MK47 PCB tube mic kit - build thread

SKJGProject said:

read the whole thread again and tried a different grounding scheme....still horrible noise

can somebody show me a clearly understandable working way on mic, psu and cable???

atm i have connected pin 7 in the cable to the shield on both sides, in the mic pin 7 to b- (pin 3), pin 3 and pin 7 united in the cable on the mic side.
in the psu my iec ground, pin 7 and pin 3 and the xlr pin 2 are going to the 0v connecor

Click to expand...

What kind of noise is it , Hum , or hiss or a combination of both or somthing else , maybe if you post a sample that could help a bit.
Best,
dan,

Here's an internal pic of my recent MK47 power supply build.  The build is based on Chungers use of a heatsink for the series resistors.  I happen to have a large heatsink laying around in my parts bin so I used it.  Definitely overkill but it works well. 

The MK47 mic is mostly built as well except for installing the capsule. 

poctop said:

SKJGProject said:

read the whole thread again and tried a different grounding scheme....still horrible noise

can somebody show me a clearly understandable working way on mic, psu and cable???

atm i have connected pin 7 in the cable to the shield on both sides, in the mic pin 7 to b- (pin 3), pin 3 and pin 7 united in the cable on the mic side.
in the psu my iec ground, pin 7 and pin 3 and the xlr pin 2 are going to the 0v connecor

Click to expand...

What kind of noise is it , Hum , or hiss or a combination of both or somthing else , maybe if you post a sample that could help a bit.
Best,
dan,

Click to expand...

FML...you should never switch pin 1 and 2 on xlr...noise is gone, only the tube crackles remain...will now leave the mic on for at least 24hours and decide if i need other tubes afterwards...

FML...you should never switch pin 1 and 2 on xlr..

Click to expand...

indeed,  ,
Best,
dAn,

and picture #2

This is an amazing microphone.  Well worth the time it takes to put it together. Thanks to Max, Ben, Tony, Erik, Chunger and everyone who has posted.  It made the build fun. There was no hum, hiss or crackling - just great sound I'm looking forward to recording.

Picture #1

this is how my mic sounds after 72 hours of burn-in....

https://www.dropbox.com/s/e2h89jsvwb5jgga/U47%20crackle.mp3

SKJGProject said:

this is how my mic sounds after 72 hours of burn-in....

https://www.dropbox.com/s/e2h89jsvwb5jgga/U47%20crackle.mp3

Click to expand...

Try other tubes, it's been posted and said before, crackling, wooshing or whatever afetr burnin is because of the tubes.
Buy some and check them out, btw these seem to be less and less available these days, i wonder why  :

Hi guys, I completed  my mic months ago. After the burning it started to work great using the couple of tubes with the Max's kit. After a few days pop and crackling started againg. I took a new couple of tubes and burned again but after few days I had the same problem... Any idea?
When it worked the sound was great, but now it's not usable.

thank you
Andrea

baol said:

Hi guys, I completed  my mic months ago. After the burning it started to work great using the couple of tubes with the Max's kit. After a few days pop and crackling started againg. I took a new couple of tubes and burned again but after few days I had the same problem... Any idea?
When it worked the sound was great, but now it's not usable.

thank you
Andrea

Click to expand...

It's the tubes. If all your voltages check out and the capsule is fine then its the tubes. I myself went through three pairs of tubes before I found happiness. What brand are you using?

check this

http://groupdiy.com/index.php?topic=53676.msg685078#msg685078

...If all your voltages check out and the capsule is fine then...

Click to expand...

so it could be the capsule too, how to exclude it and check if it's the faulty one?
Here's a sample of the noise (ignore the music and cars background).

https://skydrive.live.com/#cid=75105482BEC2CD23&id=75105482BEC2CD23%21105

As I said the tubes were burned for more than 5 days and they were definitely noiseless.
thank you

Andrea

hello,
some news about my 2 MK47,
I'm really happy with them, the mic placement is very important, more than any other mics I have!  it vary a lot between 2 positions, especially the low end,
I love them on sax, trumpet and even on some piano!
here is the frequency response using smaart7,
the 2 mics (mk47 and ref) were 2,5 meter in front of an L-acoustic MTD112,
the trace is the difference between the MK47 and an AUDIX TM1 PLUS test and measurement microphone (with correction curve),
(pink is cardio and green is omni)  this is the first mic (wich have the plexiglass spacer)


I also found that I prefer when the capsule is not to high in the headbasket (so i removed the plexiglass spacer of the equinox kit body approximatly 5 millimeters thickness )
(red is omni and blue is cardio) it's my second mic (the one without the plexiglass spacer)



edit : capsule are thiersh red line  and  tube are philips ECG  ,

soon i gonna remove the plexiglass spacer of my first mic.

Hi boys
Is there anyone who knows where to buy 6028 tubes at a reasonable price? I think I'll need a bucket of them to find the right pair.

thank you all

Andrea

Hi Andrea,

I have bought 10 Jan Philips 6028 for my mk47. First 2 tubes I tried where great no noise no popping. I haven't test the others but presume they are also good. If you are interested I can sell you 6 tubes (I keep 2 as spare).

Let me know!

RJ

One question, which impedance the mic has? I'm using a pre with a variable impedance (from 60 to 3k3 hom), is there a better setting or must I follow my ears?
One more question, is there a nice (I mean EASY) diy amplifier well suited for the mk47?

thank you

Ok, I'll try again with another question, even if it seems I haven't all that followers
Do you think it could be a good thing to clean up with isopropyl alcool the board and then put a protective laquer?
thank you.

Sorry i missed this question. The nominal impedance of 200 Ohm is the same as the original U47.
Since the High-Z section is build "in the air" with the glass insulators protective laquer is not required.

I think I haven't understood the reason (due to my immense electronic ignorance), but I take it as an axiom
thank you max and merry  christmas

SKJGProject said:

this is how my mic sounds after 72 hours of burn-in....

https://www.dropbox.com/s/e2h89jsvwb5jgga/U47%20crackle.mp3

Click to expand...

My mic sounded like this went thru mreey hell swapping components tubes ....... turned out to be the the heater dropper resitor......try another one.....

Hi,
after a 4 days no-stop test I do declare that I fixed every pop issues. I replaced the 1k5 resistor with a chassis mount one, and now everything seems to be ok.
merry christmas everybody!
Andrea