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Tbp12 + Shure Wa310 + Countryman Isomaxii Bpm + Condenser Mic


Best Answer arthurrs , 10 February 2014 - 03:47 PM

Yay, problem solved!  Thanks to a phone call from the folk at Earthworks audio, they gave me an interesting insight on their microphones.  Apparently at lower power levels used by the countryman battery power supply, they recommend reversing the polarity of the connection between the microphone and battery power supply to work better with the preamp circuitry in the microphone.  Once I inserted a polarity reverse adapter between microphone and battery power supply, and another one at the output of the receiver to my preamp, I got a perfectly flat frequency response, 0 degrees phase through the entire passband, and even more output level than before!  Ok, I'm off to the races with this setup!  Sweet!  Can't wait for my second wireless XD-V75 system to arrive at my doorstep! And maybe a third and fourth one soon.... :)

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#1 arthurrs

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Posted 10 February 2014 - 12:06 PM

I have the following configuration:

 

TBP12 relay transmitter hooked up to...

Shure WA310 adapter cable from F-XLR to TA4F hooked up to...

Countryman Isomax II BPM Battery powered phantom power supply hooked up to....

Earthworks M23 condenser microphone very flat to 25 KHz.

 

XD-V70 receiver is hooked up to one channel of a dual channel FFT.  Another identical microphone wired directly to the other channel of the dual channel FFT.

 

Comparing the direct output of the mic vs the output of the above wireless in the above setup, I see a polarity reversal and a HF shelf starting at about 1000 Hz, cutting to about -6dB by the time you get to 10KHz.

 

Ok, so a process of elimination to figure out the problem:

 

1.  Eliminate the microphones and the phantom power supply out of the equation:  a pink noise generator is plugged directly into the WA310/TBP12 and the XD-V70 is plugged directly into one of the channels of the FFT analyzer, pink noise generator y'd into the other input of the dual channel FFT, I get a flat response that is in polarity.

 

2.  Wire the two identical mics directly to the dual channel FFT, one channel using the above mentioned Countryman phantom power supply, then other mic sourcing phantom power directly from the preamp to the dual channel FFT, I get a flat response that is in polarity.

 

These mics are part of a matched set, within a fraction of a db of each other, with compensation curves applied so one can measure a flat response comparing the two without anything in between.  I even swapped them out for another known pair that tested good.

 

I'm suspecting a wiring issue between the WA310 adapter and the phantom power adapter?  Maybe the phantom power adapter doesn't like the unbalanced connection on it's output?

 

Would love to hear your thoughts/advice on this.


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#2 RonMarton

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Posted 10 February 2014 - 01:30 PM

As it happens, Arthur...

 

...I've only ever simultaneously XD-V transmitted both "sides" of a similarly battery phantom-supplied (Deneke PS-2 taking the place of your Countryman supply) stereo pair of condenser mics, (Audix SCX 25s inside a piano, various AKGs and Neumanns elsewhere) so such phase reversal as might exist in my WA310 adapters has been of no consequence for me.

 

Indeed "absolute phase" is maintained over my entire (albeit small) reinforcement rig, as ALL of my acoustic sources are sent from stage to console via TBP12 beltpacks or Line 6 XD-V handheld transmitters.

 

Following your discovery, should there ever be a need to "mix and match" cabled pickup with TBP12 wireless, I'd now be looking at swapping the pin 2 & 3 terminations inside the XLF connectors on my eight WA310 adapters, or simply reversing the phase of the "odd one" at my console.

 

To my mind, that HF roll-off is a far more serious artefact ...and one that my old ears can assure you is NOT evident when any of my inventory of "studio" condenser mics (even the current-sapping Neumann U87s) are Deneke-powered into my TBP12 beltpacks.

 

Which, I guess, brings us back to your suspicions regarding the Countryman supply ...and I reckon they're valid, but maybe impedance isn't the main issue.

 

The Countryman BPM really only supplies what we old fogeys used to know as "Simplex" powering, being a low voltage "phantom-wired" 18 volts of DC, whereas my Deneke supplies pump out the full 48, as does your FFT Test set.

 

So I'm thinking it's a fair bet that the roll-off you've observed may be the consequence of your magnificent Earthworks M23 measurement mics being "starved" of volts when they're (only just) operating from that Countryman Battery Power Module.


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#3 arthurrs

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Posted 10 February 2014 - 01:44 PM

My suspicion is the unbalanced input of the TBP12 is throwing something off between the countryman power supply and the Earthworks mic.  Maybe there's a way to make it impedance balanced in the adapter cable?  The power from the countryman is sufficient for the Earthworks mic, since it works fine plugged directly into my FFT's mic premp.  I have left messages with Earthworks and Countryman to see if they can shed any light on this situation, I'll post back any findings.  Otherwise I find this Line 6 system a very compelling one for this application...with my pink noise generator, it's flat in magnitude and phase from 10 - 20000 Hz, no companding!


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#4 RonMarton

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Posted 10 February 2014 - 01:56 PM

Sorry Arthur...

 

I misread your (2) above.

 

Can you get to either of these stores to try one of these instead of the Countryman BPM ?

 

http://www.bhphotovi...ble_Single.html

 

http://www.bhphotovi...table_Dual.html

 

From your results so far, I'd now be more inclined (as you originally posted) to think that it's the BPM's output that's loading the beltpack's input, rather than any issue between the M23 mic and the BPM's input.

 

I also share your enthusiasm for the pristine signal path provided by Line 6 XD-V wireless. Indeed, I use eight channels to replace the heavy and bulky 100 metre drum of Canare star-quad audio "snake" that I used to haul around, along with its eight-way stage boxes.


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#5 arthurrs

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Posted 10 February 2014 - 03:10 PM

Slight topic tangent, Ron I assume that you are doing recordings, are you doing them in a separate room from the microphones?  Curious on how you manage your receivers and antenna system?  How far are you from the transmitters?


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#6 arthurrs

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Posted 10 February 2014 - 03:47 PM   Best Answer

Yay, problem solved!  Thanks to a phone call from the folk at Earthworks audio, they gave me an interesting insight on their microphones.  Apparently at lower power levels used by the countryman battery power supply, they recommend reversing the polarity of the connection between the microphone and battery power supply to work better with the preamp circuitry in the microphone.  Once I inserted a polarity reverse adapter between microphone and battery power supply, and another one at the output of the receiver to my preamp, I got a perfectly flat frequency response, 0 degrees phase through the entire passband, and even more output level than before!  Ok, I'm off to the races with this setup!  Sweet!  Can't wait for my second wireless XD-V75 system to arrive at my doorstep! And maybe a third and fourth one soon.... :)


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#7 RonMarton

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Posted 10 February 2014 - 05:32 PM

That result not only also confirms my (long held) esteem of the folks at Earthworks and their microphones, but also my first suspicion that inadequate supply voltage may have contributed to this matter.

 

...I assume that you are doing recordings, are you doing them in a separate room from the microphones?  Curious on how you manage your receivers and antenna system?  How far are you from the transmitters?

 

Strange as it may seem, Arthur...

 

...and as you'll soon see from a quick look around here, it's the vast versatility and mind-boggling variety of their RF arrangements that gives rise to many of the "dropout", (range) and "interference" queries in these forums, to the extent that I now always qualify my otherwise unequivocal recommendation of Line 6 wireless with phrases along the lines of "provided you familiarise yourself with their set-up" and/or "check their knowledge base and FAQ before committing to a rig, so as to get one that suits you".

 

Yes, I occasionally do "snoop" recordings ...and my Sennheiser HD25 II (or my just recently acquired Focal Spirit Professional) headsets allow me to share the performers'  acoustic spaces, yet still be absolutely certain of how my signals will sound via state of the art monitors (from the likes of Adam, ATC, Dynaudio, Eve, Event, Focal, Genelec, Neumann, Quested and Tannoy) once I'm back in the studio.

 

As for the often vexed question of range, my five handhelds regularly yield reliable operation over three times Line 6's stated spec of 100 feet, having proven to be "bulletproof" at 100 crowded metres ( ! ! ! )  ...when operated in RF1 via my correctly configured and thoughtfully deployed P180 paddle antennae.  :)

 

Given those RF arrangements, even nitrile glove-enclosed beltpacks fitted to soaking wet Rugby referees also remain pretty much dropout-free over slightly smaller distances, with the absolutely silent nature of their occasional digital drop-outs making those momentary interruptions of very little consequence to the crowds who enjoy being "kept posted" via my PA systems.

 

( "...Get 'em back onside, Ref ! ...Red card, you blind boofhead !"  etc. etc.)


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#8 arthurrs

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Posted 10 February 2014 - 08:59 PM

Very interesting Ron!  At what point did you find the paddle antennae helpful in your work?


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#9 RonMarton

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Posted 10 February 2014 - 09:28 PM

My pre-purchase research led me to order four (two for each of my initial two rack "kits" of four XD-V70 receivers) right from the outset, Arthur.

 

That being said, I often simply use a pair of the supplied "rubber ducky" whips atop each rack when covering indoor "conference" and other less-demanding (shorter-range) applications.


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