Izen Ears Posted October 21, 2007 Report Share Posted October 21, 2007 I have had some ridiculous humming problems when using my CMIT-5u, both wireless (w/ UM400 tx + Denecke ps-1 + mc40 cable to phantom + whirlwind boom cable, Ambient carbon fiber pole) and even hardwired (Cooper 104, whirlwind cable, Ambient carbon fiber pole). I had a mean hum when using it wireless indoors with an 18k HMI nearby (I know, who the eff puts an 18k indoors?!), and also hardwired in a rap star's home! In both cases I was battery powered and untethered so it was not a grounding thing, and it increased or diminished when I changed the angle/placement of the mic. I tried different boom cables and the problem was exactly the same. I did not have the problem with the CMC6. After searching around the boards I saw a bunch of discussion about how to wire XLR cables to minimize RF intrusion. You all remember the differing theories about this, but it wasn't quite as specific as I'd like so apologies for a semi-repeating topic. Here's what I'd like to know: What brand of cable is the best for this, and how should it be wired? Thanks! And hello to John Garrett, I moved to Baton Rouge! Dan Quote Link to comment Share on other sites More sharing options...
Brian Maier Posted October 21, 2007 Report Share Posted October 21, 2007 This doesnt really answer your question but i thought I would share a similar experience. I was trying to use a CMIT-5U, Denecke PS1A, and a Lectro SM for wireless boom but kept getting this low frequency thudering (dont think thats a word...) it sounded like a helicopter that was way off in the distance that would never leave. I got some funny looks the first time I said we needed to wait for the helicopter that no one else could hear. After some experimentation it seemed to only be an issue with the CMIT when used with the SM. CMIT5U - PS1A - SM = Low end chopper noise CMIT5U - PS1A - SMA = Good CMIT5U - PS1A - UM400 = Good CMC641 - PS1A - SM = Good CMC641 - PS1A - UM400 = Good MKH416 - PS1A - SM = Good MKH416 - PS1A - UM400 = Good AT4073a - PS1A - SM = Good At4073a - PS1A - UM400 = Good A month or two ago i was in Coffey Sound speaking with Robert about the new Lectro SMA's and wondering if they had the same issue. We were able to reproduce the low end noise on with some of there gear with the same setup. So it wasn't my particular SM that was the issue. Tried it with the SMA and it was fine. I'm not sure what changed between the two versions of the SM - SMA but the new rendition seems to solve the issue. We made a recording of the A - B comparison to send to Lectro, but I'm not sure if Robert got any kind of response as I've been backpacking Europe for the last month and not had a chance to follow up. Quote Link to comment Share on other sites More sharing options...
jason porter Posted October 21, 2007 Report Share Posted October 21, 2007 I believe the SMA has a low-cut filter, that may have solved the rumbling problem. -JP Quote Link to comment Share on other sites More sharing options...
Glen Trew Posted October 21, 2007 Report Share Posted October 21, 2007 It is important, especially with Schoeps and Neumann mics, that the female XLR that plugs into the microphone have pin-1 jumped to the grounding tab. Another possibility: One time when I was having a hum issue similar to yours, the problem turned out to a cabled boom pole that had the shield attached to pin-2 at both ends instead of pin-1. Since the pole itself acted like a shield for the cable iside the pole, the problem wasn't as obvious as you might expect. Only the part of the cable coming out the top of the pole into the mic was sensitive to induced noise. Whenever the pole swung near an HMI head, there was a buzz. You have to open the connectors to check this out because cables wired this way will appear normal if using an ohm meter or cable tester. Quote Link to comment Share on other sites More sharing options...
Brian Maier Posted October 21, 2007 Report Share Posted October 21, 2007 I believe the SMA has a low-cut filter, that may have solved the rumbling problem. -JP I tried the roll off on both the CMIT5U and the SD442 neither made any difference, but maybe the curve is different on the SMA. Quote Link to comment Share on other sites More sharing options...
Izen Ears Posted October 21, 2007 Author Report Share Posted October 21, 2007 Thanks Glen for the word on the cable! Which brand of cable would you recommend? Does braided shielding matter? And Jason - I had this problem, but it was with a block 28 UM400a tx with the wireless boom, same issue with the CMIT5u. A wacky low-freq rumble. Then I started having this same rumble with lavs (Sanken and Countryman) so I sent it back to Lectro. They fixed it and sent it back and it was fine, never really got the story on it. THEN, I was using a different UM400a (block 26) and I got the rumble again. As you describe, a low-freq thudding, not a constant thud though, more like a rumbling. It happened with the lavs (didn't try a boom). I got it on all my Sankens (including an older one and a brand new one) and only on my newest Countrymen - for some reason the old school Countrymen I had (grey label, stiff cable, over 5 years old!) was clean as a whistle. Also none of the Trams made any rumble. It was awesome because the rumble first started seconds before "action!" I had to run out and swap with an old UM205 which worked fine (and always has). Didn't end there, when I sent in the UM400a and rented an SMD tx for the remainder of the show: you guessed it - more rumbles! I was told I could only use the brand new Sankens with this since Lectro changed the voltage or something on the TA5, and the Sanken I had was the only lav new enough to be wired properly. What's the deal? Where is this rumbling coming from? Why do older lavs have to be rewired for use in the SMD transmitters? Dan This doesnt really answer your question but i thought I would share a similar experience. I was trying to use a CMIT-5U, Denecke PS1A, and a Lectro SM for wireless boom but kept getting this low frequency thudering (dont think thats a word...) it sounded like a helicopter that was way off in the distance that would never leave. I got some funny looks the first time I said we needed to wait for the helicopter that no one else could hear. After some experimentation it seemed to only be an issue with the CMIT when used with the SM. CMIT5U - PS1A - SM = Low end chopper noise CMIT5U - PS1A - SMA = Good CMIT5U - PS1A - UM400 = Good CMC641 - PS1A - SM = Good CMC641 - PS1A - UM400 = Good MKH416 - PS1A - SM = Good MKH416 - PS1A - UM400 = Good AT4073a - PS1A - SM = Good At4073a - PS1A - UM400 = Good A month or two ago i was in Coffey Sound speaking with Robert about the new Lectro SMA's and wondering if they had the same issue. We were able to reproduce the low end noise on with some of there gear with the same setup. So it wasn't my particular SM that was the issue. Tried it with the SMA and it was fine. I'm not sure what changed between the two versions of the SM - SMA but the new rendition seems to solve the issue. We made a recording of the A - B comparison to send to Lectro, but I'm not sure if Robert got any kind of response as I've been backpacking Europe for the last month and not had a chance to follow up. Quote Link to comment Share on other sites More sharing options...
Morantzsound Posted October 24, 2007 Report Share Posted October 24, 2007 I use the CMIT-5 and use the UH-400 and I have had no problems. I was using the studios gear on one show and used the sm's with both a PSC and a Denecke box as that was all they had and started having problems with noise in the line and real low signals. If I used that sm with a lav against one that never was plugged into a 48v supply there was a huge difference. We discovered that since the wiring configuration was different for the lavs that use sm's that when you plugged a 48v supply with a standard ta5 cable it blew a resistor inside and dropped the signal considerably. We shipped them back to lectro and they upgraded them and all was fine. I now use the UH-400s or the um400s only now when doing a wireless boom. Steve Quote Link to comment Share on other sites More sharing options...
RPSharman Posted October 24, 2007 Report Share Posted October 24, 2007 This is interesting. I think we blew a few SM transmitters using a CMC-5 with a wireless plant setup with the Denecke power supply. This was in the very early days of the SM. We just stopped using the schoeps with the SM. But I do remember some occasional low end noise problems that really powered through on several other occasions over the last couple of years with both SM and UM400 transmitters. This was using an MKH50. I wonder why this is intermittent and not a constant problem. Quote Link to comment Share on other sites More sharing options...
Matthias Richter Posted October 31, 2007 Report Share Posted October 31, 2007 I have had that s.c. helicopter sound when using an audio 2040, a vdb 48V supply and my cmit. in the end it was just the empty battery that wasn`t indicated correctly neither with the tx nor rx. Matthias Quote Link to comment Share on other sites More sharing options...
Jeff Wexler Posted October 31, 2007 Report Share Posted October 31, 2007 This is interesting. I think we blew a few SM transmitters using a CMC-5 with a wireless plant setup with the Denecke power supply. I don't know if this sheds any light on the whole issue since I do not know much about the SM. It was discovered that the Denecke Power Supply which does not have an on/off switch is activated by plugging in the microphone, it sends 48 vdc out BOTH directuons (to the mic of course and also out the output side). So, there were a few instances using Zaxcom transmitters with the Denecke Power Supply where the transmitter was taken out by the surge of 48 vdc at the input. This has been corrected with protection now built into the Zaxcom transmitters but it is possible that the SM may have had the same vulnerability. Regards, Jeff Wexler Quote Link to comment Share on other sites More sharing options...
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