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MXL 991 Mod-AC Issue?

Discussion in 'Electronic Repair Modifications DIY' started by timshel, Oct 3, 2012.

  1. timshel

    timshel Active Member

    Hello audio equipment creepers,

    I finally fit the giant Radioshack metal film capacitors into my MXL 991. My mod was based off of this link: Gus' MXL 603 mod.

    Which I am sure some of you are familiar with. To clarify: I have not replaced the C13 ceramic with a polystyrene yet. The capacitors I have replaced are the same value as described in the mod forum post.

    Onto the issue at hand--The microphone is working but has this low rumbling sound in the signal. I can make this happen whenever I talk into the capsule at most distances. Additionally, it will come and go without me or a meaningful sound source nearby.

    So far as I can tell, it has something to do with the capsule; when I remove the capsule this rumbling disappears.

  2. RemyRAD

    RemyRAD Well-Known Member

    Yeah, I have some thoughts.

    First, you have put in a capacitor modification. You've indicated you haven't changed the ceramic one yet. And it's making strange sounds. Well have you considered finishing the modification by replacing that ceramic capacitor?

    Actually I think what you are hearing here is an extended low-frequency response that is having problems from " blocking "? Many condenser microphones actually have a low-frequency cutoff built into them to prevent blocking. One of the best-known is the Neumann U87 and it has a removable blocking capacitor. But you don't want to remove that because all that you'd get is what you are probably currently getting. Any change in air pressure around that capsule, will cause that blocking to occur. This is all due to the near DC value response of the low-frequency capabilities of the capsule. So you need to prevent that from happening. So when doing someone's modification, I'd say do the complete modification before you make any other opinions. Having been a professional engineer who has not only worked in the broadcasting and recording industry for over 40 years, I've designed equipment. I am not one for updating or modifying anything just to make it better. Better isn't always better. Better is just different. Better is what you perceive to be better. The sound your microphone is making right now indicates it is working better. What you don't like that? It's not better? Well never mind about that microphone. I've got this great little bridge out of New York City you might be interested in?

    So in the end when you remove the capsule the rumbling stops. Right. You've made it better. It sounds so much better without the capsule! None of that rumbling noise nor stupid people singing speaking or playing musical instruments. Virtually noise and signal free. Ya want to do this modification is to all of your microphones so that all of your recordings can be this quiet.

    See how marketing works?
    Mx. Remy Ann David
  3. Boswell

    Boswell Moderator Distinguished Member

    Not all film capacitors are suitable for this task. What's the exact part number or Radioshack order code of the capacitors you have put in?
  4. RemyRAD

    RemyRAD Well-Known Member

    Just the fact that he utilized Radio Shaft metal film capacitors means that he actually purchased a raffle ticket, crapshoot, lottery ticket, capacitors. So all he really might need to do is to just replace the capacitors again? Sorry but that's the way that Radio Shaft parts go. They are not parts made to extremely tight tolerances, let's face it. And he did not install that extra capacitor he indicated was in the upgrade modification. Which may have been there to prevent blocking? I don't know what the freaking modification is? But blocking is a common problem in the design of true condenser microphones. You cannot effectively reproduce DC in high fidelity playback systems and recording devices. It is where audio design becomes bogus. So there's a lot of smart people doing some really stupid things out there.

    He already indicated an incomplete modification. All bets are off.
    Mx. Remy Ann David
  5. Kurt Foster

    Kurt Foster Distinguished Member

  6. RemyRAD

    RemyRAD Well-Known Member

    That would be completely irresponsible of you Kurt. There is no recycling insignia on that dumpster.

    But then again, who would want to recycle an awful Chinese condenser microphone anyhow?

    Aliens will wonder what these tapered metal tubes were used for in those human beings?
    Mx. Remy Ann David
  7. timshel

    timshel Active Member

    Hahahaha. This is a dream thread now. Reming from Remy and the elite engineer's answer to Chinese microphones.

    I'm currently on a DIY kick building electronic thing-a-majigs and trying to wrap my head around how these marvelous (and not so marvelous) pieces of engineering work. If this mod happens to create a change in any capacity it'd be worth the $3.50 I spent. And Remy you're right, what I am looking for is something different. I don't think about making this microphone better when sticking my soldering iron into places where I have no business. The Hi-Pass filter makes some sense to me now considering the sensitivity of a diaphragm. I'll order the part and see how the new value affects the response of the ole tin can.

    Many thanks per usual.
  8. RemyRAD

    RemyRAD Well-Known Member

    Being on this DIY thing you are doing, is a great thing to do. This will teach you more than anything else. It will teach you proper gain staging. It will teach you where the most linear areas of an operational amplifier lie. And it will teach you the difference between different kinds of componentry. Not every transistor, capacitor and gold spluttered mylar films are all designed to sound alike. In fact it's the opposite. Some people design audio Quitman to have character a very specific character. Other people try to build their audio equipment to not sound like any audio equipment. Who's right? Answer. Both and neither. Technical perfection does not necessarily equal neutrality. It's a creation. It's an entity. It has its own life. And you'll glean what you can from it should you so desire to do so. And obviously your desire is quite high. You are going the way of most of the classic old-school folks like myself.

    Back in the older days of independent recording studios, much was built in-house. Complete consoles were designed and built by studio owners themselves. API used to sell console parts. So you could actually build up your own custom API consoles. And they'll still let you do that. Consoles at famous Studios that could actually afford to purchase well known, high priced consoles, actually elected to build their own such as Sunset Sound, in LA. RCA Studios, et al.. I've designed and built a custom large frame consoles as well and more than once. There is so much to be gained as audio engineers by doing this. You're definitely doing the right thing. This will put you on top of the heap of all the other wannabes. It's not just plugging in a budget microphones, using a bunch of plug-ins and making recordings. It's about understanding everything in your control room from soup to nuts. And we're all kind of nuts. Especially over mom's homemade chicken soup... with lots of noodles. And that's it. All that you need to become a really fine, engineer.

    Mx. Remy Ann David
  9. Kurt Foster

    Kurt Foster Distinguished Member

    well that 's why they called them "engineers". because they were electrical engineers. real engineers have an engineering degree and in the old days you needed a degree and the knowledge to work in / run a recording studio because as Remy said, you often had to build and maintain the gear.

    on second thought i suppose the dumpster remark was a bit harsh considering this is the DIY forum but i still submit one might be better off starting with something a bit better than the current crop of slave labor produced kit currently emerging from the far east.

    ha ha .... :rolleyes: that's the first time ever i have been referred to as an "elite" anything.

    mfffph ghaaaa suicide ahhhh!
  10. RemyRAD

    RemyRAD Well-Known Member

    I'm actually an engineering hack. I'm not out to be George Massenburg nor Bruce SwedeIn. I'm just Remy Ann David a real fine engineer. I've got my own signature sound. And people (who actually want to pay for actual audio engineering), seem to like it too. Part of my engineering skills only came about because of all the DIY I've done throughout the years. I'm not even one for modifying equipment unless there is an actual need to do so. I'm not interested in making anything better than it was originally intended to be. It's like picking out underwear. Nobody modifies their underwear that I know of. If it's not the right underwear, you replace it. You don't cut the legs off your boxers to turn them into loosefitting jockeys. Right? Actually I wouldn't know? I know I burned my brassiere before I could ever wear one. I mean I don't know too many guys that like to walk around in a jockstrap all the time. So why do women walk around with brassieres on all the time? Of course some need to. That is, I'm almost 57, and I'm still perky like a teenager. I can't pass the pencil test. And maybe that's why I don't take comprehensive notes during my recording sessions either? So if I can't remember what I need to do without a brassiere on, I've failed. I don't need anything cutting off the blood flow to my hearing, LOL. Besides, I already present enough diffusion without con fusion.

    What year is this? I think my flux capacitor has gone bad?
    Mx. Remy Ann David
  11. DrGonz

    DrGonz Active Member

    Yeah modding something today is about taking out caps that are not as high quality and replacing them w/ higher quality caps. That's not really modding anything but I digress... My main goal is that if it is not broken don't fix it. When my Emu 1820 docking station had scratchy pots and a loose headphone jack I took it apart. I cleaned the headphone volume pot and soldered up the input jack. I guess I could have replaced some caps in there but it was not broken so I left it alone.

    To start modding something is always interesting how it will turn out... To learn what components are better is a must! Modding here on this mic is not a mod but rather a stab at improving the parts. The design has not really been changed. All the caps are rated the same w/ just different ingredients inside. I am not saying this is a waste. However, when the mic sounds worse after you worked on it then I have to question even the persons soldering skills. Taking anything apart means putting it back together w/ some stress. The stress could injure anything in that circuit. The heat of the iron might be just enough to weaken traces between components. It is all so tough to determine when I was not there to participate, but I have to raise the question. Plus when they make these cheaper circuits they are all ran through a machine that solders the components in place. The solder is lead free typically. My thought would be to flow leaded solder on these boards to make they more dependable over time. Is that a mod or just a state of mind?
  12. RemyRAD

    RemyRAD Well-Known Member

    Yeah, well, I agree with you but, he is obviously having problems with " blocking ". And because he did not utilize or change the other capacitor value in the listed modification, it's an incomplete modification. Many people don't understand that many of these components interact in different ways when replacements, other than the original intended parts, are replaced, by different componentry, not set forth in the original design. So not replacing that last capacitor may be causing this condenser microphone " blocking ", issue? He replaced the standard intended capacitors with different capacitors of a different type. So that last capacitor (not replaced) may change the frequency response so as to prevent condenser/capacitor capsule " blocking ". It's not over until the fat lady sings and it's not over until the modification has been properly performed. It's not been properly performed. What gave this guy the idea that he could leave out part of the modification? And still expect it to work correctly? I think not. I might be a hack engineer myself but I'm not that kind of a hack.

    So while replacing componentry with "better" componentry, it changes the initial interactivity within its micro system. And his modification is not complete. So like I said... all bets are off. It's an incomplete mod. It's like trying to run your automobile off of natural gas without making a full conversion. And then wondering why it doesn't work anymore? Or, doesn't work better. Because it's not a good nor complete modification. You know you cannot use a bow for a cello, on a violin, even if it is " better ". Just because it's bigger and better, doesn't mean, it will work properly with the violin, without completing a more comprehensive and " better ", modification. In other words a correct modification. Not a half ass modification, which is what he performed. After all, his better components are from a half ass made component from a half ass component supplier, Radio Shaft. And what makes you think anything coming from Radio Shaft is better than any other piece of Taiwanese BS manufacturer? I mean if you wanted good capacitors, he would have ordered Panasonic's. Not, Radio Shaft. And therein lies the third variable, three lousy capacitors from a lousy component supplier. And that's supposed to make it " better "? I think not. He's replacing one lousy Taiwanese part for another lousy Taiwanese part. That doesn't make anything better. In fact that's a destructive modification. And how were his results? Lousy that's how. So that's NOT a quality modification of any sort. Because, simply put, the parts are not known to be high quality to begin with. It doesn't matter what the marketing is behind the selling. Understanding component quality is tantamount to successful modifications. So here is a person that did not save up their paper route money for a proper microphone nor a proper modification. They expected their McDonald hamburger to taste like a steamed lobster and it doesn't. And they wonder what's wrong? It just didn't taste like a lobster when they dipped their hamburger patty into the melted butter and they wonder why.

    Good modifications have to be performed with quality componentry. Not the same thing that came out of the microphone to begin with made by the same Taiwanese manufacturer that made the previous components. And that's essentially what has been done. Putting Rolls-Royce looking accoutrements onto a VW beetle still makes it a VW beetle that looks a little bit more like a Rolls-Royce but hardly performs as one. So while you think it is better, it's really no different. It's just a VW beetle with what looks like a Rolls-Royce front grill. And you can expect it to perform like a Rolls-Royce just because it looks like one. It's all that other stuff, under the hood.

    Simple modification. Just remove all the internal parts and pieces from the MX oh microphone and replace them with Neumann, parts, pieces and capsule. You don't need the physical housing because you already have the physical housing. So ya need to replace the engine in order to improve the performance. Replacing just the carburetors, means you have a VW beetle with better carburetors. And it still doesn't perform like a Rolls-Royce.

    It's like a transformer less microphone preamp. No matter the parts that are replaced, it's still going to sound like a transformer less microphone preamp. That is, until you, install a quality transformer. An American or European made, quality transformer. Not a transformer from Taiwan. And everyone knows that to be true. You think the capacitors are any different? I think not. It's only their parts made to the highest of their low standards of quality or lack thereof. And this is called Dicking with things, You know nothing about. And that's supposed to make it better? What? You want the person at McDonald's to remove your appendix? Just because they know how to cut a hamburger from a slice of beef? That doesn't sound like a smart thing to pursue? And then also to forget the ketchup, mustard and pickles. And maybe it would be a better hamburger with the original raw onions and not the new improved sautéed onions? And also because the sautéed onions really can't improve what is already a bad hamburger to begin with. Of course it might be more to your liking but is it actually better? That's a judgment call. Sure his microphone is better. It goes all the way down now to DC. It's only the " blocking " now, that's the problem. So why not try replacing the capacitor that was called for to be replaced, that you didn't replace? You replaced the leavened bread with the unleavened bread and wonder why your new microphone is all crunchy?

    Get your new McDonald's hamburgers with the new matzo buns. (For a limited time only)
    Mx. Remy Ann David
  13. DrGonz

    DrGonz Active Member

    So when we say "Blocking" are we referring here to the relation to farad rating of the capacitor? The farad ratings or internal material of C13 create an over filtering of the signal frequencies and squeeze the signal. Some capacitor internal materials could be rated at the same farad ratings but squeeze the signal in different ways. Like a tantalum versus a metal film type or a polystyrene versus electrolytic type capacitor. Each capacitor is used for different reasons and some are better at different gain stages in a circuit. I would challenge the poster to finish the mod here and get C13 replaced. OP should then follow up with us at that point to let us know how the mic is working...

    Anything else would be uncivilized.

    I really don't like calling it a mod if the person performing the mod does not really take the time to understand what it really is doing. It just seems that modding something is a shot in the dark w/ out some basic understanding of the circuit. I would challenge anyone to think why I am modding something for 10 times longer than it takes to perform the task, at least. In that time you might see an error before you commit one. In the case here the OP made a mistake and is learning from it... That is actually a good way to learn in many regards too. I hope to hear a happy outcome for the mic by the near end of this thread.

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