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Old March 19th, 2011, 04:45 AM   #16
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Re: Shure Mic not working with Olympus recorder

Apologies for the hjack but maybe this is an opportunity for someone to explain another jack related mystery to me:

I work in a school where we have dozens of just-above-entry-level electronic keyboards, mainly Casios. These see a lot of flying hours compared with similar ones that folks have at home. When (and I don't mean if) the headphone sockets go, in 99% of cases the fail mode is mono mix out of phase - ie a perfectly working pair of stereo headphones will receive a phase reversed mono mix (very faint tinny and "reverby" sound with almost no bass) equally in both ears.

Assuming this is a mechanical problem with the stereo jack headphone sockets which are soldered directly on to the output PCB, how on earth is this happening?

I've tried to think this through in terms of the order that the TRS connections are made, what happens if the jack isn't being fully inserted (or inserted too far past the tip connector in a damaged keyboard), some kind of short scenario from bits of chewing gum wrappers helpfully stuffed in to the socket, and lots of even more bizarre explanations, but I just can't work it out.

When the sockets are replaced (a BIG time consuming job) the problem goes away.
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Old March 19th, 2011, 07:49 AM   #17
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Re: Shure Mic not working with Olympus recorder

Colin: You might as well hijack it, as the OP seems to have lost interest in solving his problem. ;)

Common problem, simple explanation. The sleeve on the jack has become disconnected from the ground/common foil on the circuit board. (Typical failure mode, because often the physical mount of these jacks is via the soldered ground connections. Stress on the jacks causes the foil to fracture microscopically at that solder joint, thus losing continuity. This failure often can be repaired without replacing the jack.)

First, keep in mind that the left headphone element and right headphone element have a common connection (which also goes to the plug sleeve, and should return via the jack sleeve to circuit board ground. Also keep in mind that the amps that drive the headphones have a fairly low output impedance.

Assume there is a signal only on the left channel, right channel is silent.

Current from the left channel amp comes out the tip of the jack, to the tip on the headphones, through the left channel element, and out the common lead of the left chanel element. Now it no longer has a correct and direct path back to ground, because sleeve is open. Since the two headphone elements have a common connection, the current now continues through the common lead of the right element, back through the right voice coil, out the "hot" lead of the right element, through ring of the plug/jack, to the output of the right channel amplifier. Since the right channel amp has a low AC source impedance, the current finds its way back to ground at that point.

Now consider the direction of the current flow. It flows into the hot lead of the left element, through the element, and out the common lead (as it should). It then flows into the common lead of the right element, through the element, and out the hot lead (the reverse of the correct direction). Thus, the current is flowing "backwards" through the right element, which produces a reversed phase from that element.

Unlike the example above, in your case the keyboard is producing signal from both channels. Bass is probably nearly the same on both channels. So both channel outputs are pretty much in phase, at least for low frequencies. If both tip and ring go positive at the same time, there is little voltage difference between tip and ring, so little current flows through the phones. But if the reverb is synthesized in stereo, then the reverb portion of the audio will be different on tip from ring, so you will hear some (out of phase) reverb in the phones.

Incidentally, you would get exactly the same symptoms if the common lead in the headphone cable became disconnected from the sleeve of the headphone plug.

Does it make sense now?
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Old March 19th, 2011, 10:12 AM   #18
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Re: Shure Mic not working with Olympus recorder

Aha! Yes that does make sense, enough for me to want to try a pair of headphone with a disconnected sleeve on a fully functioning keyboard to see if I can replicate the effect. The bit I couldn't have worked out concerns the likely impedance under fault conditions at the output stage.

The repair techs are supposed to check for dry joints before replacing the sockets, I don't know if they always do. What I have heard them say is that sometimes the copper strip on the PCB has become damaged and by coating it with solder or soldering on a bridging wire replacement can be avoided.
Didn't clock the effect that this would have though - I assumed it would be further damage discovered on dismantling the keyboard.

Thanks for solving that mystery, it has been bugging me for years!
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Old March 19th, 2011, 11:27 AM   #19
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Re: Shure Mic not working with Olympus recorder

The source impedance of the output stage ought to be quite low... and that has nothing to do with the open sleeve connection. In fact, source impedance depends to an extent on the amount of negative feedback implemented in the output stage (which is introduced to reduce distortion). The more negative feedback, the lower the output impedance, until you reach the current driving capacity of the output device(s), at which point it can't go any lower.

If you disconnect your headphone common lead from the plug sleeve, while you're playing around, plug it into your stereo and play some cuts with vocals. You will hear thin instrumentals and a bit of reverb, all out of phase. Most likely the lead vocal will be missing except for some reverb of the vocal track. That's because the lead vocal is often recorded dead center, equal level on both channels; the reverb is spatialized so the two channels are not equal. (In fact this is the principle used by the "vocal eliminators" that you sometimes see advertised.)

The hardware fault described typically does not involve cold solder joints. It's what I, and your techs, described. The socket's only physical mounting is by being soldered to the thin copper foil on the PC board. When the socket receives too much mechanical strain, it remains soldered to the copper foil... at the point directly under the solder. But that copper comes unglued and pulls away from the PC board substrate. Then that little piece of foil actually tears away from the remainder of the foil (which is still attached to the substrate). At first the connection will be intermittent, but will quickly worsen.

The repair is as your tech described, too. Physically mount the new socket, if possible, using hot glue or epoxy (instead of relying only on the solder connection). Then solder the socket in place. Finally, add a small wire jumper from the pin on the socket to a point on the circuit board foil that is beyond the foil defect.

I'd have the techs build a load of 2' headphone extensions. Plug the extension into the keyboard jack, and tape the extension's jack to the keyboard case with gaffer tape; leave some slack in the 2' wire, so movement at the extension's jack does not transmit to the keyboard's jack. The students then plug their headphones into the extension. You will eventually wear out the extensions, which are expendable, but you won't have to open up the keyboards to perform a PC board repair.

Incidentally, another frequent instance of this type of failure is the DC power input on laptop PCs. Those connectors get hammered, break loose, and then there's no way to charge the battery or operate from mains power. To this day, I am using several laptops that I've literally pulled out of dumpsters, diagnosed with this problem, and repaired.

(As to why I was looking in the dumpsters to begin with... well, that's another issue.)
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Old April 3rd, 2011, 02:26 AM   #20
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Re: Shure Mic not working with Olympus recorder

Hi Greg, I read this thread and have the same problem the OP quoted. I guess I'm wondering if it's possible to plug a mic like my Senheiser ME2 which has a 3.5mm jack straight into a h1/h4 or h4n. I've tried all three without success. I've attempted pahntom power and input power on the H4n with no signal at all. If I use my wireless transmitter and receiver, I can use the 3.5mm line out of the receiver that has a XLR connection that will work perfect into my recorder. I wanted to buy a small H1 and plug this lav mic in so I could mic someone without having to spend a ton of money for another wireless setup. So this balanced mic isn't going to work with a unbalanced recorder?
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Old April 3rd, 2011, 08:51 AM   #21
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Re: Shure Mic not working with Olympus recorder

The good news is that it's possible to do almost anything, if you have enough data.

The bad news is that I don't presently have enough data to answer your specific question. (Just as we have never answered the original poster's question, because he never answered a simple question about the pinouts of his XLR-to-3.5mm adapter.)

I Googled your specific mic, then Googled the transmitter. I couldn't find any schematic or description of what is connected to the T, R, and S of that 3.5mm plug. Without knowing that, I can't tell you how to solve your problem.

If you have such a schematic, or can obtain that information from Sennheiser, we can probably figure out an appropriate adapter cable, or perhaps battery box, that will solve your problem.

Or perhaps someone else on this forum has already uncovered that information, and will share it with us.

If you cannot find the technical details of the Sennheiser 3.5mm connections, then there seems to be one other option, albeit a rather pricey one. The Sennheiser model MZA 900 P is listed as an "In-Line Preamp/Power Supply for EW Series Mics" which supposedly allows your mic to be used with a standard balanced/phantom mic input.

If you post any further technical details here, I'll certainly respond.
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Old April 3rd, 2011, 05:08 PM   #22
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Re: Shure Mic not working with Olympus recorder

Does the attached screen shot from the MZA 900P user's manual
http://www.sennheiser.com/sennheiser/products.nsf/resources/6FA58B0E0736C5F4C12574330043EE7F/$File/MZA_900_P_US.pdf
help at all? It doesn't mention the power supply needed.

The Sennheiser ME2 is not a particularly wonderful mic, but I suppose if you have one handy you would want to try it. I just plug in the receiver the my H4N and use the wireless connection.
I upgraded to the MKE 2-ew Gold - what a difference!
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Old April 3rd, 2011, 08:12 PM   #23
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Re: Shure Mic not working with Olympus recorder

Quote:
Originally Posted by Dylan Morgan View Post
. I guess I'm wondering if it's possible to plug a mic like my Senheiser ME2 which has a 3.5mm jack straight into a h1/h4 or h4n. I've tried all three without success. I've attempted pahntom power and input power on the H4n with no signal at all. I wanted to buy a small H1 and plug this lav mic in so I could mic someone without having to spend a ton of money for another wireless setup. So this balanced mic isn't going to work with a unbalanced recorder?
The ME2 with a 3.5mm plug is not a 'balanced mic'.
That said, I have tried an ME2 as well as other mics w/3.5mm connector into an H2, (with the plug-in power enabled) and they work, (left channel only) so I would assume if the Zoom H1 or H4n has a 3.5mm mic jack w/ Plug-in power, it should work. Obviously, if using the H4's XLR inputs, the mic would need an XLR battery module or XLR Phantom pwr transformer module.
The OP has a (dynamic) SM11, and that's a different issue.
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Old April 3rd, 2011, 09:45 PM   #24
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Re: Shure Mic not working with Olympus recorder

Colin:

Good detective work coming up with that schematic... thanks for the assistance!

Dylan:

If that schematic definitely applies to your mic, then I concur with Rick: that mic should work with any recorder having standard "plug in power" on the mic jack.

Note that "plug in power" is fairly low voltage, usually between 2 and 5 volts, applied through a series resistor of a few thousand ohms.

If you were to connect that mic to a typical XLR jack, with typical 48 volt phantom power turned on, there is a very good chance you would fry the mic. The only way around that scenario would be to use an adapter with an audio isolation transformer to keep the phantom voltage out of the mic; and then you would need a low-voltage battery box to provide correct power to the mic. So I strongly advise you not to try that mic into an XLR/phantom input.

But yes, based on that schematic, it appears to be the same wiring as a million other consumer and "pro-sumer", and some professional, electret mics. It should work with any unbalanced "plug in power" mic input, as long as the mic is functioning correctly.
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Old April 4th, 2011, 12:05 AM   #25
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Re: Shure Mic not working with Olympus recorder

Thank you all for your info. I actually went into an audio store a few days back and the guy tried out a xlr to 3.5mm to a "female to felmale" adaptor and then the mic plugged into it. I hope I didn't fry it because it didn't work with phantom power. I'm not home now, but will test it out asap :o... Thanks again everyone!
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