Can someone help me with my microphone schematic please

Discussion in 'General Electronics Chat' started by jonslaten, Sep 8, 2010.

  1. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    First off how's everyone doing? This is my first post btw . . . and I have no clue how to trace wiring diagrams. I know all of the symbols, I just get confused trying to trace things around.

    Ok, so here's my situation: I have this really nice Russian made microphone from the company Oktava. It's an MK-219. I have been reading posts about what can be done to open up the mic even more, improve transient response and so on. I've completed all of the physical modifications, but what's left are the electronics.

    So I have the schematic in hand and took a photo of the board to try and make some sense out of this . . . and now I'm scratching my head trying to find R1, R2, C2 and C3. There is nothing written on the board to even give me a chance to begin this easter egg hunt. I've drawn it out by hand to get more familiar with the board, but I'm getting no where. Obviously schematics were not designed to mirror the physical board that I'm staring at.

    I read that it's "standard practice" for schematics to be written from left to right. Maybe that explains why R1 and C1 increase in number as you look from the left to the right? If so, then is R1 the first resistor the Condensor/Capacitor output wire connects too?

    Anyway it calls for replacing R1, R2, C1, C2 and the FET (which I found because it looks nothing like any of the other components).

    I uploaded a photo I just took of the board, and also provided the schematic. Is it possible for someone to tell me where these components are located with the information I provided? If anyone has the time, and doesn't mind giving me a hand, I would hugely appreciate it. Also, I ordered the upgraded parts online and then getting my friend to solder them for me.

    Here are the P/N's if anyone was curious . . .

    FET REPLACEMENT P/N TOSHIBA 2SK170BL
    C2 REPLACEMENT P/N P4860-ND (COG Monolith Cap)
    C3 REPLACEMENT P/N P2019-ND (Tantalum Cap)
    R1,R2 REPLACEMENT P/N MOX200J-1000ME-ND (1G MOX Thick Film Resistor)

    So if anyone can at least answer some of my questions and more so tell me where these 4 components are located, that would be sweet. Thanks!

    jon
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    What you are asking is doable, but will take some time. There are some audiophiles here that would be the best source.

    Have you tried to find a parts list for the mic...maybe from the same source where you got the schematic?

    You also may need to take another photo of the mic assembly which shows the reverse side of the PCB. Just turn the assembly over from top to bottom; don't reverse it from left to right.
     
  3. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    Ok cool sounds good. I'll take a shot of the back of the board and load it up tomorrow. I got daughter watch right now as per the wife, so I have my hands full. Thanks for the response.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    There are millions of high quality western electret mics and preamp circuits for them.
    Why are you fiddling with an unknown and obsolete Russian mic??
     
    Last edited: Sep 8, 2010
  5. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Maybe because you can probably buy the western equivalent of $1000 gear for $200 from Russia which is a pretty good reason. You might be arguing that they aren't equivalent but that is not all one sided. In some ways Soviet technology can tend to not be as good but there are almost as many stories among people who have actually used eastern bloc gear of it being good enough and if not always reliable - at least durable and repairable. T-34 tanks, AK-47 rifles, Mig-21, Minsk motorcycles. Not the same aesthetics but in some circumstances you might rather have them than an M-60, M-16, F-16, or Harley. Free market integration and competition means that you are likely to see more and better Eastern European gear every year.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Russia is also about the only place left that still makes replacement vacuum tubes, many of rather good quality from what I hear.
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Aside from the FET these are the manufacturer's part #s:
    C2 REPLACEMENT P/N P4860-ND (COG Monolith Cap)
    C3 REPLACEMENT P/N P2019-ND (Tantalum Cap)
    R1,R2 REPLACEMENT P/N MOX200J-1000ME-ND (1G MOX Thick Film Resistor)

    so there's really no way to interpret them without writing the manufacturer.

    Just noticed, C3 does have a value written on the schematic.
     
  8. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    I am a musician and happen to know quite a bit about what works and what sounds like crap. BTW most, if not all, "American Made" microphones are now being produced in good ol China. They just slap their name on the side, hmmm, now that sucks! And they do. I'm not saying ALL, but most suck, sounding brittle and boxy. The quality isn't there.
    I too at one point never heard of these things either. But I happen to know other musicians (some with amazing, expensive studios) and they too have friends . . . so you can see where I am going with this. And could you believe that at one point, one of these nutty musicians bought one, tried it out, and was simply amazed. These "unknown" mics are actually quite well known. So if anyone is insane enough to waste a few hours of their weekend modifying their mic, and then wasting 30 bucks for a few electronic upgrades, then I am that guy.
    Do a search on modified Mk-219/319's and you'll read that they can give a Neumann a run for it's money. I'm sure you've heard of Neumann right? So you know how much those guys will put you back. Yeah I bought my russian mic off a friend for 99 bucks. So maybe I am wasting my time on a fun hobby like this.
    Anyway sorry for being a smart @$$. But when someone makes comments about something they obviously have no clue in the world about, it's just plain irritating. To each his own.
    Again I'll try to get some close-ups of the back of the board.

    Here's a link about the modded mic up against a Neumann:
    http://www.oktavamodshop.com/product_info.php?cPath=1_21&products_id=30

    General info on the mic:
    http://recordinghacks.com/microphones/Oktava/MK-219

    Here's one on the mod and internal circuitry:
    http://www.recordingmag.com/resources/resourceDetail/316.html
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Totally understand what you mean about the mikes today. I used to have a rather old Shure ES-615 I used for acoutical analysis and that thing was about as flat as you could get back then. I seriously doubt you could replace it and I sure wish I hadn't sold mine.
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    You would need to post more image of the circuit board, taken from above and underneath.

    It will also help if you can shine a torch underneath the circuit board and take image from above so that the copper trace can be seen through the board. This allows the component connections to be determined.

    This is what I've got so far. They may contain errors so more images will be needed.

    [​IMG]
     
    Last edited: Sep 9, 2010
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
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    OK, let's see if I'm understanding what you're trying to do.

    You got the mike, it works but people have figured out how to slightly modify the circuitry to improve its operation?

    You have a schematic (that mmulti-colored one) which I'm assuming illustrates the level of necessity a component should be changed to get this improved operation.

    You have a partial parts list of the improved comonents people have been changing them to, in other words that FET part # you indicate would be what you'd want to change the original to?

    --------------

    If I'm correct so far good, if not please try to get me as such then we'll discuss ideas from there.
     
  12. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    Yes you're exactly right. On a previous post i provided several links that go into great detail about what people are doing to improve an already great sounding mic. They are just upgrading some of the components to newer technology, from what I gather. Here I'll paste an excerpt from the mod page and you can read it if you have the time.

    Now what do we change?

    The whole goal of the microphone design is to make sure there is as high as possible an input impedance so the capsule sees as little loading as possible, and to make sure there is as low an output impedance as possible so the transformer loads the FET stage as little as possible. Our goal for these modifications is to make this actually be the case.

    The Front-end components:

    The most substantial sonic changes can be made by upgrading all of the parts in the front end. Desolder the FET, the capacitor C2, and the two resistors. Replace the two resistors with 1000 Megohm types. The original resistors are specified at 500M ohms but often substantially lower values can be found in these mics, especially in earlier production. Replacing them with 1000M types will substantially improve the top and bottom end response. Likewise, replacing the 680 pF blocking capacitor C2 with a higher-grade COG type of slightly larger value will improve linearity a lot.

    The original capacitors use a poor grade of dielectric that results in higher distortion.Replace the FET with a Toshiba 2SK170BL according to the photograph of the modified Revision 1 board. The original FETs have different pin configurations and come in several variants; you want the center pin of the new FET to be connected to C2 and the other two pins to be connected to the resistors R6 and R7. As long as the flat side of the FET goes toward the capsule, the center pin is connected to C2, and the ground hole is unused, you are fine. Many of these boards come with four-pin metal-can FETs in which the fourth pin is connected to the can of the FET and goes to a hole on the board that is grounded. You can see in all of the photos that these holes are left disconnected on boards using plastic FETs, and we wish to leave them disconnected when we install a new FET.

    Because such a huge variety of different FETs were used at Oktava, resistors R8 and R7 are normally selected for each particular FET, as mentioned above in the circuit description. With the 2SK170, we want to have R8 be 2.0K and R7 be 1.78K. Check the resistors in place on your board and if you see something different, replace them with precision 1% types. If you have any question, measure between the junction of R7 and the FET and the junction of R4 and R2; this is the bias voltage being applied to the FET and it should be approximately 1.3V.
    Capacitors
    Replace all of the cheap electrolytic capacitors with tantalum types. That is, C7, C8, and C9 should be changed from poor-quality 1uF aluminum electrolytics to higher-grade tantalums.
    If you encounter a Revision 1 or Revision 2 board where C7 consists of three 1 uF caps in series, replace two of those capacitors with wire jumpers and one of them with a 4.7 uF cap. It is possible, as you can see in the photo of the modified Revision 2 mic, to replace this set of three with a 1 uF mylar film capacitor, and this may bring a slight sonic improvement. Sadly, the one capacitor that would really benefit from replacement with a film cap is C8, for which there isn’t much room. The problem with the film capacitors is that they are substantially larger than electrolytic types.
    You could decide to replace C1, C4, C5, and C6 with higher-grade ceramic capacitors, which will improve the quality of the sound when the pad or bass-cut switches are enabled. Unfortunately, I think it does not improve the sound enough for me to ever want to use the pad or bass-cut functions, so I normally just leave them alone. You could make some argument that C5 and C6 are in the signal path even when the bass cut is not engaged, so you might consider replacing them. I don’t hear a substantial improvement with replacing C5 and C6 but it’s not much additional work, so I’ll leave that up to you.

    Conclusion:

    The Oktava 219 and 319 microphones have well-designed and solid electronics and quite fine capsules. Unfortunately the quality of construction and the case designs sometimes leave something to be desired, but I think all of the changes suggested in this article are well worth the effort and can improve a good microphone quite considerably.

    So from reading that you can see what I want to do here.

    Also, yes the schematic specifies the order of importance for part replacement. Here is the full list of all the parts they are talking about:

    Electronics

    Parts / Quantity / Description / Digi-Key Part

    ----------------------------------------------

    C7, C8, C9 3X 4.7 uF 50V tantalum P2077-ND

    C2 1X 820 pF COG ceramic P4860-ND

    C3 1X 100 uF 6.3V tantalum P2019-ND

    R1, R2 2X 1000M (1G) resistor MOX200J-1000MEG-N

    Possibly needed:

    R7 1X 1.78K 1/4W film resistor 1.78KXBK-ND

    R8 1X 2.00K 1/4W film resistor 2.00KXBK-ND

    C5 1X 1500 pF COG ceramic P4863-ND

    C6 1X 680 pF COG ceramic P4859-ND

    1X Toshiba 2SK170BL FET (not available from Digi-Key)


    Let me know what else you need ok? And thanks for responding back.

    jon
     
  13. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    BTW, I'm still fighting with my wife's camera to get a clear, detailed picture with a flashlight shinning through the board. I'll get it up . . . give me some time.
     
  14. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    EBLC1388, Thanks a ton for the work you've done so far!! Amazing!
     
  15. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Sounds rather straightforward to me. You've got a picture showing where the components are located and a list of what to replace them with.

    Just order replacements from somewhere like Mouser and swap them out.

    For example:
    C7, C8, C9 3X 4.7 uF 50V tantalum P2077-ND ea
    =
    3 ea. Mouser # 74-199D475X9050D1VE3
     
  16. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    No I don't have a picture, just the schematic. My original hope was that one of the schematic reading brainiacs on this forum could interpret it for me and tell me what was what. I've searched endlessly on the internet for this answer and still nothing. I've even emailed the man that does these mods to these mics for just a picture with labels, and he wouldn't do it for me. So I'm not giving up.
     
  17. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    Maybe you don't need the flashlight then.

    Picture of both sides of the board taken directly above will do.
     
  18. marshallf3

    Well-Known Member

    Jul 26, 2010
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    The picture in post #10 has, at the top, C & R #s on it or was that just an example?

    Even if that is an example it shouldn't be hard to come up with the correct #s by looking at the schematic and board simultaneously.

    I can easily find all the Mouser part #s for the suggested upgrade components.
     
  19. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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  20. jonslaten

    Thread Starter New Member

    Sep 8, 2010
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    Sorry here's the Russian schematic
     
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