A Zaxcom Newcomer’s Look at the TRX742.5 Plug-on Transmitter

April 16, 2014 – 3:03 pm

Okay, first off. I have never owned a single piece of Zaxcom gear. This is my first look at integrating Zaxcom into my Sound Devices / Lectrosonics “heavy” kit. So, this review will be written from the perspective of a Zaxcom newbie.  

Why the TRX742.5? Our team really wanted to find a wireless way to quickly switch from our analog microphones to the digital AES42 powered Schoeps Super-CMIT (preserving both channels of audio from the Super-CMIT) while recording to a Sound Devices 788t. The Zaxcom TRX742 series (in our case, coupled with a Zaxcom QRX200 Receiver) is the only single solution product on the market to allow a boom operator to go wireless with a Schoeps Super-CMIT 2U while transmitting both the DSP(Digital Signal Processed) and non-DSP tracks independently and discreetly. Our current analog wireless system consists of a Sound Devices MM-1 Preamp, a Lectrosonics SMQV Transmitter and a Lectrosonics R1a IFB for talkback. The kit is great for a wireless analog boom, but it would not work for the SuperCMIT… it lacks two channels, AES42 power and Digital transmission (or Digital to Analog conversion). That being said, much of this review will be like comparing apples to oranges, as the 742.5 crosses the boundaries compared to the other tools in our existing kit with it’s built-in multiple features.

Sound Quality We did a test between two Schoeps CMIT-5Us. One with a TRX742.5 and the other with a Lectrosonics HM. To my ear, they both sounded very good. The frequency response on the low end was very subtlety different between the two, but negligible. When we tested the SuperCMIT, we found both channels to also sound excellent on the TRX742.5’s two channel feed.

Battery Life We powered the 742.5 with three Energizer Ultimate Lithium batteries. Run Times @ 125 mW:

  • SuperCMIT Stereo mode w/ AES42 cone: 3h 8m
  • SuperCMIT Mono mode w/ AES42 cone: 3h 20m
  • CMIT-5U Mono mode w/ Analog cone & Phantom Power: 5h 58m

Note: There is a “Power roll” setting that drops the power transmission level down when you are not rolling. This can be set to be triggered by one of two events: “Deva Trigger” via Zaxnet or “Record Trigger” via the REC button on the transmitter. Without a Deva, I couldn’t use the “Deva Trigger” function.

Neverclip / Limiter In analog mode, the Neverclip limiter is impressive. I whispered… it sounds great. I YELLED, it still sounds great. Good stuff! Of note, there is no digital limiter available when using AES42 mode with a digital microphone. It will clip if the maximum decibel level is hit.

Howy at Zaxcom says “There is no NeverClip in the digital mode. You can turn off the compressor (DYNAMICS page) if you want, but I would keep it on because it can really get you out of a jam if someone starts yelling and in almost all cases it makes the audio just sound better on average.” 

Interchangeable Cones for Modern Microphones The TRX742.5 has multiple cones for use with different microphones. There are four different styles: Analog, Stereo, AES & AES42. The cones come on/off with two screws. The cones I have for testing (Analog & AES42) look very much the same. Upon closer inspection, there is a hand-written note in permanent marker on the inside of each cone which designates it’s type. As with many modern audio devices, the TRX742.5 does not support T Powered Microphones.

Timecode Integration w/ Non-Zaxcom Gear The 742.5 can be set to accept mic-level timecode via it’s audio input XLR while using the Analog Cone. You need to set the TC Input in the Extended menu to Audio Input. (To enter the extended menu, turn the unit off, hold the menu button down while turning it back on.) If you need to jam it via your 788t or a Denecke SB box, you will need to pad the signal down by 20 dB. One downside for non-ZaxNet users of the TRX742.5 while using the AES42 cone, you can not jam timecode via the audio input as the TC signal is analog signal). You must use ZaxNet enabled device to jam. One option is to add an Zaxcom IFB transmitter to the kit. This is able to pipe timecode to the 742.5 from a 788t or other style timecode box (such as a Denecke SB-T). This would also add the benefit of constantly refreshing the timecode between devices. I tested an IFB200, and with some minor setup was able to get the device to jam via Zaxnet.

Wideband Frequency, New Frequency Modulation & Encrypted Audio Transmission One of the big differences between the 742 and the 742.5 version of the TRX is that the newer version now can operate with a much greater frequency flexibility, a.k.a. Wideband, between 512 & 698 MHz. (Blocks 20 to 26 on the Lectrosonics charts). Zaxcom says their new software modulation increases the range of their transmitters. I can’t personally compare it with the older version, but I have heard from other sources that it is better. The Zaxcom signal is also encrypted from point to point between the transmitter and the receiver.

Backup Recording The 742.5 has timecode stamped back-up recording abilities. It records to a format called MARF (Mobile Audio Recording Format) which is considered as a highly reliable format. Even if power is lost, the recording will remain intact up to the point of the power loss. It does involve the need for conversion to use with some programs. It will record both channels of a stereo microphone or an AES42 powered microphone.

QRX200 integration w/ Lectrosonics Venue and Antenna Cables Antenna integration worked very well. We daisy chained the antenna leads from the QRX200 into the Lectrosonics Venue with some custom SMA to BNC cables and we were able to use our existing Lectrosonics ALP600 antenna system.

Transmission Distance We compared the digital TRX742.5 (@125 mW) with the HM (@100mW) on some range tests around the studio here. We found them to be similar with the HM giving a little better range. While the HM dropped out and was spotty… the TRX742.5 signal was gone completely. While both signals were unusable at that point, the TRX does have the backup recording option. It could certainly save the day in certain situations. This test was in and outside of the studios and was not line of sight. We also did a range walk test on the TRX742.5 between the whip antennas and the Venue/ALPs. There was definitely an increase in range using the sharkfins by about 50 to 60 feet. This also was not a clean line of sight test. The cart remained in the studio and my boom operator went outside until signal dropped out.

Zaxnet ZaxNet allows allows you to control levels on transmitters, passes timecode between devices automatically and other helpful and intelligent functions. Without Zaxnet, I was unable to use these functions. However, when I added a Zaxcom IFB200 into the workflow, I was able to pass timecode and it also allowed me to remotely control the gain on the TRX742.5.

Build Quality & Form Factor The 742.5 is about ¼ to 1/3 larger than a HM, which makes sense as it has a much larger feature set. It is about 2/3 enclosed in a decent thickness metal. The battery enclosure is plastic with a flip up lid. It is held closed by three small magnets. Two screws hold the interchangeable cones. The cones each have a standard Switchcraft style lever disconnect that is protected on three sides by the metal of the cone. An SMA antenna is mounted on the bottom. A control panel is mounted on the side with membrane style switches with a lit LED display panel. On the side above the control panel is an exposed opening for the microSD memory card.

My Thoughts Honestly, the 742.5 feels solidly built. If there was a weakness, the battery door could be it.  I have heard of reports that some TRX742 users tape or rubber band the door shut to be safe on scenes with quick moves to keep the door from opening up. That being said, Zaxcom has added a third magnet to help hold the door shut on the newer TRX742.5. According to Glenn at Zaxcom, no 742 series plug-ons have been sent in to have their battery doors repaired because of any problems with the plastic. The power switch is small, but it is protected by the battery door. The exposed memory card slot could be an issue to introduce dust or moisture if no card is in place, so I think it would be best to keep a card in the slot when in use, even if not recording.

I would have liked to see the next generation of the 742 fully enclosed in metal with a bottom-mounted battery door that also enclosed the power switch and the memory card, but according to Colleen: “You can’t do an all metal body. The reason for the nylon composite is that’s where the ZaxNet antennas are located – you can’t transmit or receive through metal!” So there you go.

Prices

  • $1995 for the Zaxcom TRX742.5 with Analog Cone
  • $200 for each Additional Cone (AES42 was the additional cone for us)
  • $2500 for the Zaxcom QRX200 Wideband Receiver
  • $40 Two SMA to BNC 50ohm Antenna Cables (To link TRX to Venue)
  • $50 Balanced Stereo Breakout Cable TA5F to XLR3M

$4785 TOTAL (Add an additional $1350 if you want to add a IFB200 for Zaxnet / Timecode)

Conclusion: If you want to go wireless with a Super-CMIT, there isn’t any option simpler than with a TRX742.5 paired with a Zaxcom receiver. That being said, there are some issues worth noting:

  • Lack of a limiter with an AES42 powered microphone
  • Need of a Zaxnet transmitter/IFB to jam timecode in AES42 mode
  • Short, but manageable battery life
  • Price is steep… but considering all the things it does, it certainly may be economical when it is used to it’s full potential.

The upside for wireless SuperCMIT users is that you get both DSP & non-DSP channels discreetly and a rock solid backup recording with timecode (if using ZaxNet) via a great sounding pair of signals. Also, you get the security of a wideband frequency range which lets you know you can find a clear frequency just about anywhere. Zaxcom has packed quite a bit of power into a very small form factor, especially considering how much gear would be needed to accomplish the same feat with the current offering of the competition’s gear. Kudos to Zaxcom for bring something truly unique to the market.

Special Thanks: to Colleen & Glenn at Zaxcom for making these products available for me to test and to Howy at Zaxcom for helping me through some technical hurdles on the gear.

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