Banzai's KM84 DIY Body & PCB kit build thread

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iturnknobs

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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?
 

mhbunch

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From memory the Pcb solders on to xlr connector which is held in place via set screws on body
 

fsalter

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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.
 

iturnknobs

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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.
 

Banzai

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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.
 

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ln76d

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Banzai said:
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.
 

iturnknobs

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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
 

Potato Cakes

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iturnknobs said:
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
 

iturnknobs

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Potato Cakes said:
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?
 

Potato Cakes

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iturnknobs said:
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
 

iturnknobs

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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.
 

Banzai

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iturnknobs said:
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.
 

wowi

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In the original whitemarket thread were some usefull hints and some pictures of the build. Maybe these guys can post this again ?

Thanks
Wolfgang
 

iturnknobs

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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.
 

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iturnknobs

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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.
 

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jrmintz

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I used mine yesterday as part of a stereo pair with one of my real KM84s and any difference was undetectable. Sounded great.
 

iturnknobs

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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.
 

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