micaddict
Well-known member
Regarding the MK47 build, noise, as well as cracks and pops have been reported. But it doesn't have to be that way.
Here are four 6028s at work, at a not so close distance:
http://www.youtube.com/watch?v=xvKaHNFycj4
Measured VF14 characteristic
- Thread starter bezen4uk
- Start date
Help Support GroupDIY Audio Forum:
Regarding the MK47 build, noise, as well as cracks and pops have been reported. But it doesn't have to be that way.
Here are four 6028s at work, at a not so close distance:
http://www.youtube.com/watch?v=xvKaHNFycj4
nielsk
Well-known member
What about EF14?
Essentially the same tube as the VF14 but with a separate heater...
Essentially the same tube as the VF14 but with a separate heater...
micaddict
Well-known member
My pleasure, but I borrowed that clip from fellow member Erich (etiefenthaler). 
moamps
Well-known member
Hi,
I've done some measurements on steel tubes (incl. VF14) recently, as part of a larger U47 project, that you may find useful:
http://www.moxtone.com/mU47_U47_part3.html
Regards,
Milan
I've done some measurements on steel tubes (incl. VF14) recently, as part of a larger U47 project, that you may find useful:
http://www.moxtone.com/mU47_U47_part3.html
Regards,
Milan
marcus4audio
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Besides the distance is not so close, I must notice that noise is really high. It doesnt sound to me as the ideal setup for pure sound recording. Is the noise generated by tubes or preamplifier? Or it's background noise?micaddict said:
Melodeath00
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- Jun 7, 2012
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- 416
moamps said:
Milan, this is fantastic!! As you mention in the article, please do test the EF800 and EF802. I am incredibly curious how those stack up.
scott_humphrey
Well-known member
moamps said:
Great writing in your article! A very enjoyable read!
micaddict
Well-known member
It's a registration of classical music plus it's a live performance. In pop music you would do close miking. For classical, often an A/B pair is used, at some distance (and in omni to boot). This means more gain on the preamp (raising of electrical and background noise) plus the wider view will pick up noises that are not coming from the guitar. Like the typical breathing noises of the player as well as noises from the room, or church isn this case.
This recording is certainly no exception, but the actual microphones don't hit me as being noisy.
Bravo Milanemoamps said:
great reading and thanks for sharingmoamps
Well-known member
Hi,
First off, thanks for the positive feedback everybody. I'm truly glad the effort is appreciated.
I'm afraid this would take too much time that I currently just can't spare. But that's certainly something for my to-do list when things ease up a bit.
Ri changes considerably for the operating point area (at the knee of the output characteristic) shown in the article. The value Ri=11kOhm is just an approximation I got from the graphs, not the actual in-circuit measurement value. To get the precise Ri value, one should measure the specific tube in the actual circuit under actual conditions.
Regards,
Milan
First off, thanks for the positive feedback everybody. I'm truly glad the effort is appreciated.
Melodeath00 said:
I'm afraid this would take too much time that I currently just can't spare. But that's certainly something for my to-do list when things ease up a bit.
bezen4uk said:
Ri changes considerably for the operating point area (at the knee of the output characteristic) shown in the article. The value Ri=11kOhm is just an approximation I got from the graphs, not the actual in-circuit measurement value. To get the precise Ri value, one should measure the specific tube in the actual circuit under actual conditions.
Regards,
Milan
micaddict
Well-known member
Yeah, cool article!
Melodeath00
Well-known member
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moamps said:
Great!
Do these operating points really tell us anything about sound, or do they just help us pick a relatively linear operating point for a tube? Also, I noticed that the EF13 amplifies many more volts when the signal swings positive than when it swings negative. From what I understand, this significantly increases THD. The other tubes look much more even in that regard.
Also, can we really trust these tube graphs to be indicative of the tube in the actual circuit? Isn't the grid resistor in the mic a much higher value than is typical for these graphs, and that can throw things off, or have I misunderstood?
I am using an EF802 in my U47 right now. It's underheated to about 5.6V, and plate voltage is 50V. I wonder if I should adjust that plate voltage down with another resistor, or if that would also effect output impedance?
With EF12 tube you may just correct the mode a little bit. It is not necessary to use different x-former. Different anode resistor, different anode currenr, different operation point. And its very close to VF14 ( closer than EF14, inspite of diff. curves). Especially in highs and middle freq-s. I'm sure.
granger.frederic
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- May 22, 2010
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- 488
Dear o3misha,
you said that ef12 is the closest.
Do you have compared it with a real vf14M in a genuine U47 ?
Do you have some shootouts ?
regards
Fred
you said that ef12 is the closest.
Do you have compared it with a real vf14M in a genuine U47 ?
Do you have some shootouts ?
regards
Fred
Not in one mic, but with the same capsule. Yes I tried Ef12 tube in comparisson with EF14 and VF14. My 2 orig u47s with VF14s are different in sound, inspite of the same type of tubes ( all VF14s are different ). I made third microphone with Haufe BV08 x-former (which is the best copy of BV08 transformer today IMHO) and I tried EF 14 ( about 10 different tubes) and only 2 EF12K. IMHO EF12k is closer to VF14. It is still not the same with VF14 in lows, but it has very close behaviour in high and middle freq-s. But you have to correct anode resistor and anode feeding for EF12. It also operates better with higher anode current -1mA than VF14 (0.5mA). EF14 has much more highs and the sound is not soft even with very low filament voltage 4.5VDC-5VDC. The bass respones of EF14 is closer to VF14, but it has less dynamic in middle freqs. But some people like it. I prefer more soft sound with good dynamic in middle freqs. Flea, Andreas Grosser, Wagner prefer Ef12 as the best tube for U47 today. And I agree. I would upload files with EF12 tube, but unfortunately I already moded this mic with original VF14 tube.
scott_humphrey
Well-known member
al·che·my
ˈalkəmē/
noun
1. the medieval forerunner of chemistry, based on the supposed transformation of matter. It was concerned particularly with attempts to convert base metals (other tubes) into gold (VF14M).
ˈalkəmē/
noun
1. the medieval forerunner of chemistry, based on the supposed transformation of matter. It was concerned particularly with attempts to convert base metals (other tubes) into gold (VF14M).
1.There are no 100% identical lamps,scott_humphrey said:
2.there are obvious sonic properties that may be close in vastly different design lamps. I recommend to talk with the basics of tube circuitry those who are going to build microphones instead of copying scheme U47 calculated completely on another lamp. Or communicate with those who really understands this: Andreas Grosser, Gunter Wagner.
3.The V/A curves say nothing about K2, K3, K4 distortions, about real sound of the tubes.
IMHO
micaddict
Well-known member
That jives with what I heard in a U47 comparison (EF12 vs. VF14). From samples mind, not in the flesh. The mids and highs were very similar indeed, but the EF12 lacked some heft in the lows. Not something linear or easy to correct with EQ, though. It was most prominent in the onset of notes. Well, to my ears anyway.
But yes, if there's magic, it's usually in the mids.
