Banzai's KM84 DIY Body & PCB kit build thread

[Winetree]

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.

 

[kante1603]

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).

 

[BramK]

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.

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

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.

 

[kante1603]

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.

 

[Winetree]

Bran,  Thanks so much for the info and pix,
              Looking forward to hearing these,
                Your mics look great,
Robert

 

[BramK]

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.

 

[Winetree]

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?

 

[kante1603]

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.

 

[Fuzz Face]

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.

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

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

 

[Colorblind]

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

 

[TillM]

Yes. Swap them, then it’s reversed.

 

[Colorblind]

Yes. Swap them, then it’s reversed.

Perfect, thanks TillM!

 

[Colorblind]

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

 

[partycentral]

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?

 

[Colorblind]

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

 

[Fuzz Face]

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

 

[Colorblind]

1000pf works fine

Cool, thanks.

C

 

[BladeSG]

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.

 

[Banzai]

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.

 

[BladeSG]

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