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noise floor on the trx900


rich

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Quote from: Izen Ears on Today at 01:40:06

I can't wait to get my TX-900AAs (less than a week!)

  Dan Izen

what freq are your TRX-900 on? When using these units in Europe (block 31, around 800MHz) they are waaaay more noisy then the Lectros. RF is getting back into the mic and you will get a noisefloor like hell. Believe me I have been in trouble with it since I bought that unit. I just stick with it because there is still some hope that some matched DPA lavs will do the trick and as you have said - the rec option is sooo cool.

Matthias

Hi Mathias. what microphones are you using at the moment? and is your transmitter fitted with the internal mod of the resistor to bias the unit for a 2 wire mic. when i bought the last 3 of my 4, this was just being made standard on all units being shipped.

when i tried my older trx900 which hadn't had the mod done with a 4063, it wasn't very happy, i could hear rf interference on the mic, even though the 4063 i was trying had a resistor fitted in the connector.

i have some b6's for my trx's too and i've not noticed any problems with them either, though the only time ive used them in anger was when an actress was walking into the sea singing, so not the most useful test of noise floor, though everything survived.

ive had one situation in an interview where the interviewee was very softly spoken, so i kept upping the gain on his transmitter via the ifb100 and had no issues with noise floor. when i checked the transmitter at the end of the interview it was at 38db.

my units are on block 33 -838-862 Mhz and block 26 660-690 Mhz to rx900s receivers into a SD442 mixer.

there is also an expander in the latest versions of the software, though as its not adjustable remotely (at the moment) it only gets used on the bench. but it does help lower the ambient noise floor.

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Hi Rich,

after month of doing all kinds of treatment to my 4 units by Ambient Munich and Zaxcom directly it turned out, that my DPA 4063 has been an earlier version which was designed for the first trx units. However the units I have bought would have needed the newer version of the DPA (as you mentioned). DPA was kind enough to replace my lavs. At the moment I am waiting for them to arrive here in Berlin.

With the B6 I had some higher noise floor but that seems to relate to its tiny size and is "normal" so to speak.

But it is still definitely a RF issue with all the lavs on the market and I would like the TRX to be ready to use with all the standard lavs out there. Zaxcom was saying that this is a problem that effects European freq only but they can`t do nothin about it. e.g. with the COS11 there is no chance for use altough Ambient had done some additional filtering. I had to return my Sankens and go for the recommended DPA instead. Crossing fingers that the newer version will satisfy me needs.

I also have tested the TRX with an ambient 48V power supply and a Schoeps CMIT and a CMC6MK41. The CMIT didn`t get any RF but was really noisy, the MK41 was noisy and got RF inj. in addition.

Did you use your TRX for booming wireless? What 48V did you take?

Cheers, Matthias

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i bought some cos 11's after hearing them working with the units at everything audio, where i bought my zaxcoms from. before i cut the cable to the length i needed, i tried the mic on the trx and it was fine. once i cut the cable down (to about 1.8m) and wired it up, i got rf noise, so i wonder - in a very unscientific way, it cable length on sanken cable affects how it reacts to the zaxcom.

when ive used the zaxcom for wireless boom , i used a kmr81, sd mm1 preamp into the sta100, which as i remember was fine but a bit clunky. were you going into the mic connector on the trx, as i am unsure how well it works with the internal mod to bias the mics and not using a lav mic.  tomorrow, if i get a chance ill set it up and see how my other mics work with the zaxcom - ccm41 and cs3e.

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However the units I have bought would have needed the newer version of the DPA (as you mentioned). DPA was kind enough to replace my lavs. At the moment I am waiting for them to arrive here in Berlin.

But it is still definitely a RF issue with all the lavs on the market and I would like the TRX to be ready to use with all the standard lavs out there.

I also have tested the TRX with an ambient 48V power supply and a Schoeps CMIT and a CMC6MK41. The CMIT didn`t get any RF but was really noisy, the MK41 was noisy and got RF inj. in addition.

Cheers, Matthias

I had the same problem with the COS-11's and I believe Sanken is still working on it (but maybe not). The first attempts to use the older DPA lav also yielded unacceptable noise floor (this due also to some initial confusion as to how the mic should be wired) but now with proper and current DPA lav the TRX-900 - DPA combination has been a dream. Dead quiet, full dynamics, no problems.

I wish the TRX-900 would support all the common lavs in use but I don't think it will ever happen --- just one of the trade-offs for using the Zaxcom wireless (which is so outstanding in so many other respects it is an okay trade-off at least for me).

I am surprised that you had any difficulty with Schoeps CMIT - Ambient power supply - TRX-900 since I have done with many times with no problem. The adapter cable that comes out of the Ambient power supply and into the TRX-900 has to be wired correctly so you might check that. As for the MK-41, if its an older (not yet RF proof) mic, this can cause trouble even with an outboard power supply. With all of my newer Schoeps (after Schoeps re-design) I have not had any problems.

Regards,  Jeff Wexler

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I am surprised that you had any difficulty with Schoeps CMIT - Ambient power supply - TRX-900 since I have done with many times with no problem. The adapter cable that comes out of the Ambient power supply and into the TRX-900 has to be wired correctly so you might check that. As for the MK-41, if its an older (not yet RF proof) mic, this can cause trouble even with an outboard power supply. With all of my newer Schoeps (after Schoeps re-design) I have not had any problems.

Regards,  Jeff Wexler

Jeff - what do you mean by wired correctly? I had a dynamic mic adapter made by Ambient that was basically a XLR female to ZAX/Sennheiser connector one.

I was comparing the sound of the CMIT via TRX and hardwired and you wouldn`t wanna deliver that as your prod sound. It was terrible noisy. But not an analogue amp noise but more a sharp (digital?) noise/hiss.

My CMC is about a year old so it`s RF improved.

Can`t wait to get the DPAs as this is my last hope. But from yours and Rich`s statements it does look promising. And as you have said it is a trade off but in the end I decided to keep the Zax for all the other good reasons: all digital, no probs with setting up multiple units, no interference, build in rec option, stereo adapter and ifb (both I have not bought yet but will do if I finally get good sound of these little boxes ;-)

But then it isn`t even just a European freq problem at all?! Amazing.

Regards, Matthias

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Jeff - what do you mean by wired correctly? I had a dynamic mic adapter made by Ambient that was basically a XLR female to ZAX/Sennheiser connector one.

I was comparing the sound of the CMIT via TRX and hardwired and you wouldn`t wanna deliver that as your prod sound. It was terrible noisy. But not an analogue amp noise but more a sharp (digital?) noise/hiss.

My CMC is about a year old so it`s RF improved.

Can`t wait to get the DPAs as this is my last hope. But from yours and Rich`s statements it does look promising. And as you have said it is a trade off but in the end I decided to keep the Zax for all the other good reasons: all digital, no probs with setting up multiple units, no interference, build in rec option, stereo adapter and ifb (both I have not bought yet but will do if I finally get good sound of these little boxes ;-)

But then it isn`t even just a European freq problem at all?! Amazing.

Regards, Matthias

The cable made up by Ambient should be fine. I still cannot imagine what the problem is. As far as being just s European thing, I don't know what was originally said about the RF problem, RF getting back into the mic from the transmitter, but it was definitely an issue here with the first Zax units and many of the microphones that we were trying to use. With the exception of the lack of usability still for my last favorite mic, Sanken COS-11, most all of the problems have gone away here (and in Europe I imagine). I really don't know what to tell you. I would have given up on the Zax units too if these problems had not been solved (since I do not use any of the ZAx specific functions like recording, remote control, IFB etc.) I use the TRX-900 because it just works so well as a traditional (which it is not, of course) wireless.

Good luck sorting it all out --- don't give up yet.

-  JW

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  I'm suddenly worried when I get my TX-900AAs, everything will sound awful.  I'll be using the Denecke PS1a phantom power with a CMIT5u, how should that TA3-XLRF cable be wired to be correct?  Also, what's the correct wiring for the Sankens & Countryman's TA3?  Why is this so complicated, it's ridiculous!

  They're blocks 21 & 22.

  Dan Izen

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First of all, I don't think any of the Zaxcom transmitters use Switchcraft TA3F connectors they use the same connector that Sennheiser uses. I can't tell you what the proper wiring is for each of the microphones you mention, I just rely on the dealer or the service person to obtain proper wiring scheme from Zaxcom. As far as it all being so complicated, I read constantly about people getting bad performance from many other wireless (notably Lectrosonics because there are so many people using them) because of incorrect wiring. Larry Fisher has been very good about posting all sorts of things in relation to how various mics are to be wired and even then, mics end up sounding terrible because something has been done wrong. I do know that the Zaxcoms do have more limited support for all the microphones out there but that doesn't mean you won't be able to get several good lavs working beautifully and of course your boom mics (with a power supply). One note of caution with the Denecke power supply (and I don't know if this problem has been corrected by either Denecke or Zaxcom or both) is that when powering up the Denecke power supply it sends 48 volts BOTH directions --- to the microphone AND to the output --- this has in the past totally blown the Zaxcom transmitter. I believe this problem has been solved but if not, it is prudent to connect the microphone to the supply FIRST, then connect the cable from the power supply to the xmtr. This is not an issue with any of the other power supplies (Ambient, PSC, etc.).

I do know that Billy Sarokin in New York, who has had more experience with all Zaxcom products than just about anyone, is successfully using several different lavs (even including the verboten Sanken COS-11) but considers the B6 his main lav.

Regards,  Jeff Wexler

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  I'm suddenly worried when I get my TX-900AAs, everything will sound awful.  I'll be using the Denecke PS1a phantom power with a CMIT5u, how should that TA3-XLRF cable be wired to be correct?  Also, what's the correct wiring for the Sankens & Countryman's TA3?  Why is this so complicated, it's ridiculous!

  They're blocks 21 & 22.

  Dan Izen

Izen,

Remote Audio makes a  3pin lemo-fxlr. it is used as Tc cable & can be used w/the denecke 48v p.s. so the same cable can be used to jam Tc into the trx900 & for the boom pole wireless application as well. it was tested by me at the shop and is being used at this time on a pretty big feature film in town.

also,

we have some countryman emw's (think tram-but a little thinner capsule) and now sanken cos-11's and they are wired by Forrest in are service dept. so I don't really know the wiring off hand. call him on Monday, maybe he can help?

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One note of caution with the Denecke power supply (and I don't know if this problem has been corrected by either Denecke or Zaxcom or both) is that when powering up the Denecke power supply it sends 48 volts BOTH directions --- to the microphone AND to the output --- this has in the past totally blown the Zaxcom transmitter. I believe this problem has been solved but if not, it is prudent to connect the microphone to the supply FIRST, then connect the cable from the power supply to the xmtr.

For another purpose I had LSC install an isolation transformer in the output of my Denecke phantom power supply. I expect this would also effectively block any phantom output back to the transmitter (if any is still present).

This is a relatively low cost installation that does no harm. The appropriate transformer is available from Neutrik for about $20 and wiring it in is pretty simple. (Although, with my soldering skills, I relied upon Mark Lesonsky at LSC)

Link to the Neutrik 1:1 200 ohm transformer:

http://www.neutrik.com/fl/en/audio/210_74481/NTE1_detail.aspx

David Waelder

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hello Matthias

I am using European Band Zaxcom,

I Had a bit of a problem initially with my older zaxcom transmitter, high frequency whine etc, bad noise floor, a couple of things which improved it dramatically for boom use., use Neutrik EMC xlr connecters, have you got the transmitter mounted on the phantom power supply, if so move it away and have a listen, the XLR to Zaxcom connecter for boom use is supposed to have a RF Filter connected, the EMC XLR has a RF Filter inbuilt, after a lot of tests, i went with using a Sound devices MM1 Preamp with line o/p then a cable with 26db pad into the Zaxcom, i went into a University sound lab and using the Sound Devices configuration the Zaxcom was as quiet as a hard wired mic used a MKH60, neumann KM185, Sanken CS3E as test mics, it works wonders now but i have to mount the transmitter away from Sound devices MM1 as it causes high whine interference when mounted on it, i think it is all to do with the zaxcom digital AM modulation, either way i cant praise enough the quality of the Zaxcom now..In my opinion the Limiter on the older Zaxcom tranmitter wasnt very good especially on boom mics, so thats another reason for using the Sound devices MM-1, I disabled the zaxcom limiter and push it hard level wise with the sound devices limiters working just (5db) below the Zaxcom digital wall..very clean and quiet.

Hope this is off some help.

Richard Paterson

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Richard has some very good real world advice here about how to avoid the RF problems associated with the use of certain microphones. I had to do a lot of those things, special care as to what XLR connector to use, separating power supplies and transmitters, etc. I know it is a pain but this is, as Richard points out, the peculiarities of pure digital transmission (something which only Zaxcom does at this time). The benefit, of course, once you get the microphones sorted out, is the absolute pristine audio, no companding, no intermod, etc.

Since I do not do wireless boom work much, I actually need to use the Zaxcom wireless primarily for talent (lav) use but also I use them a lot for plant mics (which are almost always 48 volt phantom powered Schoeps). My solution, at this time, was to purchase the Zaxcom TRX 700 (plug-on style transmitter) which supplies a full 48 volt phantom power (no external power supply needed) and also solves many of these problems when connecting microphones other than lavs. This plug-on obviously works well for the few times we do wireless boom work. I know this is a rather large expense and it would be nicer if we could use the same TRX-900 that we use on the talent, add the mic power supply we already own, but I find the ease of use of the plug-on for plant mics outweighs the cost.

Regards,  Jeff Wexler

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thanks Richard for suggestions! Will do all different kinds of testing as soon as I get my units back from Ambient. The have been waiting for the redesigned backplate there ...

Jeff - Glenn was sending over a TRX 700 for testing on the job. That`s what I actually refered to when I was saying that the CMIT and the MK41 sounded noisy and got RF. Before that I was testing with a Ambient 48V supply and as far as I remember I didn`t had probs with RF but it just sounded to noisy compared to a hardwire. But I will definitely do a run with a SD302 (as a test replace for the MM) and go line level into the TRX.

The Neutrik hint is a good one. I will look into it as well.

Should get my units this week and will keep you updated. Thanks for your support everyone!

Matthias

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Other than the built in record feature, Lectrosonics and Sony both offer digital systems.

I know that Lectrosonics has had a pure digital system, the 700 I believe, for some time now, but I don't think it is a viable product for our uses. Maybe they do have something that is the equivalent of the 400 series in a pure digital, I just haven't seen it. Same goes for Sony, although I did hear that they have a viable portable body-pack - battery operated system, I just haven't seen it. There is the possibility that the other manufacturers have not come out with a pure digital yet because they want to avoid some of the problems people have experienced with the Zaxcoms. Some of these problems may be inherent in anyone's implementation of pure digital transmission, maybe not. It remains to be seen if there will be viable competition for Zaxcom in this area. I am hoping we will see some new things at NAB.

Regards,  Jeff Wexler

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Sony will demo their new 2 channel digital receiver at NAB 08 and the early beta I tried was really nice but will only work in their camera slot system or will require a bucket. It will also feature AES out.

So, the Sony system as far as you know will not work well as a standard transmitter, receiver portable system but was designed instead for camera use? What's a "bucket" exactly?

-  Jeff Wexler

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got my units back on friday from Munich.

The new DPA 4063 has improved the situation although it is still not perfect. But the remaining RF-noise is much less than with the older version. If one cranks up the headphone volume it is still audible and it shifts with the lav cable position. But when listening to it in standard volume it sounds pretty clean.

What helped a lot is the software expander from the TRX. It brings down the noisefloor and doesn`t effect the audio in a critical way. Without the expander I still find the lavs too noisy.

The B6 doesn`t get these RF "fieping" like the DPA but it is more noisy. Again the expander brings the noisefloor down.

After some listening my current settings for the expander are: 1:1.30, -40dB, -8dB, normal

I did some testing with my boom mics too:

powered from a SD302, line out SD into an adapter cable, into the TRX.

The level tone from the SD302 sounded a bit nasty. Some harmonics on top or something. When listening AB a couple of CMITs (one hardwired into my Cooper) it sounded alright. Slightly different but more on the tasty side of life. I would still prefer the hardwired one. But it`s good to know, that I could use it this way if I have to.

All testing has been in a quiet environment so I would assume that in real life with some atmos around, some clothes rustling and the boom mic in the mix to open up the lavs - it should work.

One strange thing I have noticed:

if I push the gain on the TRX beyond 30dB the audio will become distorded - even with low level audio. 32dB is distorded and 34dB then will mute the audio!! Any ideas about that one?

Cheers, Matthias

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