Gefell / RFT m94 in Royer SDC mod

[abbey road d enfer]

Personally i prefer plate follower than cathode follower. Especially when you are able make true cardioid connection

What? The cardioid pattern has nothing to do with the presence or lack of input capacitor.

Most circuits which fit LDC, will fit SDC - maybe you will have to slightly reduce low end.

Extended lo< end is  one of the main reasons for using an LDC instead of an SDC.

I truly like Schoeps CV60 topology (of course without input capacitor,  true cardioid connection).

Again, I don't see the relationship between the directivity pattern and the head amp's topology.

Here you will find schematic:

If you take out the input capacitor, you have to find a way to polarize the capsule. What do you suggest?

For sub mini tubes, just simple follower is enough.

Why? What is the set of differences that justify your recommendation?

Like M49C without all the "broadcast filters".

What broadcast filters? Can you mention the components in the M49C that constitute a broadcast filter?

 

[vitopower]

Just had time for a quick test tonight, dropped Rk a bit to hit 40v and working flawlessly.

THANK YOU, again, to everyone who joined in, really feeling the power of GroupDIY today!
8)

 

[ln76d]

Dear Abbey,

Here we go

What? The cardioid pattern has nothing to do with the presence or lack of input capacitor.

This was many time on the forum,  so i was sure that i don't have to explain.
"True cardioid", "pure cardioid" it's just simplification in naming.
All cardioids are carrdioids, in multipattern you can also create it in a different way, but you know that very well
Here's not about  creating pattern, but colloquially named input topology.
Signal taken from diaphragm, polarisation voltage applied to backplate.
Rarely with some LDC capsules pretty good effect gives reversed connection.

Extended lo< end is  one of the main reasons for using an LDC instead of an SDC.

Yes of course, that's why i mentioned that. Few times people asked me for SDC circuits like they would be totally different from LDC. Often there's just slightly reduced low end in SDC circuits to prevent rumble in area where SDC doesn't works so well.

Again, I don't see the relationship between the directivity pattern and the head amp's topology.

As above

If you take out the input capacitor, you have to find a way to polarize the capsule. What do you suggest?

Same way as discribed, in previous post, for my circuit. Just polarisation to backplate, grid1 to diaphragm.

Why? What is the set of differences that justify your recommendation?

Becuase, i think we are looking for simple solution here. Schoeps is also simple circuit - and here is full schematic shown, where the only value of resistor is worth to change is divider for polarisation voltage. Potentially output capacitor value could be lower to reduce a little low end.  And mentioned input connection.
Main difference of CV60 plate follower and M49C plate follower is just biasing and output transformer connection.
CV60 type of biasing can be made with sub mini also, but here i'm lookig for simple solution - build and use. Much easier is setup bias for different tubes with bypassed cathode than using negative voltage from heater section.

What broadcast filters? Can you mention the components in the M49C that constitute a broadcast filter?

This was also many times on the forum, but here you go:
Feedback with R3/C3  (responsible for low frequency), then remove R4 and connect C2 direct to ground. 
Measurement input isn't truly needed, so by occasion remove R12. C6 is responsible for hi freq attenuation. With brighter capsules than K47 or M7 effect of that capacitor is more audible.
Of course Feedback with R3/C3 could be used for low frequency attenuation, but it also reduce sensitivity.
Except extra C4 feedback capacitor, which i would leave in the circuit, if you remove mentioned above components just  left simple cathode bypassed plate follower which you can find in many other microphones.
C4 i would use to optimise sensitivity. Value can be set from 1pF-10pF. Response is also more linear. With optional switch it could be used as pad. And definately leaving it in the circuit i wouldn't use another feedback to reduce low freq like mentioned R3/C3.
https://cdn.groupbuilder.com/groupdiy/u/39511/58d1402a040aa.bmp

 

[abbey road d enfer]

This was many time on the forum,  so i was sure that i don't have to explain.

First time I see it. I'm also a member of the micbuilders list and I've never seen those shortcuts there either. I guess you assumed too much.

"True cardioid", "pure cardioid" it's just simplification in naming.

This is not a simplification I would sanctify, and many eminent designers would also disapprove.

Here's not about  creating pattern, but colloquially named input topology.

IMO, it's plain wrong and misleading using a pattern description to qualify an electronic circuit. If I ever see such a malapropism used in this group, I'll send a warning.

Becuase, i think we are looking for simple solution here.

Your comment seemed to imply that using nuvistors would be different than standard tubes. And I think that's how many people would take it, hence the necessity to put things right.

Feedback with R3/C3  (responsible for low frequency),...

I may be ignorant, but I've never seen this circuit to be called "broadcast filter". A broadcast filter is a well-defined implement, that is used to control a program's VLF and VHF content in order to make it suitable for broadcasting, in particular making sure high frequencies are severely rolled-off as to avoid transmitter clipping. Again, let's not call apple an orange.
Too often I see (hear) language being perverted in a confusing way. Like hearing a compressor "pumping" when it is actually ducking. Proper communication and knowledge transmission relies on using proper terminology.

 

[ln76d]

Maybe i assumed too much, maybe not.
First time, if i remember correctly, "pure" or "true" cardioid naming i found in some Oliver Archut description many years ago. It was related to M49C optional cardioid only setting via S2. 
BTW. in case M49 and K47 it's little bit funny, because quite opposite it isn't true cardioid, since the capsule itself in this connection is  more supercardioid pattern than cardioid, but still are benefits of using this kind of capsule connection in M49.
I'll not search for examples, here you have one in description of Lucas CS4, from recordinghacks:
http://recordinghacks.com/microphones/lucas/CS-4
Also i'll be not checking whos using this naming, are those "eminent designers" are is it anyone reputable on any web forum.
Both namings you can find except gdiy on other different forum also. Micbuilders? Don't know, i'm not the part of this group.
You asked for calrification so i did and i think this is enough. It truly doesn't matter for the topic.

I don't know how people could take it, if something is unclear, then i'm trying to clarify it. I wanted to give OP some just some ideas. Mentioned earlier 6s6b-v, my example of the circuit is 5840 based, didn't think about nuvistor (since there's no any benefit of using it in my opinion) only about glass tubes. Should i write about transistors "except germanium"? Does anyone from other forum members even think about nuvistor reading this? Hope all is clear.

"Broadcast filters" description i found some time ago here on gdiy. You can find it elswhere also. It is used for Neumann microphones like M49, U67, U87 etc.  Extra frequency filtering, legends says that it was for purpose of broadcast companies.  Mostly HPF to reduce proximity effect.

 

[abbey road d enfer]

First time, if i remember correctly, "pure" or "true" cardioid naming i found in some Oliver Archut description many years ago. It was related to M49C optional cardioid only setting via S2. 

I checked the link; now I see where this term comes from, but you have completely misunderstood the meaning of "true cardioid" in the context.
When using a dual diaphragm capsule, there are two possibilities for achieving cardioid response:
A) Nulling the polarization voltage of the rear side of the capsule (e.g. AKG C414)
B) Altogether disconnecting the rear side (Neumann)

There are pros and cons to both ways. The latter - which Manning and Archut seem to call "true cardioid" -  is often preferred because it has the same sensitivity as the other modes in a multipattern mic. The former method introduces attenuation in cardioid mode.
There are other differences regarding the conservation of the cardioid pattern vs. distance. Mics using the former method become omni-directional at low frequencies and close distance, which means they lack the desired proximity effect that result in the loved "chest sound" on male vocals.

Now, the choice of the method does not presume in any way how the head amp works and how the bias voltage is applied.

"Broadcast filters" description i found some time ago here on gdiy. You can find it elswhere also.

Then it is wrong.

Extra frequency filtering, legends says that it was for purpose of broadcast companies.  Mostly HPF to reduce proximity effect.

As you admit, it's a legend. Broadcast companies may have wished to flatten the HF response peak that was inherent in the  construction of the then new capsules, but they did not particularly need an HPF, since their mixers were all equipped with the mandatory band-limiting (40Hz-15kHz) filters.

 

[ln76d]

I checked the link; now I see where this term comes from, but you have completely misunderstood the meaning of "true cardioid" in the context.
When using a dual diaphragm capsule, there are two possibilities for achieving cardioid response:
A) Nulling the polarization voltage of the rear side of the capsule (e.g. AKG C414)
B) Altogether disconnecting the rear side (Neumann)

There are pros and cons to both ways. The latter - which Manning and Archut seem to call "true cardioid" -  is often preferred because it has the same sensitivity as the other modes in a multipattern mic. The former method introduces attenuation in cardioid mode.
There are other differences regarding the conservation of the cardioid pattern vs. distance. Mics using the former method become omni-directional at low frequencies and close distance, which means they lack the desired proximity effect that result in the loved "chest sound" on male vocals.

Now, the choice of the method does not presume in any way how the head amp works and how the bias voltage is applied.

Then it is wrong.
As you admit, it's a legend. Broadcast companies may have wished to flatten the HF response peak that was inherent in the  construction of the then new capsules, but they did not particularly need an HPF, since their mixers were all equipped with the mandatory band-limiting (40Hz-15kHz) filters.

Dear Abbey,

i understand it very well.  This is just my shortcut for diaphragm to grid, polarisation voltage to backplate wiring. I was sure that this is more common here.  If not, sorry for misunderstanding. Not only Manning and Archut used it over the years. It was used also for cardioid only microphones.  Don't know the origin of Brauner "pure cardioid" series naming, but i wouldn't be surprised if this also would be mentioned type of connection. Both models also have regular multipattern versions.
Anyway i think this term came exactly from disconnecting backside of multipattern in M49c.  But what left is exactly as described above connection. So what i'm not understanding in your opinion? It is just matter to use one polarisation voltage, not grounded electrode, signal taken from other electrode than DC voltage, completely not using second diaphragm (if it's available) Nothing more nothing less.
Yes, sensitivity is higher, lack of capacitor between the grid etc. But truly  i don't want to start another discussion about it. Worth to try, worth to compare, nothing more. Especially when sdc capsule have this possibility, which for sdc it isn't common.

I didn't wrote anything about input topology wiring in case of biasing. I wrote about these two things separately.... 

Maybe "broadcast filters" term is wrong, but from what i observed, people here using that term  colloquially and knows what it means. There's many wrong and colloquially terms used  in audio world, somehow people live with this.

First C414 - to create Cardioid one diaphragm is grounded, one is polarised, signal is taken from backplate. Like with C12 with exception that  in C414 backplate isn't polarised, rest patterns is made different way. To create omni, both diaphragms are connected to each other. For figure of eight there's used negative voltage. For supercardioid half of main polarisation voltage. C12 for all the patterns have connected front diaphragm to ground. In C414 there's also capacitor at the gate but it have different purpose.  ELA M250/251 - use "true cardioid" but only with a half of backplate connected to polarisation voltage, second backplate and diaphragm are disconnected.  U87 also have signal taken from diaphragm, but there's capacitor in the way to the grid. Some cathode followers use dc from the grid like Altec or Royer, some use at the input blocking capacitor and extra node with polarisation voltage like C12a.
U47 is this what i'm calling "true cardioid". M49 in any connection don't use grounded electrode to create cardioid pattern. With multipattern connection there's  C1 capacitor between both diaphragms and both are polarised with ca. 58V. With S2 there's disconnected C1 capactor so the back diaphragm also. PSU potentiometer need to be set to 0V (omni position). 

 

[abbey road d enfer]

Dear Abbey,

i understand it very well.  This is just my shortcut for diaphragm to grid, polarisation voltage to backplate wiring. I was sure that this is more common here. 

Moderators here are scrupulous about using correct terminology. We know it's often not the case, particularly on one of the most popular forum.

Not only Manning and Archut used it over the years.

Mannig is a respected SE, but his technical knowledge is very limited; Oliver was certainly more knowledgeable, but still, he was a better microphone historian than actual designer. And I've seen both of them writing nonsense, sometimes.

  Don't know the origin of Brauner "pure cardioid" series naming,

When a brand appropriates a technical term and turns it into a marketing gimmick, a lot of confusion ensues. We endeavour not encouraging this.

So what i'm not understanding in your opinion? It is just matter to use one polarisation voltage, not grounded electrode, signal taken from other electrode than DC voltage, completely not using second diaphragm (if it's available) Nothing more nothing less.

OK, so let's find another locution for describing this arrangement, because "true cardioid" does not imply this type of connection. True cardioid directivity (meaning single diaphragm cardioid) can be achieved in several different manners. At the micbuilders group, this is described as backplate bias.

Maybe "broadcast filters" term is wrong, but from what i observed, people here using that term  colloquially and knows what it means.

Show me an example and I'll call to order the culprit. 

 

[ln76d]

Moderators here are scrupulous about using correct terminology. We know it's often not the case, particularly on one of the most popular forum.

Why so late? Both terms we discuss here are in other topics from a long time

Mannig is a respected SE, but his technical knowledge is very limited; Oliver was certainly more knowledgeable, but still, he was a better microphone historian than actual designer. And I've seen both of them writing nonsense, sometimes.

I even don't know who is Mannig. It was your example Technicians in case of microphones are not matter of my interests.
Anyway not only these two gentlemens used this term, but looking for examples is useless.

When a brand appropriates a technical term and turns it into a marketing gimmick, a lot of confusion ensues. We endeavour not encouraging this.

I didn't gave that example to show that this term is ultra corect, but to show you that it exists in microphone world
Yeah, i love "german mylar" on chinese capsules

OK, so let's find another locution for describing this arrangement, because "true cardioid" does not imply this type of connection. True cardioid directivity (meaning single diaphragm cardioid) can be achieved in several different manners. At the micbuilders group, this is described as backplate bias.

"Backplate bias" also doesn't describe this type of connection.
For single sided cardioid capsules "backplate bias" term is valid for two type connections:
- with diaphragm connected to grid
- with diaphragm connected to ground and signal taken from the backplate thru capacitor
It is also valid for two multipattern topologies.
For now  the term true cardioid i'm using and i will be unless something short and better didn't show
Hope to not get the ban from you for "true cardioid"
Beside the funny thing with first m7/k47 design and its tendency to be supercardioid over 1kHz, if the capsule design is proper cardioid, then this connection gives exactly what it should. With multipattern connection it's more complicated.