I am getting terrible interference when I try to record from my iPhone directly to my Zoom H1n handheld recorder using cables. I have a cable
that takes a mono output from the phone and feeds it into the H1n via a splitter, and the other side of the splitter has a lavalier mic, self-powered,
plugged into it. The H1n has two channels. I am using a set of headphones to monitor the recording from the output of the H1n. I built a custom
cable to get just one output channel from the phone's audio to send to the recorder. I use the other channel for the lavalier mic (my voice). The
caller can hear me from the phones mic, and I monitor from the headphones.

Theoretically this should work, but I am getting a very loud interference as soon as I activate the phone. Loud popping and chirping, especially
when the phone is held near any of the input cables going into the H1n. I tried using the phone with just the headphones plugged in, and
using the phone's mic to communicate with the caller, and this works just fine. I also don't get any interference while putting the phone near the
headphone cable. All cables are very short, but are unbalanced, as they are just cheap audio cables you would buy anywhere.

The input impedance (Z) of the H1n is listed as 2k ohms. The Z of the mic is 1k, but I don't know what the output Z is of the iPhone. I imagine that it is
somewhat low so that it would be compatible with plug in headsets.

I think that I may need to do some impedance matching between the phone and H1n, but I am not sure where to start.

I do have an Apple lightning to audio adapter on its way so that I can test that, but I don't have high hopes for that working either.

Any help would be greatly appreciated. Daniel

 

The audio cables especially from the mic MUST be shielded audio cables.

 

It sounds like the iPhone’s transmitters are getting into the Zoom’s inputs. The first thing I would try is a ferrite bead on the connection to the Zoom close to it’s connector.

Something like these should help. You can even take one of the larger ones and wrap the wire around the inside more than once if just passing through doesn’t do enough. I can’t be sure this is the cause, or the cure, but it would be my first shot at it.

 

Update: I wrapped the input cable to the recorder with alum. foil and grounded it to earth. This helped, but not enough to
get a clean recording.
I will try the ferrite wraps also. I'll also try remaking the cable with a shielded one.
Daniel

 

Update #2:
I tried the original Apple lightning to audio adaptor, and it helps. My iPhone has both the audio jack, and the lightning
adaptor. The audio jack is worse than the lightning adaptor. I have some ferrite beads coming, and I will try placing
one of those over the cable coming out of the phone.
Daniel

 

Update #3:
I have received the ferrite beads, and have placed them around the various cables of this setup. The beads help, but don't
eliminate the interference completely. I still can hear clicks in the recordings.

 

If you put the phone in airplane mode does it stop the noise?

 

Since I am recording the phone conversation, that would be problematic. The beads help enough to make the setup
acceptable, but not ideal. I somehow think that I need an isolation transformer, but I am not sure.

 

It was intended as a troubleshooting step.

 

As soon as I click the phone app, it starts interfering with the recorder. You can hear the transmitter sending out enquiring
signals to the towers. The recording setup is acting like a crude spectrum analyzer.

 

Can you take a photo of the ferrite arrangement?

 

By the way, using a VoIP provider (I use VoIP.ms) it would be possible to arrange to record any call received by a DID (phone number) which offers at least three ways to record any calls you want—placed by you or received.

There is also an app on the App Store that does something similar. If you want to record your voice in higher quality, you could do that and sync the two later.

 

You can see one bead on the iPhone adaptor, one of the cable that I made (takes the left channel from the phone only), one
bead on ea. side of the stereo splitter and one on the mic cable (which is a lapel mic that is self powered).
I've tried plugging the cable that I made directly into the phone, but I find it a little worse for noise. My phone has an audio
out.

 

The ferrites should be as close as possible to the inputs. Even small sections of cable could add noise. The one on the black connector cable should be closer to the plug which (I assume) goes into the recorder.

 

Yes, that one goes into the zoom H1n recorder. I've tried moving them around to no avail. I'm having a difficult time figuring
out why the audio adapter works better than the direct connect into the phone's audio jack. Must be on a different circuit.
I may try getting a longer cable to go to the phone, so as to place it farther away from the rest of the lines.

 

It is probably better because of greater isolation from the transmitter of the DAC in the adapter as opposed to the direct audio connection.

 

I will try making a custom cable that uses shielding to see if that helps.