Nice to meet you all. As I’m an all-purpose production guy and am admittedly not a dedicated sound recordist, I’ve lurked on this group for a bit and I’m amazed by the wealth of knowledge there is here. I finally do have a question (which I’ve cross-posted to some other industry forums); maybe someone might be able to help?
Here's the scoop. I'm having a terrible time trying eliminate really bad hiss (I mean noise, not just background hiss per a noise floor from poor quality preamps) per a wireless boom setup that I’m assembling. What I have right now theoretically should work, but there's a hiss that renders the sound capture totally unusable. Maybe it’s a simple fix that just involves adding an inline RF filter somewhere?
The signal chain is as following:
Audio Technica AT4053B (boom for indoor voice) ***OR*** Audio Technica AT875b (short shotgun for outdoors) ---(8” XLR patch cable)--->
Sennheiser MZA14 48 (supplies +48V phantom power to either mic) ---(8” XLR patch cable)--->
Sennheiser SKP100 wireless microphone XLR transmitter —(WIRELESS CONNECTION)--->
Sennheiser EW100 G3 wireless receiver —(AF Out via 3.5” male jack to XLR)--->
Sony FS7 (line in)
Again, what I hear is clearly a hiss and not a hum or a rumble. There is no AC power involved in the system, let alone an earth ground anywhere. Yes, I'd love a used SKP 300 or a Sound Devices MixPre-D (or the like), but per my budget neither is an option right now. I totally blew my budget getting the used AT4053b to at least try and capture quality indoor voice (which is apparently rare as hen's teeth to find use), and was lucky to find a used and affordable MZA14 to power it.
So after a bunch of testing, which will hopefully help rule things out, it looks like I have two separate problems here:
(1) RF SPRAY FROM THE SKP100 TRANSMITTER?: Check out the following picture of my setup. When I hold the SKP100 just like this, with my three fingers fully wrapped around the XLR connection and with the palm around the body of the SKP100 transmitter, almost all the noise goes away. Can I put something in there (ferrite RF chokes?) to shut down what may be RF Spray?
I’ve pulled the mics themselves out of the equation; the noise happens regardless of whether a mic is connected to the chain. Stripped down, it happens when the MZA14 is directly connected to the SKP100.
(2) FM RADIO INTERFERENCE: Once I hold the grip that way, most of the noise is gone. But in certain circumstances I’m now picking up variably slight broadcast radio noise. What’s weird is that I am in fact picking up FM (not AM) signals. At its worst, the sound is a couple of FM stations playing all at once. The clearest of the radio station signals is WBMX 104.1 FM, which is a powerful FM radio station (21,000 watts) broadcasting from the Prudential Tower exactly two miles away.
By the way, as far as cable quality goes, I’m planning to return the brand new 8” one (shiny cable ends) to Amazon -- but neither cable seems to do anything to significantly solve the main hiss problem. I think the coiled black cable (Pearstone, with Neutrik ends) picks up less of the lower FM signal, but there’s higher handling noise when the coil moves around – so I’ll likely have to replace both cables for this application.
Per the Sennheiser EW100, I have played with all the levels - squelch, sensitivity, changing channels, and even dropping the preamps on the FS7. No luck.
Per testing individual components in order to rule things out, the signal is totally quiet when:
* Either mic is directly connected to the FS7 just via a simple XLR cable (with +48V provided by the FS7
* Either mic is directly connected to the FS7 via an XLR cable and just the MZA14 (with +48V provided by the MZA14)
* The EW100 system is used without the MZA14 in the chain (such as with an MD46 mic that doesn’t require +48V or an EW100 G3 wireless lav transmitter)
Per my research, I thought a “ground lift” (eliminating ground pin 1) might eliminate the hiss - but that seems to be for ground loop issues - meaning hums and not hisses. I haven't tried it, but I'm guessing it won't work.
Finally, I found two older threads that may put me on the right track – but after reading those thoroughly – I'm still stuck. The threads are:
Any thoughts? Thanks in advance!