Hey mic mod guys!

R

Richard Monroe

Well-known member
Unto Mr. Joly, MSHilarious, et al.-

I've had this mic for a long time, and I can't believe I haven't thought of this before-DUH! As you know, I'm a hack, not a enjooneer, so I don't know how easy this would be, or if it's even possible. The starting point is a Shure SM82. I think it was discontinued around 1989. Even back then, it was a $600-800 or so broadcast condenser mic. But- it's a line level mic with a built in line level preamp and a limiter. It was designed to run on a Mercury battery that isn't made anymore, but I can get alkaline cells that are pretty close, or it can turn phantom power into the 9V or so that it wants. For Jolys (HA!), here's a link to the spec sheet with a partial schematic:

www.shure.com/stellent/groups/public/@gms_gmi_web_ug/documents/web_resource/us_pro_sm82_ug.pdf

The question is: How hard would it be to disconnect the preamp, limiter, and all the other ultraminiaturized junk in there, and just turn it into a mic level mic that runs on 48V of phantom power? I believe this mic has a very unusual capsule, and a really great one, which makes the mistake of trying to put the preamp in the mic. I would love to replace that preamp with an Avalon, and listen to that capsule SING! Whaddya think?-Richie
 
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I'm not a modder, but it's not that tough, just junk everything downstream of the FET and replace with whatever circuit you like. Or swap the FET too if you're so inclined.
 
SM82 modifications

It's easier to post here than send you an e-mail Richie...

Have you ever used this mic without a battery installed but on phantom power? It (or at least mine) work just fine...it still has all the benefits (or drawbacks) it would with an on-board battery.
IF you're trying to cut the built-in preamp out I guess you would actually need to get a schematic. According to the Shure documentation (http://www.coutant.org/sm82/index.html):

CAPSULE ---> FET ---> Limiter/Attenuator ---> Line Amplifier ---> OUTPUT

Maybe cutting out the Amplifier from the signal would work...any thoughts?
 
Richard Monroe said:
The question is: How hard would it be to disconnect the preamp, limiter, and all the other ultraminiaturized junk in there, and just turn it into a line level mic that runs on 48V of phantom power?
Click to expand...

Hi Richie,

It is little confusing. Do you want to disconnect preamp and still run the line level, or did you mean mic level?
Would be no problem. What is the diameter of the body?

Best, M
 
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Dimensions

SHURE SM82

Diameter of body: 20.1 mm (25/32")
Length of body: 220 mm (8 21/32")
Total length including microphone capsule: 301 mm (11 27/32")
 
I meant inside diameter... just to know if (or which) transformer would fit.

Best, M
 
Yo Marik! I should have thought of you. I found my typo (and fixed it) just before reading your posts. Yes- mic level is the plan. My main reasons are twofold. One, I want the simple convenience of plugging into standard balanced XLR mic inputs. Secondly, I want to eliminate/discard the whole preamp/limiter section, because it cannot do justice to that lovely capsule. Too noisy. It's a shame, too, because over that noise, you can hear how good the mic is.

It also has a *very* unusual pickup pattern, which I can't explain. It produces the kind of detail you expect from a good condenser, but in spite of producing a perfectly strong signal (even for line level), it has a very short "reach". Not only does it reject signals that are off axis very well, but it also rejects signals right in front of it that are at a significant distance from it. For the record, with my small knowledge of acoustics, that should be damned unlikely, or even impossible. Don't ask me how it does it.

Even if I'm dead wrong, the mic has a good capsule, and has earned a certain cult following. I can't believe I've never seen one with the preamp disabled. I'm happy to take any arrangements off line. Feel free to email me an estimate. It's a very long, thin body. Check the picture on the link above. It also has rather low handling noise. I think it sounds a little like a cardioid-only KSM44, with an annoying audible noise floor from that cursed preamp.
It's the same thing today with USB mics- building the preamp and A-D convertor into the mic saddles you with a low quality preamp and A-D convertor. I think the SM82 is too good to be hampered by its bells and whistles..-Richie
 
You should just trash the body and put the electronics into an empty case you have lying around...that way you dont have to settle fow hat transformer you are able to fit inside...if it sounds like a KSM44 then its a winner.
 
I see your point, Darrin, and it might come to that, because the body is not a very common shape. I do like it though, for what it was intended for- interviews in noisy places and voicevers. It would be a plus to keep that nice long handle and the low handling noise for certain field applications- such as plugged into the H4n.-Richie
 
Richard Monroe said:
Yo Marik! I should have thought of you. I found my typo (and fixed it) just before reading your posts. Yes- mic level is the plan. My main reasons are twofold. One, I want the simple convenience of plugging into standard balanced XLR mic inputs. Secondly, I want to eliminate/discard the whole preamp/limiter section, because it cannot do justice to that lovely capsule. Too noisy. It's a shame, too, because over that noise, you can hear how good the mic is.
It also has a *very* unusual pickup pattern, which I can't explain. It produces the kind of detail you expect from a good condenser, but in spite of producing a perfectly strong signal (even for line level), it has a very short "reach". Not only does it reject signals that are off axis very well, but it also rejects signals right in front of it that are at a significant distance from it. For the record, with my small knowledge of acoustics, that should be damned unlikely, or even impossible. Don't ask me how it does it.

Even if I'm dead wrong, the mic has a good capsule, and has earned a certain cult following. I can't believe I've never seen one with the preamp disabled. I'm happy to take any arrangements off line. Feel free to email me an estimate. It's a very long, thin body. Check the picture on the link above. It also has rather low handling noise. I think it sounds a little like a cardioid-only KSM44, with an annoying audible noise floor from that cursed preamp.
It's the same thing today with USB mics- building the preamp and A-D convertor into the mic saddles you with a low quality preamp and A-D convertor. I think the SM82 is too good to be hampered by its bells and whistles..-Richie
Click to expand...

Hey Richie,

It seems like an electret capsule and there is a good chance the noise comes from there. Also, I'd like you to be aware that part of the sound you like about it could be coming from the preamp/limiter itself... I cannot tell you for sure, as I've never tore this guy apart. In any case, if you are still up to it send the thing my way. For somebody like you, who helped so many folks with good advices for such a long time I will be more than fair. How 'bout you pay parts and shipping. If you don't like the outcome just send it back and I will stick the darn board back.
Sorry I don't have your email, but write me to ribbonmic(at)comcast(dot)net

Best, M
 
Richie and Marik -

Sounds like a neat project - make sure the results are posted on the board. I have three of the SM82's in "nearly" pristine condition and might consider altering one.

Richie - You're correct about the signal rejection for off-axis & distant sounds on the SM82 - got to be due to the limiter somehow. Since it was designed for field use, keeping the signal clean and eliminating extraneous noise must have been an intentional design element.

IF you end up repackaging the capsule and don't need the old case anymore, let me know - I'll be glad to pay a fair price for it...spare parts for this mic are hard to locate.
 
FloridaWing said:
Richie - You're correct about the signal rejection for off-axis & distant sounds on the SM82 - got to be due to the limiter somehow. Since it was designed for field use, keeping the signal clean and eliminating extraneous noise must have been an intentional design element
Click to expand...

No, a limiter would do the opposite, it can only decrease signal-to-noise. You'd need an expander or ducker to get rid of noise. That would work equally on- or off-axis, because electronics don't know what signal comes from where (in a single capsule mic, anyway).

Without an interference tube (as a shotgun has), all a capsule has is its frequency response and polar pattern to reject noise.

Also note that Shure's docs state the limiter doesn't get active until well over 100dBSPL. So according to Shure, it shouldn't be active on background noise at all (unless you're on the tarmac of an airport ;))

Best way to increase 'apparent" signal-to-noise is to make the capsule less sensitive, thereby forcing people to get close to the mic. That works quite well.

Also consider that most handhelds used for ENG are omni dynamics--this is because omnis are far less sensitive to wind noise, and you can't put a dead rat on a handheld as you can for a shotgun overhead--looks funny on camera.
 
Thanks. MS, that was my thinking. As I said, it's impossible by my limited knowledge. I sure hate it when I hear something that appears contrary to known laws of physics, because it probably means my ears suck. That's just another reason I'll be happy to send this mic to Marik, and get a more educated opinion. The recording hack gut in me says- there's a wicked mic in there trying to get out. I appreciate, as Marik said, that I may just like the color of that cheesy little preamp. I'll be surprised if it's an electret, but of course, Marik will find out for sure when he gets his grubby hands on it. I pray to my gods that the capsule isn't the source of the noise. That would be a worst case scenario.

Well, I don't know if we'll get *results* exactly, but we will get *opinions*. I also understand that Marik, by philosophy, will render an opinion based on the measurable qualities of the mic, and the characteristics of the components. I, instead, will use voodoo. Well, frequency graphs don't usually lie, but we have yet to define in numbers what sounds good, or bad. When we disagree, is it about our ears, our brains, or both? Some mics (and pres) try to tell the truth, and some try to sound better than the truth, and they all tell some truth and some lies to varying degrees. Either the truth or a lie can suck, or be a good thing. No number can tell you what sounds good.

What we *can* do is rip the unecessaries out of this mic, and find out what it's really good for. Wow- the *first* SM82 Marik Mod. That would actually be a hot property on ebay! (I'm not kidding, this mic has a weird cult following, like Edsel owners) For the record, Marik, if it ever comes to that, I'll split it with you, minus the $10 I paid for it at a flea market!-Richie
 
It's almost certainly an electret, because Shure doesn't show a polarization voltage in their block diagram. And of course the SM81 is electret. I don't know why that's a bad word, so is the KSM141, so is the KSM32. And a bunch of DPA mics, and so forth. The noise figure is quite higher than the SM81, so I'd bet it is the amplifier and not the capsule, unless they went for an unusually low sensitivity capsule.

Anyway, I don't think Shure did any externally polarized condensers until the KSM27/44.
 
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