HPX250: HPX250 - Audio issue when using external shotgun mic.

C

Chris Dumont

Member
Hi all,


Any help with this would be much appreciated.


The issue


I am experiencing an issue with my recently purchased HPX 250, that when I am using the camera in a relatively loud environment with a shotgun mic attached via XLR, I am getting a strange electronic distortion through the camera (please listen to audio sample attached). I am controlling the levels on the camera manually with the level around-18/-12db. This "electronic distortion" then peaks over that level. In trying to identify what was causing this to happen I turned the level completely to zero. The "electronic distortion" still gets through and records to the card. This is how I have a clean recording of the distortion in the audio sample.


Equipment


HPX250
Sennheiser ME66 with K6 power module.
Rycote Softie
XLR Cable (tried multiple cables)


Troubleshooting


This is everything I have done to try and find the cause of the issue but nothing has resolved it.


Changed XLR cables
Changed Channel on camera (different XLR port)
Turned the camera limiter on and off
Turned the levels down to zero (this is how audio sample was recorded)
Changed the internal (menu) mic gain option from default -50db to other two options -40db and -60db
Replicated the issue at home in a quiet environment by making a loud noise into the microphone.
Turned phantom power off and ran just on mic battery, removed battery and powered just from camera.


Not getting anywhere, I then took the camera to the dealership I bought it from and we replicated the issue not only on my camera but also on the HPX250 that they have in the showroom (leading me to believe this might be a design fault in the camera).


At the dealership we also -


Used a different mic on the camera (Rode NT3?) and ran the same test (making a loud noise into the mic) which gave us the same result of the "electronic distortion". We then ran the same test on the Canon XF305 and another Sony camera of a similar level with both mics and these did not allow the signal through. This unfortunately indicates to us that the fault is with the camera(s) not the microphone.


Verdict


I am not an audio expert nor a sound man, however, my theory is that the loud noise is causing the mic to create an electrical signal that the camera is not resisting??

I have spoken to a sound recordist that I know and played the audio sample to him, he feels that its a problem with the pre amps on the camera.


My dealership are currently doing their best to resolve this issue for me, but at the moment it is still on going. Has anyone had this issue with this camera yet? Does anyone know what this might be?


If you do own the camera, could you try the test and make a loud noise into your mic and see if that signal breaks through.


This is my first post on a forum like this so I hope this is all clear and explains the issue, look forward to your replies.

Audio Sample


I couldn't work out how to post audio on the forum so here is a link to the audio on youtube.

 
Sounds like RF from a local radio transmitter getting in there somehow -- there is just a hint of modulation on the signal that could be some kind of program content. That, in turn, could be the result of a bad ground, cold solder connection, missing or insecure shielding around a component or circuit board. I take it you didn't try a second 250 -- that would probably give a definitive answer. Have you tested in a variety of different locations that might have varying RF environments (closer or farther from broadcast transmitters, cell phone towers, etc.)? It may sound silly, but make sure your own cell phone is turned off (or left in the car) when you're testing.

One thing you might try is connecting the shell of the XLR cable at the camera end to the shield in the cable -- or conversely, disconnecting it if it's wired that way now. (The standard is supposed to be NOT to ground the shell, but there are cables out there made both ways.) Just changing cables might not demonstrate this if they were both wired the same way.

You don't say whether you're using phantom power or the internal battery with the ME66, although I presume you were using phantom when you tested with the NTG-3. Try it both ways.

My bet is that you have a defective camera, but it's worth trying a few more simple things before sending it in.

- Greg
 
Thanks for replying Greg.

I have tested it in numerous locations so I'm sure its nothing to do with radio signals. That signal sample is only created by making a loud noise into the mic. I have used numerous XLR cables which were fine on other cameras including the 160. the cables I'm am using have Neutric connectors but I'm not sure how they are wired as regards to grounding. I tested it with and without phantom power. I have also used phantom power with the battery removed from the ME66.

I have ran the same tests on another HPX250 which was exactly the same. Thats why I'm now thinking it is a design fault in the camera rather than my one being defective. When making a loud noise into a mic on the HPX250 competitors such as Canons XF305, the electronic distortion is not preset at all which further more suggests it is a fault with the camera.
 
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Hum,

I am going to try the same test this week and see what I get. If you tried it on different 250's and the same issue, then it tells me its the camera. I will let you know what I get later this week or weekend.
 
Amazing.

What I did to create the issue outside of operating in a loud environment is position the shotgun mic 10/15cm ffrom my mouth and make a relatively loud ahh. This is done with the levels set to manual and completely at zero so you shouldn't hear anything technically. You will be able to see the "electronic distortion" on the audio metre and monitor it with headphones. As I say, this happens normally when operating in a loud environment. This is the method I used to replicate the issue however my dealership had replicated it by playing loud music from a radio.

The main reason this is such a big problem is that is uncontrollable and records onto the audio channel ruining your audio.

Thanks for the replies so far, anyone have any further ideas as to what is causing it or is willing to test it, please let me know.
 
If you're good at soldering, try switching the wired pins on ONE of the XLR cable connectors from pin 3 to pin 2, etc. If it's the same problem, go back to he original wiring, and switch Pins 1 and 2. I'm also an electronic tech, and have seen mis-wired circuit boards and internal connectors on equipment.
 
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Chris,

I did a test with my HPX250 just as you described and here is what I discovered.
I happen to have the same Sennheiser ME66 microphone as you do and when I used it for the test, I got the same result as you did,
a distortion in the channel even though the level was completely turned down. A crackling distortion coinciding with the loud level.

But when I repeated the test using a different microphone, this time a Sennheiser MD421U which is a dynamic mic, The crackling distortion
did not occur. I wonder if it is somehow related to only condenser mics or maybe just the ME66?
 
Has anyone tested this using the built-in mics? I'm planning on buying a 250, and will often be within 5 feet of some very loud music (wedding reception).

I can't have this kind of issue with the internal mics. I'd have to find another camera if that was affected as well.
 
Hi mmaller,

Thank you for taking the time to do that test. It seems that this is definitely a fault in the camera design across all HPX250's. It's definitely not the ME66 that is causing it as I have tested it with a Rode NT1/NT3? which gave the same result. What you say regarding whether it is a condenser mic or dynamic is very interesting. Panasonic's microphone, The AG-MC200G I believe is a dynamic mic. This would indicate why people haven't experienced it if they are using that. For me, I want to be able to use any mic I choose on the camera, especially Sennheiser ENG microphones. For a professional camera, this just doesn't seem right. As I have said before, the biggest problem for me is that it is uncontrollable and releases that signal randomly with no way (as yet) of preventing it.

Again, thank you for taking the time to check.

Jim, I have tested the internal mic for you and I'm happy to say it does NOT suffer from the same issue. This probably to do with the fact that its either a dynamic mic, has different circuitry or both.

Anyone else experiencing the "electronic distortion" with a condenser mic (or something else) please let me know.
 
It seems as Chris noted that this is a problem across all HPX250's.
Like Chris said, I didn't buy this camera to only use a certain type of microphone. My ME66 is my camera mounted shotgun of choice.
If this is a problem across the board, what are all the owners of HPX250's going to do now?
Or what is Panasonic going to do?
My camera is a little over a month old at this point, and I don't think my retailer will take it back.
What is the course of action now?
 
I am trying hard to replicate this scenario with a new 250 using a 416 gun mic phantom powered. It does not generate the distortion as far as I can tell. Will test over the weekend with an ECM77 phantom powered. I have wound up the gain on my headphones and monitor amp but cannot detect the problem you are having.
 
Does this happen only when you have the switch "on" on the capsule? If you're not using the mic, and you have the audio pot on "0", just turn off the mic, then there won't be the distorted sound.
 
It sounds to me like the particular mic in question is generating a voltage too high for the first stage pre-amp in the camera. The cure will almost certainly be to attenuate the signal from the mic. If it was me, I'd just open the XLR plug on the mic and add a couple of resistors. All manufacturers are caught between making the first stage pre-amp with enough gain to handle low sensitivity mics and low noise. This limits the maximum signal level the input can handle.
 
JohnnyD,
I believe that Chris has indicated in his original post that this distortion occurs when levels are set correctly for the mic, but if the sound that the mic is recording suddenly has a loud transient or the overall volume increases then that distortion is also recoded onto the clip along with the audio. He said it makes no difference whether he has auto gain or limiting engaged on the camera,
the distortion comes thru. What is really strange is that this distortion is recordable even with the audio level pots on the camera turned to no gain.

This does not occur with a dynamic mic as far as I can tell.

Chris, please correct me if I am wrong in describing your situation.
 
Thank you all for replying on this.

mmaller - I have contacted my dealership who are doing their best to find a resolution. They have contacted their supplier who in turn have contacted Panasonic, I'm now waiting on a response. It may be best to contact the company you purchased it from who should help you.

Bruce196 - Its interesting that you haven't been able to replicate it on that particular mic as yet. Of course that could be because of the mic or we are doing slightly different things to replicate it. If needs be I will make a short video of what I do to replicate the signal.

JohnnyD - I have replicated the issue with the mic capsule switched off and on. I may have mis understood what you just posted but if not - Its not a question of just unplugging the mic, the sample I gave of the electronic distortion is with the level at "0" so you can't hear the sound I was trying to record, only the "electronic distortion". Normally I would have it up so I'm recording the sound I need but if the actual environment levels are quite high, the electronic distortion adds to the sound I want, ruining the recording.

Mike Warren - This sounds very likely from what I have been told as well. Adding a couple of resistors is a nice idea but for me out of the question. I have spent a lot of money on this gear and I just want it to work without having to perform operations on it and modify parts.

As I mentioned before, I have replicated it with two mics and had the same results so far on two different HPX250's. One mic being the Rode NT1 and the other the ME66. My standpoint is that the camera is an ENG camera that in the UK has been approved by the BBC. The ME66 has been out for a while and probably should have been tested in development of the camera to ensure compatibility, if not, it should have been publicised that it might not be compatible with the camera. The thing that can't accept is that it CANNOT be replicated on the cameras competitors such as the Canon XF305 or Panasonic's own AG-AC160EJ which in many ways is the same camera.

For me at the moment, the camera is not fit for purpose and I need to get it sorted in order to run by business which is a small video production company. Hopefully, it will be a quick fix with an update for the firmware, fingers crossed. Again, thanks for all your replies and if anyone else replicates this issue, please let us know.
 
I very much doubt it can be fixed with firmware. It sounds to me like it happens before or right at the digital level control. What surprises me is that you say it doesn't happen on an AC160. I would have expected them to have the same audio input circuitry. I wonder if the HPX370 has the problem?
 
Something is amiss with the audio circuit. Later tonight, I'll test with my ME80 and reverse pins 2 and 3.

Years ago, many European countries had pin 3 hot and pin 2 cold. Usually, the cold line was grounded before or after the audio transformer in the receiving circuit. Pin 1 was always ground. Transformers have pretty much disappeared in video cameras. Everything is coupled with caps, resistors and transistors. For the last many decades, pin 2 has been hot in audio XLR's, but once in a while you might run into an older mic that still uses pin 3.

Will be testing later
 
A firmware fix was just wishful thinking Mike. It seems to me that this is definitely hardware. I will test the AC160 again this week at the dealership. I'm sure when I tried it last ttime it didn't do it. I would imagine that the circuitry is a little different as the 250 can record 4 channels of audio and I think the 160 is only 2. Haven't been able to try the 370. Won't have access to one.

Thanks JohnnyD for this info. To be honest it makes sense but it is a little beyond me. I wouldnt have thought the ME66 is that old, I would have thought that if something like that changed and became the norm then companies like sennheiser would just changed the wiring in production, especially as its a current product or perhaps not. I look forward to hearing what you find.
 
I have a 250 and no problems with the audio. I did have problems with the ME66 though! Massive problems! I use different phantom powered mics now Sennheiser 416 and AKG C568 EB and none of the problems occured since then. I do however agree that the audio circuitry of the 250 is less good than on my old HVX201 AE. It clips faster and sounds more brittle to me...
I doubt firmware will be able to do anything. Its the audio boards which are either designed worse or hold cheaper components.
 
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