EOS 70D AC line noise on mic

[Mandi]

This isn't a Canon-specific issue but does affect my video recording setup using my 70D.

I have an external lavalier, wired mic.  On both my phone and my camera I have the same issue:

Running on battery - all good works and sounds great.

Running on AC power - very loud buzz (AC line noise I assume)

Any ideas or reccomendations on how to filter that out?  A setting or a separate device like an in-line filter?

I sure can't be the only one using AC power and a mic.

Thanks!

[wq9nsc]

I am not clear whether you are referring to an AC adapter for the mic or if you are using the Canon coupler with your Canon and an AC adapter with your phone?

If the problem occurs with the microphone using an AC adapter, it is likely an issue with the adapter.  Wired microphones require very little power for the built in impedance converter, preamp, or bias source for a condenser type element but it must be exceptionally clean because of the low signal level involved.  Very few aftermarket adapters provide sufficiently pure DC for this purpose but if it was supplied by the manufacturer it should be.

DSLR cameras and smartphones typically have a fairly high impedance audio input making it far more likely to pick up electrical noise in the environment, this is why professional audio is done using XLR connections with balanced low impedance lines to reduce this sort of issue.  There is a slight chance that your adapter cord itself is picking up noise and coupling it to the microphone.  Most, but not all, modern devices sense when voltage is present rather than a mechanical switch to go between battery and line supplied power when an adapter is plugged in.  If your microphone works this way, plug the adapter into the DC input socket of the microphone but not into the AC outlet and see if  the interference still shows up.

If you mean there is an issue when the camera or phone is powered by its AC adapter, then the problem is more complex because it may be from the adapter for these devices not being clean enough for good audio coupled with a microphone that has lower than typical output requiring higher gain.  Very few camera or phone power adapters provide any sort of ground to the house ground system and with these any noise appearing on the line is imposed on the device being powered by the adapter.  Depending upon the noise sources, plugging the adapter into an isolation transformer will help because the shielding between the primary and secondary in these devices greatly reduces the transfer of "garbage" on the line from primary to secondary.  Unlike the fairly clean AC of 20 years ago, the AC delivered within a house is very dirty due to all of the very cheap and poorly designed switching type supplies used with almost all current consumer garbage which creates all sorts of interference and transfers that to the line.  You may be able to turn off the offenders in your own home when using a video setup but you can't do this if recording elsewhere.  IF you have to have something other than the internal battery power when using the system remotely, you may need to investigate a good quality sine wave inverter with its own internal battery to power your AC adapter thus avoiding AC line noise via direct connection to the line.

Rodger

[Mandi]

Same unpowered, wired mic into either the phone or the camera.

Phone or camera running on internal battery power - sound is good.

Phone or camera running on ac power adapters - strong hum/buzz

I agree it's from the dirty AC, but it's been years since I've had to fix any of this and 'back in those days' there were stores where you could walk in and get line filters, caps, etc needed to clean it up.

I am working in my home, not remote at this time. 

You idea is, just to make sure I get this:
DC battery---> inverter to AC ---> AC adapter for camera

So, dc to ac to dc. 

but since the invertver is running on it's own isolated source, no noise interference from the normal house line.  yes?

I was hoping there was a simple in-line filter option. 😕

[wq9nsc]

You can try a simple line filter first but that isn't likely to work with the type of noise common on AC lines today.  Schaffner makes some excellent high performance line noise filters but they are designed to be chassis mounted, the simple plug in type filters like you may in retail stores are simple and tend to not be terribly effective. 

Isolation transformers often are very effective because of their shielding and some plug and play units are available but not many are available in the low power size that you need so you may have difficulty finding a unit that isn't excessively costly, large, and heavy.  Avoid the "autoformer" types that are often found on Ebay and the big online shopping types which aren't a real isolation transformer but instead are a simple tapped auto transformer designed to cheaply convert between 240/120 supplies and 120/240 volt products.  These offer zero attenuation of noise on the line.

Mouser Electronics is where I have bought most industrial electronic components for years and they have these products but they are NOT simple plug in devices and you would have to mount them to a chassis and wire in the proper three wire power plug (with proper circuit breaker or fuse) and an AC outlet.  If you go this route, Schaffner offers excellent filter modules but they aren't cheap AND there is no guarantee that it will work.  So first see if Best Buy or some online source has an inexpensive plug in filter and give it a try.

If you go with the battery inverter route, look for something that is referred to as a true or pure sinewave inverter because these provide the cleanest output and the best provide a waveform that is nearly a pure sinewave.  So called "modified" sinewave inverters produce a dirty output that won't kill most electronics but the output is a slightly softened square wave rich in harmonics and other "garbage".

Rodger

[Mandi]

Just an FYI for anyone who might have a problem like this.  It's fixed.  This did it:

Digital Energy EMI Sound Filter/Noise Reducer - 25 Foot Long 14/3 Cable - 6 Outlet Metal Body Surge Protector Power Strip | 1200 Joule, Heavy Duty Construction

I found the line filter I was looking for.

ps- Was never a mic problem.

[Waddizzle]

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@Mandi wrote:

Just an FYI for anyone who might have a problem like this.  It's fixed.  This did it:

Digital Energy EMI Sound Filter/Noise Reducer - 25 Foot Long 14/3 Cable - 6 Outlet Metal Body Surge Protector Power Strip | 1200 Joule, Heavy Duty Construction

I found the line filter I was looking for.

ps- Was never a mic problem.

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Who made the AC adapter for the microphone?

[Mandi]

There was no AC for the mic. The mic is not powered externally.

Both the EOS and my phone can either run on AC or DC (battery).  The AC option that I often need for longer video projects resulted in the line noice when using an external mic.  (same when using the phone)

Using this filtered power strip cleaned it up.  🙂

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@Waddizzle wrote:

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Who made the AC adapter for the microphone?

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[wq9nsc]

Mandi,

Glad you found a line filter to solve the problem and thanks for posting the update rather than just letting the thread die with no ending. 

I got involved with one of these situations several years ago with a friend who was working with some very sensitive and picky test gear in an industrial zoned area and it took both a line filter and an isolation transformer to sufficiently tame the garbage on the AC line.

Rodger

[jasonlnheath]

So this is a very old thread but I had the same issue and fixed it.  It was not due to a bad microphone.  It was due to noisy power.  In other words, the ac power source was not properly grounded.  In my case, I have a usb powered ac converter.  when plugged into my usb hub, it created terrible noise.  But when I plugged the usb converter into a power adapter (like an iphone plug) and then plugged the adapter into a properly grounded power socket, the noise went away.  Hope this helps someone else.

[jaewoosong]

you'll need a good power conditioner to filter out ac line noise.  something like furman power conditioner (SS6B).  most DACs/power delivery on cameras aren't great for line noise compared to dedicated high end AV equipment which often have better DACs and power conditioning.  my assumption is that you are using a dummy battery AC adaptor for you 70D with wired lav mic connected directly to the 70D.

DAC = digital audio convertor chip