MK47 PCB tube mic kit - build thread

Hi Guys

Finished mine, First test , Just a big Hum
once fixed the ground problem,
sounds awesome .... ( almost )
I have a problem :
the output level is quite low !!!
I have to push the gain really up to get something ( but it sounds good ! )

my PSU voltage is fine
what else can I Check ?

another question :
is there a side on the beez neez capsule ? ( I mean it only depends on how it is wired and any side can be the front or what ??? )


Thanks

yes any side can be front

Thanks
and what about the low Output level ? anybody has an idea ?

madreza said:

Thanks
and what about the low Output level ? anybody has an idea ?

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in the thread:

Just finished building up one of these, but the output level seems really low.  Any ideas?  What mic should I compare it to as far as output level?
Thanks in advance!
Best,
Bruno2000

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Problem was with transformer connections.  Both work great now.
Just FYI, the output seems to be a few dB hotter than a U87, but more natural sounding.
Best,
Bruno2000

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Maybe same problem?

Hi Max...  I was wondering if it would be possible to add a "rumble filter" to this circuit. I looked at the U67 and U87 schematics but don't quite understand how to do it.  What are the implications using a HP filter before the amp? It seems quite delicate up there...

b

I think I just about throw the towel in .....I simply cannot stop this mic from cracking & popping ....I bought 10  nos tubes but still pops with those I replaced all the caps, powers supply is silent with other mics....I thought I solved it after cleaning the board & components one more time the noises stopped for a good while, last night I sat working for hours on the PC listening to the mic for noises silence was golden, yet today I record 1 verse of a song & its starts & doesnt stop! I give up....

Question is the transformer ratio the same as a real BV8 & was that 12:1 ? Im thinking of using this tranformer for another mic C12 style or Royer I wonder if would work....

Thanks

Hi gary o... maybe if you posted photos someone would see something... the capsule, the top bits, the replaced caps. Which capsule and body are you using?

You said the crackling started when you began to use it. Is the crackling triggered by sound?

Also, how were you able to test the power supply with other mics?

I get a brief bit of crackling as it warms up but then it becomes stable. I have a second MK47 ready to swap in when I find the time. I absolutely love this mic. It seems a shame to give up on it. 

Thanks bobine ...The cracks are not triggered by sound..... they seem totally random, they can start at any time I have had hours of silence, hours of silence with one or two cracks, Ive hours of cracking & nothing else....

The noises can be fairly quiet but more so really violent & often in sustained attacks as if dragging the HT lead all over the circuit sounds terrible.

I had a tech friend check over the mic & solder joints & also the power supply he found nothing wrong I suggested it could be a capacitor......I have already replaced the 3 capacitors, the small first died....the paper oils smell strange & seems to ooze a little oil I guess... also was getting warm.....I thought this was my problem but no....I replaced the other 1 uf anyway

The power supply I made I can produce 120V via switch I use it to power AKG C28A & a SP TB1(C12 ish) I made from scratch.....

The MK47 is in a large metal can for now not a real mic casing I have a violet vin 67 lollypop fitted I have also tried a lomo lollypop a Oktava MK101 head, ADK Vienna head & a RK47 capsule with solid tube grill......I have other expimental mics made this way SP Tb1, Ela M250, sony C37A, G7 havent had a single crackle from any of them.....

Sadly its gettiing messy where i have swapped components so many times now ......my best spell of silence came after spraying switch cleaner over board & components & cleaning with cotton bud......but this even could be coincedence ....the pops came back I clean again & so on....

I had to leave the thing alone for now as I will break it the next time it cracks.. Iv took the lolly off it and disconnected it from the PSU as it was hard wired.....If i get inspiration and patience I might have another go.......I might just take it completly apart and re assemble point to point like my other mics....next time I order from farnell I will order knew resistors......

last night I made a very quick royer circuit point to point worked first go no pops & crackles

when building my first G7 i had the same problem .
(i build it on pertinax perfboard though )
the crackling just wouldn´t stop.and was about to throw the f****ing thing into the trash.
i got a can of this and use it since then with best results.
  http://at.rs-online.com/web/p/reinigungsfluessigkeiten/4586980/
(sorry don´t have an english link here , this is actually a destinated pcb cleaner.)
(the G7 never worked on pertinax though )
maybe your cleaner leaves residue on the pcb ?
you made sure to clean the brown pieces of flux , they don´t come off with cleaner and cotton buds ?
(i dont´use Q-tips , they tear up , i use old toothbrushes)

since then all my G7´s and the Mk47 worked from the start without any popping or crackling.

Any ideas on the source of this sharp spike at 8165hz? There is a larger spike an octave above (and perhaps the hint of one around 4khz). Could these be lower harmonics of much a higher frequency oscillation?
This is the MK47 (BN capsule) by itself in a closed room. You can also see why I'm interested in a rumble filter. :-\ 


EDIT:  I just did some more tests and ruled out the microphone! Looking at the power supply, now.

Hey Gary O,

I had an issue that sounds just like the issue that you are having. In mine I swapped out the 1k5 5 watt resistor. The one that shipped with the kit was bad. I have not had a single pop since!  It took me forever to figure this out but it works now.

This mic is so so great. Don't give up on it.

Andy

Well thanks guys for all your kind advice you did inspire me......Nashkato I did throw mine in the trash silly & costly i know but felt good for about 5 seconds.......after trying the transformer in a quick royer mic I made in protest to the cracking, I scooped up the pieces.......The 10nf cap was broke it was the second one I replaced that....I resoldered a few joints agian & cleaned as I went....Andy the 1K5 had come off so I left it off I connected 2 x 680 R & a 150R high wattage resistors together to make well 1510R it was what was laying around.....put it all back in the case connected lollypop head....

and.......No pops crackles.......but Im not gonna hold my breath.....thanks for the help.....

bobine what powers supply do you use.....

Thanks once again...

Hi,

speech sample male voice.

for reference schoeps mk4 cardioid

http://flutemusic.ch/schoepsmk4sprache.wav

Max mk47 with AKG ck12 delrin capsule

http://flutemusic.ch/U47testsprache.wav

Recording chain: dav preamp - mytek 8x192 converter - reaper


sorry- my doughter was practicing the cello downstairs.


Erich T.

I've been thinking that a U48 configuration (w/ Fig 8 instead of omni) might be more useful to me than a U47. The only real difference between the circuits is that the 48 has a 1nf cap between the switch and back diaphragm, a couple 150M resisters (with a 10nf cap to ground in between) feeding back to the 1k5 (1k7 on a real 47/48) heater dropper resistor.

This seems like it would be a straightforward mod. Is there something I'm not considering? The only part that seems like it could be problematic is that it would mean running a wire around the top pcb down to the heater resistor. Would that introduce interference or something?

Assuming it's doable at all, it would also be nice to be able to switch between omni and fig 8, which would probably have to be an internal switch, but would be less of a hassle if you decided you really needed the other pattern than just not having it.

Thoughts?

some voice recordings made with MK47 with Dale M7.
soundcloud

I'm sourcing a potentiometer for the power supply. Are these specs OK?

Max. operating voltage: 120V
Breakdown voltage: 200V

Thanks in advance,
baadc0de.

baadc0de said:

I'm sourcing a potentiometer for the power supply. Are these specs OK?

Max. operating voltage: 120V
Breakdown voltage: 200V

Thanks in advance,
baadc0de.

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http://www.tube-town.net/ttstore/product_info.php/info/p4385_Rheostat-Alpha-1-kOhm---5-Watt.html

baadc0de said:

I'm sourcing a potentiometer for the power supply. Are these specs OK?

Max. operating voltage: 120V
Breakdown voltage: 200V

Thanks in advance,
baadc0de.

Click to expand...

The one I used was 5 watts 500 volts.  From Mouser, CTS part #:  026TB32R501B1A1

Sold out.

lonepariah said:

Hi everyone! Although I have been soaking up the wealth of information here for months, this is my first post. I am very interested in buying an Mk47 kit. Does anyone know if they are currently in stock for purchase? I tried emailing Max from io audio, but he did not reply and I don't want to bother him if they are sold out. If that is the case, I definitely want to get in line!

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There's a thread in the White Market where you should post your interest.  At this time, he's sold out but trying to get an idea of interest before moving ahead with the next production run.

Cheers,
--
Don