Attn: Jeorg - How goes the digital recorder install?

So far so good. The Marantz is programmed to automatically record worship services and the resulting MP3 is transferred to the server immediately afterwards. The front panel controls are blocked so nobody can mess with the machine. We will probably unblock them once we have an audio team scheduled and, most of all, well trained. Manual operation is rather simple once it's programmed right. Hit the record button and it begins to spool audio onto MP3, later hit stop and that's it.

We do have some issues with the CAT-5 spitting out EMI into pastor's wireless mike receiver (Shure Marcad) but that thing has problems with just about any noise source. Light switches and such. The Sennheiser receivers perform much better so some day we want to switch everything to that system.

Before we make this permanent and stop backup tape recordings we will have to clean up all the cabling. Holes are mostly drilled already, cable trays are installed, and I cut the 19" rack to custom height. But we don't want to risk a major hickup for the Christmas services so our IT guy and I will tackle that job right after Christmas. Run cables properly, install shielded CAT-5, some ferrites, spread audio and power runs apart, ground everything. It is unbelievable but even high end stuff like the Marantz recorder or the Sennheiser wireless does not have ground terminals (%^#&!!). So I'll have to take the drill and some self-tapping screws.

Is this perhaps because so few people would know what to do with a ground terminal? I've read through the proper way of grounding using nice, wide, low-inductance braid, but of all the "grounded" systems I've seen, many just use something like 12ga. wires that are run many feet to some star ground... and that sort of wire is already not that great of a "ground" by the time you hit high HF, much less VHF or UHF.

---Joel

Thanks Jeorg! What is the separation between the Marantz and those wireless receivers? Same rack? All my Shure wireless are in the back, but the recorder is in the front, so I shouldn't have any noise problems...

Charlei

Yes, in the same rack, about 2ft from the diversity antennas to the CAT-5 jack of the Marantz. If you guys ever need new mikes take a look at Sennheiser. The only things too flimsy on those are the mute buttons. Sennheiser said that pastors use those too often. Well, they advertized them for worship use. Duh! Maybe more of their engineers should go to church ...

True, but even 12AWG can work wonders on a crackling audio problem. As long as you keep the run short, under 1ft or so. Now we have to drill each and every one of the boxes, vacuum the burrs out, screw back together. I guess that'll take all morning. It is also quite disappointing that "high tech" gear comes with anodized aluminum panels and 19" racks are powder-coated. The only method to get a decent ground there is the Dremel tool and then it doesn't look good anymore.

On a sunny day (Wed, 17 Dec 2008 09:49:59 -0800) it happened Joerg wrote in :

Joerg

mm, not sure about that Marantz, but I grounded my Chinese 10inch amp by using the XLR input, ground pin (do not normally use that input). So just plug in ground. As you can see, those XLR are grounded real good (yellow green wire goes to case): ftp://panteltje.com/pub/PA3000/xlr_rear.jpg

case):

Well, we use that XLR jack and I don't have much faith these days that the desiners knew how to route that peoperly on the inside. Nothing beats a good old ground stud.

case):

Except, of course, when using the ground stud adds in ground loops throughout the rack. Had that happen to me once in a big installation. Ended up going through the entire rack and adding insulation between the rack ears and the rack on each piece of equipment... :-(

Charlie

using

case):

That can quickly lead to a hazard. In that case I always go the iso xfmr or DI route. Sometimes Radio Shack has decent audio transformers, sometimes autoparts stores do, and if it has to be really good there is MuxLab.

Proper audio equipment never has ground terminals to avoid ground loops. At least that's what I've been told when working at a company that did a lot of similar audio systems in churches. Usually the amplifier was the only thing that was grounded.

There are special mixer amplifiers that can use a microphone to mute the pastor automatically when the organ plays. If I may promote one I designed:

using

case):

Yeah, but problem occured when project had three racks, on in booth, one stage left, one stage right, on at least two different phases, plus various other equipment in other locations. We measured 1-3VDC between the various portions of the same room's ground!

Charlie

I wouldn't characterize that as "grounded real good", at least as far as RFI/EMI problems are concerned. It doesn't look as if the XLR jack pins are connected to the XLR jack shell (and hence to the case) via a direct path - they're just connected to the yellow/green ground wire which then goes to the case.

This is a recipe for (in fact, it's almost the definition of) a "Pin

From what I've read, it's best of all to keep the RF entirely out of the cabinet (ground to the outside of the chassis), and when that's not possible (as with XLRs) it's important to minimize the length and inductance of the ground strap between the connector ground pin and the shell/chassis.

It the case of this particular bit of kit, it'd probably be better to connect the XLR pin 1 directly to the shell of the connector (I think I see a small screw fitting on the shell right above it, which might be a suitable grounding point).

See

using

to case):

Wow, that would be a good time to get to the ground of that. Since this is probably a place of public jurisdiction a certified electrician should be called. Before a current heats up a signal wire and something catches fire.

On a sunny day (Wed, 17 Dec 2008 14:15:31 -0800) it happened snipped-for-privacy@radagast.org (Dave Platt) wrote in :

Yes, I was not 100% clear about that, on the XLRs the ground pin leads, and that is the one I used (not the shell). So I am not using the yellow / green wire that goes to chassis, but a hard to see black wire that goes to the PCB, the ground of the differential input.

The reason I used the ground is this: There are phone input (tulip) connectors I use. If you plug these in, and the rack is not grounded, then you get a huge hum surge out of the speakers, as the signal pin will make contact on those tulips before the ground does.

So just to prevent hum, nothing to do with safety, although it provides some shock hazard protection, as the other end of the ground wire is screwed on the PC case (where the audio comes from), and the PC is grounded to mains ground. So no earth loops this way, and no unexpected noises when plugging in those tulips in the line input. Has worked perfectly that way, there is a same ground system to my CB radio transmitter. Not even a lot of 27MHz RF power does anything to this setup.

You can't sell that to America :-)

Main reason is that pastors chant, at least in Lutheran Churches. For example during the "Lord, have mercy" part of the liturgy. But yeah, long term we'll form an audio team and then just turn the slide pots up and down.

That belief is IMHO founded on a lot of misconceptions. It is how situations like this happen, to be exact it was last Saturday at 4:30pm at our church: A women's choir used it for a public performance. They had invited a tenor singer doing an a capella sans microphone. He's obviously quite famous so photographers were there. One of them stood next to the audio booth, fired off his camera .. brrrzzzzt ... *POCK* ... rat-tat-tat ... phsssss. EMI straight into the ("professional") audio gear, from the flash circuitry of his camera. So here's me doing a mad dash from 3rd row to the back and turning down all slide pots, hoping I'd remember how they were set for when the women's choir starts again. Whew!

I sure wish audio engineers were taught at least a wee bit of RF know-how. It would save us from a lot of grief. A ground terminal _is_ important. Here's another reason: Most racks are painted, and of course nobody ever bothers to tape the threads. So is most gear. Now you screw all this into the rack. Some of it makes contact, some not, other gear maybe a little but only when there is a full moon. All depending on chance. IMHO that is most certainly not a professional setup but, unfortunately, a very common scenario.

Another test you can do: Take a GSM cell phone and turn it off. Walk up to a running audio rack, then turn the phone back on and listen. You'd be surprised how many audio engineers do not know that opamps with bipolar inputs such as the nice low-noise NE5532 have parasitic RF rectifiers right at the inputs, the BE junctions:

Someone turns that big battery of fluorescents on, RF pulse comes along ... *POCK*.

using

to case):

Radio & TV studios usually use 3" or wider copper strap to bound all the racks together, and connect one end to the ground system. I've had bad ground loops in an old studio that required removing all the grounding you are talking about adding, to keep the AM transmitter's signal from being detected & causing feedback. That station was built right after W.W.II at Ft Greely, AK. We had to bond the racks, and drive

You should have been able to turn down the master gain control and leave everything else alone. For systems with multiple uses I always make a chart that listed every control, and the settings for that use. Then when the operator gets there with only minutes to spare, a quick look and they can tell if they are in the ballpark.

I wish EEs would learn to use star washers between rack panels & the rack at each mounting screw to properly ground things when installing equipment. :) They don't show that way, yet provide a good contact. The old racks with the clip on nuts had sharp edges to pierce the paint on the rack panels from the rear, but I've see a lot of home made racks with wood sides & separate rails used to dress up installs in public places. The best racks for good grounding & easy access are this style:

They are used in high RF areas to ensure the bonding of all the rack panels. The open backs make it easy to access the wiring and to add or remove equipment. If they are set into a wall, they can look as good as the fancy wood cover racks that seem to be in style for churches & public buildings.

That is caused by one of the big cost cutting moves. The elimination of the transformers & balanced Inputs and Outputs. I used to get lots of calls from churches that installed their own equipment. Some of them thought they could get an estimate and go buy the same, or similar equipment and do the job themselves. They would ask for a bid, then use my specifications to buy the equipment and let a member hack together a system. When they saw the input transformers were listed as 'Optional' in the manufacturer's ads, or that single conductor, high impedance microphone cable was cheaper than the shielded pair, they always cut corners. Then a radio station, CBer or police radio would come blaring through the speakers during a service. Sometimes it cost more to clean up their mess than I had quoted to do the job right, in the first place.