Improving ye old mic locker with DIY mics

[Rybow]

Hello everyone! With my move to New Zealand fast approaching, I thought I'd share a couple of mics that I just finished up. Well, as finished as they can be. Alas, my workshop is no more. Sold to the denizens of Vancouver for a fraction of what I invested. Although, shipping it all to NZ would cost me a lot of dough, so it's not a total loss.

My mic locker was simple. SM 7b, sm 57, e609, Apex 435, Apex 180 x 2, and an AT 2020. Typical workhorse mics that get the job done. Lacking in good condenser's or mics with personality, so I tried my hand at building a few.

The Rolls Royce

I like opening acts, but I thought I'd start the show with the headliner.

KM 84 circuit, TAB funkenwerk T49 transformer, RK 47 capsule. Wired for cardioid and omni, and I included the pad switch. I put a trimmer in for the source bias resistor. I intended to set it by voltage, build a tone generator, and then fine tune the calibration using the sine wave to gate method. Still have to build that tone generator. Put inside a 2" diameter brass tube with a brass end cap. Single layer grill made from a soup strainer. DIY baby! I do want to change the grill for something better, but I would have had to buy enough mesh to do 100 microphones. I'll change it later on, but for now, it works. I also wish I had time to polish it, but I am liking the dirty look. For a shock mount, I've found I can just squeeze it into my AT 20 series shock mount.

This mic is all about thick and detailed mid range, which is lacking in my other condensers. I have used it on my voice (singing and metal screaming), female vox, electric guitars in omni, and some acoustic guitar tracks that I played back through my monitors and recorded in omni. Common theme was the very strong mid range and thick low end. Very nice. Omni works flawlessly and sounds great. The output is nice and hot requiring only 30db's of gain from my pres. This mic also picks up a lot of room reflections, which I actually like. It's a great mic, and currently the rolls royce of my collection thus far.

The Pipe bomb

Made from spare parts and parts sourced from local plumbing stores, the Pipe Bomb was my practice mic. I figured before building the Rolls, I should get some practice in. 32mm K67 capsule from my Apex 435 and the MK 012 circuit. I also made sure to include Dorsey's improvements and Gus's HF de emphasis modification. During assembly, I discovered that even a single layer grill would not fit in the 1.5" tube along with the capsule, so I grabbed some brass strips from a hobby store and made a head basket. The picture is flattering, the head basket is a bit wonky, but it works!

So far have tried it on my vocals, female backing vocals, electric and acoustic guitar. I really like it on acoustic guitar. Nice bite, and the HF de emphasis makes a big difference. A very nice mic for a $50 investment.

Simple Upgrade

My Apex 435 was my first ever microphone. I recorded everything with it, and I still think you can't do any better for the money.It started developing some issues later in it's life, so I stopped using it for awhile. With all the other mic mania, I thought it was time for an upgrade! Polystyrene input cap, changed every ceramic I could with a polyester film or polystyrene, and changed the capsule to a 34mm 797 audio K67 type that I bought from a forum member. I was planning on doing the Royer mod to this mic, but that will have to wait until I get set up again in NZ. Unless there is a DIY'er in Wellington who is willing to share their workshop?

Very nice sounding mic. Nice high end detail without being harsh, and a clean, transparent tone. I haven't been able to use it on much, but on vocals, it really does sound good. Hopefully, I'll be able to get more use out of it in the future. $35 plus a couple of caps. The strap on the circuit board is due to my big stupid hands losing one of the tiny screws. 

Thanks for checking them out! Thanks also to the forum members who helped me out in the KM 84 and 012 threads. Big props to Gus for all the invaluable info you have shared on this forum as well. As you can see, all 3 mics are on the budget side of things, but I am on a budget these days. All 3 deliver big bang, and they each add a colour to the crayon box. I was hoping to get some sound samples done, but I have already parted with my mic stands and acoustic treatment. Oh well, the eye candy will just have to do I guess.  ;D

 

[emrr]

Good stuff, thanks for sharing. 

 

[Matthew Jacobs]

This is dope!

 

[gary o]

Cool stuff inomniaclown brilliant.......proper DIY & many flavours per buck......Im just in the middle of some DIY mics housed in cat food cans....Interested to hear about the 012  HF de emphasis circuit.....I love that Oktava circuit it sounds great....

 

[Rybow]

Thanks for the comments guys! Much appreciated. It was a labour of love & hate, but mostly love.

Gary- Cat food tin mics! Now that's cool. Can't wait to see those.

I also really like the 012 circuit. I am actually trying to convert my 180's to use the 012 circuit, but I didn't spend enough time dialing in the FET's.

The HF de emphasis is Gus's mod to the 012 circuit. You take a 0.027uF film cap, and connect it between the base of the source follower and ground. You can vary the capacitor value between 0.022uF and 0.047uF to set the corner frequency of the filter. Works really well, and is very easy to implement. I think I ended up with around 0.033uF in there.

 

[tchgtr]

This is great stuff, I-clown. I too have put the MK-012 circuit into an MXL 2001 body and capsule, and liked it very much. Gus's HF de-emphasis was an easy add-on, and I used it on acoustic guitar also, and liked it. I used a slightly different cap value (I think it was .033uf also - just the nearest I had on hand), and I guess I'd better figure out how to get an example of that up here. It was a bit understated, and .027 might indeed be a bit better, but still very balanced and nice, similar to the actual MK-012 SDCs.
  I since put a Royer circuit in that 2001, and have two MK-012 P2P boards waiting to go into something. Maybe my M-Audio Nova, as the more I look into that circuit, the less I like it. Not sure the boards will fit in that mic body tho.
  There are photos of Gary's mics up here somewhere, maybe in the MK-012 thread, but I'll let him dig them up. They're quite bizarre, in a good way.
  Maybe look into tea strainers for head basket mesh. I actually have one in my kitchen that fits in the top of a teapot, and is almost the perfect size and shape.
Good luck with your move.

 

[Rybow]

Hey tchgtr! Thanks for your comments. The move is going well so far. Just getting rid of stuff, packing stuff, you know how it is. I actually wish more of you guys lived in Vancouver. Then I could badger everyone to come and take this crap off my hands!

The Oktava circuit is nice, and I'm sure you could fit it into the Nova body. There isn't much in that circuit. I did both my mics P2P. That's the way to go if you ask me.

The KM 84 circuit is the real surprise to me. The sound is just killer. Has a nice "vintage" vibe. Whatever that means to anyone. To me it's big, rounded, kind of wooden sounding I guess. Anyway, I like it!  8)

Still thinking about the Royer mod. I was going to experiment with the 6205 tubes once I got to NZ. Maybe an overdrive pedal, or use one as the first gain stage in a preamp. We shall see what happens!

 

[gary o]

Hi I clown so you prefer the KM 84 to the Oktava then?.......been thinkin about the KM 84 circuit for a while now.......I been reading yr posts seems a little fiddly to select & set up the right FET tho......

all the best....

 

[gary o]

Forgot to ask have you tried RK47 in Oktava circuit minus  eq capacitor ? & K67 in KM84 I suppose that would sound too bright tho......I been thinking about the RK47 capsule & also the RK12.........Im bit worried about K47 type capsules tho , I have a Lomo  what seems to be K47 capsule & I hate it,....doesnt seem to be faulty but to my ears it doesnt live up to my other capsules.....Im worried that other I wont like other K47 re makes.....

 

[Rybow]

Yeah, I do like the KM 84 circuit a bit more. The 012 circuit has a nice clean tone to it, but the 84 will give you some flavour. Probably has a lot to do with transformer choices. I did have a CM 2480 that I was going to try out, but as soon as I heard the mic, I was sold.

I actually didn't have too many issues after I got my method down. I set a source R of 8.2k and sorted my FET's by the drain voltage. Out of my 10 2n3819's, I measured 2 that gave me 20V. I found that a higher drain V @8.2k gave a lower source V with the drain adjusted to 10V via source R. My source V came in at around 2V, which is higher than the 1V that I have read as being optimal in this circuit, but I honestly have no issues with this mic adjusted the way it is.

I didn't try the RK 47 in the Oktava, or the K67 in the 84, but I did put the RK 47 in my Apex 435 for a time. Standard schoeps style circuit, no roll off. Sounded quite nice in there actually. Not as bright as the k67 type, but still very nice. Does need a little high shelf to bring up the "air" if desired. I actually was hoping to swap capsules around and do some comparisons, but I ran out of time.

 

[Gus]

It is good to read that people have tried the low-pass filter change to the 012 circuit.

FWIW my favorite microphone is a solid state external powered microphone with a k67 capsule, it is a design of mine.  I am giving up building tube microphones.  Tube microphones can sound very good but you have the issues of tube selection and microphonics.

I have not been posting about circuit designs of mine.  I have a number of different adjustments to circuits/sims like the MXLV67/2001 etc some using the stock transformer.  A few hybrid solid state tube circuits/sims for currently made tubes.  A number of both phantom and external powered solid state condenser circuits/sims.  I need to find time to start building them.  I have another add on to the 012 circuit drawn up.

 

[Rybow]

It is good to read that people have tried the low-pass filter change to the 012 circuit.

FWIW my favorite microphone is a solid state external powered microphone with a k67 capsule, it is a design of mine.  I am giving up building tube microphones.  Tube microphones can sound very good but you have the issues of tube selection and microphonics.

I have not been posting about circuit designs of mine.  I have a number of different adjustments to circuits/sims like the MXLV67/2001 etc some using the stock transformer.  A few hybrid solid state tube circuits/sims for currently made tubes.  A number of both phantom and external powered solid state condenser circuits/sims.  I need to find time to start building them.  I have another add on to the 012 circuit drawn up.

Thanks again for sharing that mod Gus. It really opened up the possibilities of that circuit. Would love to see your add on for the 012 circuit as well!

I thought about using an external power supply with my KM 84 mic, but that was just to easily implement the figure 8 pattern. However, I just decided to keep it simple in the end. Still a possibility.

Would love to see some more of your ideas when you get the time. If you need testers, I am sure there are a bunch of people on this board who would love to prototype some stuff.