micparts T-47: A fantastic DIY microphone

I'm posting this because a few people asked. First of all, if you are an objectivist, go away. This project employs a microphone capsule that doesn't have a flat response. It's also a transformer coupled (NOT transformerless) design with a single active component, a JFET, where I intentionally chose a resistor to bias the JFET for higher second and even order distortion.

I had been looking for a large diaphragm transformer coupled microphone, particularly a vintagey sounding one, for some time now. The problem is that they don't make 'em anymore. Well, they actually do. But the problem is that we would have to cough up around $4000 for Neumann U47 FET. That's bullshit. I know Neumann is a respected name in microphones; but I f'ing hate them. Over the decades, they've cheapened their microphones while keeping their prices astronomical. It's for the mystique, the brand name. @Psalmanazar and I talk about studio gear every now and then and we joked about recording studios may have a Neumann on hand just for the cachet, but in reality probably use other microphones.

For this project, I pretty much used the parts from the micparts T-47 kit (https://microphone-parts.com/collections/microphone-kits/products/t47-microphone-kit) with the exception of the capsule which came from @Soliloqueen. I can't down turn playing with creations from fellow members, encouraging them to make good shit. This capsule is intended to be similar to the K47 capsule of the U47 which has a bump in the presence region (it's intentional) and is still under development.


Note Sonicap boutique part and good WIMAs that would make Dannie Ritchie proud.

Anyway, I feel like I've scored a fantastic deal with a little bit of elbow grease. I know that my current gear (MOTU Ultralite mk4) is not anywhere good enough to capture the resolution, texture, and nuance that this microphone is capable. It's the nature of the design: a single transistor (JFET) followed by a transformer. The downsides are higher distortion, especially at higher SPL, which limits max SPL. This is a different approach from more modern designs with tons of transistors and super low distortion. Many modern microphones even employ opamps - yuck - which is even another step backwards in terms of capturing the immediacy and nuance of recording.

The first question I often got was this: was this easy to build?

My answer is that is was brain-dead easy. It's million times easier to build this than to repair most Modius DACs. I do have a decent amount of experience with soldering irons and had only gotten better because of necessity. However, I still think it's an easy first time project. I will cover some bases first.

 

I will not purport to be a master of soldering. I will also not tell you that DIY is always cheaper. DIY requires considerable upfront costs with good tools. Even a first timer will benefit from good tools. Micparts makes this build super easy though. All the wires and leads are pre-tinned with solder (from what I can remember). They provide an excellent instruction manual with step by step procedures (of which I didn't bother to read most).

Before we begin, I suggest the following if one doesn't have any gear or much experience:

1. A Metcal PS-900 Production Soldering station. I basically threw my Weller with temperature adjustment into the trash after using this. The soldering iron is ready 10 seconds after turning it on. You do not fuss with any temperature adjustment. It's set depending upon the tip. It's got some kind of high-tech deal where power delivery is adjusted via RF sensing. The specs say that the output frequency is 450kHz. Bottom line is that this iron feels significantly less hot than any ones I've used before with better capability to get the solder flowing. I have not destroyed anything because of excess heat using this iron. The downside, it's $250+. Good tools aren't cheap. I refuse to use any other kind of soldering iron. The Metcal spoils you.
2. Superwick fine braid soldering wick. You will screw up or have a brain fart. When you do, add an extra blob of solder and then use this wick to wipe up the spot. Actually, remove the part first. Blob the pin near the hole to melt the solder to pull the part out. Then wick it up. A solder sucker can help too, but get a big one. The small suckers don't work. I don't think this project needs a solder sucker. It's pretty much small holes on the PCB.
3. 60-40 tin lead solder. Don't be a retarded audiophile and use silver formulations. Just don't. Although the Metcal will save your ass if you f**k up.
4. Magnifying glass with light on a clamp. Unless you have 16 year old eyes with better than normal vision. I'm over 50 now. My eyes suck. Even if you have good vision, it doesn't hurt to have one of these because it lessens eyestrain.
5. Carburetor cleaner with Q-tips to clean the board. You are supposed to use alcohol. This works x50 better, but is arguably worse for the environment.
6. Practice on a CMOY board: https://jdslabs.com/product/cmoybb-diy-kit-rechargeable/

Here is the main PCB for the T-47 kit (the manual is in the background).


Note that the manual has decent-sized print with big photos. It's not like a Topping DAC instruction manual which requires a microscope to use.

The process of stuffing the board was dead easy. I only have one suggestion. The instructions say to lift one leg of the JFET up from the board (it needs to be far away from the surface of the board). If I had to do it again, I would lift the leg up a few mm higher. The reason is is where four or five other connections terminate, including one from the capsule. Having this up a bit higher makes it easier to reach with the soldering iron.



Here is the same point, but from a different angle. Sorry, it a bit out of focus.


Note the switch on the bottom. This board will support cardioid and omni directional patterns. Keep in mind which is the front of the mic when you slide the board into the body! Changing the pattern requires opening up the microphone body. It takes less than minute to do this - it's just a matter of unscrewing the end cap that keeps everything in place.

 

This is the other PCB that houses the transformer. It's a house brand. There are at least two Cinemag transformers that will work - they have different distortion profiles.


Note that I did elect to bias the JFET for added second harmonic. Micparts provides two resistors. It's not a ton, just a bit more. I can elect to reduce this effect by turning on the pad switch which lowers the output. This is because the harmonic distortion isn't constant, it's only goes higher at higher levels. Now combined with different transformers (which have the same type of behavior, i.e. THD goes up with a hotter signal), this could be a tweaker's delight. As I like to say, roll transformers (or bias) rather than tubes. Yes, there's an art to using microphones. (OMG, how are audio "science" people going to deal with this? Audio is like cooking or painting? The horror!).

 

Here it is at my workstation. I use it for my cybersecurity consulting work in M&E. (Yeah, I got dragged back into it). Anyway, I found this project super rewarding considering how easy and fast it was to put together. There is an immense level of satisfaction and joy knowing that you are using something that you assembled from parts. (Again, I recommend that newbies put together a CMOY first).

 

Those are all transformerless designs and not exactly what I was looking for. I also wanted to highlight what some members are trying to do. Thanks for ruining the vibe.

 

Yes, this is what large diaphragms are for, along with a lot of other stuff like vocals, guitar, bass drum, upright bass, cello. These kinds NOT good for high-hats, cymbals, triangles, etc - where a small condenser is better. You get the idea. The large condensers have a richer sound than the smaller ones. The smaller ones are "faster" and can keep up with higher frequencies.

if you had to go with one mic on violin, without complex arrangements of multiple mics and mixed in (funny how the modern world can make stuff more complex), just use a large condenser. Put it on a stand and have the microphone up high to face the body. It's crucial that you hit the front of the body of the violin because that's where the lows come from. Two to three feet away is a good start. Closer will pick up details like the rubbing of the bow on the strings, fingers moving on the fingerboard. It depends what you want to do and what you want to pick up.

With this capsule, you may want to EQ down the highs a few db. I am thinking 5.5kHz with a Q=1 as a starting point. Play with omni and cardioid patterns and distance. You should be able to get big sound with a good sense of the room. Unlike voice, you will not need to treat the room or have panels. Note that this approach is very different from a violin pick-up mic.

You can get some spectacular recordings if you or anyone else plays in the house.

 

More photos. Capsule and what comes in the box for the circuit board. As we can see, there's really not much work to do.

 

Any decent microphone will be too much for the MOTU. Sure an AT 2000 or 4000 series into the MOTU will be better than a Blue Yeti USB; however once we get something better, the MOTU really shows it's limits. I've been looking for a Neve or Neve clone mic-preamp. @philipmorgan suggested the Daking Mic Pre One. Maybe this directly into the MOTU's line level in would yield better results. I don't know how good the MOTU is as a pure A to D. I'd be willing to bet Schiit's discontinued Jil line level A to D is much better.