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XD V-75 TR system strange interference!
by jamesmaxn on 2013-01-09 15:31:28.8180

Right, I have a 8 way Xd V75 system and had a issue with a pocket pack. Firstly it's a all up to date receiver wise but need to check the pack's maybe that is the issue,,, I'm using DPA4066, 4067 not happening on any other transmitter just this one unit. The sound is as a constant noise in the 1k region with a white noise sort of thing going on. Goes away when you compleatly envelope the transmitter in your hand? Changed the channel, position, receiver! So thinking the pack is faulty or is a software issue, one of the 8 systems was a older software version so had to update it. Would that be a problem for the pack!

Also this is all brand new and never used before! Rehearsals underway for there first show!!!!

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-09 16:49:11.9170

I got to this as soon as I could, James...

I'm thinking that it's very unlikely to be a firmware "update" problem.

That "fizz-like and shashy, harmonic" noise may very well be the one that I sometimes get when using my "break-out" cables to run various mics via the TA4 connectors of (any one of) the eight TBP12 beltpacks that I routinely operate.

Click onto my pink avatar at left for details of my location equipment and M.O.

If that's indeed the issue, then it's caused by the inadvertent pick-up and "passing on" of the transmitter's own data stream through "leakage" into the unbalanced (analog signal) wiring from the DPA's mic "head" to its screw-on "microdot" connector.

Two things to check:

  1. Remember that the DPA's microdot system is UNbalanced, so any attempt to "neaten" the performer's cable by "bunching" the cable anywhere in the vicinity of the transmitter will create a perfect inductive pickup for feeding its RF data stream into your signal path. Any such "bunch" or "loop-wound" shortening must only be achieved through the use the performer's body as an "RF shield", other words you'll need to "gather" this excess wire on the side of the performer's body that's opposite the beltpack transmitter. Should attending to this NOT effect a "cure", then..
  2. My two complaints with all of DPA's fabulous miniature mics are both the lack of solidity and the price of their microdot hardware, so make absolutely certain that the shield is indeed making its connection via their expensive microdot to TA4M "barrel" adapter. Try another barrel adapter if you have one available.

Fingers crossed...

Re: XD V-75 TR system strange interference!
by dboomer on 2013-01-09 21:45:54.3220

That sounds like a hardware issue with internal clocks and syncing.  Use the "contact us" link at the bottom of the page and open a service ticket. and we'll take care of it.

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-10 01:28:28.9210

It just occurs to me that one quick way of confirming whether it's indeed the beltpack (hence not the unbalanced mic connection that I'm suspecting) would be if you happened to have another "trouble free" DPA headset mic and adapter, or (even better) a Line 6 lavalier mic to substitute for the combination that's giving you the problem.

Should the beltpack prove to be OK with another mic, you will be well on the way to localising the fault.  

Re: XD V-75 TR system strange interference!
by jamesmaxn on 2013-01-10 01:32:34.9460

Was begining to think it would be a hardware fault as it is just the pack, dose it with the mic connected and without, although a little less of the noise is apparent. The audio quality is fine just this noise. All except a few of the dpa's have new 4 pin connectors on them, the others have the expensive microdot adaptors, the ones i terminated and the microdot ones are exactly the same. When i get to the venue later i will have another play.

Problem is now im in the uk and i got the systems from Thomann Germany so no overnight replacement from them.

Oh well!!!! Will have dig out my old sennheiser's to do the gig.

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-10 01:47:25.5320

As an aside, I'm always amazed by the harmonic variety and shattering loudness of the digital "storm" that I can induce from my TA4 to XLF mic cables when they're left un-terminated.

However correct location of the cable once the mic's connected invariably yields the pristine audio that I've come to expect from my XD-Vs.

As you've tried other combinations, it looks like the amazing Don Boomer's right "on the money" yet again, so your suggestion of a Sennheiser replacement would seem to be the only practical way to get on the air, unless these guys can either lend you a replacement or know of someone who hires them out: 

Re: XD V-75 TR system strange interference!
by jamesmaxn on 2013-01-10 04:08:30.3150

Well thankyou for all your help so far. Indeed the little use i have had from the system has yeilded some great results, the dpa's as you would expect are superb and the sound through the line 6 system is as good if not a little smoother than the senn g3 5oo's i have been using! Will let you know what happens!

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-10 04:55:20.0310

"Goes away when you completely envelope the transmitter in your hand ?"

That's still "bugging" me as I would not expect un-clocked or otherwise corrupt data to respond like that, whereas attenuation (by the salt-water filled human anatomy) of RF-induced "stray" digital noise certainly does.

I look forward to hearing the results of whatever further experiments you're able to try in the little time you have before "curtain up".

Re: XD V-75 TR system strange interference!
by jamesmaxn on 2013-01-10 15:19:49.2410

Right I had some time this evening in the theatre to get my head around the problem. Im thinking I'm adding too much gain at the desk end, with all the transmitters active the interference is apparent on all but very quiet.

I made all my DPA's connections on the TA4's by copying the pins in the Microdot to TA4 adaptor that was with one I had laying around.

Pin 1 ov

Pin 2 10k to a Zener then to pins 3,4 with the hot soldered between the Zener and resistor.

Had a play tonight changing the resistor values, not much difference, had no caps to try replacing the Zener with a cap. Next thing to try.

Reason I'm trying all this is even with a powerfully singer wearing a headset the receivers VU led display only flashes on the first 1-2 LEDs!! Is this normal or should I be getting a hotter signal?

So adding the extra gain at the mixer might be why I'm hearing this noise?

Guess I will just try some more configurations on the TA4 to get better results.

I still get a good sound from each receiver but think I should be getting more into the transmitters!

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-10 15:58:26.8300

I reckon you needn't bother with a cap instead of a zener, the actual method of blocking DC back to the input would seem to be irrelevant and everything else in your wiring would seem to be exactly as you and I would expect.

In the event that you're listening at a very high "critical evaluation" PFL level on headsets, then maybe you are right in thinking that your perception of the unbalanced mic-induced noise floor is (dare I say it) "too critical".

However, if you feel you really must have extra gain at that input, (and if you have the time to do so) I think you'll need to at least double the value of that "pull-up" resistor to about 20 or 30kΩ.

An earlier discussion related to such a "gain-maker" (albeit for a Shure headset) can be found here:

If it was me, I'd prefer the extra headroom and so would leave the values as they are, ...UNLESS there was a need for absolutely pristine individual multi-track recordings for later album-related re-mixing and/or overdubs.

Even then, it's my experience that the "Norm" setting of the superb adaptive processing that Line 6 calls their "Dynamic Filter" performs a "clean-up" that's more than adequate for most applications.

I just hope that you've enough rehearsal time remaining to try it, although enabling just the "Norm" setting ("live", at the receiver/s) would almost certainly pass un-noticed in "the house". 

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-10 18:49:43.3480

Oh, ...and very much "by the way"...

I find that the "Audio" LED column on the front panel can't be interpreted as any form of "meter", but has the effect of being more of an "audio activity" indicator that's ideal for quickly locating a given source of "splatting", intermittent disconnection or other such heart-thumping annoyance that's been created at the on stage "business" end.

Re: XD V-75 TR system strange interference!
by dboomer on 2013-01-11 09:13:27.4580

Re: Audio Meter LEDs

Maybe a little different than you might be used to.  Think of it as 4 LEDs and not 5.  The top one on V75 (not V70) indicates clipping and is red.  So "normal would be 2 or sometimes 3 LEDs lit green while giving you proper headroom.

Re: XD V-75 TR system strange interference!
by jamesmaxn on 2013-01-13 14:47:11.7530

Thanks for all the help and suggestions! We have had a few rehearsals now within the v75's and so far they have been fine! Looks like 3 of the dpa headsets were causing the weird interference I was talking about.

I'm thinking it's down to the mics been old, not had the time to do more research into the problem to be honest.

As soon as I changed them for some Chinese specials off eBay I got much better results although a sound quality dip.......

Still a few more runs then the shows.

I also re-located the rack to FOH so the directional Antenna were facing directly towards the stage. I had them back stage, mainly moved the rack so I could see the signal levels etc.....

By the way I'm using all 8 with the 8 way distro and active antenna's.

I will get to the bottom of the dpa problem when I have more time.!!! Still impressed with the sound!

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-13 15:31:21.3570

Me too. I've yet to experience a more natural-sounding or versatile range of miniature microphones than DPA's, including their newest "d:fine".

"On the road", my only two concerns have been

  1. The price of (and the occasional connection problem with) their microdot screw-on system and
  2. That their amazing bass response can yield feedback "surprises" in the event that adequate subsonic roll-off has been overlooked.

I'd be very surprised if the age of the "culprits" was to blame, as some very old "originals" are still on the air every night here, sounding exactly as they did when first unpacked.

However, I seem to remember that two sensitivities were on offer when the range was introduced about ten years ago, so perhaps you've three of the lower sensitivity version among yours.

Re: XD V-75 TR system strange interference!
by jamesmaxn on 2013-01-29 04:29:27.4360

Right!! Late follow up to my orignal post!!

The Panto went well!! Had to substitute the weird mic with a UHF unit but here's the thing!!

On down time between peformances we obviously tried swapping packs, headsets, Lapel mics, receivers and still the same problem on only the one person!!!!!!!!!!!! thinking she was somehow electricly charged!, yes i know strange conclusion but realy had no other explenation i gave up and just used a uhf sennheiser and problem solved.

Now i'm on another production with all 8 XD75's all still in mode 2, this new venue is a school with every channel on the scan feature Full on the wifi!!! Networks everywhere!!!!

But with the rack on the stage and local P180 antenna on stage all was fine.

Now here is the strange thing. One pack was attached to the back of a womand bra as i did in the last production i did, and again that same noise!!! Moved the transmitter to her waist and a belt to hold the pack on and all was fine!!

So i'm thinking that the metal in the bra's are somehow creating a interferance field?

has anyone else had a simlar situation??

I must admit i still havn't tried changing the RF mode.

Re: XD V-75 TR system strange interference!
by dboomer on 2013-01-29 08:11:21.7390

I see a couple of points in your post that concern me.

You are using the mics even though the scan shows  full interference bars on the channels you are operating on?  That is risky, especially in RF2 mode.  I would suggest switching to RF1 mode.

Interference ... even if the performer's costume is causing interference, that interference cannot become audio in the radio.  We send a code in the header of every digital packet and when the receiver receives anything that does not have the code then it does not make sound.  And if that reception is "audio" that doesn't pass either as your are still in the digital world.  I can't say for certain, but the most likely cause is a mechanical one.  Did you also try swapping transmitters?  

Re: XD V-75 TR system strange interference!
by RonMarton on 2013-01-29 16:23:47.6810

Your taking the time to post that "follow up" may prove really valuable for others suffering "strange interference", many thanks!

First of all, I cannot emphasize strongly enough the importance I also attach to Don Boomer's sage recommendation that you switch ALL of your transmitters to operate in the (far more robust) four-frequency-diversity "RF1" mode.

Now to the vexed issue of (...ahem) undergarment support.

Don is (as ever) absolutely correct as far as the pristine excellence of all audio once it's actually in an XD-V system's transmission path, but I'm sure he'll agree when I say that his comments really only apply AFTER the analog audio has actually been bit-mapped.

Which brings me back to another vexed issue that I touched on earlier, ...the problems I've repeatedly experienced with the unbalanced wiring from DPA's (otherwise superb) miniature microphones.

I'm referring to the fact that ANY waveforms fed into the beltpack's TA4 connector's "+ and -" will always be transmitted with the utmost fidelity.

If those waveforms happen to contain a proportion of the transmitter's own encoded RF signal (in the case of the support garments in question, reflected from adjacent underwiring metalwork and induced into a length of unbalanced mic cable) ...then that's what will be heard.

Hence my earlier recommendation ("Point 1" of "two things to check" in my very first reply to this discussion) regarding the care I've found that needs to be taken in dealing with excess cabling from DPA mics.

As I also mentioned earlier, anyone can easily experience the "racket" of such accidental induction by plugging an un-terminated length of XLF to TA4 mic adapter cable into a Line 6 beltpack and then listening to its receiver's output.

A variety of "bunching, bending, grabbing" and "moving alongside the beltpack" manoeuvres will then yield a truly impressive array of "soundscapes", ...some of which may well prove useful for a future audio work.

So, matchlessly natural that the sound of DPA miniature mics may be, it's been my oft-repeated experience that the nature of their cabling means special care MUST be taken with their fitting, especially to such iconic figures as the operatic "knight in chain mail" and/or the buxom "fair damsel" whose hand he seeks.

"Arise, Sir James ...and may thy Noble Quest grant thee and Sir Donald the just peace that thou desirest."  

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