Transformer understanding notation - voltage ratio, Z ratio, impedance

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jafo

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Hi guys,

I try to understand different writing styles of transformer-specs.
In many projects you use an 1:1 ratio transformer e.g. 600:600 ohms input or a 10k:10k interstage/bridging or step up/down transformers like 1:10 200:20kΩ mic input or 2:1 2400:600Ω output.

When I look on some Haufe-specs I´m kind of confused.

Attached you will find a RK744 datasheet.

Übersetzungsverh. meaning ratio is 1,4:1
Quellwiderstand meaning source resistance is 200Ω
Lastwiderstand meaning load resistance is 10kΩ

and then there is Impedanz meaning impedance which is 15kΩ at 40Hz

the transformer came out of a Neumann-EQ

What irritates me is:

I thought that turns ratio was corresponding to resistance-ratio.
Now I read 200Ω:10KΩ but 1,4:1 ratio. That lets me expect I was wrong.

or…

do I have to look at the reflected resistance on the primary? 10kΩx1,4=14kΩ
That is near to 15kΩ (listed impedance) so is the later just rounded?

Next point: why 200Ω? If its a EQ I have had assumed it has 10k or more input.

Are these 200Ω and 10kΩ just set values for testing the transformer and not the real-world values?


In my wishful thinking this transformer is a 15kΩ:10kΩ line-input with a voltage-ratio of 1,4 to 1
that I can use for line-level stuff like EQs and comps etc.

Can someone please explain how to read this data and/or if I am on the right way?

Thanks in advance,
Jan
 

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PRR

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> I thought that turns ratio was corresponding to resistance-ratio.

No.

Double the Voltage, Half the current, is four times the resistance.
 

jafo

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Thank you PRR,

PRR said:
Double the Voltage, Half the current, is four times the resistance.

I've read this sentence a couple of times but not often enough I guess. Sorry!

To put it into a formula:

a transformer with a ratio of n1:n2 transforms a signal like this:

V: V*(n2/n1)
I: I*(n1/n2)
R: R*(n2/n1)^2

For the Haufe-transformer mentioned above this means:

ratio: 1,4:1

-> V*(1/1,4) = V*0,71
-> I*(1,4/1) = I*1,4
-> R*(1/1,4)^2 = R*0,51

But what is R to multiply this factor with?
Is it the Impedance of 15K?

Thanks again,
Jan
 

abbey road d enfer

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jafo said:
Übersetzungsverh. meaning ratio is 1,4:1
That's the turn ratio, which also happens to be the open-circuit voltage ratio.

Quellwiderstand meaning source resistance is 200Ω
That's the recommended source resistance/impedance. Failure to adhere results in out of spec performance, in particular too high a source impedance results in increased distortion.

Lastwiderstand meaning load resistance is 10kΩ
Again that's the recommended load impedance. Too high results in high frequency hump, too low results in HF loss.

and then there is Impedanz meaning impedance which is 15kΩ at 40Hz
That's the guaranteed minimum impedance that the source will see at 40Hz; that implies a primary inductance of 60H, which seems to be a lot.


Next point: why 200Ω? If its a EQ I have had assumed it has 10k or more input.
In teh absence of schemo, It's difficult to tell.
 

jafo

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Thanks for the precise explanation.
abbey road d enfer said:
In teh absence of schemo, It's difficult to tell.

As mentioned above the transformer came from a Neumann EQ. I measured and sketched the schemo of the tiny input-board labeled MO-21 it was connected to.

Thanks,
Jan
 

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abbey road d enfer

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jafo said:
Thanks for the precise explanation.
As mentioned above the transformer came from a Neumann EQ. I measured and sketched the schemo of the tiny input-board labeled MO-21 it was connected to.

Thanks,
Jan
R1=122r, really?
 

jafo

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I will double-check it. I thought this is for damping etc. since DCR of the primary is 122r too. I will measure again and report.

Thanks,
Jan
 

CJ

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read this and you will e a transformer genius!  :D

https://babel.hathitrust.org/cgi/pt?id=uc1.b4154646;view=1up;seq=7
 

scott2000

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CJ said:
read this and you will e a transformer genius!  :D

https://babel.hathitrust.org/cgi/pt?id=uc1.b4154646;view=1up;seq=7

Thanks!! That's awesome.....

I may have posted this before but,

This guy has some pretty good  beginner transformer explanations too.....  His tube theory stuff is neat as well......

Transformers 101 part 1....not transfomers..... :eek:..lol

https://www.youtube.com/watch?v=gwaGAyjS6hU

Transformers 101 part 2

https://www.youtube.com/watch?v=Z1Xyn1Uy2kU

Impedance matching

https://www.youtube.com/watch?v=-yI8dCrcgSI
 

jafo

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abbey road d enfer said:
Maybe the transformer is connected as a step-down, i.e. primary and secondary are swapped. 2.49k is too low for loading teh secondary.

I followed the traces again. The card-signal input goes to the secondary of the transformer, the side with the higher DCR labeled rt and gn on the data sheet. The other side (with DCR of 128r) goes to R1/ground.
Does that mean it's revered, and now acting as 1:1,4 with a recommended source impedance of 10k and recommended load impedance of 200Ω? Does the value for R1 makes sense then?

Trying not to fish in muddy water...what's R2 doing? Does it higher the impedance seen by the opamp for better noise specs?

Thanks Abbey Road for your help and patience!

CJ, Thank you. I will read it!

Best,
Jan

 

abbey road d enfer

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jafo said:
I followed the traces again. The card-signal input goes to the secondary of the transformer, the side with the higher DCR labeled rt and gn on the data sheet. The other side (with DCR of 128r) goes to R1/ground.
Does that mean it's revered,
Yes.

and now acting as 1:1,4 with a recommended source impedance of 10k and recommended load impedance of 200Ω?
It's actually acting as a 1.4:1 step-down. The recommended load impedance would be about 5k, but the designers have probably optimized for flattest frequency response.

Does the value for R1 makes sense then?
Yes it does, since the transformer is used outside its optimised-operation for mic preamp.

what's R2 doing?
In conjunction with the R3/C1 network, it tames the resonance of the xfmr.
 

jafo

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Thanks Scott! I've got a lot to learn.

abbey road d enfer said:
It's actually acting as a 1.4:1 step-down. The recommended load impedance would be about 5k, but the designers have probably optimized for flattest frequency response.

Ok, that's one of the points that irritate  me. Looking at the data sheet I would have assumed that when you use the transformer "the right way"  there is a 200Ω source, e.g. a mic connected to the primary, then signal is transferred with 1,4:1 ratio (so voltage is reduced) to the secondary. This secondary is optimized to be connected to an amp with 10KΩ input.
Reading from left to right so to speak. But why would one use a step down transformer with a mic-level signal.

Now you say when it is used in reverse it acts as an step down. That would make sense on an eq-input but when I read the data, again I do not see it :eek:

abbey road d enfer said:
Yes it does, since the transformer is used outside its optimised-operation for mic preamp.
So when I use it  "the right way" I would have a mic-input transformer with a ration of 1:1,4 with a recommended load-resistance (R1) of 5k?

Is this a common way to use a transformer? Is this transformer just relatively universal to use or did the Neumann-guys  just wanted to save money/research and used one "compromise-transformer" for several tasks?

Thanks again,
Jan
 

abbey road d enfer

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jafo said:
But why would one use a step down transformer with a mic-level signal.
Nobody said it was correct to do that, but it's perfectly adequate to use it as a step-down for line level.

Now you say when it is used in reverse it acts as an step down. That would make sense on an eq-input but when I read the data, again I do not see it :eek:
All transformers are reversible, but the manufacturer does not cover each and every variant. Th edesigner is supposed to do his homework and evalute the performance in a different configuration.

So when I use it  "the right way" I would have a mic-input transformer with a ration of 1:1,4 with a recommended load-resistance (R1) of 5k?
Th e manufacturer says you should load the secondary with 10k, but you may find that a different load gives better (or worse) results.

Is this a common way to use a transformer?
Yes.

  Is this transformer just relatively universal to use or did the Neumann-guys  just wanted to save money/research and used one "compromise-transformer" for several tasks?
The Neumann engineers were known not to be penny-pinchers. Maybe they had this xfmr in stock and preferred to use it rather than have another part in the inventory.
You can't call that a compromise.
 

jafo

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I did not want to call them penny-pinchers, more pragmatic people.
Thank you for responding to all of my questions and bring some light in the darkness.
I will read/watch the suggested stuff and consider what to build around and with these transformers.

Best,
Jan
 
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