MK7 - tube mic project

[julien31]

Thanks a lot, I'm gonna try it ASAP.

 

[mad.ax]

What Rodabod said, but let's be more precise about the coupling capacitor... There's indeed a 1nF cap in the MK7, but it is used to couple the back membrane with the front one. The front is direct coupled to the grid just like in a U47.

You can use it for testing purpose thought. Disconnect the two leads coming from the capsule at the points marked 'capsule front' and 'capsule rear'. Then attach your generator 'hot' to the 'capsule rear' side of the 1nF.

Axel

 

[EEMO1]

I finally got my mic working.

after building, re-building the psu for like 3 times, building the
heater section a couple of times, taking a break from the whole mic,
getting the psu voltages right, no sound, replacing caps... Im finally
finished. Through the whole process I even started to question my
building skills. Yeah, It kicked my nuts alright.

the problem the whole time was the tube mount. the metal has a slight
concave so the ground points were actually not grounded from the
tabs/screws above. fixing that with some spacers and adjusting the
voltages back up... BAM, it works! very small noise from the tube, but
nothing I can't live with. no hum nothing. beautiful! I feel really
stupid of course, why did it take so long for me to catch that...
*"@!$...

thanks max, you're the best!

 

[Sredna]

What kind of noice do you have?

Often youll have to go through a couple of tubes to find a quiet one,
just make shure to burn in the tube for at least 24 h.

What tube do you use?

 

[EEMO1]

I think I have about 15 ef86 tubes to try. philips miniwatts, valvos and the type that emperor suggested... I think im good.

 

[EEMO1]

so... got to do some vocal recordings with the mk7... compared to my g7 that sounds fabulous, the mk7 is pretty honky. got 2 different male vocals, the other one was almost annoying...


any ideas on how to look into this?

 

[Kingston]

any ideas on how to look into this?

It's most likely not the amp, which should be very flat, with the exception of the output coupling cap which controls your bass extension. But that one is a 1st order high-pass filter. would not contribute to "honk" unless you have a far too small cap and you'd have no bass either.

So the most obvious culprit is the mic body, and the metalwork in general. Is that a donor body? Did you ever compare the original (china?) circuit to your G7. You would have most likely noticed the "honk" there as well.

Next culprit would be a broken/maladjusted capsule.

 

[ioaudio]

eem01,

which capsule is in use?
output capacitor?

should not honk.

-max

 

[pasarski]

Moi Eemo, is it a T.Bone t.bone SCT700 body? I have a mic made in that body and I find it a little honky, there's a bump at about 1.2khz and something weird below and above also IIRC. I've started to think it's because how the plate holding the capsule is assembled. There's lot of open area in the sides that let's the sound get in to the cavity below and back up. The stock metal plate also sits above the grill's edge so there's a direct way for sound to travel to the cavity. I'm thinking of glueing a fat rubber band or something inside the grill to separate the capsule daprtment from the "echo chamber" below.

 

[EEMO1]

hey,


max,

it's a dale m7, output cap is the default cap that you suggest. haven't had the time yet to test other caps out...


for the other recording I did, the sound was spot on. on the first one... honky. I also recorded some snare hits to see a little bit of the transients etc. sound was spot on with that one.

kingston & pasarski,

it's indeed the t.bone sct700. I have a spare dale m7... maybe i'll test that one out just in case.


-eemo

 

[gary o]

Julian31 did you sort your mic out ? I had similar problem but with a MK47 turned out to be my own silly fault , I had a cap connected to wrong side of resistor all soted now sounds great ! best of luck to you.....

 

[barney]

Finally finished one of my MK7 with Beezneez K7 capsule.  Wow. Still early days but it definitely sounds good.  Sound comments now so take as you will - kinda vintage sounding, rolled off in the top, but really sits in the mix.  This was with my own voice and a male artist and ac guitar.  Yet to try it on female vox.  Now need to finish another mk7 and mk47.

Thanks Max for sharing.

 

[EEMO1]

ok, got rid of the honkiness.

I made a small disk out of thin but not so fluffy foam, that I attached to the top of the metal plate that holds the capsule mount. so... no more open cavity to the whole body (t.bone).

Also, I double checked and adjusted the voltages after changing and selecting tubes.


did a couple of runs recording acoustic guitar. sounds sweet!


I guess if you want to use the t.bone donor body, you need to close off the basket from the rest of the body. I have a plan in mind for my mk47 build, but more on that later.  bought another t.bone sct700 without the 7-pin cable for 20€.

 

[tmuikku]

ok, got rid of the honkiness.

I made a small disk out of thin but not so fluffy foam, that I attached to the top of the metal plate that holds the capsule mount. so... no more open cavity to the whole body (t.bone).
...

Sounds easy task, do you happen to have any pictures? I've got sct700 body as well and I wan't to try a quick fix before Skylar bodies arrive. Did you try any other materials? Do you think anything works there ( for example "sinitarra", I don't know the english term )?

ps. congratulations for cheap donor body

 

[EEMO1]

hey,

I would imagine anything goes. sorry, don't have any pics.


I chose foam, since you need to stuff the foam disk through from a smaller hole (the head basket) than the foam disk itself. didn't want to put anything near the tube or the high impedance section i case of heat/noise etc.

 

[buschfsu]

Anyone compare an mk7 to the mk47?

 

[matta]

Hi Guys,

I'm looking for a bit of help and thought it best to post here instead on in the Black Market as it is directly related to the MK7 project.

Being on the *** end of Africa getting the polystyrene/styroflex caps are near impossible and was wondering is by chance any of you bought extra stock I could buy off you?

Just looking for:

1 x 10nF 160V styroflex
1 x 1nF 160V styroflex

I'll pay the costs of the parts and international shipping if you do.

Thanks in advance!

Matt

 

[Apache5]

Hi, I can send these two if you want. I PM you

Arnau

 

[matta]

Thanks Arnau,

I've replied to your PM, thanks!

Cheers

Matt

Hi, I can send these two if you want. I PM you

Arnau

 

[plumsolly]

I finally got my Mk7 up and running in one of Skyler’s bodies! I am using an ef86 and one of Dale’s capsules. In initial tests, it sounds fantastic – I am really excited! No problems with noise of any kind.

I am using Max’s passive power supply design with the custom Edcor PT I have lower B+ and heater voltages than I’d like. I can only get the heater voltage at the tube up to 5.3vdc, even with the pot shorted. I have 11.7vac at the secondary of the PT, but only 11.97vdc after the rectifier. I am using 4.7 ohms for the first R after the rectifier. My line voltage is about 116.5vac.

I am having a similar problem with the B+: 157vac out of the PT, but only 202vdc at the output of the rectifier and 139vdc at the output of the PS.

Any thoughts on raising these voltages?

Thanks and best, Ben