Transformer design - EMF Equation frequency help  - Page 1
Forum section: electronics / projects

author: Tomer
author_rank: Regular Contributor
timestamp: December 31, 2018, 11:22:41 pm
content: Hello all,Thank you for your help.I am trying to take first steps at designing a transformer for a Ribbon microphone.To my best understanding i will have to use the EMF equation in order to calculate primary winding number.The equation is asking for f "f be the supply frequency in Hz". Since I supply the transformer with an AC signal ranging from about 20hz to 20Khz, i don't know how to currently populate the equation ?If someone can clear that up it will be great!Thank you,Tom

author: spec
author_rank: Frequent Contributor
timestamp: January 01, 2019, 03:13:41 pm
content: Quote from: Tomer on December 31, 2018, 11:22:41 pmHi Tomer,Firstly, if I understand your post correctly, the transformer frequency range would be 20Hz to 20kHz, rather than 20MhzYou seem to be wondering which frequency to use for your transformer calculations when a range of frequencies is involved. The answer would be to choose the lowest frequency, but for high quality applications you would normally go to approximately half the lowest frequency. So, on that basis, you would design your transformer to handle 10Hz.You would chose the primary inductance to support the lowest frequency and the highest required voltage so that the current flowing through the primary winding does not saturate the transformer core.The high frequency performance of the transformer depends mainly on the winding method and wire type, because of the skin effect, leakage inductance, and stray capacitances. For this reason you will need bifiliar layered winding and litz wire.Unless you are contemplating winding your own transformer for the experience, I would recommend that you simply buy a ready made transformer for this application, especially if you need high quality audio, because this is a specialist area.

author: dmills
author_rank: Super Contributor
timestamp: January 01, 2019, 03:28:58 pm
content: Wideband audio transformers are HARD, at low frequency you need a stupid amount of primary side magnetising inductance, at high frequency you need very low winding capacitance to keep the resonance with that stupidly large magnetising inductance well out of the audio band, and you usually want some voltage gain as well, so the secondary is even harder then the primary.....There is some documentation of the practise in "The radiotron designers handbook" by Langford-Smith, but this stuff is just difficult.I would either buy something from the likes of Jensen or Lars Lundal or try to design something solid state, a common base stage using several parallel BJTs might be interesting for this application.Regards, Dan.

author: Tomer
author_rank: Regular Contributor
timestamp: January 01, 2019, 04:19:34 pm
content: Hello Spec,Thank you very much for detailed and easy to read answer.I do want to build it myself, I would like to learn more about transformer design and i am lacking the basics.I will spend time learning about "bifiliar layered winding and litz wire" as currently i don't know what they are.* Yes the Mhz is a mistake, i will correct that in the original postThank you,Tom

author: Tomer
author_rank: Regular Contributor
timestamp: January 01, 2019, 04:21:00 pm
content: Hello Dan,Thank you for the reply, i will check the book that you recommended.Thank you,Tom