But, I purchased a furman RP8 and that seemed to clean the sound up very well (including the sound card, mixer and a number of other mics). However, my Marshall mogami v69 still picks up the classic rock station very clearly, even when plugged into the furman. I've tried switching the cord that runs from the power supply into the mixer, nothing changes. I've also tried putting a three prong adapter on the power cord of the power supply (even shaving off the larger prong and flipping the plug to reverse polarity), but the signal is still clear. Is there anything else I can do? This is my best mic and I like it a lot and would love to be able to use it. Any feedback would be greatly appreciated.

-kevin
 
sorry, i don't have an answer but....

try contacting marshall directly, form what i've heard around here thier customer service is top-notch.
 
Hi Kevin,

It seems like it sucks to be you right now. Can you tell us more about your set up...a list of gear and how you've got it connected up.

What your hearing is likely AM detection picked up in transistor or diode junctions. Most quality gear is designed to minimize this detection by employing various bypass and decoupling techniques. Since all of your equipment is working at the audio level, this one could be tough. I would strongly urge you to not mess with the power plugs. It's just a bad idea really.

Firstly, make sure the ground in the electrical source is properly connected all the way back to the utility panel and that the utility panel has a good ground/earth connection. This us usually done in two places...one at a ground rod (at least one ground rod) which should have firm contact with the soil. The second ground connection often used is a "wet" water pipe, usually the water source for the building. I realize that this may be out of your control...that's one of the bummers of apartment dwelling and it may be tought to get the super/owner to take your complaint seriously.

After that, get out the volt/ohm meter,...make sure the chassis of each piece of equipment you have measures at zero or very close to zero ohms with reference to ground (the ground pin in the utility plug on the wall). Don't forget to check your Furman as well since you probobly plug everything into it and your computer (assuming you're recording to a PC). I would suggest that you do this by disconnecting all cables from each of these devices except for the power plug and making sure they don't otherwise have a physical connection to each other. The idea is to make sure that each chassis gets it's ground through the power cable and not through a shield or other conductor in one of your interconnecting audio cables.

Since you did mention modifying power plugs, make sure that the original type power plugs for each of your equipment devices is used. Meaning, that if it came with a three prong power cable, use it.

I think this covers the basics of the obvious, and asside from ensuring the above, it is still possible for RF to enter into equipment and be amplified to the point where you can hear it. You'll want to try to isolate the likely components. The culprits will be devices with active gain stages. Even though yes...it could be crappy cables allowing RF in...the reason you hear it is due to an active PN type junction detecting and eventually amplifying the signal somewhere in your signal chain.

The mic itself is a possible source (does this happen with other mics?), the V69 power supply is another possibility (again make sure it has the correct power cable and that the chassis is grounded through the power plug back to the power source). Then of course there's the mixer, have you tried plugging the mic into different channels? Is it possible to try another mixer.

Lastly, there's cable managment, ideally it would be advised to group the cable types and keep them seperated from each other. Bundling the audio seperately from power cables is always a good idea and keeping DC (Wallwarts) away from AC and audio is a good idea as well. 3 or 4 inches from each other should be fine. If you find that the RFI is entering through the cables, reclocating the cables and/or using snap on chokes may be helpful.

In short, you've got a tough situation but with patience, you should be able to identify the source and deal with it. Sometimes these thing get real messy. Several years ago, I helped a friend with a similar problem (Ham Radio not audio) but we ended up modifying his gear by selecting very small RF frequency capacitors (I'm avoiding going into the electronic details) and bypassing various transistor junctions. This may be more than you are willing to get into.
 
chessrock said:
At least it's not picking up country or rap stations.

Feel lucky about that.
Click to expand...

Indeed. Or Philip Glass.

But seriously, yes, if it just started appearing at the new apartment, unless you just happened to move right under the radio station's tower, my bet would be a grounding issue.

If you're looking for a quick solution and have unpaved dirt outside, what you could do is to drive a grounding stake into the ground, run a wire up the side through a window, then buy yourself a two prong to three prong adapter that has a wire for the third prong (as opposed to just having a little stub of metal) and solder the ground wire to the wire on the adapter.

Total cost, including the wire and grounding rod.. probably under $20. The savings in sanity... priceless.
 
well, to give a run down of what i'm dealing with..........on the rack a sytek 4 channel preamp, art pro vla compressor, delta 1010 and furman rp-8. all of which are plugged into the rp-8 and then pluged into a three pronged wall outlet. also on the table a computer and monitor, two powered monitor speakers and a mixer (alesis studio 24) which also go through the furman. since i'm out of furman outlets, I unplug the compressor and preamp, plug in the marshall v69 power source and take its xlr output into the mixer's input (channel one). the marshall maintains its strong radio signal. FM, definitely. i've called every music store in town and people have recommended wrapping the power supply in tin foil (didn't seem to work, perhaps the joke was on me), using ferrite chokes (didn't seem to work, radio shack employees exhibited shocking apathy, providing little emotional solace nor a general understanding of their inventory) and pulling off the ground pin from the xlr going into the mixer (too scared fuck up cable, but desperation might lead me to this soon). Just now I was listening to the latest R&B hits on Z 107 (no more classic rock) and discovered that the signal changed the most when I manipulated the 7 pin cable that connects the mic to the power supply (raising it up and down, even touching it and walking away from it, as if it wishes to taunt me). Oh, yeah, I also took everything apart and moved the whole set up to the other side of the god damn room, but that resulted in only a broken file cabinet and a small, yet worrying outburst that I am ashamed to admit. After calming down, I decided to write again and see if any of this could shed light on my little dilema.
-kevin
 
Kevin...I feel your pain...I really do. I wish I could come out and give you a hand. If it were me, I would be breaking out the o-scope and volt meter about now. The problem is that your entire set up is acting like a big antenna. :(

Are you saying that the only time you have this problem is when you have the MXLV69 mic connected up? No other mics do this?
 
i appreciate your understanding, its a bitch. a big fat-ass bitch. after i return my ferrite chokes, I guess I'll get my hands on some of the devices you've mentioned. there are a couple studios in fairly close proximity that I will contact tomorrow. i am even considering contacting the company that owns my building and asking if some sort of electrical engineer/handy man can come over and at least check the grouding situation downstairs. it seems as if there must be some logical series of events causing this to happen, which in turn gives me hope that there must also be a solution. i presume that this equipment is designed to pretty much work anywhere except underwater or in space. even my right speaker is now transmitting something mysterious. hope remains.
kevin
 
i've checked out the radio tower situation, nothing too close, but I just called the landlord(s) and discovered that this particular building is so old that it might not be properly grounded (to earth anyway). I went downstairs, brushed back the cobwebs and found a thick bundle of wires latched onto what appears to be a water pipe, so maybe it is grounded there. I still have no idea.
kevin
 
Yeah that sucks...and I can relate.I have some bad wiring/grounds in my house and pick up a Mexican radio station (news in spanish and horn playing music :D ) thru my tube amp...and I live out in the weeds :eek: I was told there's a big spanish speaking radio station a couple hours to the west of me and that must be what I'm picking up. I bought a furman deal after talking to the amp company,and it helps a little but short of a house rewire job,about all I can do is noisegate it out. :rolleyes:
 
k bucks said:
i've checked out the radio tower situation, nothing too close, but I just called the landlord(s) and discovered that this particular building is so old that it might not be properly grounded (to earth anyway). I went downstairs, brushed back the cobwebs and found a thick bundle of wires latched onto what appears to be a water pipe, so maybe it is grounded there. I still have no idea.
kevin
Click to expand...

That would be what passes for a ground in some buildings, yes.
 
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