justinheronmusic

Transformer Theory
« on: June 16, 2020, 10:48:53 AM »
 Can someone explain (microphone) transformers to me? I never really understood.

- What dictates the windings ratio and the impedance?
- What are the effects of having a mismatched transformer?
- What effect does the laminate have on the transformer?

 If anyone has any resources for me on this subject, or articles that they found helpful, I would love to learn.
Justin Heron
Artist / Recording Engineer


EmRR

Re: Transformer Theory
« Reply #1 on: June 16, 2020, 01:24:06 PM »
Start with the Jensen white papers. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

CJ

Re: Transformer Theory
« Reply #2 on: June 17, 2020, 05:02:10 AM »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

rackmonkey

Re: Transformer Theory
« Reply #3 on: June 17, 2020, 10:32:45 AM »
Start with the Jensen white papers.

Start here:

https://www.jensen-transformers.com/wp-content/uploads/2014/08/Audio-Transformers-Chapter.pdf

You may need an account on jensen-transformers.com to access it.
Whether you think you can or you think you can't, you're probably right.

abbey road d enfer

Re: Transformer Theory
« Reply #4 on: June 17, 2020, 06:21:53 PM »
Can someone explain (microphone) transformers to me? I never really understood.

- What dictates the windings ratio and the impedance?
Wiki is good for answering that. Voltage is proportional to the number of turns. Since power out equals power in (because xfmr is passive), current is in reverse proportion, so impedance grows with the square of turn number. Turn number ratio is same as voltage ratio.
Mic input transformers are needed because most electronic circuits are not very good with 150-200 ohm sources. There is a notion of Optimum Source Impedance, where S/N ratio is optimum.
A good xfmr for a mic pre has an input impedance of 150-200 ohms and a secondary impedance that matches the OSI of the electronics.

Quote
- What are the effects of having a mismatched transformer?
How mismatched? Officially, matching impedances is for providing maximum power transfer; it occurs when the source Z is equal to the load Z.
But I think this is not what you're interested in.
For mic pres, matching the OSI is the goal. The more the secondary impedance differs from the OSI, the worse the S/N ratio.

Quote
- What effect does the laminate have on the transformer?
Subject too complex for answering in a short post. There are two major ingredients in xfmr lams: iron and nickel. The rest is in pharmaceutical doses.
Iron is able to carry more power, nickel does it more smoothly.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

justinheronmusic

Re: Transformer Theory
« Reply #5 on: June 17, 2020, 08:06:07 PM »
Wiki is good for answering that. Voltage is proportional to the number of turns. Since power out equals power in (because xfmr is passive), current is in reverse proportion, so impedance grows with the square of turn number. Turn number ratio is same as voltage ratio.
Mic input transformers are needed because most electronic circuits are not very good with 150-200 ohm sources. There is a notion of Optimum Source Impedance, where S/N ratio is optimum.
A good xfmr for a mic pre has an input impedance of 150-200 ohms and a secondary impedance that matches the OSI of the electronics.
 How mismatched? Officially, matching impedances is for providing maximum power transfer; it occurs when the source Z is equal to the load Z.
But I think this is not what you're interested in.
For mic pres, matching the OSI is the goal. The more the secondary impedance differs from the OSI, the worse the S/N ratio.
 Subject too complex for answering in a short post. There are two major ingredients in xfmr lams: iron and nickel. The rest is in pharmaceutical doses.
Iron is able to carry more power, nickel does it more smoothly.

 This was one of the most helpful replies that I have gotten on groupdiy in a long time. Thank you for be patient with me and helping to educate me in this. This is a good launching point to explore greater heights in this subject.

 As far as everyone's links, thank you so much for helping to provide me with not only the tip of the iceberg, but the rest of the iceberg as well. I look forward to getting into this a little more.

 What does it take to wind your own transformer?
Justin Heron
Artist / Recording Engineer

rackmonkey

Re: Transformer Theory
« Reply #6 on: June 18, 2020, 12:33:13 AM »

 How mismatched? Officially, matching impedances is for providing maximum power transfer; it occurs when the source Z is equal to the load Z.
But I think this is not what you're interested in.


I read this as you (the OP) asking about using a transformer in a circuit in a way that disregards the nominal source/load it was designed for. If that’s what you’re asking, the results vary for different transformers, but there are some general patterns.

Generally speaking, using, say, an input transformer specified for 150/600 source impedance and 10k load impedance in a circuit where the source impedance, load impedance or both are significantly higher or lower than the transformer was designed for will result in a shift in frequency response. Depending on the specific conditions, you may see a drop off in low end response or a drop off in high end response, and/or a rise in one or the other.

But this isn’t always the case. Some transformers are more sensitive to such misuse than others. Some may show little change in response from higher or lower than nominal source or load impedance, particularly some 1:1 transformers. In my experience, however, most will show at least some shift in response when these parameters are shifted up or down.  For some, the shift will be drastic.

It’s easy to test this out yourself. Do a series of sweeps with a function generator on a transformer with different series resistor values on the input (between the generator and the primary of the transformer under test, taking into consideration the output impedance of your generator) and different parallel resistors across the secondary. Watch how the response changes on the bode plot with each sweep with the different resistor values on the input or the output.

If this wasn’t what you were asking about, please clarify.
Whether you think you can or you think you can't, you're probably right.

CJ

Re: Transformer Theory
« Reply #7 on: June 18, 2020, 01:04:58 AM »
some easy to understand stuff here>

https://www.sowter.co.uk/faq.php

this is my favorite transformer article of all eternity right here>

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

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

gyraf

Re: Transformer Theory
« Reply #8 on: June 18, 2020, 07:51:00 AM »
Magnetic circuits and Transformers, 15. ed., 1965, MIT:

https://babel.hathitrust.org/cgi/pt?id=uc1.b4154646

/Jakob E.
« Last Edit: June 18, 2020, 08:09:07 AM by gyraf »
..note to self: don't let Harman run your company..

justinheronmusic

Re: Transformer Theory
« Reply #9 on: June 18, 2020, 08:31:59 AM »
If this wasn’t what you were asking about, please clarify.

 You read correctly. Though it is important for me to know concepts in both PSU as well as audio transformers, I am particularly interested in audio transformers, and the effects of mismatching in relation to distortion, frequency response, and wear and tear, if any on the circuit.

 When I run into a situation where I reach the limits of my knowledge, that is when it is best time to level up and overcome the limits. I am having 3 different transformer related situations that remain rather ambiguous to me, and I would like to feel confident in answering questions that keep coming up with the builds I am working on.
Justin Heron
Artist / Recording Engineer


EmRR

Re: Transformer Theory
« Reply #10 on: June 18, 2020, 10:57:37 AM »
I am particularly interested in audio transformers, and the effects of mismatching in relation to distortion, frequency response, and wear and tear, if any on the circuit.


Another, well worded entry basics, is whatever the Audio Cyclopedia Vol 1-3 has to say.  The 'New' Audio Cyclopedia Vol 4 may have something, but less detailed.    Find and download Radio Designers Handbook Vol 3 also, if there's anything there it's much more scrutable than the well known Vol 4. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

ruffrecords

Re: Transformer Theory
« Reply #11 on: June 18, 2020, 11:05:08 AM »
I just wrote a huge long post and attached a document to it only to get dreaded upload folder is full error message and I lost the lot. So, shortened version:

Last year I specified a couple of custom transformers both of which were designed by groupDIY members (CJ and Volker). In doing this I learnt a lot about the basics of designing real transformers so I started to write an article about it but never finished it. Even so I thought you might find it useful. Can't post it here so I have uploaded it to my web site. Go to:

http://www.customtubeconsoles.com/diy

and scroll down to and open the Iron folder. In there you will find AudioTransformerDesignBasics.pdf.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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