Moniterman's Thompson adapter cable

[Anorton]

Moniterman or anyone else,

Thompson's webpage claims you can use a microphone with a quarter inch jack
http://www.petersontuners.com/index.cfm?category=151

Will this Thompson cable work in MT with something like a Shure SM48?
If I can't get it to work with the iRig, I'm hoping this cable might do the job.

[jorgren]

The Peterson cable is passive and lacks any monitoring capability. It's not adequate for a dynamic mic or a guitar, because it will pass 2.8 Volts DC from the iPxxx to your source device, and cause crackles (sparks inside the device). Also, the iPxxx has a low impedance input, which will dull the tone of a guitar. It's meant strictly for using the Peterson tuner, not for listening or recording with. With the SM48, I don't think you'll have enough gain. The iPxxx expects an electret condenser mic with built-in FET amplifier, and those provide more output than the Shure dynamic mic.

If you want to record from a mic, with monitoring, you could:
(1) Use the iPxxx earbud/mic, which will provide a surprisingly decent tone for such a tiny mic
(2) Put your mic through a preamp or mixer, and use the KV Connections cable
(3) Try the Amplitube iRig adapter, which will provide a little bit of gain. I don't know whether you'd find it's enough gain or not.

If there is a different cable, made by Thompson, please provide a link and we'll take a look.

[Anorton]

Thanks. I don't know why I wrote Thompson. Terribly sorry for the confusion.

[porkpeye]

I have a cable on the way from these guys: http://www.iPhone-XLR-cable.com

Will advise once I receive it if it works ok.

[porkpeye]

I have a cable on the way from these guys: http://www.iPhone-XLR-cable.com

Will advise once I receive it if it works ok.

I received the cable and can confirm it does not work correctly. Well, it almost works....

Here are the details:
The cable is split from the TRRS 1/8 plug to a Neutrik male XLR on one side, and a stereo headphone jack on the other. Headphone jack works perfect for monitoring on playback or recording. However, the XLR doesn't function correctly.

In my testing on the iPhone 4 the first thing I noticed was a rhythmic signal on the meter which turned out to be a clicking noise that only manifests itself when something is plugged into the xlr connector. It also gets recorded along with any other audio. If nothing is present on that connector the sound does not appear. The next thing I noticed was that the internal iPhone mic was still active after plugging in an external mic. I tried both a self powered Rode NTG-2 and a MAudio dynamic with the same result.

I tried plugging the cable in first before attaching a mic which does not work. I then tried plugging the mic into the cable first then into the iPhone. Curiously that actually managed to get audio from the external mic to show up but still with clicking noise, and more intriguingly switching between the external mic and the internal mic on each click.

Where to go from here I have no idea at this point.

[jorgren]

Wow, that's odd. What kind of mic did you plug in? It's very difficult for me to get any info from that site. They apparently didn't test it with IE8, and the pictures either don't show up, or they show up and then disappear.

But anyway, the iPhone needs to see resistance in a certain range (kept secret by Apple, but from my readings, somewhere between 1K - 10K; others say 1K-4K). The combination of your cable and mic need to present that resistance to the iPhone's mic contact. Wrong resistance will result in the phone not recognizing the mic.

I don't know about the clicking problem. Has anybody here experienced that?

[porkpeye]

What kind of mic did you plug in?

I believe I mentioned "Rode NTG-2 and a MAudio dynamic". One is a shotgun condenser mic powered by AA battery, the is a straight dynamic hand held mic.

[porkpeye]

It's very difficult for me to get any info from that site.

I use a Mac so I wouldn't know about that. I can tell you there isn't a whole lot of info there though.

The one bit that is useful info is this small bit of call-out text attached to photo of cable: Bias voltage blocking circuit inside XLR

That is most likely what is causing the issue.

[pwnified]

The one bit that is useful info is this small bit of call-out text attached to photo of cable: Bias voltage blocking circuit inside XLR

Yeah. With passive components they probably used a capacitor in series, but it sounds like they got the parallel resistor value wrong. It should be around 1K. My r-c math is a bit rusty, perhaps jorgren could tell us a good value for a cap to filter the dc and allow audio in the range 20-20K to pass through, being fed into a 1K load.

[jorgren]

With a 1K resistor, you would need an 8 microfarad capacitor. However, the mic port also has a load, so you would be a little safer with 16 microfarads. Be aware though that newer iPhones and iPods have their own hipass filters, so you may not get anything below 40 Hz, 80 Hz, or even 160 Hz, depending on your model. Also, this input needs a fairly strong signal, not all mics will do the job.