MK47 PCB tube mic kit - build thread

[Phrazemaster]

The Heisermann capsule is very highly regarded around here, although I've not used it.

eBay could be OK for tubes if you plan on getting a bunch and testing them; same with other retailers.

I'm a fan of Bowie's tubes (Chris Whitmore) because he tests them each before you buy them. If that interests you then you can PM here on the forum and he'll hook you up. You'll pay more through him, but you'll get better tubes and stellar service.

No he doesn't give me kickbacks; I'm a satisfied customer.

 

[guisquil]

Do I need to buy the Holder STS 7 to use the Thiersch STW7 blue line with this kit?

Thanks

 

[burglar]

Hi Folks,

I did the first vocal session with my MK47 the other day.  Noise performance I think is great, it's really quiet.  I'm using a BeesNeez M7 and Jan Philips 6028 tubes.  I know with no context, listening to and critiquing the voicing of a microphone is impossible but I felt on the day I was expecting more low end and a more "lush" sound.  It felt a little bright and hard in the mid / upper mid.  The singer was quite strident in the mid range however and tended to roam at the top of his register, but I thought I'd post a snippet to see if this is consistent with what you would expect from your MK47 on a fairly aggressive vocal such as this.

I have to say, listening today, I feel differently about the sound of the vocal.  I think the mic has done a good job of smoothing what could have potentially been quite a harsh recording.  Anyway, would be great to get some feedback.

Vocal chain:  MK47 - Sound Skulptor MP73 - Antelope Orion 32........

https://www.mediafire.com/?b2fh25bxeelb32u 

B

 

[micaddict]

  Has the guy calmed down a bit now?

I hope you're not going to shoot me for saying this, but I don't think any mic will return much low end and lushness with a vocalist in this state.

 

[burglar]

ha ha, I know what you mean micaddict, he was a character both on and off the mic

we'd spent the day cutting quite gooey drums and guitars with lots of low frequency information and I think the vocal just took me by surprise TBH.  I was expecting more body. 

 

[micaddict]

Hey, but I like samples of built microphones.
We need more of that.

And assuming the song was three minutes or so, was it all like this or was this the um ... climax, so to speak? In the latter case it might be worthwile to hear what came before (and maybe after) it.

 

[burglar]

Ha ha, that was the opening verse of the first song )

There are some lower register phrases.  Here's a snippet:

https://www.mediafire.com/?hmnp8d80v9is5ym

I listen to this and it just seems a little hard in the mid range and not very forgiving.  I've worked with BeesNeez and Flea 47's before.  Having heard him cutting monitor vocals through a 58 all day I know what I was expecting, or hoping to hear from his voice, and this just wasn't it.  It sits in the mix lovely and it takes processing really very well, it's just not what I was expecting.

Perhaps I ought to try some GE tubes as some have said the Jan Philips are a tad harder with less lows?  Anyone with experience here feel free to chime in.  Otherwise maybe a Blue Line is in my future.... 

 

[micaddict]

Thanks for the second clip.
Mid forward for sure, but as a pop vocal in a mix it should work.
Some vocals actually do work better with an SM58. And that's a mic you can "eat".
How far was he off the MK47?
And was he in a booth?

 

[burglar]

He was about 8 inches off the grill and he was in a booth so to speak.  I have a series of 8x4ft acoustic panels, filled with 2" rockwool and covered in felt, he was singing into two of these in an apex configuration with 4" rockwool covering the wall behind him so the space was fairly dead for sure.  This is where I cut most of my vocals so I am familiar with how the space sounds with my other mics.  It's not a small area and I don't ever find it to have the honky mid problems associated with small booths. 

The mic's sound is very workable and I could see it being a good tool for certain applications its just I'm wondering whether everything is ok here cuz it's not what I would expect from a U47 clone.  I was expecting more enhanced and large low mids and really a smoother top end.  That said I have barely used this mic other than the 24 hour burn in i did on the tubes.  I don't know if the capsule needs bedding in??

 

[micaddict]

I think I would bring him a little closer to the mic and/or back off the acoustic panels a bit.
And for proximity effect the 47 should be in cardioid of course.

I don't know what our overseas friends will add while I'm asleep, but if need be I'll elaborate on the nature of the beast tomorrow.

 

[burglar]

I'll try working the proximity more next time.  perhaps it was just the nature of his voice. 

I'd be really interested to hear other peoples finding with regard to the BeesNeez M7 and other tube brands.  I can't find any GE or RCA here in the UK.  If anyone has any which they'd be up for selling make yourself known!

 

[micaddict]

I was going to elaborate on the sound signature of a good U47, by itself, and when compared to an M49 and a U67 (the latter usually works better on rock vocals BTW and IMO). But since you've worked with a Flea U47, I think you've got a pretty good idea. No VF14 in that one, but it is in the ball park.

BeesNeez M7 should be a very good one and in case there's something not up to spec with it, Ben will do you good. Although it doesn't have "thick" PVC, it is tuned to sound like the original, so it could be a little darker on top than their K47 variants.
Did you try a cheap Chinese K47 first? Not that that would be better of course , but having heard two capsules in the same mic gives you a better picture of the rest, if that makes sense.

The Jan Philips seem less problematic than most others, but some have said they found them a little hard sounding. Not on my voice, but I haven't sung through RCA and GE. Before-and-after-shootouts would be welcome. The trouble with the alternatives seems to be that most are either noisy or microphonic (or both).
Also, the Jan Philips is a quality, glass vacuum tube and it was made in America decades ago. How much hardness could such animals add to a microphone circuit?
BTW to my ears an original U47 sounds "harder" than an original M49. Apples and oranges to some extent, but not as much we might think.

Anyway, with matters like these it's always nice to have a reference.
The first question would be:"Does my MK47 sound like it should?" Since the kit comes without a capsule, there's no one answer, of course. But by now maybe we could or should have a better picture than we have. This thread was started in 2010.

The second question could be:"How does a MK47 compare to a real U47?" Even examples of the latter will vary BTW. But have we seen any shootouts between the two? It would make sense IMO. The MK47 is not just a DIY microphone. It was designed to be like a U47 and it can even use the vintage PSU.
So, did anyone see such a shootout? I've been on a sabbatical, so I might have missed it.

The third question could be:"How does the MK47 compare to the MK-U47?" The first was designed to fit in the short body GT-2B. The second was designed for the classic long body and consequently can house bigger parts. Max will correct me where and if I'm wrong, but I expect the full BV8 to extend a bit in the sub bass range. Also, I expect it to have a somewhat different behavior dynamically. And that's something which doesn't show in standard frequency plots.
So a shootout between the MK47 and the MK-U47 woud be a nice thing, too IMO. And this is something Max could do or organize himself. 
Or did I miss that one, too?

 

[ln76d]

The Jan Philips seem less problematic than most others, but some have said they found them a little hard sounding.

Does any of those which said that they found a little hard sounding Jan Philips attempted to make any measurement of  voltages inside microphone? Or everyone just treat a piar of 6028/408a (from various manufacturers)  as an drop in replacement for VF14?

 

[burglar]

I was going to elaborate on the sound signature of a good U47, by itself, and when compared to an M49 and a U67 (the latter usually works better on rock vocals BTW and IMO). But since you've worked with a Flea U47, I think you've got a pretty good idea. No VF14 in that one, but it is in the ball park.

BeesNeez M7 should be a very good one and in case there's something not up to spec with it, Ben will do you good. Although it doesn't have "thick" PVC, it is tuned to sound like the original, so it could be a little darker on top than their K47 variants.
Did you try a cheap Chinese K47 first? Not that that would be better of course , but having heard two capsules in the same mic gives you a better picture of the rest, if that makes sense.

The Jan Philips seem less problematic than most others, but some have said they found them a little hard sounding. Not on my voice, but I haven't sung through RCA and GE. Before-and-after-shootouts would be welcome. The trouble with the alternatives seems to be that most are either noisy or microphonic (or both).
Also, the Jan Philips is a quality, glass vacuum tube and it was made in America decades ago. How much hardness could such animals add to a microphone circuit?
BTW to my ears an original U47 sounds "harder" than an original M49. Apples and oranges to some extent, but not as much we might think.

Anyway, with matters like these it's always nice to have a reference.
The first question would be:"Does my MK47 sound like it should?" Since the kit comes without a capsule, there's no one answer, of course. But by now maybe we could or should have a better picture than we have. This thread was started in 2010.

The second question could be:"How does a MK47 compare to a real U47?" Even examples of the latter will vary BTW. But have we seen any shootouts between the two? It would make sense IMO. The MK47 is not just a DIY microphone. It was designed to be like a U47 and it can even use the vintage PSU.
So, did anyone see such a shootout? I've been on a sabbatical, so I might have missed it.

The third question could be:"How does the MK47 compare to the MK-U47?" The first was designed to fit in the short body GT-2B. The second was designed for the classic long body and consequently can house bigger parts. Max will correct me where and if I'm wrong, but I expect the full BV8 to extend a bit in the sub bass range. Also, I expect it to have a somewhat different behavior dynamically. And that's something which doesn't show in standard frequency plots.
So a shootout between the MK47 and the MK-U47 woud be a nice thing, too IMO. And this is something Max could do or organize himself. 
Or did I miss that one, too?

Thanks for your post micaddict,

I powered my mic up for the first time with a Chinese K67, it sounded good, lots of low end and a very full sound.  Again, not what I would expect from a U47 but not lacking in low frequency.  It sounded rich but a little excited in the top end, which I would expect from a K67 in a circuit with no high frequency de-emphasis. 

I'm going to get an RK-47 from microphone parts to try in place of the M7, as well as some GE tubes.  I will report back with my findings.....

 

[burglar]

Ok so,

I installed GE 408a's and it's a different mic!  Loads more low end.  It is such an improvement i think the Jan pair must have been defective.  Anyhow, happy chappy

 

[micaddict]

Thanks for the update!

 

[ln76d]

Does anyone get 34V at the plate?
Could someone check for me what's the voltage at the 100K when it's disconnected from the plate when the tubes are in the circuit? I'll be much thankfull

 

[JW]

Is 34V at the plate what you're getting? That is exactly what is specified in the U47 schematic. I haven't tried disconnecting the 100K resistor as the mic is complete, but fwiw I did get one 100K in the kit that was quite a bit off. From memory I think it measured something like 82K.

 

[JW]

I wonder if someone can help me understand what I'm measuring here.

I have two of these MK47's that I built.

Here are the voltages I'm measuring

Mic 1:
Heater at tube 1:    18.4V
Heater at tube 2:    17.0V
Voltage at the plate before the output cap 51V
Voltage between the 2M and 3M resistors: 56V

Mic 2:
Heater at tube 1:  16.4V
Heater at tube 2: 17.9V
Voltage at the plate before the output cap: 50.5V
Voltage between 2M and 3M resistors: 55V

The U47 specifies 34V at the plate, so am I high, or is this typical with the 2X 6028 tubes?

Also, the U47 specifies 63V at the capsule. If I measure at the capsule after the 100M resistor, I'm getting 5.8V. I'm guessing this is unreliable because of the High impedance at this point? The voltage I listed as 55V between the 2M an 3M resistors comes right prior to the 100M. Is this too low or is it again, unreliable because the impedance is still too high?

Are the heaters okay? Total heater voltage for both tubes (in both mics) is a good amount less than 40V, (20+20 for both 6028's)

 

[ln76d]

Yes, it's typical for 6028 - i don't know how those tubes can be considered as related to VF14.
Specs are different. Good that many folks like it, but is it anyway close to U47?
You readings are fine for 6028. There 's no option to get real U47 specs here.
For plate is correct, for polarisation - yes your multimeter input impedance is too low, for heaters - it should be a little underheating. 40V was a big underheating for VF14. To get similar result (in theory of course) for 6028 you should get around 13-14V I doubt that these tubes can work with that low heater voltage.