MK7 - tube mic project

[Kingston]

Interesting. Who sells these PIO caps in the USA?

m.

ebay

 

[Skylar]

How are you doing with the mic body project?

Check out the thread. We're moving right along, but a couple months behind schedule now!

 

[tardishead]

Well I had the chance to test my MK7 against an original U47 in a vocal session. And it holds up really really well. In fact on this occasion we went with the sound of the MK7. The U47 sounded a little too pushed whereas the MK7 was so smooth. I thought that maybe the U47 tube was biased a little on the hot side perhaps. Anyway I am really pleased with my mic - I highly recommend this design.

 

[desol]

Skylar, that looks awesome!! ...and thanks for the heads up on the caps!
Interesting...

 

[0dbfs]

I am going to try a quick p-to-p mk7 with self bias and a Bulldog T49 (TAB's lower cost BV11 style) with a PF86 on an Apex 460 while I anticipate the coming of Skylar's EQU47's and hold off on the full mk7 kit, DIY PSU, fixed bias, Dale's M7, lewilson's holder, etc

The documentation and elsewhere in this thread states using a 2.2k cathode to gnd for self bias. Is there no need for a bypass cap (i'll try it in any case but was wondering about original intent)? Will 2.2k work out for a PF86 as well as an EF86 using self bias?

Thanks!

-jonathan

 

[ioaudio]

yes 2.2k is a good starting point and works with both ef86 and pf86.
you can add a bypass cap to get a little more gain.

tardishead - thanks for the great review!

-max

 

[0dbfs]

Hey Max,

Thanks! Finished this one up today and it sounds great from my first impressions. That's with a stock Apex 460 capsule, 2.2k self bias resistor, no bypass cap, a different transformer (TAB T49), a PF86, and some generic caps in place of the styroflex + output cap. I've got another 460 and T49 that I'm going to set up like this. I'll have to order some additional parts to get the fixed bias going but I am really happy about this right now.

The heater in my PF86 is running at 5.7V with self bias. I'll have to drop it a little more to get to the recommended 4.7.

Now I really can't wait to finish up my two mk7 kits.

Thanks!

Best,
jonathan

 

[rodabod]

The heater in my PF86 is running at 5.7V with self bias. I'll have to drop it a little more to get to the recommended 4.7.

That's cooking. Be careful...

 

[0dbfs]

I added a series 2.4R 2W and it's dead on 4.70 now.

I've got a handful of wirewound clarostat pots that are low R values and high wattage so they helped me determine the required value in this case.

Best,
jonathan

 

[zebra50]

Just finished my EF12 version of this - needs a couple of *tweaks*, but sounding pretty fncking good already. Will get some pix up soon.

 

[starfish]

After over a year of staring at my mk7 kit, I got a donor body thurs(hdw) and just finished the mic.
Using a modded china supply, dale capsule. Fixed bias. Got the heater close enough to test by tweaking resistors - 7.3v after 2.2r in mic - the regulator only adjusts .1 volt either way(?).

Disconnected shield at mic and ran XLR grounds to board instead of XLR jacks. No hum. Fairly quiet with 1st tube I tried. Still need to tweak a little, but my first impression is that this is my new favorite mic!

Thanks to max and everyone,

I musta read this thread a half a dozen times.

 

[starfish]

Trying to figure out my B+. I have 146v entering the mic, 132v after the 20k(18k actually), but only 43v at the spot marked 60v on the schematic. Any ideas?

 

[ioaudio]

likely just a measuring error (your DMM has a input impedance of ~2megOhm)

 

[starfish]

Thanks

I also am getting .1 volt on the chassis(ground) in the mic. I thought maybe the capsule was leaking through the (thiersch) mount. I put a layer of circuit board on each side where the mount attaches, but no difference. Leaky capacitor? 10nf?

Mic sounds very good and is quiet enough to use, but ?

 

[snipsnip]

Hi Max... Do you have any plans to run another batch of kits? Im guessing a few people might want to stick them in the Skylar bodies?

Thanks
Jake

 

[tommypiper]

Just finished my EF12 version of this - needs a couple of *tweaks*, but sounding pretty fncking good already. Will get some pix up soon.

Looking forward to your pix.  What version EF12 did you use and what schematic?  cheers.

 

[riggler]

Skylar:

I was asking about the housing around the transformer in your mic. What is that.

+1 about the PIO caps. Made a difference in my G9 preamp believe it or not!

Can you provide a part number on the capsule pins / sockets you used?
Those ROCK!

 

[Skylar]

Skylar:

I was asking about the housing around the transformer in your mic. What is that.

+1 about the PIO caps. Made a difference in my G9 preamp believe it or not!

Can you provide a part number on the capsule pins / sockets you used?
Those ROCK!

The transformer is housed inside a mu-metal can; it's sealed in there at the factory (Altran), so I don't know if you can get it separately.
[If you're looking for a good microphone transformer, try Jeff & Ed's 2622 in reverse.]

I don't have the part numbers for the pins/sockets on hand right now.
I've used several different types of pin-and-socket combos during my tube-mic-building-phase of the past few months.
Check out Harwin or Mill-Max on Mouser.
I bought a ton of different Harwin pins/sockets, as they are a little less expensive compared to Mill-Max.

 

[Skylar]

Wait a sec!

I was thinking about a totally different mic!

Yeah, the MK7 has Max's transformer on the PCB.
Right below it, I've got a PIO capacitor...I think that's what you're talking about, riggler.


Now, what I was mentioning in my previous post was this mic, where I've used the 2622 in mu-metal can.



Sorry for the confusion.

 

[riggler]

Man I feel like a moron. You're right Skylar! I was looking at that capacitor. Should have thought "only 2 big terminals"...