Confused from transformer symbols, what is the difference? (pictures) - Page 1
Forum section: electronics / beginners

author: HMS
author_rank: Contributor
timestamp: August 26, 2023, 04:31:51 pm
content: Hi Everyone,I have an old hand microphone and found the schematic with a transformer symbols. but I noticed the some have a line in between and some don't?I appreciate your explanation on how can I know the type and how to get its readings? is it only resistance of each side? or there is inductance measurement as well? and how?. it is a very tiny audio transformer to isolate 48V phantom power from PCB.thanks!

author: TimFox
author_rank: Super Contributor
timestamp: August 26, 2023, 04:45:53 pm
content: Drawing 1 has an extra layer: an electrostatic shield between the windings, brought out as a separate wire.By convention, the solid lines (one or more) represent the iron core, and dashed lines are non-magnetic conductive layers.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 26, 2023, 05:51:46 pm
content: You want to find the datasheet for the transformer in question if you can. Is there a part number in the diagram or BOM?Once you know the impedance, turns ratio, frequency range, power rating, etc, then you can find a proper substitute. Some of this info can be determined experimentally, or by understanding the circuit that it's being used in.

author: HMS
author_rank: Contributor
timestamp: August 26, 2023, 06:36:44 pm
content: thanks for your help.regarding measurement, the first side reads (53.81) Ohm and the other side reads (363.87) ohm . there is no information nor datasheet for that part. it does not have any writing on it. that is why I am confused on how to get its readings by testing then look for a similar part.is measuring resistance through a multimeter sufficient and enough to get the required replacement? as you know, it is used inside an old condenser microphone PCB. so, it is an audio transformer for microphones.Do I have to buy an LCR to measure inductance reading?

author: TimFox
author_rank: Super Contributor
timestamp: August 26, 2023, 06:52:44 pm
content: The DC resistance of the primary and secondary windings does not help quantify the transformer.If you need to measure the device yourself, you need to measure the primary and secondaryinductancesand the mutual inductance between windings.One of many articles on the transformer model with these inductances and the resulting impedance ratios and frequency response:https://abracon.com/uploads/resources/Abracon-Exploring-Transformer-Basics-Understanding-Transformers-Part-1.pdfDo you have an LCR meter or other method (not a DMM) to measure inductance?The "magnetizing" inductance at the primary is measured with the secondary open circuited.The "leakage" inductance is measured at the primary with the secondary short circuited.(A complication to all this is the inherent capacitances within the physical transformer, but the inductances give the basic impedance ratio, low-frequency cutoff, and high-frequency cutoff, which depend on the resistive loading in the circuit.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 26, 2023, 06:54:50 pm
content: Well, if you know the impedance of the microphone element, and which side of the transformer it attaches to, then you have a good idea of the impedance of the winding on that side.I see it's a condenser mic... So it has circuitry as well, but the output impedance should be marked on the mic casing somewhere.DC resistance won't give you the actual impedance, but it does give you a clue about the turns ratio. To figure that out more accurately, you'd need an audio signal gen and AC voltmeter. But if the transformer is faulty, then measuring this could be misleading.Can you post the schematic that you have? Does the mic have any sort of label on it that lists it's impedance?

author: HMS
author_rank: Contributor
timestamp: August 26, 2023, 07:48:54 pm
content: You are correct, for condenser microphones the impedance is mentioned for the microphone which is 200 Ohms like all other microphones. I think this will help because when measuring in DC the resistance of primary and secondary are different than 200 Ohms which made me confused. from what i know in microphones , the transformer should be of 1:1.

author: TimFox
author_rank: Super Contributor
timestamp: August 26, 2023, 08:19:52 pm
content: For a condenser microphone with internal amplifier, there is no reason for the transformer ratio to be 1:1; the ratio depends on the amplifier design.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 26, 2023, 08:22:28 pm
content: Quote from: HMS on August 26, 2023, 04:31:51 pmAre you running this thing on 48V? Because it looks to me like it needs to run on 9-12V phantom voltage:

author: wasedadoc
author_rank: Super Contributor
timestamp: August 26, 2023, 09:14:12 pm
content: Quote from: HMS on August 26, 2023, 04:31:51 pmThe transformer does NOT isolate the phantom power from the PCB.

author: HMS
author_rank: Contributor
timestamp: August 27, 2023, 02:53:11 am
content: Quote from: wasedadoc on August 26, 2023, 09:14:12 pmyou are correct. a capacitor isolate DC 48V from the PCB. the transformer balance the output with the Pre-amplifier in AC domain.

author: HMS
author_rank: Contributor
timestamp: August 27, 2023, 02:57:11 am
content: Quote from: wasedadoc on August 26, 2023, 09:14:12 pmthis is a modified circuit replacing battery source to use Phantom 48V. the "Shunt" on the circuit was a battery, then removed and closed with a "Shunt" direct connection while other resistors added to do the correction.

author: HMS
author_rank: Contributor
timestamp: August 27, 2023, 03:06:29 am
content: Quote from: Kim Christensen on August 26, 2023, 06:54:50 pmgrate information. i don't have an LCR and thinking to buy it to understand and get the information about transformer technical specs in a short way.BTW, i have impedance measurement device NTi-Audio MR-Pro (https://www.nti-audio.com/en/products/minirator-mr-pro-mr2) but i don't know if it can help on doing the measurement ... probably by using (Pin 1&2 or 1&3)

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 27, 2023, 03:10:54 am
content: Quote from: HMS on August 27, 2023, 02:57:11 amWas the resistor you added the same as in the diagram you posted? Or is the circuit completely different?

author: David Hess
author_rank: Super Contributor
timestamp: August 27, 2023, 03:40:28 am
content: The solid lines represent the transformer core and should be absent for an air core transformer. The dotted line is an electrostatic shield between the primary and secondary to remove capacitive coupling between them.

author: HMS
author_rank: Contributor
timestamp: August 27, 2023, 05:16:34 pm
content: No, the one i have does not have it. it is the one that use a 9.45V battery. I attached the original circuit with no 2.2K Ohm resistor.

author: HMS
author_rank: Contributor
timestamp: August 27, 2023, 05:25:13 pm
content: Quote from: David Hess on August 27, 2023, 03:40:28 amthanks a lot.here is the picture of the transformer I am trying to know its reading.

author: HMS
author_rank: Contributor
timestamp: August 27, 2023, 05:27:14 pm
content: Quote from: Kim Christensen on August 27, 2023, 03:10:54 amno, kindly find the actual circuit schematics in my previous reply.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 27, 2023, 05:31:09 pm
content: Well, take your NTi-Audio MR-Pro and use it as an audio generator. Set it to 1Khz, output maybe 100mV and connect it to the 200side of the transformer. Use an AC millivoltmeter to measure the AC voltage across the 200winding (Adjust NTi-Audio MR-Pro as need to get your 100mVac) then measure the AC on the other winding (Leave NTi-Audio MR-Pro connected to 200side). Note these readings and post them here.

author: wasedadoc
author_rank: Super Contributor
timestamp: August 27, 2023, 06:55:18 pm
content: Quote from: HMS on August 26, 2023, 06:36:44 pmYou have not said why you want a replacement. Do you have reason to believe it is faulty?

author: HMS
author_rank: Contributor
timestamp: August 28, 2023, 02:35:24 am
content: Quote from: Kim Christensen on August 27, 2023, 05:31:09 pmhere are test readings:Frequency (Hz): 1000(RL) Impedance(Ohm): 3900Phase: +50Primary Volt (mV): 100Secondary Volt (mV): 194.16Vs-Vp= 94.16Vs/Vp= 1.9416i think we can say it is a 1:2 transformer.attached measurment graphes.

author: HMS
author_rank: Contributor
timestamp: August 28, 2023, 02:54:46 am
content: Quote from: wasedadoc on August 27, 2023, 06:55:18 pmI am not replacing it, I want to make another circuit with the same components. the transformer was the only thing I was confused about.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 28, 2023, 04:00:27 am
content: Quote from: HMS on August 28, 2023, 02:35:24 amLooks like it. 800Ω <--> 200Ω impedance matching.

author: HMS
author_rank: Contributor
timestamp: August 28, 2023, 05:11:06 pm
content: After all above information, datasheets don't show similar readingsand all the transformers a found are very large not as small as this one. also, some datasheets show other information regarding DCR Ohm and other stuff which make me more confusedany help regarding where to find similar size transformer?thanks a lot.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 28, 2023, 11:22:36 pm
content: I wouldn't worry too much about the DCR values, as long as they are similar or lower than the one you are replacing.You may also be able to use the more common 600Ω : 150Ω transformer as well.