Banzai's KM84 DIY Body & PCB kit build thread

[Colorblind]

I just received some M2x5 stainless steel set screws from McMaster Carr: the one I tried seems to be the proper thread, but sticks out around 2mm when fully screwed in and I don't like that.  Originally M2x3 were recommended and I believe I will like that a lot better.  McMaster Carr has these:
p/n 90251A151 Thread-Locking Cup-Point Set Screws, 18-8 Stainless Steel, M2 x 0.4 mm Thread, 3 mm Long, packs of 10--and I think they are going to be really great.  They have an imbedded nylon thread lock.  They also take a TINY Allen wrench.  The one I have that fits measures 0.87 mm, flat-to-flat, on my calipers.  It's like 1/3 the diameter of a pencil lead and you have to go to a fairly serious hardware store to get them.  If the new screws present any problem I will post about it.

Yep, I just went through the same thing -  bought M2x5screws and found out they were too long, so I got some M2x3 ones.  I got those along with the super small hex wrench for cheap on eBay.  The holes don’t match up perfectly on one of my mics,  so I had to take off the body tube, insert all the screws, put the tube back on, and then back out the screws  until they hit the inside of the body tube. Still seems to hold just fine though.

 

[Banzai]

You're absolutely right. For whatever reason remembered using M2 x 5, but they're definitely M2 x 3mm. Should measure twice, post once..... Sorry guys :-X

I put them in from the outside after body sleeve is already on. Fully remove them to open. The original's screw-in-to-open feature isn't worth the pain of having to drill them out.

If ever, you can also cut your 5mm screws to right length with a decent cutter. Then screw in and out of an M2 nut a few times to repair the threads.

 

[maarvold]

You're absolutely right. For whatever reason remembered using M2 x 5, but they're definitely M2 x 3mm.

The ones I ordered with the nylon thread locking inserts are nice, but fit the threads a bit too tightly.  If I did it again, I'd get regular M2 x 3.  FWIW. 

 

[Banzai]

The ones I ordered with the nylon thread locking inserts are nice, but fit the threads a bit too tightly.  If I did it again, I'd get regular M2 x 3.  FWIW.

Also slotted are a safer long term bet. Heads on tiny hex screws can round out, creating the same problem.

 

[choolder]

hi guys, I have a huge gain difference between my 2 mics (almost 20 db) and I'm bypassing the capsule. Any tips where to start? I can bias them differently so they match but it's a huge different bias and they clip very differently.

 

[volker]

Maybe a reversed transformer on one of them.

 

[choolder]

My technician also measured with the transformer and he gets the same result measured from the fet.

Any other ideas?

Thanks!

 

[TillM]

Did you bias with osci or with DMM?

By the way.
I finished my mic body’s with hammerite.
It’s not perfect for the first try, but I really like how it looks like.

 

[mickdundee63]

Just finished two. Build was relatively straightforward it is indeed tight in there but with all the advice in this thread no major issues. Great project! Been waiting for an SDC project for ages. They already sound great. Honest, balanced and articulate. No scope here so going to bias by ear. Would this be a correct approach?

1. Feed a sine wave out of my DAW into interface.
2. Take line out from interface, connect positive to capsule spring pin (via 1000pf capacitor), negative and shield to the pin one xlr pad on the circuit board.
3. Connect mic via xlr to interface input and monitor via headphones
4. Apply phantom power
5. Increase DAW level and adjust bias trimpot alternatively to maximise volume and minimise distortion.

 

[mickdundee63]

Hmmmmm I can pass the audio out and return it to hear the sine wave, but I've got a massive hum that makes it impossible to analyse. I don't think it's a ground loop because if i bypass the mic and just loop the sine wave from my line out back to my mic pre there's no hum. I mean, don't all microphones generate hum with the body casing removed??

 

[mickdundee63]

OK so I moved my interface to a new ac location that was less busy. Solved my initial problem and successfully biased the first mic. Second mic stopped halfway through the biasing, now I'm reading continuity between all pins on the xlr. Presuming i gave too hot a signal and have blown the fet? Pull it out and test it?

 

[TillM]

Yes, this seams like the FET is broken.
When my working mic lost audio, when biasing, It was everytime the FET.

 

[mickdundee63]

Ya ordered a new FET so will try that out. But the existing one doesn't have continuity between it - so not sure how a short is being created and even if it is, how that short would create continuity at the other end on the XLR pins. But I'm a bit n00bish on this so will have to keep studying...

 

[mickdundee63]

So figured this out, bit of a weird one but in case it helps someone else: I pulled components and narrowed the short to the xlr3 pad and r10. While poking around I noticed that i could connect to ground by probing the ridge around the circuit board. I had a lot of solder on the pad so I reflowed it and moved it down away from the edge of the board and the mic began functioning again. This seems like a weird thing to happen, particularly as the mic was initially working then cut out during biasing. Anyway worked for me.

 

[jrasia]

Can someone help be diagnose one of my amps.  1 mic is working great, but the other has VERY low output and very thin.  Seems like a ground issue or something.  Not sure where to start.  On working body I measure about 1k ohm between transformer G and R+ solder points on the board, but on bad mic, I measure open.  All solder work looks fine, having a hard time tracking down what it might be.

 

[Ricardus]

What's the status and availability of this project?

 

[Strat96]

What's the status and availability of this project?

Banzai told me after all these matters settle down with the quarantines he will be putting together another round of orders.

 

[12afael]

interesting. I got different capsules from the first and second batch.  at least the grill is different.  and to me they sound different.  I still need to swap them and see if it is not a pcb difference(bias?) one just sound full and with clear high and the other have a bit more harsh high end.

 

[kante1603]

Similar capsule sound issues here,but from within one batch.Definetely capsule-related,travels with swapping between several amps.I have three,two of them sound quite close to each other and do have that KM84ish vibe,while the third sounds totally different,too harsh and kind of cheap.
Best,


Udo.

 

[choolder]

Hi there, will there be new kits for sale in the future?
I have 2 mics and really like them, I would love to have 2 more

Kind regards,

Peter