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Project Specific Discussions => Microphones => Topic started by: iturnknobs on October 25, 2018, 05:53:44 PM

Title: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on October 25, 2018, 05:53:44 PM
So, I am starting an official build thread for this project. Much of the information that I was counting on using disappeared with the White Market thread. It would be great if members could repost any valuable information for this build that may have disappeared. Anyone know how the PCB attaches to the body, or does it float free internally?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mhbunch on October 26, 2018, 01:52:53 AM
From memory the Pcb solders on to xlr connector which is held in place via set screws on body
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: fsalter on October 26, 2018, 12:16:02 PM
One piece of information which is very useful...and i had missed it, leading to problems, is that you have to be sure to solder the trimpot LAST!, or you’ll have problems soldering jfet and 1 gig resistor.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on October 27, 2018, 11:13:36 PM
Anyone happen to have the schematic? Trying to make sense of the original circuit vs. the new pcb.  Any image files available would be helpful. I'll  drop a mouser BOM file if someone has the schematic. Just want to cross reference first.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on October 28, 2018, 12:42:23 AM
..for easy reference
KM83-85 schematic
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on October 28, 2018, 06:08:19 AM
BOM:  https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f5036488e2

Schematic: https://www.docdroid.net/nVr2ndC/diy-km84-schematic.pdf

Original Schematic: see attachment

If you take the original schematic, and place the board on top of it (top of board facing left), you can see it's also a literal copy. Board layout follows the original schematic layout.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: ln76d on October 28, 2018, 06:45:37 AM
BOM:  https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f5036488e2
Schematic: https://www.docdroid.net/nVr2ndC/diy-km84-schematic.pdf
Original Schematic: see attachment

If you take the original schematic, and place the board on top of it (top of board facing left), you can see it's also a literal copy. Board layout follows the original schematic layout.


And that's the way i like in boards design!

For unfamiliar with the circuit (which is truly simple and awesome) with value of C2, feedback capacitor, you can adjust sensitivity for the needs. If microphone will work with higher SPL then higher capacitance, if you need more sensitivity then lower. 1-12pF range is enough for most tasks. Don't reccomend removing this capacitor.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on October 28, 2018, 09:41:24 PM
When looking at the Cinemag CM-5722 is it correct to connect the wht/brn to the wht/red and also the wht to the wht/blk leads before assembling the rest of the mic?

http://cinemag.biz/mic_output/PDF/CM-5722-Data-Sheet.pdf
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on October 29, 2018, 12:57:13 AM
When looking at the Cinemag CM-5722 is it correct to connect the wht/brn to the wht/red and also the wht to the wht/blk leads before assembling the rest of the mic?

http://cinemag.biz/mic_output/PDF/CM-5722-Data-Sheet.pdf

I did mine after it was placed on the PCB. It seemed to be easier to manage the cables and fit it in the PCB.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on October 29, 2018, 07:46:26 AM
I did mine after it was placed on the PCB. It seemed to be easier to manage the cables and fit it in the PCB.

Thanks!

Paul

So that's a yes on connecting the leads together? Does the CM5722 just float in the cut-out, or is there a method to secure it?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on October 29, 2018, 11:59:58 AM
So that's a yes on connecting the leads together? Does the CM5722 just float in the cut-out, or is there a method to secure it?

For the leads you follow the drawing you posted from Cinemag's website. The transformer will just fit in there and might require some very minor trimming/filing to get it to fit. It does just float in there but won't move when the PCB is inserted into the body. You can also do what I did and apply a small amount of hot glue for added security.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on October 30, 2018, 02:09:06 PM
I seem to remember from the previous thread, members having to physically trim something in the capsule assembly before fully assembling mic. I do not seem to have any clearance issues anywhere when doing a trial assembly. I am guessing I need to solder a small jumper wire from the brass hex like appendage on the capsule to the solder terminal post on the pcb. Not exactly sure. Just trying to not take one step forward just to take two back.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on October 30, 2018, 06:39:24 PM
I seem to remember from the previous thread, members having to physically trim something in the capsule assembly before fully assembling mic. I do not seem to have any clearance issues anywhere when doing a trial assembly. I am guessing I need to solder a small jumper wire from the brass hex like appendage on the capsule to the solder terminal post on the pcb. Not exactly sure. Just trying to not take one step forward just to take two back.

The hex standoff makes direct contact with the plastic spring connector. No need for anything extra.

The tabs of the plastic spring connector need to be widened for the board to fit inside them. They're 1.4mm slots – our boards are 1.6mm.

Lastly, once the body is fully assembled, you need to trim the pin of the spring connector flush with the top of the body tube. Screw on capsule, and done.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: wowi on November 02, 2018, 12:03:36 PM
In the original whitemarket thread were some usefull hints and some pictures of the build. Maybe these guys can post this again ?

Thanks
Wolfgang
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on November 02, 2018, 12:35:50 PM
I will post some tonight. I made some assembly errors. Let's hear it for the Hakko FR300.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on November 03, 2018, 07:48:10 PM
 This is how far I pushed the pcb into the XLR bottom bell to avoid having the terminals touch the 2.2k resistor.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on November 03, 2018, 07:52:22 PM
I used cut resistor leads to put through the terminal posts so that I could lay down C1 on the backside of the pcb. You should try to bend them back towards the XLR so that they(and C1) have a lower profile to help fitting the plastic spring connector.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on November 03, 2018, 07:55:28 PM
This is what I am doing so that I can replace R3 with a fixed resistor after biasing. I can get a soldering iron in there, but not my Hakko FR300.

Hope this helped some.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jrmintz on November 06, 2018, 04:17:36 PM
I used mine yesterday as part of a stereo pair with one of my real KM84s and any difference was undetectable. Sounded great.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on November 15, 2018, 01:16:15 PM
I'm having issues biasing. I am referencing Matador's post @ https://groupdiy.com/index.php?topic=46109.40 for the correct procedure. I am injecting 1kHz @ 200mV at these points in the circuit.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on November 15, 2018, 01:23:19 PM
...and here is where I am attempting to check signal at fet drain which also is the junction of C2, C4 and R4. I do not seem to be reading anything with my scope. I have double checked scope operation by referencing the injected signal. I have tried this with phantom power applied and not. 48v does not seem necessary for this calibration. I have built 2 of these mics and each is the same. I thinik I am either making a silly mistake or my FETs are no good. Seems odd that 2 would be bad, but I did buy "real" 2N3819s off eBay from someone in the UK. Any ideas?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on November 15, 2018, 01:26:28 PM
Ruud give an advice at the white market, you can’t bias it like a U87, I remember that he told, that’s capacitor is needed for.
Maybe he can tell us something about the biasing again.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: wowi on November 18, 2018, 03:59:07 AM
I am not shure, but i think you have to feed the signal into the coupling cap c1.
So you can go to the capsule terminal.

To the CM-5722: Can i cut the Whi/Brn  Whi/Red and the Whi/Blk Whi cable or do i have to connect them ?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on November 18, 2018, 04:23:43 AM
Connect them
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mrcase on December 05, 2018, 05:34:54 AM
will there be another batch of these. I remembered there was talk about that. ;)
I would love 2 of these!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on December 06, 2018, 05:41:05 PM
will there be another batch of these. I remembered there was talk about that. ;)
I would love 2 of these!

Next week  ;)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jrmintz on December 07, 2018, 07:58:38 PM
Yay!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on December 09, 2018, 09:32:12 PM
I'm wanting two!!!  Can't wait to order. 
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: RuudNL on December 17, 2018, 03:11:35 PM
Next week  ;)

One week later now...
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on December 25, 2018, 04:20:14 AM
White Market thread is open!

https://groupdiy.com/index.php?topic=68360.0

(https://i.postimg.cc/hGf1DX0n/GDIY-KM84.jpg)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on December 28, 2018, 05:12:23 AM
Hello, everyone,

Just in case the White Market thread disappears with information like calibration, I thought I would post it here for safe keeping. Many thanks to RuuDNL for originally providing this procedure:

"Connect a signal generator through a capacitor (~1000 pF) to the gate of the FET. 1Khz or so is fine.
Replace the source resistor temporarily with a 10 K.ohm trimpot.
Increase the level of the signal generator until you get distortion (oscilloscope or distortion analyzer).
Adjust the trimpot for lowest distortion and symmetrical clipping.
Measure the value of the trimpot and replace the trimpot with a fixed resistor with the value you measured.
That's it
!"

And a further explanation:

"Just connect the capacitor to the 'pin' that connects to the capsule.
The audio generator signal feeds to the (not connected) side of this capacitor.  (And the ground wire of course.)
The capacitor is to separate the polarisation voltage. You don't want +46 V or so on you signal generator!
If you don't have an oscilloscope or a distortion analyzer, you can also do this by ear.
Turn the trimpot slowly until minimal distortion (on a sinewave) is heard.
Then increase the level of the signal level, and adjust the trimpot again.
Of course you need to connect the XLR to an amplifier!
"

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on December 28, 2018, 09:53:45 AM
THANKS for posting that procedure!!!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: adam.schw on January 11, 2019, 10:56:19 AM
Hey guys, I’m wanting to pull the trigger on a couple of these, but I don’t own or have access to an oscilloscope, so I’m a bit concerned at how I would calibrate. Anyone have a guide on a work-around?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on January 11, 2019, 11:50:10 AM
Hey guys, I’m wanting to pull the trigger on a couple of these, but I don’t own or have access to an oscilloscope, so I’m a bit concerned at how I would calibrate. Anyone have a guide on a work-around?

Read the above post again. All the way through this time....


Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: GraemeWoller on February 03, 2019, 03:37:46 PM
Hi Peeps,

It's been a while coming, work, kids, life, fishing, etc... but here's a .pdf build guide to help everyone out with getting their mics together. It's talking to the newest DIYer but hopefully it'll be a handy way for anyone to get stuck into the fun without too many headaches!

http://bit.ly/2ML5aOv

Rock On!

Graeme
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on February 09, 2019, 09:23:01 AM
Hi Peeps,

It's been a while coming, work, kids, life, fishing, etc... but here's a .pdf build guide to help everyone out with getting their mics together. It's talking to the newest DIYer but hopefully it'll be a handy way for anyone to get stuck into the fun without too many headaches!

http://bit.ly/2ML5aOv

Rock On!

Graeme

Thanks for the build guide. I think that the one thing I didn't see is that the opening for the transformer is a bit small. I had to file the opening bigger to get mine to fit. This should be done first, before populating the pcb with components so leads aren't potentially broken. This might make life a bit easier. Check to see that it fits first, before populating.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on February 16, 2019, 10:11:13 AM
Just a comment about one of my mistakes hopefully to help others:

My signal generator defaults to 10kHz and 10Vpp when starting and this appears to burn out the 2n3819 in circuit when attempting biasing. That issue combined with a couple faulty transformers have caused me some significant troubleshooting time, but golly gee... I'm getting better at this DIY thing.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on February 16, 2019, 10:50:22 AM
https://groupdiy.com/index.php?topic=68862.0

Here's a link to some HAUFE BV-107 information.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Jim50hertz on February 23, 2019, 04:48:06 AM
Anyone who has used the AMI T8 transformers have any clues as to which wire is which here?

(http://i288.photobucket.com/albums/ll162/jim50hertz/6EA3B34A-2A78-44D0-ADD1-5746E02889A5_zpsd3ebflsd.jpg) (http://s288.photobucket.com/user/jim50hertz/media/6EA3B34A-2A78-44D0-ADD1-5746E02889A5_zpsd3ebflsd.jpg.html)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Gus on February 23, 2019, 08:26:48 AM
Anyone who has used the AMI T8 transformers have any clues as to which wire is which here?



Is that how they are supplied?

If you have a DMM set it ohms and measure blue to blue and grey to grey first to check it. Blues should be higher resistance

Next test for the polarity will need signal generator and a scope you will need to look at the output and compare it to the input to check the polarity, or you could install it in the microphone and check the polarity against another known good microphone
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on February 23, 2019, 09:45:01 AM
I also built a mic with the AMI.  Mine was less symmetrical than the one in the picture... on mine, there is a blue+grey pair that is anchored near the middle of the transformer and a pair that is more near the edge.  I think I measured with an ohmmeter to determine which is primary and which is secondary; I used the center blue+gray pair as the high: I used a Sharpie felt tip marker to put a stripe on those two.  That mic came out Pin 2 = high: correct in my world. 

FWIW, I took my mic to one of the designers /developers of Audio Precision test gear to help me with biasing and he scratched his head for several minutes about the 'mystery' wire coding--it really bugged him. 
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jrmintz on February 23, 2019, 10:19:34 AM
(http://www.sethglassman.com/AMI%20T8.jpg)

Be sure to leave enough extra grey wire to reverse the leads if the mic's polarity is reversed.

I finished my mic by cleaning the brass well and spraying it with a couple of coats of lacquer.  I think that's the easiest way.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on February 23, 2019, 01:22:00 PM
I would double check the wiring with the guys at AMI/Tab. I've built other mics using their T13/T14 transformers and one color set of wires is primary and the other is secondary. The one issue that I with a T13 is that the label for secondary and primary were printed opposite of what they actually were, but they were the same color for each side of the transformer. I don't know the DCR reading for the T8 but for the T14 is about 900R for the primary and about 20R for the secondary. The trick to determining polarity (at least what I've found) is you pick a side where the pairs of leads come out of the transformer. So in the case of the T8, I would use the left blue/gray pair as the (+) polarity for primary/secondary, so blue(capacitor) and gray (Pin 2) and the pair on the right as the (-) pair (Ground and Pin 3). The label on the box could be in error as I have had, but the color leads were still grouped together just backwards.

I have a pair of T8's waiting to be put in my kits when they arrive. I'll take some measurements later and get back to you.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jrmintz on February 23, 2019, 01:42:33 PM
Yes, the blue wires are the primary and the grey wires are the secondary. The left pair of blue and grey come out of what looks to me like the top of the coil and the other pair the bottom. Which pair is top and which is bottom really doesn't matter as long as the primary and secondary aren't mixed up. If you connect the secondary wires incorrectly and the polarity is wrong you can always reverse the leads as long as you don't cut too much off. I would suggest checking the polarity against other mics under any circumstances. Having one mic wired with reverse polarity and not knowing it could be a very unwelcome surprise.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on February 23, 2019, 01:51:06 PM
Correct. I got a bit confused to your post as you mentioned using a blue/gray pair as the primary and I think you meant to say positive. I think. And a reverse polarity mic wiring is indeed and unpleasant surprise.

At any rate, for those who want to verify your leads (in case you do get one that is backwards), I took measurements off of my T8 and for the primaries (blue) I get 220 ohms DCR and the secondaries (gray) I get 20 ohms.

I am curious how these will stack up against the Cinemag versions I've already built.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on February 23, 2019, 02:11:43 PM
Yeah sorry guys--I m uh idiot--I edited my post above like 5 times.  I have transformers/transformer diagrams on the brain and I just now edited my post for a sixth time because it was wrong. 

BOTTOM LINE: the STRONG impression I got from the tech I worked with on biasing--a man who is looked up to by my usual guy who was the chief engineer at Jensen Transformer when Deane Jensen was alive--is that for there not to be proper full documentation of what is happening with each transformer wire--is just not professional and a recipe for trouble. 

As to the sound quality of these mics, the passage of time will tell the full story but, so far I am pleased when compared to the 2 hand picked Neumann KM84's I already own. 
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: duantro on February 24, 2019, 11:48:26 AM
I got my round 2 parts yesterday.  I didnt see the insulated turrets in the BOM, and didn’t get any with body parts. Can anyone tell me what size these are, so I can order the correct ones the first time around? I’ll probably look at mouser since I’m in the states. Thanks.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on February 24, 2019, 01:11:27 PM
4th item on the list:

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f5036488e2
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: duantro on February 24, 2019, 01:31:16 PM
4th item on the list:

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f5036488e2
Thanks, I found them, they we’re stuck hiding  in  the mouser bubble wrap!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on February 25, 2019, 05:15:11 AM
To make the BOM list easier to navigate you can sort by 'Customer No'.

Puts everything in order.

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on February 25, 2019, 05:30:18 PM
I'm a bit confused about the bias processing.
Ruud described it in two ways.
On the other hand its described to feed the signal through the gate (middle leg) with a capacitor.
At my opinion, I must connect my oscilloscope to the drain leg to bias the FET.
The other explanation is, to connect the capacitor to the capsule, which would be the  source leg and feed the signal in it.

I'm confused and was not able to bias the mic.
The explanation from Ruud is flawless, but I think I've a thinking error.
Hope somebody can help me.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on February 26, 2019, 02:14:00 AM
... is that for there not to be proper full documentation of what is happening with each transformer wire--is just not professional and a recipe for trouble.
It is completely pointless. Doesn't add any cost to use different colours, and save everyone the hassle. Same issue on all their wired transformers.

I'll talk to Moby and see if he can do a run of BV107's for us :)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: rockinrob86 on February 26, 2019, 09:12:01 AM
The cinemag one sounds nice!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: craigmorris74 on February 26, 2019, 10:35:35 AM
Got my mic up and running.  Sounds lovely!

Graeme, thanks for the build guide.    The only things that I would add to it would be to make sure to orient the tantalum capacitors correctly, and when you attach the cone to the front, mic sure the wire is oriented the way you want it to be (toward the correct turret and above all the other connections).

Craig
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on February 26, 2019, 10:42:09 AM
I'm a bit confused about the bias processing.
Ruud described it in two ways.
On the other hand its described to feed the signal through the gate (middle leg) with a capacitor.
At my opinion, I must connect my oscilloscope to the drain leg to bias the FET.
The other explanation is, to connect the capacitor to the capsule, which would be the  source leg and feed the signal in it.

I'm confused and was not able to bias the mic.
The explanation from Ruud is flawless, but I think I've a thinking error.
Hope somebody can help me.

I clipped my signal generator to the mic. Positive to the spring loaded contact touching capsule(without capsule). Negative to ground/chassis/pin 1 of the mic. I connected an XLR "y"(f/m/m) to the mic. I connected one side of the "y" to a pre-amp providing +48V. I then connected my oscilloscope(positive to pin 2 and ground/chassis to pin 1) to the other side of the "y". I understand that there is DC voltage at this point, but it did not SEEM to affect my biasing process. I can say that I fried two 2N3819s by sending way too much voltage at them. Shouldn't need more than 1V @ 1Khz, maximum, to determine bias at max input. Not sure when they "give way" but 10V  is definitely enough. Was for me, twice. Check for continuity/resistance at your primary and secondary of your output trafo before starting. I received some faulty ones(2 at once) from a particular company during this endeavor. That combined with my fried transistors made for some real GDIY troubleshooting.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on February 26, 2019, 11:00:40 AM
Here's a link to some stuff about biasing that might be helpful:

https://www.dropbox.com/s/rx6q7vprdjfy9hi/DIY%20KM84_Biasing%20Procedure.zip?dl=0
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on February 26, 2019, 02:12:36 PM
Can the 10k, 10M, and 2k2 be 1/4W instead of 1/2W? I don't want to start a sea of  questions asking can this part be substituted for this one, but I feel that the several I built when the first round happened I used 1/4W for those values and I was fine. I'm mostly just trying to use parts that I have in hopes of lessening the inventory of components that I already have.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: stelin on February 26, 2019, 04:20:19 PM
I need some help with my two DIY KM84 mics:

This is my first build of FET-mics, so I might have missed something.

I have two problems:
Both microphones have a self-resonance (see the spikes in the picture).

One mic has a normal output level (compared to my KM184), the other mic has about 6 dB lower output. They both sound OK (sounds very flat, all the way down. More so than my KM184. The high-end is not as “essy” as the KM184, also as expected).

I have not adjusted the bias yet. I started with R3 at 10k and the self-resonance was very bad. Dropped it to 3.9K, and the self-resonance was better but still there. Same thing for both mics.

And yes, the PCBs are very clean.

Does the self-resonance have to do with the bias adjustment or is it something else?
I’m using the 3U GZT-84 transformers that came with the kit, but I don’t that has anything to do with my problem.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on February 26, 2019, 05:06:08 PM
I finally got around to biasing my four kits from the first round with Cinemag transformers and was having a bit of trouble getting a reading with the 1000pF cap inline with the signal generator and the brass contact for the capsule. I thought it was my preamp or my generator, but I tested those straight to the scope and they were fine. I wound up ditching the cap and when straight from the generator to the mic and I was able to get a stable sine wave on the display.

I tested these with my voice and they sound really big and smooth. And stunningly quiet. I just need to order some parts for the other two kits with T8's to see how they compare. Also, they need a couple of seconds to charge the capsule. I had one make intermittent clicking sounds for several seconds when I first applied phantom power, but then it stopped and I have not been able to reproduce that noise sense.

I've attached a photo of what I was getting with the cap inline. It was a film capacitor and I don't know if I was supposed to use a ceramic one. The generator is an NTI Minirator Pro and didn't seem to be affected by the polarization voltage.

Also, for these kits I used 1/4 resistors all the way through as that is what I believe was on the original BOM and I haven't noticed any problems so far.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: stelin on February 26, 2019, 05:20:26 PM
Potato Cakes; what value of R3 did you end up with after biasing?

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on February 26, 2019, 05:44:56 PM
I have no idea. I had permanently installed the trimmers so after I saw symmetrical clipping I reassembled the body and capsule and called it good. It's too much hassle for me to do the temporary trimmer install then try to find the closest resistor to what makes the circuit biased. It's mostly because I'm lazy, but for this particular build I didn't want to solder anything more than once.

If you're getting 6dB down you may not be getting a good connection to either pin 2 or 3 inside the mic at between the transformer output and the XLR. Or it could be because it is not biased.

For self resonance, I would send some pink noise at the transformer input and see if it's coming from that. I'm not familiar with the 3U GZT-84, but I don't know where else it could be coming from unless there was something off with the capsule.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on February 27, 2019, 08:10:31 AM
I clipped my signal generator to the mic. Positive to the spring loaded contact touching capsule(without capsule). Negative to ground/chassis/pin 1 of the mic. I connected an XLR "y"(f/m/m) to the mic. I connected one side of the "y" to a pre-amp providing +48V. I then connected my oscilloscope(positive to pin 2 and ground/chassis to pin 1) to the other side of the "y". I understand that there is DC voltage at this point, but it did not SEEM to affect my biasing process. I can say that I fried two 2N3819s by sending way too much voltage at them. Shouldn't need more than 1V @ 1Khz, maximum, to determine bias at max input. Not sure when they "give way" but 10V  is definitely enough. Was for me, twice. Check for continuity/resistance at your primary and secondary of your output trafo before starting. I received some faulty ones(2 at once) from a particular company during this endeavor. That combined with my fried transistors made for some real GDIY troubleshooting.


Thanks ! That makes it much clearer !
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Moby on March 04, 2019, 09:26:09 AM
It is completely pointless. Doesn't add any cost to use different colours, and save everyone the hassle. Same issue on all their wired transformers.

I'll talk to Moby and see if he can do a run of BV107's for us :)
Hey Banzai, thx for contacting me. I wrote you some message by PM but no response. Can you lease drop me e-mail regarding this?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on March 06, 2019, 12:20:30 PM
Hey Banzai, thx for contacting me. I wrote you some message by PM but no response. Can you lease drop me e-mail regarding this?

Hey Moby, thanks for your pm. Will reply asap!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jrmintz on March 08, 2019, 01:36:18 PM
Does anybody know the thread size of the little set screws that hold the xlr into the mic body?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: craigmorris74 on March 09, 2019, 10:36:00 PM
Hey folks,

My buddy who isn't a forum member got in on the group buy and bought a couple of kits.  He successfully biased one of his mics and was working on biasing the second one when it stopped working.  I'm guessing he shorted something out with his screwdriver while biasing.  He says his JFET has continuity between gate and source and gate and drain, so I guess it's shot.  Could he have fried anything else?   This is the second project he's ever worked on, so he's a bit of a DIY newbie.  Any help would be appreciated.

Thanks,
Craig
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on March 09, 2019, 10:49:49 PM
To verify if anything else was damaged he would have to meter all of the resistors and capacitors whilst following the schematic. He also needs to check the transformer. There's no way of knowing what he did, so after he changes out the FET and it still doesn't work he'll have to check all the other components.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: craigmorris74 on March 09, 2019, 11:00:01 PM
Thanks for the tips, Paul!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on March 10, 2019, 06:21:59 PM
Does anybody know the thread size of the little set screws that hold the xlr into the mic body?

Three screws holding the body sleeve should be M2.

Will check tomorrow.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on March 13, 2019, 03:10:58 AM
I just finished building numbers 5 and 6 with the AMI transformers and I also used 10pF caps instead of 4pF just I wanted to pad it a little and I also didn't have any 4pF caps. When I went to bias them I noticed the bottom of the wave form wouldn't square off like the top but was more slanted. I don't remember the Cinemag version I built behaving like this, but still was able to finish the procedure. My scope is also an old Tektronix, so maybe it's just tired.

On initial testing I had one that had mostly constant static noise which was not remedied by swapping capsules. I reflowed a number of solder joints and I feel that the culprit was the lead from the capsule to it's isolated pin as it move a little closer to the pin when I reheated the connection indicating a possible half cold solder joint. Now it's perfectly fine like and ready to be put to use. Once again, as with a vast majority of the problems when building anything here, it's either a bad solder connection or component placement.

For the bias trimmer, I find it less accessible with the adjustment screw facing towards the connector then to the side like the first version (green PCB) and I'm sure there was a reason when the layout was updated. I wrapped my screw driver in electrical tape up to the blade to avoid shorting and destroying anything as it slipped several times when turning it. I guess I need to get one of those fancy types with the shroud covering the blade. Still don't know why trimmers don't use Phillips screw heads.

A little note on the Cinemag vs. AMI side debate that seems to have taken place during this process. I lent my other DIY KM84s with Cinemags to a fellow recording friend to track drums and he could not have been happier with how they sounded on overheads and hi hat. The drummer also liked them. Maybe the AMI version would not have been as preferred with extra top end on cymbals. Unless there is a side by side comparison I don't think anyone's going to know. It seems that with either transformer you are going to end up with a great sounding microphone as also reported by others who have built them with both of these transformers. It just comes down to whether or not you want to spend $75 and wait a couple of weeks (Cinemags are usually made to order) or $120.

Many thanks to Banzai and Graeme for making this available to the rest of use. These fantastic sounding mics that I hope to put to frequent use once I put my soldering iron down.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Nele on March 15, 2019, 05:59:20 AM
Just a small heads-up to say I'm organizing a group-buy for cinemag transformers:

European Cinemag GB (https://groupdiy.com/index.php?topic=72010.0)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jrmintz on March 17, 2019, 06:09:26 PM
Does anybody know the size of the screws that hold the white thing onto the board? I didn't seem to get any and I want to pick some up in the morning. Thanks.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on March 20, 2019, 06:44:26 PM
Does anybody know the thread size of the little set screws that hold the xlr into the mic body?

Sorry for the slow reply, but just to expand on this for everyone:

These tiny set screws are a menace – the heads tend to strip at the slightest bit of force. I would advise to replace with M2 x 3mm stainless steel slotted set screws. These will have to be fully removed for the body to come off, but they're also much stronger.

Another option is to use a single normal M2 screw to hold the body together whilst testing and modding. Then when the mic is ready and won't need to be opened and closed a lot, use the set screws to finish the assembly.

Also found it best when tightening the XLR connector screw into the XLR shell, to remove these set screws first. I had one or two where as soon as I removed the set screws, a previously tight XLR ended up being very loose (that was obviously happening everytime the set screws were extended into the body as well).
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: pH on April 01, 2019, 07:48:02 PM
Enjoyed the easy build and really liking the sound of this microphone.
However I'm noticing that it's picking up some RFI or computer hash noise in my small recording area, none of my other microphones have this problem.
When people say that the KM 84 is a bit noisy is this what they mean?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on April 02, 2019, 03:26:31 AM
All of the ones I've built from the first batch and this one have been dead quiet, and I have EMI issues with certain things in my space.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: jplebre on April 07, 2019, 11:59:36 AM
Hey guys, any tips to install/secure the GZT84 trafos?
I'm afraid of pushing it in, but seems that it won't slot as the cables make the wrapper a bit wider than the rest of the trafo's body
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: craigmorris74 on April 08, 2019, 11:34:30 AM
Hey guys, any tips to install/secure the GZT84 trafos?
I'm afraid of pushing it in, but seems that it won't slot as the cables make the wrapper a bit wider than the rest of the trafo's body
I had to file away a bit of the PCB to get mine to fit.  Be careful not to cut any traces if you do that.  I added a couple of drops of glue to hold them in place as well.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: GraemeWoller on April 08, 2019, 06:50:26 PM
Enjoyed the easy build and really liking the sound of this microphone.
However I'm noticing that it's picking up some RFI or computer hash noise in my small recording area, none of my other microphones have this problem.
When people say that the KM 84 is a bit noisy is this what they mean?

They're fun little buggers to build alright, I'm pleased you're digging it!

Did you make sure you'd cleaned the flux up well? It's easily forgotten about, but it makes a hell of a difference to stray hums, buzzes, and general shenanigans.

Is the RFI definitely on that mic and being recorded, or is it just on the outputs to your monitors? My Apogee Duet 2 can be a bit of a pain with digital hash from time to time. Not saying that's your issue, but worth asking.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: GraemeWoller on April 08, 2019, 06:56:13 PM
Hey guys, any tips to install/secure the GZT84 trafos?
I'm afraid of pushing it in, but seems that it won't slot as the cables make the wrapper a bit wider than the rest of the trafo's body

It can be the same with the Cinemags too, the wrap dimensions vary a little, or so I've noticed. As Craig said, give it a little file on the sides of the cutout, just enough to get the trafo in but leaving a little friction to keep in place. A dab of hot glue will keep it from moving if you need a little more reassurance. :)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on April 08, 2019, 08:02:59 PM
+1 for hot glue.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: damianschwartz on April 09, 2019, 05:40:49 PM
For the leads you follow the drawing you posted from Cinemag's website. The transformer will just fit in there and might require some very minor trimming/filing to get it to fit. It does just float in there but won't move when the PCB is inserted into the body. You can also do what I did and apply a small amount of hot glue for added security.

Thanks!

Paul
I asked Cinemag for a quote, they told me they can send the trafo with the leads hooked up internally, meaning you have four leads, or the 8 leads out. What did you guys choose?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on April 09, 2019, 07:50:26 PM
I would think having access to all eight leads would be ideal so everyone can stick to the original schematic and the layout provided. That way the questions and confusion on hooking it up would be kept to a minimum. I am only speaking for myself, of course.

I got my threads crossed. Four wires would be easier with this board yes. The AMI option only has four wires.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Mworthin on April 10, 2019, 12:16:51 AM
The boards in this thread only have pads for 4 connections...The CM-5722W is the one with 4 leads.  I would think it would be simpler to use since there is no impedance switch on the output side of the transformer,  unlike the original, so there is really no need  for the extra wires.   Use the data sheet they wil send as the colors of the wires for primary and secondary are different from those on the PCB printing, at least on mine.   

If you use the other more traditional one, just be careful how you hook up the unused leads so that you get the windings in the proper sequence. 

David at  Cinemag says they are identical otherwise

—Mark
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on April 10, 2019, 01:12:58 AM
Edited my above post. Four wires is better. I thought I was on a different thread. Don't ask....


Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on April 10, 2019, 07:05:31 AM
Cinemag 5722 (8 wires):
R - Red
G - Green
B - Blue
Y - Yellow

Cinemag 5722W (4 wires):
R - Red
G - Brown
B - Orange
Y - Yellow

(https://i.postimg.cc/CxZYGpHb/KM84-PCB-Transformer-pads.png)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Mworthin on April 11, 2019, 01:36:42 AM
Banzai...that’s awesome.

And Paul, I didn’t want you to think I was being critical...I just thought it was easier not to have the extra leads for this application.

—Mark
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on April 11, 2019, 11:12:13 AM
No worries. I totally didn't take it the wrong way. I just spaced out as to which thread I was replying.

Thanks!
Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: iturnknobs on July 07, 2019, 10:48:06 AM
Has anyone been having RF/induction issues manifesting as noise in these microphones? I was using these in an orchestral situation and had to mute them because of noise. Took them home to troubleshoot and my phone induced the same noise from 3 feet away. Noticeable hum from large transformers a few feet away also. Phone turned off, issue gone. Not really usuable in a group of 60 with cell phones in their pockets. Did I do something wrong or miss something during assembly? They have been great, otherwise. Ideas?

-Brian
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on July 07, 2019, 11:16:02 AM
Has anyone been having RF/induction issues manifesting as noise in these microphones? I was using these in an orchestral situation and had to mute them because of noise. Took them home to troubleshoot and my phone induced the same noise from 3 feet away. Noticeable hum from large transformers a few feet away also. Phone turned off, issue gone. Not really usuable in a group of 60 with cell phones in their pockets. Did I do something wrong or miss something during assembly? They have been great, otherwise. Ideas?

-Brian


Hello Brian,


I know the original KM84s from the late 80‘s,they were prone to pick up noise from everywhere on stage,e.g. lights and dimmers.Although I like their sound very much they sometimes were not useable.Issues went away by swapping to Schoeps,but that‘s a different story.
I don‘t know if the clones behave the same but have ordered them and will find out anyway.
If they do then I‘m sorry to say that either you gain control over the musicians and don‘t allow them to have cellphones with them while recording (I‘m in the position to do so) or the hard way and change microphones to different types/brands.


Hope to have helped,


best regards,


Udo.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on July 15, 2019, 03:35:44 AM
Hello,

for those who are using the 3U GZT-84-Transformer,the Primary DCR should be around 920 Ohms,the Secondary around 42 Ohms.
Just to let you know.

Best regards,

Udo.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: duantro on July 15, 2019, 01:41:53 PM
Hello,

for those who are using the 3U GZT-84-Transformer,the Primary DCR should be around 920 Ohms,the Secondary around 42 Ohms.
Just to let you know.

Best regards,

Udo.
Good tip. I'll add that the lead coloring is the same as the Cinemag 4 wire posted above here^
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: stelin on July 16, 2019, 03:41:31 PM
Hi Brian!

I've built two KM84. They both pick up RF-noise, from cell phones and cell phone towers.
One just a little bit, but the other one is practically useless.
I have not been able to determine why they are different.

Have anyone found a solution to this problem or maybe know why they are so sensitive to RF-noise?

- Stefan
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 16, 2019, 05:15:46 PM
 Any tips on how to get the three tiny screws out at the bottom of the body? On one of my bodies, they came out fine. On the other, they are way farther down, and super tight. I’ve heard they strip easily, so I’m trying to avoid that.

Thanks,

C
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on July 17, 2019, 12:35:55 AM
Any tips on how to get the three tiny screws out at the bottom of the body? On one of my bodies, they came out fine. On the other, they are way farther down, and super tight. I’ve heard they strip easily, so I’m trying to avoid that.

Thanks,

C

If screws are all the way in you can pull the body tube off. Much easier to unscrew from just the connector housing.

Recommend replacing them with stainless steel M2 x 3mm. You can also just use a single regular M2 screw. Holds just fine.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 17, 2019, 09:18:45 AM
I'll give that a go and order some stainless screws. 

Thanks!

C
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BramK on July 17, 2019, 01:32:07 PM
To those with the Haufe transformers - how are you mounting them on the Rev B boards? Are modifications to the PCB required? I'm gently playing Tetris here trying to find a fit, but worried about the delicate leads on the trans. Any pics of your installs or guidance would be much appreciated. Thanks!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on July 17, 2019, 07:02:55 PM
 Hi BramK,
I remember, that I put a file and made it bigger.
Then you can push it in, like the cinemag ones (as seen on the pictures).
But I've to say, the difference between the Cinemag and Haufe transformers is not noticeable.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Fuzz Face on July 17, 2019, 11:24:18 PM
The 3U and Cinemag were both slightly too large for the cutout for me.

I have a set of files for guitar work and used a small one to slightly enlarge the cutout. You could use a dremel or whatever you’ve got (making sure not to cut into the surrounding traces)

I was thrown off at first but I like that the hole was slightly too small. It took very minimal filing to make the transformer fit and then I was able to get a really nice fit that doesn’t require glue or anything.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BramK on July 20, 2019, 03:07:22 PM
Thanks Till & Fuzz,

I ended up using a file on a few edges and was able to fit the Haufe in snuggly.  Here are some photos of orientation for anyone else using the Haufe:

(https://i.imgur.com/sR0VxB6.png)
(https://i.imgur.com/1IGQkXY.png)
(https://i.imgur.com/OHDG0dR.png)
(https://i.imgur.com/vLaEjFz.png)


In regards to bias'ing, I ended up with 6.73K on mic 1 and 7.96K  on the other. Does this look symmetrical enough? The negative wave is narrower than the positive swing. Signal generator was applied directly to the capsule pin without a 1000pf cap (I tried using one but the scope reading was crazy and phasing with it in series), scope probe attached to the drain and grounded on xlr pin 1.

(https://i.imgur.com/3aMPv36.png)

Mic bodies are off at the powder shop!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on July 20, 2019, 05:29:10 PM
Hi Bram,
yes this should be more than okay !
This is how my Haufe ended up in the pcb.
Cool that it worked with the scope.
After I damaged two fets with using a scope (my fault), I put my DMM on the capacitor backwards and turn the trimpot after I read 10v with my probe.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Winetree on July 21, 2019, 04:22:32 PM
Bram, 
 I've got 4 mics sitting with just the transformer wiring to  connect.  After pulling one wire out of a transfo, I gave up.
 Could  you post the definitive wiring for the Haufe transformers.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on July 22, 2019, 06:35:37 AM
Hello,


did my 3 kits finally, biasing went well.
Thank you both Mike and Graeme for these wonderfull kits,it was a pleasure building them.
I can confirm that the supplied set screws should be exchanged to better ones.
For the transformer I had the 3U types,with a bit of „dremeling“ they went in well in the end.
Two drops of hot glue hold them in place nicely.
I did a quick testing today,and I was very happy with what I heard.A silky top end,just like the originals,never harsh.
Attached pic of proof during test setup.


Best regards,


Udo.

(Edited typo).
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BramK on July 23, 2019, 08:14:33 PM
Bram, 
 I've got 4 mics sitting with just the transformer wiring to  connect.  After pulling one wire out of a transfo, I gave up.
 Could  you post the definitive wiring for the Haufe transformers.

Hi Winetree, apologies for not responding sooner, I wasn't getting thread updates.

1. On the Haufe transformers, on the side that has only 2 white wires,  solder these together.
2. On the opposite side, solder together the yellow and green wires.
3. Then follow the color conversion guide below to connect to the PCB:

HAUFE --> CINEMAG (PCB Designation)

Black   ---->   Red (R)
Red      ----->    Green (G)
Blue   ------>  Blue (B)
White ---->  Yellow (Y)

To make things less confusing, I extended the Haufe leads with the cinemag color wiring.

(https://i.imgur.com/xv2UapFl.jpg)


And here are the finished mics after painting (and Neumann badges... just for funsies  ;D)

(https://i.imgur.com/BHe15YWl.jpg)
(https://i.imgur.com/loqS4Jrl.jpg)


Thank you Banzai and Graeme, I've only had a few moments to test these out on acoustic and voice, but I'm loving what I'm hearing so far - they sound clear and smooth and the noise floor is impressively low. Not experiencing any RFI/EMF interference that a few others had mentioned.

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on July 23, 2019, 10:00:30 PM
Congrats to your builds.


May I ask how you removed the mesh out of the brass tubes for painting?
It looks like they are glued in?


Thank you in advance,


best regards,


Udo.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Winetree on July 24, 2019, 12:03:32 AM
Bran,  Thanks so much for the info and pix,
               Looking forward to hearing these,
                Your mics look great,
Robert
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BramK on July 24, 2019, 12:41:38 PM
Congrats to your builds.


May I ask how you removed the mesh out of the brass tubes for painting?
It looks like they are glued in?


Thank you in advance,


best regards,


Udo.

I soaked them in acetone for a few minutes.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Winetree on July 24, 2019, 02:38:07 PM
On the first group buy, the screen was a separate, cut rectangle you placed in the mic.
Did they glue them in on the second batch?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on July 25, 2019, 12:44:45 AM
On the first group buy, the screen was a separate, cut rectangle you placed in the mic.
Did they glue them in on the second batch?
Hello Winetree,


yes,looks like glue put on 4 spots inside.


Best regards,


Udo.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Fuzz Face on July 25, 2019, 09:51:56 AM
Hi Winetree, apologies for not responding sooner, I wasn't getting thread updates.

1. On the Haufe transformers, on the side that has only 2 white wires,  solder these together.
2. On the opposite side, solder together the yellow and green wires.
3. Then follow the color conversion guide below to connect to the PCB:

HAUFE --> CINEMAG (PCB Designation)

Black   ---->   Red (R)
Red      ----->    Green (G)
Blue   ------>  Blue (B)
White ---->  Yellow (Y)

To make things less confusing, I extended the Haufe leads with the cinemag color wiring.

(https://i.imgur.com/xv2UapFl.jpg)


And here are the finished mics after painting (and Neumann badges... just for funsies  ;D)

(https://i.imgur.com/BHe15YWl.jpg)
(https://i.imgur.com/loqS4Jrl.jpg)


Thank you Banzai and Graeme, I've only had a few moments to test these out on acoustic and voice, but I'm loving what I'm hearing so far - they sound clear and smooth and the noise floor is impressively low. Not experiencing any RFI/EMF interference that a few others had mentioned.

Those look amazing! I gotta powdercoat mine now  ;D
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 25, 2019, 12:00:53 PM
(http://www.sethglassman.com/AMI%20T8.jpg)

Be sure to leave enough extra grey wire to reverse the leads if the mic's polarity is reversed.

I finished my mic by cleaning the brass well and spraying it with a couple of coats of lacquer.  I think that's the easiest way.

I just finished one of mine using the AMI transformer. My wiring looks similar to this, but left to right goes: blue, grey, blue, grey.  The transformers came in bubble wrap with no data sheet. My DMM showed a higher resistance when measuring blue to blue than grey to grey, so I connected the transformer as shown here. I did a quick comparison with an AKG 451b and the mic sounds great already (have not biased the FET yet), but the polarity is reversed compared the AKG. Is this just a matter of swapping the grey transformer wires around?

Thanks,

C
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on July 25, 2019, 12:33:32 PM
Yes. Swap them, then it’s reversed.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 25, 2019, 12:46:08 PM
Yes. Swap them, then it’s reversed.

Perfect, thanks TillM!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 25, 2019, 01:43:48 PM
One question regarding the biasing procedure. I'm planning to bias them by ear, using the stock signal generator that comes with Pro Tools. I'd be coming out of a TRS patch bay.  What I'm trying to figure out is how to "inject" the 1k sine wave into the capsule pin. 

Can I just use a cable that is TRS on one end (coming out of the patchbay), and raw cable on the other end in this configuration:  positive to capsule pin, negative and shield to pin 1 on the mic XLR? 

Once that's connected, apply +48v to the mic and adjust trimpot for least amount of audible distortion?

Ok, that's two questions.  ;)

Thanks,

C

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: partycentral on July 25, 2019, 03:10:02 PM
One question regarding the biasing procedure. I'm planning to bias them by ear, using the stock signal generator that comes with Pro Tools. I'd be coming out of a TRS patch bay.  What I'm trying to figure out is how to "inject" the 1k sine wave into the capsule pin. 

Can I just use a cable that is TRS on one end (coming out of the patchbay), and raw cable on the other end in this configuration:  positive to capsule pin, negative and shield to pin 1 on the mic XLR? 

Once that's connected, apply +48v to the mic and adjust trimpot for least amount of audible distortion?

Ok, that's two questions.  ;)

Thanks,

C
Seems like that should work, except I'd add a 1uf capacitor between the capsule pin and the signal source - don't want to apply polarization voltage to your interface outputs!
Getting a line level signal up to 1Vpp may be a stretch depending on your interface as well; in the past I used the amplified headphone output of an interface for this, which seemed to work nicely, but could possibly have drawbacks beyond my understanding.

I'm having a quandary on biasing myself - biasing this mic by ear vs. asymmetry of the clipped input wave. Optimal trimmer resistance for either biasing method varies by ~800ohm - should I be giving preference to one, splitting the difference, etc.? For quiet instruments - acoustic guitars, etc., the recorded results are equal to my ears; but I'd like to use these as drum overheads where bias method may have more of an impact.

any strong preference?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 26, 2019, 02:17:33 PM
Seems like that should work, except I'd add a 1uf capacitor between the capsule pin and the signal source - don't want to apply polarization voltage to your interface outputs!
Getting a line level signal up to 1Vpp may be a stretch depending on your interface as well; in the past I used the amplified headphone output of an interface for this, which seemed to work nicely, but could possibly have drawbacks beyond my understanding.

I'm having a quandary on biasing myself - biasing this mic by ear vs. asymmetry of the clipped input wave. Optimal trimmer resistance for either biasing method varies by ~800ohm - should I be giving preference to one, splitting the difference, etc.? For quiet instruments - acoustic guitars, etc., the recorded results are equal to my ears; but I'd like to use these as drum overheads where bias method may have more of an impact.

any strong preference?

Ok, great. I've got a 1000pf film capacitor to use for biasing based on Ruud's suggestion on page 2 of this thread. Do you think that would suffice, or am I better off with a 1uf cap?

Thanks,

C
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Fuzz Face on July 27, 2019, 09:20:21 AM
Ok, great. I've got a 1000pf film capacitor to use for biasing based on Ruud's suggestion on page 2 of this thread. Do you think that would suffice, or am I better off with a 1uf cap?

Thanks,

C
1000pf works fine
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on July 27, 2019, 10:07:20 AM
1000pf works fine

Cool, thanks.

C
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BladeSG on July 27, 2019, 10:37:50 AM
I just finished building the first out of 2 and all I'm getting is loud hum. I used the AMI T8 and was a little unsure of the wiring but I don't think this is the problem.

Is it safe to connect to XLR to supply 48V phantom to check voltages per schematic with the capsule and body removed?

Thanks in advance.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on July 27, 2019, 12:53:33 PM
Loud low frequency hum is always a ground or shielding problem.

Make sure pin 1 is connected to the PCB ground and mic body. Check for continuity between the body sleeve and XLR pin. Should be around 1ohm.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BladeSG on July 27, 2019, 11:08:01 PM
Loud low frequency hum is always a ground or shielding problem.

Make sure pin 1 is connected to the PCB ground and mic body. Check for continuity between the body sleeve and XLR pin. Should be around 1ohm.

Thanks Banzai.

Thats exactly what the problem was. I remember thinking about the grounding when I assembled it yesterday!!!

Working fine and sounds great (still needs biasing), thank you again!

Cheers,

Steve
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Dr nEon on July 28, 2019, 05:44:50 AM

For the transformer I had the 3U types,with a bit of „dremeling“ they went in well in the end.
Two drops of hot glue hold them in place nicely

(Edited typo).


Hey Udo,  I'd be keen to know where you applied the drops of hot glue?  Seems this is a popular method, but so far no one has posted a pic of where the safest place on the TX/PCB is to put this glue.

+ Your trio of KM84's looks great! :)

Cheers
nEon
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on July 28, 2019, 06:01:58 AM


Hello nEon,


doesn‘t really matter as long as it does not exceed the pcb edges (the long sides).If that happens simply cut the excess away with a sharp knife.In my case I applied each one big drop of hot glue diagonal into the gap between tx and pcb.
Hot glue is not really that hot,you won‘t damage anything,just keep glueing time short.
Will take a picture when I open them again,I‘m waiting for better set screws atm and might also try some polishing or even painting,who knows.Right now they‘re just cleaned.
Anyway,as said just some hot glue to keep things roughly in place,once assembeled it doesn‘t matter anymore.


Hope to have helped,


Udo.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BladeSG on August 03, 2019, 05:20:06 AM
Hello, everyone,

Just in case the White Market thread disappears with information like calibration, I thought I would post it here for safe keeping. Many thanks to RuuDNL for originally providing this procedure:

"Connect a signal generator through a capacitor (~1000 pF) to the gate of the FET. 1Khz or so is fine.
Replace the source resistor temporarily with a 10 K.ohm trimpot.
Increase the level of the signal generator until you get distortion (oscilloscope or distortion analyzer).
Adjust the trimpot for lowest distortion and symmetrical clipping.
Measure the value of the trimpot and replace the trimpot with a fixed resistor with the value you measured.
That's it
!"

Thanks!

Paul

Might be obvious but I've never used a scope before and just bought a cheap one...

I understand where the signal generator connects to but where do I connect the lead going back into the scope (I'm assuming not at the XLR because I need to plug in a mic cable to feed phantom)?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Dr nEon on August 03, 2019, 06:24:53 AM
In my case I applied each one big drop of hot glue diagonal into the gap between tx and pcb.
Hot glue is not really that hot,you won‘t damage anything,just keep glueing time short.


Thanks Udo,

So did you arrange it so that your glue connected with the metal laminations part of the transformer, at the ends?   I was planning to do it  this way, to keep the glue away from the windings..

I actually have some servisol silicon adhesive  here. (the kind we use to anchor large electrolytics to the pcb).  I thought I might use that instead. I do also have hot glue... I wonder if there's an advantage in either product?

Many thanks for your help!

Cheers
nEon.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mcrowe on August 04, 2019, 09:07:04 AM
Word to the wise: be careful not to let the XLR pins get too hot when soldering the connector to the board. On my first attempt, I was having a hard time getting the solder to take to the pad, and as I was attempting to get it right, the pin got so hot that it softened the surrounding plastic and it actually moved a bit in the housing. It still fits in a female XLR connector (though it's a bit tight), and I did manage to get it mounted in the end, but I would prefer not to have made that mistake.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kante1603 on August 04, 2019, 10:12:37 AM

Thanks Udo,

So did you arrange it so that your glue connected with the metal laminations part of the transformer, at the ends?   I was planning to do it  this way, to keep the glue away from the windings..

I actually have some servisol silicon adhesive  here. (the kind we use to anchor large electrolytics to the pcb).  I thought I might use that instead. I do also have hot glue... I wonder if there's an advantage in either product?

Many thanks for your help!

Cheers
nEon.
Hello nEon,


yes,I „connected“ the lamination-edges  with the inner pcb edges/corners.In one case (of three) even one single drop held te transformer in place easily.
I‘m not familiar with the mentioned servisol silicon adhesive,sorry.


Hope to have helped,


best regards,


Udo.



Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on August 04, 2019, 10:48:36 AM
The hot glue is probably easier to remove if you make any changes to the transformer. This is how I do mine as well.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mcrowe on August 04, 2019, 05:12:35 PM
I completed my build today, got them biased up for symmetrical clipping with no issues, and began to test them. The two capsules I got sound noticeably different. Compared to each other, one has more lift in the treble and sounds overall more even, while the other one sounds more muted in the treble and seems to have some unusual resonances in the midrange. I swapped the capsules around between the bodies, and the tonal characteristics followed the capsules, so I'm fairly confident it's nothing to do with the build. Has anybody else experienced this, and is there anything I can do about it?

Here are a couple samples of acoustic guitar to illustrate what I mean. This is the same performance with the mics arranged vertically as close as I could get them. Forgive my very sloppy rendition of something that sounds sort of like 'This is a Low' by Blur.

Mic 1 (http://maxcrowe.co/sounds/km84/KM84%201.mp3)
Mic 2 (http://maxcrowe.co/sounds/km84/KM84%202.mp3)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BladeSG on August 04, 2019, 09:54:33 PM
Might be obvious but I've never used a scope before and just bought a cheap one...

I understand where the signal generator connects to but where do I connect the lead going back into the scope (I'm assuming not at the XLR because I need to plug in a mic cable to feed phantom)?

Anyone?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mcrowe on August 04, 2019, 11:01:27 PM
Anyone?

See page 3 for a post covering this question.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: BladeSG on August 05, 2019, 03:57:06 AM
See page 3 for a post covering this question.

Thanks, not sure how I missed that!

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Dr nEon on August 05, 2019, 04:24:56 PM

Hope to have helped,



You did, Udo, thanks..!   :)

I ended up using the servisol silicon, as, since I have a 3U transformer with a very wide windings/taped bit, I had to file every side of the transformer cutout .. It all had to be made bigger to be able to insert the transformer, so once it was in place, there was a fair bit of play around the edges.

The servisol silicon was workable for a long time before setting , which allowed me to fill the gaps precisely  using a tiny jewellers screwdriver, and clean up around solder pads to make sure the glue was nowhere near any connection...  Even though the silicon is an electrical insulator,  I didn't want any unnecessary gunge on the primary side, as we go to so much trouble on this circuit to keep the pcb as clean as poss (albeit at the high impedance end..).

The silicone has held the transformer nicely, yet doesn't seem to be a 'rock-hard' product , like some of the stuff you find holing down caps on pcbs.  This seems better, incase it ever needed removal..

Having just fired up,  hearing the familiar, and lovely, Neumann sound from these things, I certainly wont be changing the 3U transformer; it's there to stay!  8)

Thanks again, everyone,  and special thanks Graeme and Banzai for this great project!

Cheers

nEon.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: roger.unc on August 06, 2019, 09:53:08 PM
Howdy - I'm building four KM84s. The gain on the first two turned out fine with AMI T8's that came in one box. I built the next two mics with a T8 pair from a second box and they are super, super quiet . The quiet mics are wired identically to the first two mics. The wiring on all transformers looks the same. I pulled the T8's from the quiet mics and took these measurements:

Blue pair: 215 ohms (same as first pair of T8s)
Grey pair: 22 ohms (same as first pair of T8s)
1V sine wave @1kHz on blue = .046V on grey
5V sine wave @1kHz on blue = .238V on grey
1V sine wave @1kHz on grey = 2.3V on blue

Unless I'm wrong (which is quite often the case) that gives an almost 22:1 ratio on the pair of quiet T8s? They are supposed to be 7:1. Am I wrong on my math or technique? Just trying to rule these out before I troubleshoot elsewhere - or before I reach out to AMI.

Thanks,
Roger

Edit: 1kHz not 1Hz. Sorry!
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mcrowe on August 07, 2019, 11:49:02 AM
Am I the only one whose capsules sound noticeably different?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: damianschwartz on August 13, 2019, 04:55:02 PM
Finally had the chance to build my mics.

All went smooth thanks to all the info gathered during this time. Both worked at 1st attempt and everything seems fine.

However...
One mic sounds stunning, better than my friends original 84 (which is loosing lows due to age-capsule issues)
The other one has much more gain, like about 3-4 db more, and it's also darker, or with more bottom end, which could actually be just the proximity effect due to the higher gain. Swapped channels on the pre´s, same thing.

Not sure if this could be related to different fet betas, or the capsule. Bias went good on both units... Fets are supposed to come paired... any ideas?




Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Potato Cakes on August 13, 2019, 06:23:51 PM
Finally had the chance to build my mics.

All went smooth thanks to all the info gathered during this time. Both worked at 1st attempt and everything seems fine.

However...
One mic sounds stunning, better than my friends original 84 (which is loosing lows due to age-capsule issues)
The other one has much more gain, like about 3-4 db more, and it's also darker, or with more bottom end, which could actually be just the proximity effect due to the higher gain. Swapped channels on the pre´s, same thing.

Not sure if this could be related to different fet betas, or the capsule. Bias went good on both units... Fets are supposed to come paired... any ideas?

Did you swap capsules? Is the the transformer wiring correct? There's always the standard issue of a bad component/placement/solder problem. There isn't much to the circuit so just simple process of elimination should reveal the culprit.

Thanks!

Paul
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: kingkorg on August 13, 2019, 07:01:58 PM
Swap the capsules, test again, measure capacitance value of the capsules they should be within 5pF tolerance. Measure FR of the capsules with REW with exact same volume-placement. One can really not rely solely on ears here.

Check the size of the holes in the plastic backplate of the capsule if they are the same, they should be the same size/arrangement for both capsules. I am talking about this clear plastic part of the capsule.  These chinese capsules have specs all over the place, so i wouldnt expect them to very consistent. They can be, after all, ordered from Shuaiyin for 8 bucks plus shipping.

(http://cdn.recordinghacks.com/images/blog/2013/603S-capsule-components.jpg)

(http://cdn.recordinghacks.com/images//mic_extras/monoprice/600800-pcb.jpg)
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mcrowe on August 24, 2019, 08:04:40 AM
Finally had the chance to build my mics.

All went smooth thanks to all the info gathered during this time. Both worked at 1st attempt and everything seems fine.

However...
One mic sounds stunning, better than my friends original 84 (which is loosing lows due to age-capsule issues)
The other one has much more gain, like about 3-4 db more, and it's also darker, or with more bottom end, which could actually be just the proximity effect due to the higher gain. Swapped channels on the pre´s, same thing.

Not sure if this could be related to different fet betas, or the capsule. Bias went good on both units... Fets are supposed to come paired... any ideas?

These differences are identical to what I experienced. Try swapping capsules; I'm almost positive the tonal characteristics you're noticing will follow. The additional low end you're noticing out of the hotter capsule wouldn't be due to greater proximity effect; that's due to physical placement rather than output level.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: adam.schw on September 06, 2019, 07:51:30 PM
Finished mine up! It's a pretty quick build if you know wtf you're doing (I didn't). Sounding all good from what I can tell! Thank you everyone for all the knowledge dropped in this thread, it was very helpful.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on September 25, 2019, 05:27:51 PM
If screws are all the way in you can pull the body tube off. Much easier to unscrew from just the connector housing.

Recommend replacing them with stainless steel M2x5. You can also just use a single regular M2 screw. Holds just fine.

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. 
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Colorblind on September 26, 2019, 08:27:04 AM
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.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on September 26, 2019, 03:18:37 PM
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.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: maarvold on September 26, 2019, 11:51:02 PM
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. 
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: Banzai on September 27, 2019, 12:31:16 PM
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.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: choolder on October 02, 2019, 05:10:08 PM
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.

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: volker on October 03, 2019, 02:52:58 AM
Maybe a reversed transformer on one of them.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: choolder on October 04, 2019, 02:50:43 AM
My technician also measured with the transformer and he gets the same result measured from the fet.

Any other ideas?

Thanks!

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on October 05, 2019, 05:53:49 AM
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.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mickdundee63 on October 28, 2019, 12:20:21 PM
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.

Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mickdundee63 on October 30, 2019, 02:05:03 AM
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??
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mickdundee63 on October 30, 2019, 05:55:41 AM
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?
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: TillM on October 30, 2019, 06:04:11 AM
Yes, this seams like the FET is broken.
When my working mic lost audio, when biasing, It was everytime the FET.
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mickdundee63 on October 30, 2019, 10:39:12 AM
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...
Title: Re: Banzai's KM84 DIY Body & PCB kit build thread
Post by: mickdundee63 on October 31, 2019, 05:28:52 AM
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.