Measured VF14 characteristic

[ricardo]

http://www.linearaudio.net/index.php?option=com_content&view=category&layout=blog&id=81&Itemid=105
It's a dead tree magazine .. actually a set of lovingly bound books.

You'll have to search Yahoo MicBuilders for Scott Wurcer's stuff.

http://www.johnhardyco.com/pdf/990.pdf
The appendix has good stuff on NPO/CGO caps though not with a microphone emphasis.  They DON'T distort so look elsewhere for distortion.

 

[granger.frederic]

Dear Misha

C1 is not a part of a LPF : Low pass filter but a part of a HPF : High pass filter

learn electronic basics please!

C1 is definitely NOT in the signal path, you havn't understood the basics of condenser microphones

Let me explain you the U47 schematic with very simple words:

C1 and R1 is an HPF for the capsule voltage polarization , they put the back plate of the capsule at 58v with virtually no current, thus it's a static voltage, and you need a static voltmeter to measure it.If your B+ is stiff, you have NOT some AC signal at this point.

when the sound hits the diaphragm, the capacitance of the polarized capsule change a bit, and produce a very small voltage variation on R2 (around the grid potential). This is the beginning of the signal path.It is at this point,the signal is very small and at high impedance, thus needs to be converted to low impedance, and amplified in the tube.

C2 finally blocks the DC and let the modulation go into the output transformer, which converts the signal to an impedance of 200/50 ohms.

A very simple and efficient schematic.

C1 is for filtering and ceramic is very good for the job.Neumann has often installed a ceramic capacitor at this place, and surely NOT TO MAKE SAVINGS, and with no impact on the sound.

 

[o3misha]

Dear Fred :
It was a typo. Of course, HF filtrre. But...
AC Signal from capsule directly is going throgh C1! How the signal is going to grid??? Think about it. If you will remove this cap you will loose the signal, because the polarization will be grounded. C1 is most important cap in U47. It works as signal cap as it works in any other microphone but it placed in another place. You should learn a bit theory too.
Best!

 

[granger.frederic]

Misha ,

please stop talking too fast and think twice before posting.

How could a filtering cap could ground the polarization?

STOP SAYING STUPID THINGS

U47 has no coupling cap between the diaphragm and the grid because Neumann has chosen to put the diaphragm at grid potential (near 0V) and the backplate at 58V.As the capsule is a capacitor, it stops the DC coming from the R2/C1.
In a C12 for example, there's a 1000pf between the back plate and the grid, because the backplate is at 60V, thus the DC is stopped by the capacitor.
But this has NOTHING in common with C1 in a U47.

 

[o3misha]

I am realy don't want to argue with you. Maybe you will ask anyone else?
Stop insulting me, I did not say a word offensive to anyone here and not used to tolerate such an attitude. Please, stop saying :
STOP SAYING STUPID THINGS. Its rather about you.
Fred, you don't understand the basic things. I can't argue with you. C1 is working as filtering cap for polarization and most important its working as coupling cap. Its influence is the same as in any other microphone like in C12 (they use 1000pf in other place, but it works very similar). If you remove it,- the capsule will be grounded, and you will loose the sound. Please, stop thinks that you know everything.
I am shure, that any other expert will tell the same.
PS
As a consolation, I can tell you that very many people underestimate the value of C1, so that you're not alone in your delusions. I'm sorry that I could not get through to you, I hope in time you will learn to be more attentive to others' experience. I hope you will not write anything more offensive? Just do not use my advice and everything. My message can be useful to others who understand the essence of the input coupling capacitor C1 in the U47.

 

[granger.frederic]

Please,
if you have time to waste, remove C1 (i did before), and listen to the sound.It's still here, but you will probably have some hum.

ask yourself why many people underestimate C1 ?

You said that if you remove C1 the capsule will be grounded, It's exactly the opposite, if you remove C1 you just loose the AC ground coupling for the backplate.Thus the signal will be poor and small, because the capsule backplate looses its 0vAC potential.

C1 is definitely a filter and an AC ground coupling, NOT a coupling cap for the signal coming from the diaphragm.

Do you know that ONLY AC could go trough a capacitor ??????

I think i could learn from you, but i'm still searching what ...

Maybe after a tech will explain you the basics of microphones schematics, you will delete your posts , as usual ...

 

[o3misha]

ufff.. You even don't understand why I deleted my posts? Stop talking b...sh.t
In general we discussed the offtopic moments in the deleted posts:
1. I said that acryl is not best material for high impedance circuit. If it is possible - use macrolon as best material for that.
2. I said that EF14 is not good tube for replacing VF14 in U47
3. I said if you have a problem with leakages in HighZ chain you have to clean all components and to use urehtane varnish to avoid new problems. I'm sorry that I put my thoughts again here, but Fred insists that I changed my mind about it. I don't.

Without C1 all AC signal  will going through grid resistior to tube, you right. But you will have all noise from resistors and some signal you will loose on polarizing resistor, not much but....I will test it myself as soon as possible.  In general, yes you are right, you will still have signal but very dirty. As far as C1 is necessary in the schematic to filtre  noise from feeding and resitors , you have it in mic. But you don't understand that it is not just filtering cap! It is also coupling cap, because with C1 all AC current from capsule is going through C1 and then it is coming to tube. So, I agree that C1 is filtering cap and without it you still have the dirty signal. I forget, that without c1 current chain still has to get the tube. But because it is coupling cap it affects on sound.
I will not delete my posts, because I think that everybody have to know about importance of C1. I think we both made a mistakes...

 

[granger.frederic]

It is also coupling cap, because with C1 all AC current from capsule is going through C1 and then it is coming to tube. So, I agree that C1 is filtering cap and without it you still have the dirty signal. I forget, that without c1 current chain still has to get the tube. But because it is coupling cap it affects on sound.
I will not delete my posts, because I think that everybody have to know about importance of C1. I think we both made a mistakes...

misha,

sorry but you're speaking about something that is out of your knowledge.

please call a tech, he'll explain to you that c1 is just a filtering cap and its second role is to put the backplate of the capsule at 0 VAC (not 0 VDC...) , that's all !!!!
AND that the signal goes to the capsule diaphragm to the grid WITHOUT traveling through C1.

1/ About Acryl, i remember in your deleted posts that you stated that is was unusable in mics....now you say that it's not the best ...
2/ EF is not a good tube ?? maybe for you , but not for me and lots of other professional recording studios...
3/ you had problem with leakage, cleaning is ok , varnish is useless if it's clean.But you can ruin your mic with some varnish, we're in a democracy , you will just devalue your U47 in the second hand market.

 

[micaddict]

.

 

[o3misha]

I said that I had a problem with acryllic part in U47 head, thats why I recommended to avoid using it in DIY mics. The problem was solved by mr. Thiersch via cleaning and 3 times varnishing of acryl. Without varnish it was  leaking again and again- I have e-mails from him. Period..The same I learned from Andreas Grosser. I think I have already all necessary info about acryl from them.
Ef14 - your choice.
IMPORTANT: I think I understood you wrong. When you said remove you mean just remove, without soldering backplate to ground. Wow...I did mean you loose signal if you remove c1 and ground the capsule.
In the signal most important for us AC current which is flowing through C1. Signal is not just going through grid resistor or directly to grid if there is C1! If you remove C1,-thats another matter.
About importance of C1 I said everything right, don't warry I read many literature in the past and tested caps in my mic. And you did not tested it. If I understand you correctly: c1 does not  affect on AC current from capsule at all, and with any type of it you have the same result? Its wrong and I tested it. Period. So I have something that you have not. All that said about C1 says that you don't understand how it works realy. I hope that someone will join us and will give you more detail explanation. I already know how it works in U47. I think you will agree with me if any good tech will explain you or you test it. But the moment I am not agree with you. And my clients, who are singing in my mics with different c1 caps hear the difference. I decided to use one PIO c1 and one Polystirol c1 in my two mics. Please, stop comments my messages, you are saying nothing new and really useful. We already did once...

 

[MagnetoSound]

@granger - misha is absolutely right - C1 is definitively in the signal path, and it's quality is essential as it provides a clean, low impedance audio path for the backplate which originates at GROUND. It is this very signal path that decouples the backplate to ground.

The low-pass filtering of the cap C1 in conjunction with the polarising resistor is an added benefit - not the primary function - of the backplate cap. By contrast, the high value of the polarising resistor IS chosen specifically so as to make a good filter for the backplate supply.

 

[granger.frederic]

Dear MagnetoSound,

AS you said very modestly that you have the knowledge, let me tell you something:
in a mic capsule the signal initiates because of the membrane movement. The distance between the backplate and the membrane changes, thus the capacitance changes (in a DC polarization) as well. this produces a voltage swing or oscillation, and the signal begins.It begins in a U47 at the front diaphragm.
You said that C1 provides "a good low impedance ground path", sorry but C1 is in a high impedance section. I add that inside C1 the AC electrons are going from the backplate  TO the ground , NOT to the diaphragm: basics of decoupling.
C1 is not really in the signal path, as it's here to filter and put the back plate to the 0 VAC referential (i can repeat that until i die...).It has more or less the same impact on sound than the other filtering/decoupling cap C3 .Without C1 ,no 0VAC potential for the diaphragm, thus the signal is very dirty and small.
C1 is essential,for sure BUT, as it's not a real coupling cap but a filtering/decoupling cap, its quality is not that essential, and NEUMANN has often put a Ceramic cap or MKT, in this place.

But we all know that Neumann techs are incompetent...

You should try and silver and gold PSU cable, you will surely have a VERY GOOD LOW IMPEDANCE GROUND PATH.LOL.

So we have someone who has THE knowledge , and another who GIVES ORDER to not answer at his post, WHAT'S NEXT .....?

I add that if all our decoupling caps must be changed to PIO in all our studio gear, we'd better stop to make music right now...

COUPLING CAPS are another story...

Cheers
FRED

 

[o3misha]

Fred, signal is flowing  from both sides of capacitor: backplate and membrane in our case. That's the key. That's why c1 is in signal path.

 

[granger.frederic]

Dear misha,
this is my last post
the AC signal can't flow from both sides because it is DECOUPLED to the ground,  on the backplate, by C1, the famous ....

Seriously , the only tone shaping capacitor in a U47 is C2, because it's a COUPLING CAP.
the others have a little impact on the sound because, they are DECOUPLING CAPS.

Regards
Fred

 

[o3misha]

The central electrode is connected in series with a С1  to ground.  Hence nonlinear distortions appear due to non-uniformity of the processes in the two capacitors: cap and C1. Condenser C1 discharging  much slower than cap works  - they have different time constants, then the effect of C 1 can not fail to hear. It's not big, but it is quite audible, so, dear Fred, C1, - the real coupling capacitor. You don't know deep processes in mic. It is not static electronic scheme. All processes must be considered in terms of instant change, not as a static schemes. Influence even 0.02% - will be reflected in the sound picture in the audible range. Even the capsule is working non simmetrical.
Process of oscillation of the membrane to the electrode and vice versa is not symmetrical. Standing charge on С1 is an additional hindrance to C1 worked synchronously with capsule. There are other nuances, but I see that talking to you is useless.
Your time to die?  ;D

 

[granger.frederic]

Please learn what a decoupling capacitor is and then talking with me will be usefull...

I add that, because i'm a good boy, i've tested 5 different caps in C1: a mkp wima, mks wima , styroflex, ceramic and ero mkp.very easy to swap btw
Guess what ?
Absolutly no difference.

 

[o3misha]

http://www.linearaudio.net/index.php?option=com_content&view=category&layout=blog&id=81&Itemid=105
It's a dead tree magazine .. actually a set of lovingly bound books.

You'll have to search Yahoo MicBuilders for Scott Wurcer's stuff.

http://www.johnhardyco.com/pdf/990.pdf
The appendix has good stuff on NPO/CGO caps though not with a microphone emphasis.  They DON'T distort so look elsewhere for distortion.

Ricardo, unfortunately I did not found 500-1000V NPO/CGO ceramic caps with necessary 10n value. I found only low-voltage 50 or 100 volts NPO/CGO ceramic caps. Are there NPO/CGO capacitors on 500 volts?

Fred, I explained already all things to U. You don't understand,-its your choice and your opinion to think whant you think. the best way is to try, if you don't beleave the real facts in terms of physics. Not me,- you don't understand what is c1 in u47. First of all learn more how it works  series capacitors with different time constant.

 

[granger.frederic]

Learn what parallel is as c1 is in serial with the capsule. Lol.

 

[o3misha]

Yes, I alredy saw my typo, before I see your answer. You should show tact and stop ernichat.
Frankly, my typos go from simple excitement . English is not my native language, so I use online translator. Sometimes I make mistakes. it does not matter as in the previous report I stated all right.
About your test: polystirol; mkp and other caps with plastic dielectric are very close, they have very similar harmonic distortions and ESR and impedance factors. Ceramic caps are even "faster", but I personally don't like most types of ceramic caps because of its distortions.  You should try silver mica and PIO caps. These types of caps have absolutely different parameters and sound very different. I did not say that you have different mic with Pio or Mica or MKP or Ceramic caps. -but there is difference in high frequences.

 

[granger.frederic]

Dear misha english is not my native language also, so you're forgiven.

However, we're 3 techs here, and we all think that C1 is just a decoupling cap and has a 0,02% impact on sound.

Cheers