What makes Sowter or Carnhill etc. transformers better technically?

As i stated in the subject, when audio and transformers are in the same subject i hear these two brands frequently.
I am not a novice in electronics nor an expert. I would love to hear as much technical info as possible, or you can point me to some sources.
What makes these transformers audio transformers and why are they trusted and chosen technically?

This is my first post in the community btw, all the best to everyone!

Well, there's no boilerplate argument at all, other than the fashion of the day.  There are many very good transformers, from any era, dependent on the budget you intend to spend, and one should not fall prey to fashion. 

alisomay said:

What makes these transformers audio transformers

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They are designed and optimized to pass audio (not being snarky). A power transformer is not optimzied for a 20hz-20khz frequency response.  ;D

alisomay said:

why are they trusted and chosen technically?

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You have to read the datasheets to answer that. Sowter is popular because they have replicas of many transformers that are just not avaliable. Carnhill, well...because Neve.
Look at the cinemag website, its easy to browse there various offerings, get a general overview of what is desirable in an audio transformer and see the different specs. Some have 4 windings, some are optimized for different levels etc.


Also, welcome to the forum. If you are looking for a specific bit of info, try searching for it too. I think you will find there is an absolute goldmine of information here.

it is a matter of personal taste,  just like music,  you could probably narrow it down to

a) transformers that put out what you put in,

b) transformers that alter what you put in,

Thank you.
I would never and can't underestimate the experience of over 60 years old transformer maker businesses that witnessed the recording and music industry at its heart, but since we are DIY people can't we learn how to make good audio transformers?

First, it is an interesting subject and would be a joy to be able to make a component yourself, or with someone.

Second, for example i live in Istanbul, and i have a local transformer maker in my neighbourhood, they are two old guys and very sweet people. They wound one transformer for me and one choke, they included me in the process and we experimented together. Each of them costed around 15-17 $ for me. I designed and sketched a tube pre with those.    These transformer makers have the patience and the tools but not they are not engineers. They know about simple formulas and turn ratios etc. If i can or you can learn the depth of this and provide the details and knowledge to your local transformer maker ( if you have one ) then maybe we can get that quality a bit cheaper?

Also these audio transformers are insanely expensive for me because the value of Turkish money. (1 £ ~5.5 Turkish Liras, 1 bottle of water in England = 1 £ , 1 bottle of water in Turkey = 1 TL )


So from your answers i understand that i need to read and test these aspects about transformers

size of core
core material
size of wire
interleaving techniques
shielding
winding quantity
-----
Impedances
reactive inductances
capacitance

any more?

Also to answer emrr , some part of me agrees with you
To answer CJ, well you are totally right, it depends to situation i guess sometimes people choose a sometimes b.

alisomay said:

size of core
core material
size of wire

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These are easy, based on low-frequency power, voltage and current. Not much different than calculating for a power transformer, except frequency. However, in audio applications, we sometimes indulge in exotic core materials, with some Ni content, that gives a smoother B-H curve, at the cost of reducing power handling.

interleaving techniques

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That is VERY important; interleaving increases the coupling coefficient, resulting in lower leakage inductance, which in turn improves high-frequency response. Read about xfmr lumped-element model.
The way layers are laid and interconnected is very important; the start of a winding should be as far as possible to the end of same winding in order to reduce parasitic capacitance, which is also a source of high-frequency loss. No magic formula here; one has to picture the layers and signals.

shielding

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Not very complicated; shielding reduces capacitive coupling between primary and secondary, but increases coupling between windings and ground (supposing shield is connected to ground).

reactive inductances

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???? inductance is always reactive.

Thank you for the details.
I will read about xfmr lumped-element model.

As i understand so far with transformers,

To control these properties:

Inductance
Capacitive Loss, Parasitic Capacitance
Resonant Peak (as a property of the inductors)
DC Resistance
Impedance
Current Rating


We modify :

Winding Ratio
Wire Type, Wire Isolation Material, Wire Width,
Wire winding style (how scattered or perfect?)
Wire winding tension
The core material
Wire terminal distance
E - I Core or Toroidal or Ferite??
Isolation material Between the Layers
Interleaving

So after all these adventures
One can have good control over the final transformer.
By the way i tried to buy some different types of copper wire to experiment with these, oh man they are expensive because they are not selling small amounts but i think i will manage it somehow.

So far i can understand that the frequency response is essential of coupling transformers which could carry our ac signal which we want to transduce to sound later on.

What about power transformers?

For example one would like to have good high frequency response in a coupling transformer but maybe want less hf response in a power transformer. Do i think this right?

Are there any spesific specialities should a power transformer of a pro audio equipment have other than silence and stability. We filter it extensively anyway after rectification right?

alisomay said:

For example one would like to have good high frequency response in a coupling transformer but maybe want less hf response in a power transformer. Do i think this right?

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That's correct.

Are there any spesific specialities should a power transformer of a pro audio equipment have other than silence and stability. We filter it extensively anyway after rectification right?

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The main issue with power transformers is magnetic radiation that generates hum in sensitive circuits. Most of the effort goes towards minimizing radiation by a combination of low flux (more turns-per-volt basically), geometry (toroids or double-C radiate less than EI), exotic core material, clever tricks (humbucking) and shielding.

leakage inductance can be important also.

CJ said:

leakage inductance can be important also.

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For a PT?

I presume you're meaning transformers used for mic-level and line-level applications. There are also "audio transformers" used for vacuum tube power output stages.

For a cheap "audio transformer" you could pull one from an "All American 5" five-tube radio from decades past. It's the thing between the 50C5 output tube and the speaker, and is (was) often mounted right on the speaker. It certainly passes signal through most of the audio band. You could probably use it to connect a ribbon mic (connect it to the speaker side of the transformer) to a high-impedance input (tube grid or FET amp/buffer).  I wonder how it would sound.

Jensen Transformers has some good info on its website, some of it you have to register with your email address to get, but it's good reading and worth it.

But even that is just application data and won't give you what you're asking. I do know the core for mic/line-level transformers is some "special" kind of iron or steel that's not used in other (more 'conventional') transformers, and that by itself makes for lower distortion and higher cost.

There are some excellent transformer winding tutorials on youtube that even include the math behind the presenters decisions. Most of what I have found has been on power transformers though

I would love if CJ made some videos about DIY audio band transformer manufacturing 

There are some great papers on the Sowter site too

gonna marry this gal right here>

https://www.youtube.com/watch?v=uoU3ff7FY2s

no wait, i mean this girl>

https://www.youtube.com/watch?v=-mLSVWP4OS8

this is called a sweat shop right here>

https://www.youtube.com/watch?v=02VMfMml4iU

^ understandable  ;D thanks for sharing

here is the sowter paper that CJ pointed out to me years ago

http://www.sowter.co.uk/pdf/GAVS.pdf

Beautiful, i'll check these links and videos and write again.
By the way i am eager to do some experiments and share them here also.
Lately i was planning to build a EZ1290  . I bought most of the components other than the transformers. A friend is comming from london soon then I'll do different versions with a sowter or a carnhill and with a transformer we'll wind custom from the local shop.  It will be fun

Where abouts in the UK are you?

Cheers

Ian

Interesting topic.
As someone who as never worked with transformers and is starting to build some preamps, i was wondering how the OEP are comparing to the other ones you guys mentioned ? i like those prices but maybe it's not worth it.. just wondering

ruffrecords said:

Where abouts in the UK are you?

Cheers

Ian

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I don't live in UK. Couple of good friends living there. One of them will soon bring some carnhill transformers(CA-18-VTB9045) to me and some other components around 12 of April. .
I live in Istanbul. We have a dull market here for electronics components related to pro audio here, About transformers, I don't know if my dream(collobrating with transformer winders) is irrelevant but the local old guys are pretty well transformer winders, They don't have a perception about pro audio.  With some culture, technique and tests maybe we can make something with them

alisomay said:

About transformers, I don't know if my dream(collobrating with transformer winders) is irrelevant but the local old guys are pretty well transformer winders, They don't have a perception about pro audio.  With some culture, technique and tests maybe we can make something with them

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I have found that working with non-audio winders was preferrable in the end, because they don't have preconceived ideas about how an audio transformer must be done, and they are cheaper, since they don't include in the price any intellectual property. I must say it was easier for me 'cause I've been formally trained in transformer design. That's why I encourage you to read about it.

abbey road d enfer said:

I have found that working with non-audio winders was preferrable in the end, because they don't have preconceived ideas about how an audio transformer must be done, and they are cheaper, since they don't include in the price any intellectual property. I must say it was easier for me 'cause I've been formally trained in transformer design. That's why I encourage you to read about it.

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Wow that's motivating! Thank you!
Would you advise any source books?