MK47 PCB tube mic kit - build thread

[Skylar]

Thermally conductive adhesive/epoxy should work fine. There are special adhesives made for this sort of thing. Google it.

Regarding pinouts:
If you're building both the mic and power supply it doesn't matter! It's up to you to decide whatever pinout you want! If you want the B+ voltage to be pin 4, then it's pin 4. Just make sure you stick to the same pinout for the mic and power supply.

 

[jrasia]

Thanks for all the responses fellas!  Greatly appreciated.

In regards to the pinout....I know I could technically wire it any way I want....but is there a standard?
I mean, what if I wanted to use an original u47 PSU or an aftermarket PSU for that matter? 
I know the PSU should deliver 105 VDC @ approx 55mA and thats about it.

I don't think I'll be building my own PSU as I don't have a means of etching my own PCB boards.

Can someone recommend an off the shelf PSU that has switchable patterns?  Beezneez, or Peluso?

 

[lonepariah]

Can someone recommend an off that shelf PSU that has switchable patterns?  Beezneez, or Peluso?

I am also interested in this. Any recommendations?

 

[imo]

the power supply is very easily built point to point(or with tag boards) you can get these at any place that sells amp building parts. I think it is helpful to build power supplies; a linear and easy way to understand circuit flow. Plus, if you need to change resistors you aren't burning traces in the process.
I think the U47 pinout is:
1- Signal-
2 signal +
3 ground
5 B+
6 pattern

Hope this helps
Ian

 

[david-p]

Whatever the pins used by the original U47, if you are using a vacuum tube amplifier I advise not following the same convention.  It appears to be a little-known fact that you could get an exciting electric shock if you plugged the Neumann U-47 mike into a cable that was already connected to a switched-on power supply.  This was because the HT pin mated before the ground pin. 

For instance, if you are using the Equinox body and the excellent 7-pin Binder connector, you will notice that pin 7 (the centre one) mates first.  To avoid the effect described above, this should be the ground connection.  Since the voltages you choose for your power supply are likely to be different from those used by Neumann, the choice of function for the rest of the pins is up to you.

David

 

[electrisizer]

hi need to replace one tube...

do you have a good source for germany?

do the tubes have to be a matched pair?

 

[monkey]

Whatever the pins used by the original U47, if you are using a vacuum tube amplifier I advise not following the same convention.  It appears to be a little-known fact that you could get an exciting electric shock if you plugged the Neumann U-47 mike into a cable that was already connected to a switched-on power supply.  This was because the HT pin mated before the ground pin. 

This isn't true: Neumann made pin 5 of the Tuchel connectors for U47/48, etc (carrying B+) is shorter than the rest for this very reason.

 

[david-p]

Whatever the pins used by the original U47, if you are using a vacuum tube amplifier I advise not following the same convention.  It appears to be a little-known fact that you could get an exciting electric shock if you plugged the Neumann U-47 mike into a cable that was already connected to a switched-on power supply.  This was because the HT pin mated before the ground pin. 

This isn't true: Neumann made pin 5 of the Tuchel connectors for U47/48, etc (carrying B+) is shorter than the rest for this very reason.

You make think that it is not true; but I write as one who has experienced the effect live -- with a microphone that may well have been manufactured earlier than the one you refer to...

David

 

[mad.ax]

Regarding the 'standard' pinout for the Binder connector, I suggest using the pinout of the Neumann mics using that same connector. KM253 & M250.
Just forget about pin4 (since you don't need heater voltage) and use pin 3 for switching the relay.
Axel

 

[mad.ax]

Can someone recommend an off that shelf PSU that has switchable patterns?  Beezneez, or Peluso?

I am also interested in this. Any recommendations?

If you mean switchable patterns as in omni/cardio selcted by a relay as in the MK47, there isn't any to my knowledge. DIY!
If you mean switchable patterns as the usual 9 positions switch or potentiometer, that won't work with the MK47.

Axel

 

[Benny]

Just finished my MK47 with Skylar body and Q47 capsule. It works perfectly from first powerup. No noise, hum, pops or whatever. It just sounds great. I'll let the tubes burn in now and start further testing tomorrow. Thanks to Max and Skylar for a great project.

 

[lonepariah]

Can someone recommend an off that shelf PSU that has switchable patterns?  Beezneez, or Peluso?

I am also interested in this. Any recommendations?

If you mean switchable patterns as in omni/cardio selcted by a relay as in the MK47, there isn't any to my knowledge. DIY!
If you mean switchable patterns as the usual 9 positions switch or potentiometer, that won't work with the MK47.

Axel

Thanks Max. Yes, I was referring to omni/cardioid.

Looks like I'm going to have to do some studying before I start my build...

Best,

Chris

 

[baadc0de]

I've done my first of two (finally got the cable sorted out) but nothing much happens on power noise.. I just get loads of hum and funny noises that differ if someone steps up to the mic or not, so I guess the outside world is influencing it a bit.

From what I read it could be a number of things.. from the 10nF styro to the big cap.. I'll measure some things up.. my B+ is at correct voltage, heaters power up..

 

[grantlack]

If your plan is to make a MK48 (sacrifice the omni patern to favor a figure 8 ) it's doable.
In the U47 the 2M/3M extract 60V from the 105V PSU in order to polarize the front of the capsule. If you'd polarize the back with 105V, you wouldn't get a real figure 8 pattern (cause you'd need 120V). So for the U48 they changed the voltage divider  to 3M/3M. That gives 52.5V to the front, and then 105V at the back is right.

Glad I asked, I was working from a non-original (and incorrect) document. Still should be a pretty simple adjustment, I'll give it a whirl once I get more familiar with the mics.

I've done my first of two (finally got the cable sorted out) but nothing much happens on power noise.. I just get loads of hum and funny noises that differ if someone steps up to the mic or not, so I guess the outside world is influencing it a bit.

From what I read it could be a number of things.. from the 10nF styro to the big cap.. I'll measure some things up.. my B+ is at correct voltage, heaters power up..

Have you fired up the psu without the mic and listened to audio output? Sounds like it's in the mic, but might as well rule out other things where you can.

 

[baadc0de]

Hey..

no, without the power supply the mic is ofcourse dead silent. The B+ comes to the mic at a healthy 100-105V.

This is what it sounds like, 21dB gain (result of normalization) in the DAW and my TC electronics preamp set at half gain, without the pad.
http://dl.dropbox.com/u/12679166/xx.mp3

I'm including this sample because it may help someone later or someone might remember something.. it's a power on cycle, so it starts silent and then ramps up.

 

[grantlack]

no, without the power supply the mic is ofcourse dead silent. The B+ comes to the mic at a healthy 100-105V.

seems silly on its face, yes, but if you were picking up hum in your audio signal from the power supply/cable it would likely still be audible even without the microphone attached.

the crackle sounds like my tubes did in my first mic before a good two days of burn-in, though mine was much more intermittent.  if you've already done a burn-in, have you double-checked your cable shield/chassis grounding?  i had an mkl-2500 with poor grounding, and the handling noise was similar to this.

 

[baadc0de]

I've actually missed a link from tube grid to front capsule.. I can hear myself now faintly within all the noise (which is still much louder than the signal) but at least something is happening. Gotcha on the cable thing, just never happened to me before. Also, no burn in performed here yet.. but I'm confused about the really low signal from the mic, I thoughtI should resolve that first before I have the guts to leave the mic on for more than a few minutes..

 

[baadc0de]

Also, I measured DC between the front and backplate or the back and backplate and it was like 4.7Volts both cases... isn't that very very low? Or is this measured differently?

 

[grantlack]

could it be that one leg of your audio is disconnected or shorted to ground?  my output was crazy low when i made that goof, and it was more like a noise to signal ratio than the right way around.

not entirely sure on the capsule voltage, hi-z does funny things to multimeters.

 

[baadc0de]

well, touche..

the A+ and A- leads were reversed.. I somehow assumed that the righ hand one was A+ but it is actually A-.. though that didn't fix much. The level is still very very low and I seem to have a grounding issue. The buzz/hum is mostly 60hz harmonics and a lot of them go away if I touch the binder connector and the pattern switch.

Is the power supply (I used zayance's PCB version) supposed to connect to ground at the 0V output? I have it setup that way, so pin1 from 3-pin XLR, pin1 from 7-pin XLR and the 0V from power supply are all going to ground and at the other end of the cable, that's going to the B- connection. The PCB inside the mic isn't connected to the body with anything metal.. is that a problem?