U47 with Phaedrus VF14 M tube

[abbey road d enfer]

May I quote myself?

Sure!

And what I can say is that the two VF14s I analyzed were almost identical in terms of parameters.

Thanks for making that clear.

 

[tomas.borgstrom]

I really don't know mate, but I would prefer to have a tube in an U47 (than any solid state circuit) even if it behaved a little different than the VF14M.
To be honest I really don't care about the VF14M, that tube is long gone, the best tube for an U47 mic is one that still exists in the present whatever that is.

People need to forget and bury the VF14 for good, it doesn't exist and will not exist again, don't make it ghost, we should move on an accept the U47 with different tubes.

I agree. All the solid state tube replacements I've heard sound more firm and tight in the low end and not as smooth in the high end.

 

[tomas.borgstrom]

I have a mint VF14M and I have seven VF14 (not M) in my shop at the moment. Neumann must have had some very strict criteria when they selected them. All healthy VF14 I've heard sound as they should (at least to my ears) and they are low in noise. If they are worn out the plate voltage drops, they loose bass and they get noisy.

 

[oscarhuang]

I agree. All the solid state tube replacements I've heard sound more firm and tight in the low end and not as smooth in the high end.

That’s what I try to say. Even compared to the EF800. Lack of that bass and airy feel. I hope my English describe is right this time.

 

[Big Valley Audio]

Just to add to the mix. And I will preface this by saying I don’t have test measurements to back this up so I apologize in advance and if this idea infuriates you then please skip the rest of my post and continue yelling at clouds………

I did tests with an original Neumann U47 mic using the original VF14M that was in the mic, a modern Telefunken VF14K and a Phaedrus VF14M tube and I found the Phaedrus to be closer to the original than the modern Telefunken which I found to be too harsh surprisingly.

In blind tests ( all engineers I asked to listen ) also came to that same conclusion.

*This must be what poking a bear feels like*

 

[kingkorg]

The only reason i am persistent regarding measurements is so that we can put the finger on what we are missing in all those vf14 substitutes. And then maybe come up with a solution.

Obviously there is something missing.

However, sending a signal generated by free software "REW" into the gate of a mic with VF14 and other alternatives and doing some sweeps at different levels would definitely reveal without shadow of a doubt what those subtle differences are. This requires no special equipment, is easy and free to do. I've been tricked way too many times by my own ears to trust them, that's why i measure stuff. Which also tought me that people sometimes pay thousands of dollars for a built in eq curve of -2db @10k because a 50yo component is performing out of spec.

 

[oscarhuang]

I swapped Phaedrus back to EF13. I read Moxtone Lab A journey into the legend U47 again ( I read more than 20 times). I read every single word and test the voltages. Looks very close to he did. I still not test the frequency respond yet. But yes, that familiar tube sound is back. Here are some results I did

 

[Big Valley Audio]

The only reason i am persistent regarding measurements is so that we can put the finger on what we are missing in all those vf14 substitutes. And then maybe come up with a solution.

Obviously there is something missing.

However, sending a signal generated by free software "REW" into the gate of a mic with VF14 and other alternatives and doing some sweeps at different levels would definitely reveal without shadow of a doubt what those subtle differences are. This requires no special equipment, is easy and free to do. I've been tricked way too many times by my own ears to trust them, that's why i measure stuff. Which also tought me that people sometimes pay thousands of dollars for a built in eq curve of -2db @10k because a 50yo component is performing out of spec.

kingkorg,
My slightly snarky comment wasn’t aimed at you it was more of a reaction to some posts that seem to go sideways very quickly on here ( the recent 2N3055 debate comes to mind)
I wish I would have performed the test you described when I had the opportunity but the client was more interested in just comparing the sound. Hopefully I get another chance one day!

 

[oscarhuang]

Here is some test with EF800. Same power supply. 1.8k ohm on cathode .

 

[oscarhuang]

The only reason i am persistent regarding measurements is so that we can put the finger on what we are missing in all those vf14 substitutes. And then maybe come up with a solution.

Obviously there is something missing.

However, sending a signal generated by free software "REW" into the gate of a mic with VF14 and other alternatives and doing some sweeps at different levels would definitely reveal without shadow of a doubt what those subtle differences are. This requires no special equipment, is easy and free to do. I've been tricked way too many times by my own ears to trust them, that's why i measure stuff. Which also tought me that people sometimes pay thousands of dollars for a built in eq curve of -2db @10k because a 50yo component is performing out of spec.

I did the test with REW. Test equipment Apollo X6 interface. This is the photos with my diy u87 and u47 with EF13 tube, AMI BV8

 

[oscarhuang]

The U47 circuit has very flat respond from 20-20k HZ. That is very good results. U87 is roll off from 3k. -8 db at 20k HZ.

 

[kingkorg]

Ok, now what you should do if you want to see the difference between the tube and Phaedrus, or different tubes, is repeat the process at several different injection levels and post the whole legend with THD levels in percent and for example 2nd, 3rd, 4th harmonic.

You can stop with highest level that gives you say 5% thd. Also paying attention that the circuit is biased similarly and operating conditions are close. You don't want to get different results because of not adjusted plate resistor for example. Could be you don't have to adjust anything.

The good thing is you can save these measurements and repeat later whenever you get new tube.

What is the level you injected here? Can you repost THD levels again with legend and those harmonics i mentioned? You don't have to start sweep so low, 30hz- 22K is fine range.

 

[oscarhuang]

Ok, now what you should do if you want to see the difference between the tube and Phaedrus, or different tubes, is repeat the process at several different injection levels and post the whole legend with THD levels in percent and for example 2nd, 3rd, 4th harmonic.

You can stop with highest level that gives you say 5% thd. Also paying attention that the circuit is biased similarly and operating conditions are close. You don't want to get different results because of not adjusted plate resistor for example. Could be you don't have to adjust anything.

The good thing is you can save these measurements and repeat later whenever you get new tube.

What is the level you injected here? Can you repost THD levels again with legend and those harmonics i mentioned? You don't have to start sweep so low, 30hz- 22K is fine range.

This is my first test. There is still a lot to learn and improve. Thank you so much for always giving me tips. This test I didn't do very well. Many data are not fully recorded. I strive to do a full experiment next time. Thanks again.

 

[oscarhuang]

I tested whole day just for fun. REW is help a lot at least for the EQ. I tested my DIY U87 and tried to installed RK87 capsule into a tube circuit. Then I found CCDA circuit is very easy become a de-emphasis circuit. This T Bone Retro schematic as my reference. I changed c11 to 1000pf and c9 c10 to 0.01uf. Output transformer I used advanced audio Bv8. Advanced audio really like CCDA circuit. Lower distortion, lower impedance and more headroom. Here is my test with different capacity of the c11. For my taste, I prefer 1000pf. Specially thanks KingKorg and RuudNL.

 

[snigglepit]

That's the main reason why the grid-leak resistor in tube condenser mics rarely exceed 500 Meg. There was a notable exception using 7Gig resistors though. I don't remember what model it was...

Hiller M59

 

[vitopower]

I did the test with REW. Test equipment Apollo X6 interface. This is the photos with my diy u87 and u47 with EF13 tube, AMI BV8

Thanks for these tests. Would be really great to hear the EF13 in the circuit, did you ever post clips anywhere?

 

[oscarhuang]

Thanks for these tests. Would be really great to hear the EF13 in the circuit, did you ever post clips anywhere?

No. I didn’t have any audio. I’m planning to do it. Still waiting for my nos EF13.

 

[oscarhuang]

Here is the clip for my U47.

 

[vitopower]

Nice job, sounds great, thanks for sharing! And big thanks to moamps, I've read the "Journey into the Legend" so many times and that research really gave us some solid info to work with.

 

[Papa Tango Charly]

I did the same comparisons,but I prefer the phaedrus verison instead of ef800

Hello Do you sell this microphones?