musix2000

C12 pattern switch resistors each 50k, not 400k.
« on: December 28, 2017, 09:03:46 PM »
Hello ...
Since years diy-members use 400k resistors for the C12 pattern switch.  I think because of misunderstanding the original schematics they used. In a C12-schematics from 1959, beside the resistors ladder, is written by hand: 0,4Mo, lin. (0,5Mo/WID.) This means that the common resistance of the 8 resistors is 400k. (lin. = linear, WID. = german: Widerstand = resistor).  0,5M for each of the 8 resistors makes no sense, this is a fault they made in this schematics. They forgot a "0".  0,05M (50K) is the right value to get linear steps and 50k resistors you find on the original C12 pattern switch .
I attached a copy of a schematics from 1960 without this fault. I have another schematics from 1957 which also shows 50k resistors, with an additionel picture of the inside of the pattern switch.
Kind regards .....


RuudNL

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #1 on: December 29, 2017, 04:15:06 AM »
The question is: would this make a real difference? (Since the voltage from the switch is not loaded.)
The only thing I could imagine is that it takes a little bit longer to charge the capacitor.
But this could even be an advantage: less "thumps" when changing the directional pattern.
There is a solution for every problem!

http://www.vansteenisaudio.nl

musix2000

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #2 on: December 29, 2017, 01:26:32 PM »
I do not believe that there are still linear steps the higher the resistors values are. If it wouldn`t make a difference 500k, 1M or more could be used. With these there also will be a change in the current flow, but I don`t know if this plays a role.
Would be interesting for me to hear what people using 400k resistors measured on each step (voltage and current).
« Last Edit: December 29, 2017, 01:39:30 PM by musix2000 »

RuudNL

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #3 on: December 29, 2017, 01:41:00 PM »
With these there also will be a change in the current flow, I don`t know if this plays a role.

IMHO there is no current flow, unless the capacitor has a leak current. (It is only the voltage that counts!)
I don't think it makes any difference if you use 10 K resistors or 400 K resistors.
Since there is no load, all steps are always the same.
But it would be interesting to hear other opinions...
There is a solution for every problem!

http://www.vansteenisaudio.nl

musix2000

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #4 on: December 29, 2017, 03:58:47 PM »
Hello RuudNL
Please be patient with me, I`m not an expert, I´m still learning.
The current going through the 8 resistors from + to ground,  don`t changes play any role with relation to the whole 120V circuit?

moamps

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #5 on: December 29, 2017, 05:08:06 PM »
Hello ...
Since years diy-members use 400k resistors for the C12 pattern switch.  I think because of misunderstanding the original schematics they used. In a C12-schematics from 1959, beside the resistors ladder, is written by hand: 0,4Mo, lin. (0,5Mo/WID.) This means that the common resistance of the 8 resistors is 400k. (lin. = linear, WID. = german: Widerstand = resistor).  0,5M for each of the 8 resistors makes no sense, this is a fault they made in this schematics. They forgot a "0".  0,05M (50K) is the right value to get linear steps and 50k resistors you find on the original C12 pattern switch .

Welcome to GDIY and Happy New Year!

This was already discussed here:
https://groupdiy.com/index.php?topic=53318.msg680233#msg680233

Gus

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #6 on: December 29, 2017, 09:52:35 PM »
It makes a difference.

MagnetoSound

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #7 on: December 30, 2017, 12:05:31 AM »
It makes a difference.

Because ...?

Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

Gus

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #8 on: December 30, 2017, 09:42:02 AM »
It changes the loading on the unregulated B+ part of the power supply.

MagnetoSound

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #9 on: December 30, 2017, 02:10:20 PM »
It changes the loading on the unregulated B+ part of the power supply.

Yes, it does, but by less than 0.3mA, which corresponds to a drop of approximately 0.1v.

I wouldn't worry about that too much. 🙂
Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold


Gus

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #10 on: December 30, 2017, 02:13:20 PM »
Don't think about voltage drop.



Khron

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #11 on: December 30, 2017, 02:14:46 PM »
Then what other "loading" effect is there?

Don't think about voltage drop.

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MagnetoSound

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #12 on: December 30, 2017, 02:31:05 PM »
The only other effect I can think of is a slight change in the compliance of the B+ rail to line voltage fluctuation, which is still in terms of voltage drop (or increase) of miniscule proportion.

What are you thinking of, Gus?

Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

Gus

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #13 on: January 01, 2018, 10:03:49 AM »
I will give one thing it changes

Look at the biasing used.
It is cathode bias(resistor is in the neg return) with the bypass cap being replace with a filter. this filtered - voltage is then used to bias the tube.
Note where the bias voltage is derived
More current means more of a voltage drop across the resistor changing the bias
HOWEVER this is cathode bias so readjusts

Now what else changes?

MagnetoSound

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #14 on: January 03, 2018, 12:22:21 PM »
I will give one thing it changes

Look at the biasing used.
It is cathode bias(resistor is in the neg return) with the bypass cap being replace with a filter. this filtered - voltage is then used to bias the tube.
Note where the bias voltage is derived
More current means more of a voltage drop across the resistor changing the bias
HOWEVER this is cathode bias so readjusts

That's what i thought you'd say.  ;D

However, I return to the tiny tiny change in value here - 0.1v out of 120v, is it worth worrying about? The effect on bias current will be of a similar order, less than one tenth of one percent.

Quote
Now what else changes?

The current flowing in the resistor ladder itself, of course. There will be a difference in thermal noise.

Will you hear it? You tell me.  ;)

Dan

I don't think people realize what an embarrassment of riches this place is   -  Paul Gold

musix2000

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #15 on: January 04, 2018, 03:04:47 AM »
A lucky new year for all of you!! Thank you moamps, I hadn`t seen this before.

It`s interesting to hear your opinions. But on some places it seems a bit like to make a victory out of an error.
50k is what the engineers used for the C12 pattern switch in the 50s and 60s, not 400K or 500k. For a 1:1 copy of this mike the values shown in the original schematics are needed, nothing else. For each component of the C12 the value was exactly calculated by the engineers (min. and max.).  I`m sure they knew what they did and this was their best! You can change the values of several components and it still might work and be a good mike, but the more is changed the more this mike is far away from the C12. 

RuudNL

Re: C12 pattern switch resistors each 50k, not 400k.
« Reply #16 on: January 04, 2018, 04:46:17 AM »
Do whatever you want.
If it is good for you, it is fine with me.
(But I still doubt if the different resistor values would make any audible difference...)

If you want to build a historically correct C12, there are many other things to worry about.
To start with, you would have to find an original CK12 capsule in good condition and the correct transformer, used in the years they produced the C12 microphone.
Well, good luck with that!
I think these elements are much more important than the resistor values in the variable voltage divider, because they make an audible difference!
« Last Edit: January 04, 2018, 05:20:02 AM by RuudNL »
There is a solution for every problem!

http://www.vansteenisaudio.nl

musix2000

Re: C12 pattern switch resistors each 50k, not 400k. New
« Reply #17 on: January 04, 2018, 05:26:02 PM »
Yes RuudNL, you are absolutely right. Capsule, transformer, tube, wires, insulating the vibration of the tube from pcb by dampers, and, and ..... all plays more role. To find the components being used in the 50s and 60s is very difficult, but not impossible.
Everybody can do what he likes, I don`t mind, and if someone knows better, why not? I`m still learning.
I`m not an engineer, I think as most of the groupdiy members. And I don`t say this is good and that is bad!! What I said is, that 400k resistors are used because of a fault in the schematics and if someone wants to come as close to the original as possible he should use the guideline as it is. What else as to come as near as possible to the quality of the sound is the cause people use the C12 schematics?
2 years ago I started a research for schematics and pictures of all microphones AKG made from C1 ... C12 ... C23 ...C60 ... to ELA M250/51(e). Then I searched for the best available modern components, the "modern" C12 and ELA M251e by Telefunken with their components were one base for this search. I looked into the datasheets of these components, and after I found some better. Also I analysed the components being used in the 50s and 60s. It took a while until I`d found karbowid resistors and polystyrene capacitors by siemens. I even found good ceramic tube capacitors for the ELA M 251e and  20uf liquid tantal capacitors, they look very similar to those used in the ELAs .
I`d seen an article of an engineer who had changed from the original CK12 in his old C12 to the CT12 by Tim Campbell, and this engineer said, that he didn`t hear a difference ...
CT12, JAN GE 6072a microphone grade tube (used by Telefunken today) or GE 5 Stars, or .....?? , a good transformer, maybe by Haufe, the right components, a construction that avoids influence of mechanical vibrations, this might come very, very close to the original. So why should I use changed values of some components generated by an error??  (There are some changes in the C12 and ELA M 251e made by Telefunken, not all values are the same as in the old schematics.)
But for everybody else: Do whatever you want.
If it is good for you, it is fine with me ....

« Last Edit: January 04, 2018, 07:27:09 PM by musix2000 »