MK7 mic finished

[Emperor-TK]

I thought I'd record the details of my MK7 build here, in case it might be of help to anyone else.

Final product:
"Stellar" Chinese body, $150 new off ebay.  Same as many other mics, such as  T-Bone SCT-700 and the Nady TCM-1050
Filled the engravings on the body with JB Weld and sanded flush
Painted with Rustoleum primer and Rustoleum gloss enamel spray paint (almond color reminds me of a Soundeluxe/Bock)
Mylar Thiersch M7 capsule
remachined the body's top plate out of acrylic to better isolate and lower the capsule
GE EF86 tube
fixed bias
Group buy shock mount
Power supply built in a BK Precision DC power supply case, modified and repainted (DC bench power supply ordered off ebay and was rendered useless by UPS, so I recycled the case)
mic power supply made with Moby's board
Used Gotham 7 pin cable from Redco
Triad inductor
Triad 12VAC power
200VAC transformer from stellar power supply

Next step is to roll some tubes and play around with output cap sizes.  I haven't formed an opinion on the sound yet, positive or negative.  Mt initial impression (with a random tube in it) is that it is woollier than I expected, but I'm not sure if it's a good woolly or a bad woolly yet.  The random tube is dead quiet though.  When Skylar's bodies are ready, I'll try a swap and see what changes with the new grill, etc.  My capsule is sitting a little high still, even after re machining a new lower acrylic mounting plate. 

What didn't work:
I could not get the stock Chinese power supply to work with fixed bias under any circumstances.  I couldn't get the hum to an acceptable level, even after completely rebuilding the heater section with Max's retrofit design using the Vreg.  I played around with every grounding scheme with no luck.  Also, this mic had a 11.5VDC heater supply, and even with the extra voltage and using schotkey diodes, the hum was still there.  Rebuilding the power supply with the inductor and a new 12V transformer fixed the problem.  The mic is now dead quiet.  Even after rebuilding the power supply, I had to play around with the ground connections a little to make the hum completely vanish.  The scheme I wound up with is depicted below.

 

[hautacam]

very cool!

 

[Lowfreq]

The new paint job looks great!! ;D

 

[user 10827]

wow, Id love to do one of these if i had the patients, congrats,

how does it sound?

 

[Gus]

Looks very nice.  I like the paint color with the chrome.

A little off topic is there still a working link to the older DIY magazine articles for building microphones and capsules?  IIRC one had a very nice power supply circuit.

 

[Rossi]

Looks awesome, great job!

Thanks for sharing your grounding scheme. May be of help when I finally get the time to complete my MK7 project.

 

[illacov]

Where did you get the badge?

Did you make it yourself??

I would love to find out how you did it, it looks fabulous!

Peace
Illumination

 

[Emperor-TK]

The badge was laser engraved from black anodized aluminum.  I had a whole sheet made, and cut them apart with a very heavy duty paper cutter (practically a sheet metal sheer).  I then used a plastic headed fretting hammer to bend them around the body to shape (before painting).

-Chris

 

[illacov]

Where did you get the laser engraving done??

How much was it?

Care to pm me some details??

Thanks
Peace
Illumination

 

[skipwave]

Beautiful build!

Well done as usual.

 

[funkymonksf]

Kickass! That's a beautiful job. Have you tried it out yet?

 

[dissonantstring]

hi ETK,
what a nice looking MK7 mic and PSU build.  i love the paint job and with rustoleum no less.
did you put a top coat over the almond colored enamel?

was the engraved badge done by FPE?  i've designed one in FPD for a mic, but am hesitant because it looks like such an intricate job on a small area, but i'm thinking that chae could do it more accurately with his laser engraving set up.

once again beautiful.  hope you get it to sound as good as it looks in the end (which i'm sure you will).
happy holidays to ya!
kind regards,
grant

 

[ioaudio]

very tasty color & nice build!

re: psu - the transformers used in the supplies of the cheapo mics seem to vary quite a lot. but your new psu looks and i´m sure sounds a lot better anyways.

not sure from the out-of-focus part of the pic - is there a chance of the yellow cable accidently touching the capsule?
you could carefully drill/mill the acryl part to lower the capsule.
btw they left out the inner third layer of the wire mesh at the top-cap.

-max

 

[Emperor-TK]

Thanks everyone for the kind words.  Also, thanks to everyone that was involved in putting this project together (Max, et al.)

RE the badge:  I had Vermont Laser Works do mine years ago, but I'm sure Chae can do the same.  I can't remember what it cost, but laser engraving is relatively cheap.  The badges probably cost less than $0.25 when getting a whole sheet made.  Intricate designs are no problem, but only 2D is possible.

RE the paint: no top coat.  The enamel itself is very hard after a few days and has a very nice gloss.  It also goes on thick and has excellent flow leveling, creating a very professional look.  Try to spray it in a clean environment though, it takes a long time to set up and is a magnet for dust.

RE the power supply:  Based on my experience I'd recommend just starting with the choke supply.  Like Max said, the Chinese transformers vary a lot, and I had one of the higher voltage ones that still didn't work for me.  I wasted a lot of time working on that supply, and it seemed others haven't had great luck either.

RE the capsule:  It's an optical illusion, the wire has good clearance  ;D.  It's hard to tell, but the capsule is already sunk about 1/2 to 2/3 of the way down into the acrylic plate.  It's close to the real U-47 but the cross piece on the basket still looks like it sits a little lower on mine.

 

[Gus]

Heard this microphone today.  A very nice microphone.  It was right at the top compared to some well regarded microphones.  I liked it.

Nice transformer and circuit Max.

 

[Michael_Joly]

Where did you get the badge?

Did you make it yourself??

I would love to find out how you did it, it looks fabulous!

Peace
Illumination

Hey Langston, did you forget to update your sig here with full disclosure of your sales and marketing affiliation with JJ Audio Mics? best, MJ

 

[seavote]

Looks very nice.  I like the paint color with the chrome.

A little off topic is there still a working link to the older DIY magazine articles for building microphones and capsules?  IIRC one had a very nice power supply circuit.

i know ive slacked off on the mic meta upkeep but the articles i think your referring to are still avialable on the web.

http://www.conditionedresponse.com/DIY/microphones/index.html

the non modded version of the PSU for this project seems to work well. most complaints (hum,noise) seem to be occuring with projects that modded the t-bone sct700 PSU. thats how it seems to me. if anyone is having issues with ioaudio's PSU please correct me. mine will be complete soon,so i'll report the results

 

[Silvas]

Very cool looking indeed !

 

[tommypiper]

Awesome.  

Fab.


Where did you get the BK Precision DC power supply case?  

EDIT: OK, I see you ordered it off ebay and it was damaged and you salvaged the case. ...

 I love that PS case.  

 

[plumsolly]

Power supply built in a BK Precision DC power supply case, modified and repainted (DC bench power supply ordered off ebay and was rendered useless by UPS, so I recycled the case)

Best, Ben