Banzai's KM84 DIY Body & PCB kit build thread

[Whoops]

... and what you absolutely don't do, like Whoops above, is declare the world is ending because a mic you just built doesn't sound right. That's not how DIY works and shows a poor understanding of what it takes to build a microphone.

Can you please let me know where did I declare the "world is ending"?
Because I never declared that or anything similar so you are just being disrespectful.

I have so many years of engineering experience and recording that I will never loose my sleep because of a poor microphone, I just use another one and move on.

What I declared was related to McIrish files where the Banzai KM84 is compared to a real KM84 and 2 other SDC mics, and listening to those files is really easy to notice that the Banzai KM84 sounds nowhere similar to the KM84 and actually the frequency response is far from what you would expect of an SDC mic.
Other members confirmed the same thing, so it's not an isolated case...

If the problem is related to the capsule, transformer or builders lack of knowledge I don't know.
RuddNL was able to try a KM84 capsule in this mic body and it solved the issue so it's something to investigate.

But if people are having difficulties in adjusting and tuning the circuit, and get a bad performance from the microphone, then it's your responsibility as a seller of these kits to provide info, guidance and documentation from the start that could prevent people from ending up with a microphone with a wrong frequency response.

So do your work, be more clear and help your clients out instead of coming here attacking other members.

 

[Banzai]

Can you please let me know where did I declare the "world is ending"?
Because I never declared that or anything similar so you are just being disrespectful.

I have so many years of engineering experience and recording that I will never loose my sleep because of a poor microphone, I just use another one and move on.

What I declared was related to McIrish files where the Banzai KM84 is compared to a real KM84 and 2 other SDC mics, and listening to those files is really easy to notice that the Banzai KM84 sounds nowhere similar to the KM84 and actually the frequency response is far from what you would expect of an SDC mic.
Other members confirmed the same thing, so it's not an isolated case...

If the problem is related to the capsule, transformer or builders lack of knowledge I don't know.
RuddNL was able to try a KM84 capsule in this mic body and it solved the issue so it's something to investigate.

But if people are having difficulties in adjusting and tuning the circuit, and get a bad performance from the microphone, then it's your responsibility as a seller of these kits to provide info, guidance and documentation from the start that could prevent people from ending up with a microphone with a wrong frequency response.

So do your work, be more clear and help your clients out instead of coming here attacking other members.

The Whoops show continues...

 

[Banzai]

We actually can't imagine! Something interesting I've noticed about the DIY community and the folks who put kits together: the consumers have no context for how many pieces are being sold. I've noticed it's rare on the whitepages to see a quantity cap ("I'm making 100 PCBs and then it's done").

Every batch has been several hundred kits.

BY NO MEANS is this a criticism: DIY means many things for many people. For example, some guitar pedals come with matched FETs and the bias resistor predetermined and sent to you ready for soldering. Plug & Play. This project is not that. Perhaps some folks who bought into this project were not clear on that fact?

I understand. From this batch, half were sold to microphone builders before the white market sale started. That's how each component of the kit was confirmed, including the tone and balance of the capsules. Nothing has changed from the last batches to this one.

What matters is that whatever issues anyone runs into, there are solutions for it. About 30% of these were sold with 3U transformers. We know at least another 30% were built with AMI's, which leaves the rest as Cinemag units. These will all sound different to each other and need something different. That's the nature of DIY.

 

[McIrish]

Although I really didn't like the sound, it's not what I expect from a SDC condenser, I can understand that it could be useful for some sources.

The problem is that these kits are advertised as "Banzai KM84" and are supposed to be Neumann KM84 clones, that's why people buy the Kits, and the reality is the sound is nowhere similar to the KM84, neither to most SDC mics, then it looses all the point.

I'm quite convinced at this point that there's something terrible wrong with this project, like I said before maybe the Capsule is not good, or the transformer, the body head or a combination of these 3...

I suspect the Capsule...

Yep. I'd agree. It doesn't sound like a KM84 at all. I'm still working on doing tests and experiments with different capacitor values. I don't want to give up quite yet. I'm also rethinking the provided FET in the second batch. The bias resistor has to be very high in value which does reduce the current to drive the transformer. At first I thought this didn't have any effect on sound but maybe it does. It was a fun experiment and maybe I will get it a little closer in sound to a KM84 at some point. I will post back after I do more tests.

 

[Banzai]

Unfortunately I agree with you.
I bought a pair from a previous batch, but they didn't sound anything like a real KM84.
So I sold them...

I made an improvised adapter to connect a K84 capsule head to the 'Banzai' body and hey! There was the KM84 sound again. So...

 

[Banzai]

Yep. I'd agree. It doesn't sound like a KM84 at all.

Agreed, Revision 1 of the McIrish KM84 DIY w/ 3U transformer doesn't sound very good. It's not representative of what this kit is capable of.

(also, there's no "Banzai KM84". I didn't start this build thread, and we've never called it that. Each one of these is your own build, you're doing all the work!)

I'm still working on doing tests and experiments with different capacitor values. I don't want to give up quite yet.

Why would you give up? You're only in the troubleshooting stage.

I'm also rethinking the provided FET in the second batch.

These Central FET's ending up in your mics was inevitable. If I didn't provide them, we would have listed them in your BOM's.

If there is a difference with the Fairchild's in these builds, your experience will be valuable to everyone else. Last time we built one of these was 3 years ago.

It was a fun experiment and maybe I will get it a little closer in sound to a KM84 at some point. I will post back after I do more tests.

It's supposed to be fun! Zone out all the bullshit(ters), and have fun with the project. If after you try a few things it still doesn't work out, you can send me your mic and I'll match a capsule to your electronics. Will give us a chance to see if there's a problem with either your capsule or transformer too (both are possible).

From other people's reports over the years and kits I've heard built with them, the best sounding transformer for this build is the AMI. It's expensive, but it has that extra you might be looking for. The Cinemag sounds good too and is more affordable. Only caveat is that Cinemag transformers always have linear bass and never roll off. Which is why I'm not really worried about Corgan's mics. His extra bass might just be the Cinemag sound.

 

[RuudNL]

I never said it is a bad microphone, but after I had a chance to compare it with a real KM84, I noticed that it sounded completely different.

 

[Banzai]

I never said it is a bad microphone, but after I had a chance to compare it with a real KM84, I noticed that it sounded completely different.

Was that before or after you and your 'collegue' compared a €40 transformerless Pronomic to a 'real' KM84?

 

[McIrish]

Oh boy, I'm really sorry for stirring this up. I appreciate everyone's input and opinions. After all, it's all personal taste. I posted the clips of my build so others could hear how it sounds in comparison to a few other SDC mics. It wasn't meant to say one is better than the other. It just shows how they are alike and how they are different. On another site, the kit was the one most people liked. But, that wasn't the point of the test. It was just to show differences.

I actually bought two of the kits and built them both. I don't remember which one I grabbed for the testing. I unfortunately didn't mark which was which. Maybe the other one sounds a little different? Who knows. I haven't had time to test. I think the low end can be adjusted with C4 and C3. The original schematics have much lower values for those. C3=1.5uF and C4=1uF instead of 4.7uF for both. That's bound to make a big difference. I do like tinkering and testing and comparing and I will continue to do so.

The Maiku capsule (at least on the one I tested) has a smooth top end and will be very useful in many situations. And... who knows, after I make some cap changes or a FET or transformer change, the low end may be more subdued and the rest of the mic will sound closer to the KM84 I used. But, I never thought it was going to be an exact match anyway.

BTW, no one here really knows who we all are or what our experience level is. There are beginners to advanced builders here. I have 35 years experience as a technician, designer and programmer. I have enough experience to put together a microphone. It's not my first and it won't be my last. I do enjoy the process. If i said something that offended anyone, I apologize. That was never my intent.

 

[Banzai]

No need to apologise and you didn't stir anything. Complete opposite, thank you for the soundfiles and letting everyone in on your process!

 

[stokesmusic]

Just finished my pair this morning. I bought them from another user on here who ran out of time, and they are from the first batch.

Everything went super smoothly, and the mics biased easily, one of them at 10k the other at 10.1k. Injected sine wave is symmetrical, as was a sine wave recorded through the capsule. I did a quick recording test of my voice and it sounds clear and nice. I built them to record classical cello, and I'll do a test of that when the mic clips arrive.

Thank you so much Graeme and Bonzai for these awesome kits, and the user who generously sold me the kits

MIC CLIPS!

I spent a few hours looking through clips that fit 22mm bodies. The original Neumann clips seem like they could stretch to fit the extra mm, but they are $54/ea... Crazy.

I just ordered some Sennheiser MZQ100 clips, because they were the least ugly to my eye. What have you guys gone with? Any better suggestions?

 

[stokesmusic]

In other news, I found a video demonstrating nickel plating in a very clear way, so I'm going to nickel plate the bodies myself. [Nickel Plating Guide]

I also ordered some Ferric chloride to etch some copper badges. I haven't finished the badge design yet, but I'm planning to use a purple enamel/nickel color scheme like the original. Here's the guide to acid etching I'm using, if anyone is interested [Acid Etching Guide]

Does anyone know the thickness of the original badges or a color code for the original badge color?

If I survive these experiments I'll post my results!

 

[mrgrooves666]

In other news, I found a video demonstrating nickel plating in a very clear way, so I'm going to nickel plate the bodies myself. [Nickel Plating Guide]

I also ordered some Ferric chloride and made a power supply from an old cell phone charger and gator clips to etch some copper badges. I haven't finished the badge design yet, but I'm planning to use a purple enamel/nickel color scheme like the original. Here's the guide to acid etching I'm using, if anyone is interested [Acid Etching Guide]

Does anyone know the thickness of the original badges or a color code for the original badge color?

If I survive these experiments I'll post my results!

Thanks for sharing the nickel plating guide, that it so cool I might try it myself with mine.

 

[mrgrooves666]

I'm curious, are these compatible with the Mic Parts SDC capsules. They supposedly tweaked them to be closer to the 84's. I wonder if someone has tried these, if they fit, and how would they fare against the Maiku..?
I'm aware this is not a KM84, but I do want to get as close to the sound as possible. I also found the excellent sound bits shared by McIrish, particularly the ones of interest in this thread, somewhat dark, and somewhat bumped in the mud region (250-300) considerably. I like Maiku's capsules quite a bit, but this came unexpected. I have not even had time to start these builds yet, have other 2 in the queue first lol, I don't want to jump ahead, but in my humble experience I've found that indeed the capsule makes 70% or so, if not more, the sound of a mic, so I'm not sure how much can be tweaked to adjust the response with cap or traffo changes...Anyway If this are compatible with the Banzai mic, I might be willing to get a pair and try them out, see if they fare better...?

 

[McIrish]

Just a little info on the mods I made. Changing C4 to a 1uF film did not make any real noticeable difference. I also (stupidly) bought NOS 2N819 FETS from Ebay. That was a waste of money. I can barely get any signal through them, no matter what the bias is set to. It seems pretty odd, unless their pinout is completely wrong, which would mean they are NOT NOS. Maybe these are why Banzai went with the non-Fairchild FETS. Anyway, I ended up putting the one made by Central that has to be biased with 18.5k R3 back in. It's now working again but no change to the tone. I may try a couple more things but I think I will soon just let it be what it is; a nice sounding smooth SDC with a bit more heft to the low mids.

 

[mrgrooves666]

Yikes don't tell me that, I also ordered some Fairchild 2N3819 from ebay, curious to try them, wich ones did you get?

 

[McIrish]

Ebay - 2N3819

Those are the ones I bought. I have to say, I only tried one. I was able to get the drain voltage to +10v, but it did not pass much signal at all no matter how I changed the bias. If I set my generator to 10k, it did pass some signal but not at the level it should. Something was definitely strange with that FET. I ended up putting the Central 2N3918 back in and rebiased for that. I didn't want to run the risk of lifting traces with all the mods I have been trying. The mic is back to normal now with the original FET. I cannot recommend those FETs in my link. Something isn't right about them.

 

[mrgrooves666]

Fk, same ones I got...

 

[Banzai]

Anyway If this are compatible with the Banzai mic, I might be willing to get a pair and try them out, see if they fare better...?

Instead of buying anything from micparts, get one each of the Cinemag 5722W and AMI T8 transformers.

Then build your mics, and try all 3 transformers (3U, Cinemag, AMI) to see what the differences are. As you have a pair you can do direct A/B testing.

Might change your mind on the importance of transformers and how much they affect sound.

 

[Banzai]

Ebay - 2N3819

Those are the ones I bought. I have to say, I only tried one. I was able to get the drain voltage to +10v, but it did not pass much signal at all no matter how I changed the bias. If I set my generator to 10k, it did pass some signal but not at the level it should. Something was definitely strange with that FET. I ended up putting the Central 2N3918 back in and rebiased for that. I didn't want to run the risk of lifting traces with all the mods I have been trying. The mic is back to normal now with the original FET. I cannot recommend those FETs in my link. Something isn't right about them.

Linear Systems LS846 = 2N3819 replacement.

https://www.digikey.com/en/products/detail/linear-integrated-systems-inc/LS846-TO-92-3L/14312177
Lots of other FET types are suitable replacements too.

Don't worry about lifting traces either. These are high quality boards (eurocircuits.com). If you're worried about too much heat, you can drill the holes out instead. Use 0.8mm or equivalent drill bits.

-----

One thing about coupling capacitors (C4) – they set the bass resonance point. When you go down in capacitance, you increase the frequency of the resonance point, making the bass sound more present. Mic with 0.5uf will have a more audible and "bigger" lowend than 1uf etc

C3 has the opposite effect. Higher capacitance = more bass.