MK012 Mod

[pantsonfire]

Hey-
I did a lot of searching on the web and various forums trying to find details on the MK012 “D*****” mod. I have the Recording article, but I had hoped to find more info on individuals’ experiences with the mod as well as updated info, as the article is a few years old now. I found some helpful stuff, but not the all inclusive source that I had hoped for.
This post is an effort to fill the gap I found in my searches, and to hopefully pay back a little of the wealth of info I have garnered from the Lab. Will someone please let me know if I am wrong in any details or if I am violating any copyright law. Please.
Part sources and part numbers for this mod are included throughout this post where they are relevant. I would print them all together, but it might resemble the list in Scott D*****’s article, and I wouldn’t want anyone to think that I was plagiarizing him.


Here is an image of the casing of the MK012. Please note that you drive the screws INTO THE BODY OF THE MICROPHONE!!!!! to release the board. A very small, big mistake here can start your modding experience off on a negative note.

Okay, there are 3 screws to turn IN... once you’ve done this, push on the plastic pad at the top of the body and simultaneously pull on the XLR connector at the bottom of the body, and wrangle the board out of the casing.

Here is a pic of the board from one of my mics with all the original components:

Here is a shot of the parts I bought that I didn’t need to (they are all caps.) Apparently, my mics are some of the newer releases that have better components based on Scott D*****’s mod article, even though they were purchased 4 years ago. The only parts I didn’t replace are the blue vinyl coated caps C3, C4 (both Digikey part number4073PHCT-ND), and C5 (4047PHCT-ND), because they were the same as the caps I bought from Digikey. You won’t see C5 in any of my photos. It’s the big blue cap on the back side of the board from most of the components. There are only 4 parts soldered on that side, so if you need to replace it on your mic, it will be easy to determine which cap it is.

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The first part I replaced was the capacitor labeled C1 (Mouser part number 140-50P2-821K-RC). I started here because it was an easy swap. Check this pic:

I put an 820pF ceramic disc cap in as replacement for the stock cap. Scott D***** recommends a COG ceramic cap, which I would have used, but I had trouble sourcing them when I was in the mood to search.

Next was C2 (Mouser part number 74-199D25V10-E) another easy tradeout...

Okay, now it gets a bit more difficult. Swapping out the FET labeled Q1 (an npn transistor 2SK170BL from http://www.tech-diy.com/smallsignal.htm under Small Signal Transisitors and JFET's ) is not such a big deal, but you should do it in conjunction with replacing R1 and R2 (both Mouser part number 588-MOX-200001007JE). This is the Big Tangle, in my opinion. Scott D*****'s article suggested putting in 2-1G ohm resistors in series, so that’s what I did. The part number above is for the 1G ohm resistors I used. Pricey.

I soldered my resistors together and I wrapped them in heatshrink tubing...

Here they are in place.

I had to bend and push things so that they would fit within the original profile. There is no room for give in this mod. The first time I tried it, the resistors 1 and 2 were scraping the sides of the casing and it just didn’t work. Keep everything as low profile as the parts you haven’t changed yet, and you should be fine.

Lastly, I replaced the transistor Q2 (Digikey part number 2N5087-ND.)

Here’s an important note I think. If you look at the image with all the original parts in it, you’ll notice that by the time I finished this project, both of the FET’s flat sides were oriented 180 degrees away from their original positions. This is one of the problems I had when trying to perform this mod by the Recording article. The photos in that article showed replacement components alongside original components. In regard to transistors, that can be very misleading. I read forum posts that said “just install it like the photo”, which is exactly right in regard to Q1, but exactly wrong in regard to Q2. This is also one of the points on which I would really appreciate someone correcting me if I am wrong. My conclusion is based on the schematic in the Recording article and the voltage readings listed there.

Lastly, here’s a pic of all the parts I removed from one of my mics. I am just putting this here so you can, hopefully, get an idea of the scale you’ll be working on.

These mics sounded good before this mod and they sound good after. I’m posting this as a matter of disclosure, not as an endorsement of the modification. I have to spend time with changes before I can really offer a material opinion. The process however, is as described.

Please let me know if other, different photos would be helpful, and I will post reasonable requests to this thread

Best of luck.

 

[emrr]

Great run down! Thanks for adding it. I have a pair of these from the earliest batches into the US (1996-97?), and one preamp needs some work. I've meant to get to it for some time now. Maybe this will kick it into gear.

 

[Gus]

I have worked on a few 012s

Changing the fet and high value resistors and the BJT PNP IMO is a waste of time the stock are fine.

I would have left the stock input cap or used a poly (what you like) 1000pf input to gate cap

You can find a film 1uf or bigger for the Al C2 you replaced

Also what do you want to use them for? if acoustic you might have wanted to keep them stock YES stock one time testing modded and stock 012s the stock circuit sounded better than modded with an acoustic. Yes the sound "followed" the body not the capsules

 

[Rossi]

I have two LD Oktavas that use the same preamp as the 012. I modded one of the preamps. Incidentally very much like Gus suggested, using a 1u WIMA MKS for C2 and a polysterene input cap. I left the transistors alone. The stock FET is okay, and Oktava usually select the source resistors individually. So if you replace the FET, your new FET may not be optimally biased anymore.

To be honest, I can hardly hear a difference between the stock and the modded preamp. Which isn't too bad, because both sound fine. If I were to do it again, I might use a polypropylene input cap instead of the polysterene one. Or maybe just left the ceramic input cap in there. Ceramic caps sound fine with Oktava capsules IMO, they give a slightly gritty structure with nice punch. Polypropylene gives similar punch with cleaner, more hifi treble. So far I haven't really got the same kick out of polysterene that others seem to get. Maybe there are different qualities of polysterene caps (mine were quite cheap). Or maybe it's a matter of taste, but to me polysterene sounds almost as murky as ceramic caps but without the punch the better ceramic caps seem to deliver. There are different grades of ceramic caps, and the Oktava caps seem quite okay.

 

[pantsonfire]

Thanks for the Wima info Rossi. That is the first brand I looked at after reading Gus' post, but I had not found any yet that I thought would fit in the 012 body. Perhaps I'll order a couple and see if they'll work. I have not decided that this project is totally done. I am definitely considering replacing the input cap again with something more hifi. Polypropylene may help smooth out the high end for drum overhead use, which is my focus for these. All of my voltages are within 1/3 of a volt to the voltages listed on the schematic, so I am hoping I am okay as far as biasing goes.

The change I have heard in the mics' sound is a significantly more open top end, which should work well for my purposes. I can certainly appreciate the detail these things have on acoustic, but I already have my go to mics for that job.

Best.

 

[Gus]

I just reread my post. It might read harsh but it was not meant that way

I should have added it is cool to see someone take the time to take pictures of their work.

Now that you have changed some parts you can record and then change other parts if you don't like the sound and record again.

The ceramic cap changed might work fine.

C2 has a bit to do with the sound I have seen Al and Tant in the stock

The simple change might be two parts C2 and the input cap

 

[pantsonfire]

No worries Gus. I just looked at some Wima caps I have left over from another project. The largest value I have is .22uF and I don't think I could get that to fit in the C2 position much less a 1uF poly(what you like) cap. Do you, does anyone, have any suggestions about another brand to try? Nothing I see in the Mouser catalog looks like it'll fit.

 

[Gus]

older panasonic Vs fit.

 

[Rossi]

I'm pretty sure I used a Wima MKS-2 cap. Wima is what you usually get in Germany. If you wanna go polypropylene on the input cap, try BC components. They sound very good and are small enough for most SD mics. May be a tight fit, though. Different input caps are definitely worth experimenting with. Always try your modded mic on something like acoustic guitar. You won't get anywhere without actually comparing. Make sure the levels of your soundfiles are well matched.

 

[Flatpicker]

I probably modified more than 30 of these for people and got all sorts of varied results. Sometimes night 'n day improved and sometimes just different, but nearly always it went from bigger "body" with unfocused highs to clearer highs with thinner "body". I tried every combination I could think of, but could never seem to achieve the best of both.

Also, I could never seem to tell what the customer was going to like. Many times I'd get no feedback for the ones I thought were night 'n day improved. OTOH, sometimes when I felt the mod offered no improvement, the customers were so pleased they'd want to make a Buddha-like figure in my image and offer sacrifices to it.

Funny too, because I don't even own one of these myself.

 

[emrr]

interesting. chasing your tail. I'd bet you mean 'thinner body that still has the same tendency to blow out on the bottom end from vibration and air motion', too. I wonder what a paralleled cap approach would do in this case; leave the originals in and bypass with something nicer. Maybe not enough room.

 

[mikep]

i have 820pF silver mica input caps in my 012's. Its hard to say if there was much improvement. I *Think* the top end is nicer?

 

[skipwave]

I've got 1000pF silver mica caps in mine. They are clearer than they were stock, I think they had some sort of glass thingies stock. I never did go back and try polypropylene to compare. Oh well. They work on toms and some electric guitar overdubs (I prefer my ribbons for the main guitars). They were nice on a marimba, vibraphone, and glockenspiel ensemble. I used them live on a violin/viola duet over the weekend.

 

[Scodiddly]

I'm now working on a couple of dead units for a friend, and so far I've managed to trace out the component layout to match the schematic. If I end up with a usable (non scribbled) version I'll post it here. One weird thing, the XLR pins 2 and 3 are reversed from what the Dorsey schematic shows in both mics. These are the more recent ones with the serial number and better components. I'll have to do a polarity check if I get one working. Or check one of my own ones.

Anyway, I'm going to start by changing Q2 (the PNP) since I have some 2N5087 available. Doing a circuit disturbance test (prodding with my finger while powered up) against a known good mic body shows that there should be a lot of noise, instead of practically none. Guess I need to retrieve my ESR meter from the office, too.

Fun little mics, anyway, I do like my stock ones quite a bit for certain things like piano. And the PCB layout is very elegant, with just one jumper hidden under the two big electrolytics.

 

[Flatpicker]

Re-reading my post above (I forgot I posted that!), I should have mentioned that I only tested them on acoustic guitar. I think most folks were using them on drums, so what worked (or not) for guitar could be opposite for drums and other sources for all I know.

FWIW, silver micas sounded brighter to me. I always thought polypros or polystyrenes of the same value yielded a more natural top end, but it just boils down to what you like.

Also I could never hear any real difference by swapping out the PNPs, but as always, YMMV.

 

[Scodiddly]

Well, in my case I'm starting with non-functional bodies. So the cheapest first attempt at a fix is the PNP.

On the upside, I probably would not have risked any of my 012's on this sort of research. So it's a chance to try some stuff with little risk.

EDIT: It was the PNP in both of them. Now I just need to figure out a replacement for the little plastic thing that has the socket for the capsule pin on one of them.

 

[Rossi]

Recently one of my 012 preamps was broken. I suspected the PNP for some reason, but it turned out to be one of the output electrolytics. Which, by the way, are quite hard to replace, as most lytics of that cap value come in a different (fatter) physical size. Also 68 uf isn't too common.

 

[Scodiddly]

I finally got around to putting together a schematic to go with front and back PCB parts layout - see below.

And please let me know if I made any mistakes. One known issue is pin 2 vs. pin 3; the ones I've seen were reversed from the Dorsey mod schematic.

 

[Gus]

http://www.groupdiy.com/index.php?topic=27049

what are the PN markings on the fet?

 

[clintrubber]

[quote author="Scodiddly"]And please let me know if I made any mistakes.[/quote]
No mistake, but indicating cap-polarity for the electrolytics is always nice to have in a schematic (despite it being obvious here).

Regards,

Peter