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Thread: 3.5mm to XLR issue

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    3.5mm to XLR issue

    Hi All,

    Back again with more questions. I got an Audio Technica short-shotgun mic and an ATR3350 lav mic to go into a Scarlett 2i2 interface. The XLR works great but the lav is inaudible. The mic itself works well as tested through other devices but nothing is coming out of the Scarlett.

    There are three potential issues I know of and who knows how many others. I'll start with what I know. The ATR3350 is said to be dual-mono -- I'm guessing both the tip and ring are connected. I'll check the continuity when I get home. I'm trying to plug that into the Scarlett with a stereo 3.5mm to 1/4" adapter. I'll check the continuity on that too. Would I need a dual-mono 1/4" adapter?

    The second possible issue is impedance. The lav is 1k ohms. The shotgun is 100R. I know there are high-2-low Z adapters but don't know if those are the fix.

    The last known issue is phantom power. The Scarlett has that available but it only works on XLR pins. I've been trying the 1/4" jack in the middle. If any potential adapter comes with a 3.5mm-2-XLR form factor, does the phantom power (necessary for the shotgun) mess-up the little batter-operated lav? Rode has the VXLR adapter which seems to be just a re-pin device. The HOSA MIT-129 looks like it has a mini-transformer inside to change the impedance. In looking around the net some folks say the adapters work well but I haven't found any comments on +48v coming in on the pins.

    As always, any ideas are welcome. If this is a lost cause, you won't hurt my feelings by saying so. Thanks, sh

  2. #2
    Moderator / IAIB Pro Broadcaster mcphillips's Avatar
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    The ATR3350 does not require phantom power. It has its own battery. It is also unbalanced. If you're using a 3.5-to-XLR adapter, the adapter is probably shorting pins 1 and 3 on the XLR connector. That screws up phantom power, which has to be disabled on the XLR jack into which the 3350 is plugged.

    The 1/4" input jack on the Scarlett is probably line input rather than microphone input level. It will not have enough gain for a microphone.
    Please direct all questions for me to the forum so that all can benefit.

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    Hi mcphillips, The Scarlett has a choice of either line or instrument for each of the two channels. The jacks are the kind with the XLR and 1/4 in the same part. The phantom power only goes to the XLR pins so you don't have to worry about getting juice on the phone plug.

    scarlett2i23quarter_1.jpg

    Impedance aside, I'd never heard of a dual-mono before. I'll bet American money that when I get the ohm-meter on it, the sleeve is shorting to the ring. The 3.5mm looks like every other stereo plug in the world. If it isn't actually that, the 1/4" stereo adapter is going to get confused.

    The other concern is that if the impedance is still badly mismatched, will a stock 3.5 mm male to XLR-male adapter be putting DC on the lav? With the 48v on for the other mic, the pins will be charged. sh

  4. #4
    Moderator / IAIB Pro Broadcaster mcphillips's Avatar
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    Quote Originally Posted by luthierwnc View Post
    Hi mcphillips, The Scarlett has a choice of either line or instrument for each of the two channels. The jacks are the kind with the XLR and 1/4 in the same part. The phantom power only goes to the XLR pins so you don't have to worry about getting juice on the phone plug.
    The input impedance of the typical instrument input is often 1 Meg ohms and higher. The lav is looking for input impedance in the 250 to 1K ohm range. While the instrument input may work since it has the same gain as the mic input on the 2i2, you're probably going to get noise. The instrument input is definitely noisier than the mic input, as you can see on the 2i2 data sheet.

    Impedance aside, I'd never heard of a dual-mono before. I'll bet American money that when I get the ohm-meter on it, the sleeve is shorting to the ring.
    Dual mono in this case means that the tip and the ring are shorted together. The idea is that if you plug the mic into a DSLR or audio recorder with a STEREO input, mic audio will record on both the left and the right channels. The mic is unbalanced. In fact, all mics are unbalanced unless they contain a transformer or active circuitry internally to convert from unbalanced to balanced. Going into a mixer, you should connect the tip to pin 2 of the XLR and the sleeve to pins 1 and 3. That's what the Rode 3.5mm to XLR converter does.

    The 3.5mm looks like every other stereo plug in the world. If it isn't actually that, the 1/4" stereo adapter is going to get confused.
    Yes, it's a standard plug, but the wiring is not standard. The plug is called a stereo plug, but there is nothing stereo about this mic. It's a mono mic that bridges the input on a recorder with stereo inputs. What adds to the confusion is that some condenser mics use the ring to send +5VDC bias voltage back to the capsule. This mic doesn't work that way. It has its own battery. If you use a 1/8" TRS to 1/4" TRS ("stereo") adapter, the same audio signal appears on the positive and negative pins of the balanced XLR mic input (pins 2 and 3), and no audio will be heard.

    The other concern is that if the impedance is still badly mismatched, will a stock 3.5 mm male to XLR-male adapter be putting DC on the lav? With the 48v on for the other mic, the pins will be charged.
    What will happen with the adapter depends on the wiring of the adapter. Not all adapters are the same. If you have one that connects tip to pin 2, ring to pin 3, and sleeve to pin 1, it's not going to work. Pins 1 and 3 have to be shorted for most mixers. I assume that's true for the Scarlett. The problem is, if you connect an adapters with pins 1 and 3 shorted into an XLR jack that has phantom power, you may very well kill the phantom on the other inputs. (Some mixers isolate the phantom for this reason) but in any case, you can get some really strange results by shorting the phantom on an XLR mic input.

    Here is more information from the Audio-Technica website that you may find helpful:

    Please note that the connector is a stereo connector. Even though the microphone is mono, we send the signal to both tip and ring since most cameras are expecting a stereo connection. If you are using a 3.5 to 1/4 adapter into your mixer, depending upon you adapter you could very well be canceling out the audio. Also, please note that your device must expect a microphone level input many camera can be set to either a line or mic level. If it is set to line the microphone signal will be extremely weak.
    Even this response adds to the confusion by calling the 3.5mm connector stereo. Yes, it is the same connector used for stereo audio, but it is a three-circuit connector - not a stereo connector.

    Here is a customer's response from the Audio-Technica webiste, edited for readability:

    What I understand from the support is that the mic is an unbalanced mic, and the stereo mini jack is just mono but connected to both channels. This means that when you hang it on a balanced input from a mixer, the signal is out of phase and you hear nothing.

    If you want to put this mic on a balanced input from a mixer then you need to connect it to a XLR connector pin 1 and 3 to avoid that it gets out of phase. BUT you get a lot of noise then because it is a unbalanced mic. So the choice to make a condenser mic unbalanced is not such a great idea.


    Support says it is a mic for DSLR camera's and needs to be connected to a mic input. This only works for DSLR camera's that got a input that can be adjusted by a potentiometer or something similar digitally.
    This guy really doesn't understand the configuration, but he's getting close. The out-of-phase discussion is unnecessary in this circumstance as results may vary depending on the wiring of the input jack on the recorder.

    To beat this dead horse, most of the people on the AT forum who are complaining about his mic not working would get a different result if they used a 3.5mm female TRS jack to a 3.5mm TRS plug adapter if they are connecting to a MONO mic input. The tip of the TRS jack connects to the tip of the TRS plug, the sleeve of the TRS jack connects to the sleeve of the TRS plug, and the ring of the TRS jack and plug floats. This wiring scheme keeps the +5V DC bias voltage from the recorder from reaching the mic while providing proper audio input to the tip and sleeve of the MONO mic input. If the mic input is stereo, the mic should work without an adapter.

    Getting back to your situation, I've never used a Scarlett, so I don't know what your problem is. Make sure that your batteries are good. They probably are since they last a long time, but the mic will definitely not work if they're bad. You can check them with a volt meter or a cheap battery checker. (Radio Shack has a decent one for cheap if you can get to a store before they go out of business.) If I were you, I'd connect the mic to the XLR input with a properly wired adapter while making sure that phantom is turned off. (The switch applies phantom power to both XLR mics at the same time.) If that doesn't work, you could have a bad mic.
    Last edited by mcphillips; 11-07-2014 at 06:18 AM.
    Please direct all questions for me to the forum so that all can benefit.

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    Thanks mcphillips, it turned out to be just mismatched jacks. I've been building guitar amps for 25 years and have a shop full of parts. I clipped 8' off the too-long lav cable and soldered a 1/4" jack on. The single conductor went to the tip and the shield went to the sleeve and the ring. I couldn't find a schematic of the jack so I grounded the sleeve in case the Scarlett used a stereo switch to reference ground.

    It works well although I've only tested it far enough to be sure it makes noise. Fidelity and reproduction have to wait until we do the dry run. I still have the option of hacking a 3-pin XLR cable if this needs more power although I'm inclined to just get a proper XLR lav mic if this little unit comes-up short. That should complete the hardware I need for my office.

    This weekend (if the chip arrives) I'll rebuild my assistant's computer. She will be doing the editing. She has a basic i3 computer that is going to get upgraded to an i5-3570k processor, more RAM, a new power supply, an SSD for the OS and programs, a PCI-E card for USB 3.0 and a GTX 750 ti GPU. The new CPU has the Intel Graphics HD4000 on board. That would be a big step-up from the HD2000 there now but I've had good luck with discreet cards on other builds and it is nice to have dedicated memory. It might be overkill but that is less expensive in the long run than underkill.

    I'm sure I'll pester IAIB again as the project unfolds but for now, life is good. Thanks again to all who have visited my thread and enjoy your weekend. sh

  6. #6
    Moderator / IAIB Pro Broadcaster mcphillips's Avatar
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    Quote Originally Posted by luthierwnc View Post
    Thanks mcphillips, it turned out to be just mismatched jacks.
    What does that mean?

    I've been building guitar amps for 25 years and have a shop full of parts. I clipped 8' off the too-long lav cable and soldered a 1/4" jack on.
    Jack or plug? TS or TRS?

    I couldn't find a schematic of the jack...
    A schematic of a jack?

    The reason I'm asking for clarification is this thread will probably be the result of numerous Google searches for ATR3350 issues. It would be best to make the thread complete for the benefit of those searchers.
    Please direct all questions for me to the forum so that all can benefit.

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    What does that mean?
    Assuming too much. When you have what looks to all the world like a stereo plug, you expect it to act like one.

    Jack or plug? TS or TRS?
    TRS plug because that's what I had but I would have used TS otherwise. I shorted the ring and sleeve to do the same thing.

    A schematic of a jack?
    Switchcraft 12B.jpg

    Sure. This is the schemo of the famed Switchcraft 12B. When you use these as the input jack of a battery-driven FX pedal using a mono instrument plug, The ring references ground for the circuit but the sleeve is the battery ground. They get continuity through the barrel of the plug. That way, when nothing is plugged in, the battery doesn't go dead. That's why you see guitarists unplug all their pedals unless they have a 9v transformer driving the devices.

    The TRS plug on the mic had "dual-mono" on both the tip and sleeve. I couldn't find the schematic of the 2i2 but I'd now safely bet it is a stereo jack looking for a ground reference just behind the tip. If I'm right, all I was doing was shorting the hot.

    For the ATR3350 file, this is really the graphic to share:

    3.5mm to XLR.jpg

    I will keep this as an option if the 1/4" plug doesn't work as well in practice as it does in the squeal-test, sh

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    Member docizzen's Avatar
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    Mike Phillips is THE MAN!!

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    Hi mcphillips, I don't know if my feeble efforts are sticky quality but I do hope this helps other frustrated ATR3350 owners (or other 1/8" mic owners). This is a Neutrik combination XLR and 1/4 jack schematic. I don't know if this is the kind used on the Scarlett but it fell from the same tree. Ignoring the XLR, the 1/4 has three switched leaves.

    Neutrik xlr .25 jack.jpg

    If you have a garden-variety guitar cord, the tip is the signal, the sleeve is the ground and the ring (stereo) doesn't matter. If you used a stereo cord because it was in the bag and the gig starts in 5 minutes, it would work fine because the stereo leaf will also ground on the barrel of the jack. Either it is also grounded or it is disconnected. As long as the tip leaf doesn't have continuity with the sleeve, you're golden. I've certainly played with guitarists and singers I wish had a dual-mono cable

    Then we get to the concept of dual-mono (new to me) with the tip and sleeve connected. If that stereo leaf is grounded, you are shorting 100% of the signal to the buss. Like in my previous post, lots of gizmos use the stereo leaf to create ground continuity for the power source. It could also use one of the leaf switches to make sure phantom power doesn't get on the plug.

    Long-story short for other ATR3350 owners, you can't use a BestBuy headphone 3.5mm to 1/4" adapter to try to plug this into a Scarlett and probably many other combo XLR 1/4" jacks -- even though you can't tell it from a stereo plug without a meter or owner's manual. Just to flog the horse, I think I'll take the DVM to work with a stereo plug and check continuity on the solder pins. If it is something different that what I just said here, I'll say so.

    Cheers and enjoy your weekends, sh
    Last edited by luthierwnc; 11-07-2014 at 08:37 PM. Reason: additional information

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