I want to build the "Death of Zen" audio amplifier and I found a video on YouTube of someone who built it and used a 10 mH choke for smoothing of the pulsating DC. I found an old transformer from an audio amp (line 6 low down studio 110) and I found a spot that is 10 mH on my LCR meter. Would this be suitable?

  • \$\begingroup\$ It's not clear where the coil is used and this makes it almost impossible to make a sensible answer. BTW I checked the link. You have enough rep to post a circuit showing the inductor LOL \$\endgroup\$ – Andy aka Oct 14 '13 at 20:39


A transformer is made of (at least) two windings that are coupled together through a ferromagnetic core (iron plates). A choke/inductor uses exactly the same principle, but only has (usually) one winding. Both transformers and inductors need not to have a core - may be simply a set of wire loops (aircore). Such device is not subject to an effect called core saturation. This prevents transformers and inductors with a core from functioning properly when forced to conduct excessive amounts of current. This is probably not your case though.

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  • \$\begingroup\$ A transformer doesn't need a ferrite core either. Aircore transformers exist, and are quite recognizable in one of their forms -- a Tesla coil. \$\endgroup\$ – Bryan Boettcher Oct 14 '13 at 18:58
  • \$\begingroup\$ In addition to insta's comment, cores vary in shape, size, and material. You can have a torroidal cores, rod cores, and several other shielded or magnetically-closed configurations. \$\endgroup\$ – Shabab Oct 14 '13 at 19:43
  • \$\begingroup\$ this does not answer the question at all -1. \$\endgroup\$ – Andy aka Oct 14 '13 at 21:12

The inductor in the video the labeled "10mH 5A". That means that it has an inductance of 10mH at 5A. Above 5A the inductance decreases as the electrical steel core goes into saturation. So, in practice you can use this inductor model with currents of up to 5A.

Though an inductor looks very much like a transformer lacking one winding, there is a fundamental difference: An inductor core has an air gap and a transformer core has not. This air gap length is one of the most critical quantities when designing an inductor. To make a long story short, with increasing air gap length you get

  1. less effective permeability (leading to less inductance) and
  2. more saturation current.

So without an air gap (as in the transformer) you get very little saturation current and the core could saturate at a few milliamps, depending, among other things, on the core cross section and the number of turns on the winding you are going to use.

In summary that means that using a transformer instead of an inductor might work if you stay far away from the rated current of the winding to be used, but in practice this does not make much sense as the transformer is severely under-utilized and thus too big and too expensive when compared to a proper inductor.

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  • 3
    \$\begingroup\$ Not true - inductors do not need an air gap and transformers can be certainly made with air-gaps - in fact I made one today -1 for use of the word fundamental - you are fundamentally wrong I'm afraid. You also miss a vital reason for air gaps in ferrites - it linearises and flattens the dependency of permeability (hence inductance) with temperature. Saturation is due to effective length of magnetic field AND current too - H is ampere turns per metre where the "per metre" is the effective length of the magnetic field. \$\endgroup\$ – Andy aka Oct 14 '13 at 20:34
  • \$\begingroup\$ I don't really want to pay $30 for an inductor,newark.com/hammond/159zj/dc-filter-choke-10mh-5a-15/dp/66F7270 \$\endgroup\$ – skyler Oct 14 '13 at 20:50
  • \$\begingroup\$ @Andyaka You can make a transformer with an air gap, 0.1mm can reduce inrush current tremendously. And there seems to be an application for an inductor without air gap, but I must admit that I do not have an idea where this could be advantageous. After all, this is a question-answer platform and thus I do not want to load my answers with specialty knowledge that applies only to an extremely small number of cases. Maybe this leads to overly drastic simplifications... But why should I mention the temperature characteristics of ferrite? Electrical steel is just about perfect in this application. \$\endgroup\$ – realtime Oct 15 '13 at 19:59
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    \$\begingroup\$ @realtime - inductors without air-gaps are frequently used in switch mode power supplies. Not giving a full answer wouldn't have attracted my comment but saying the air-gap is the fundamental difference between L and Tx did. \$\endgroup\$ – Andy aka Oct 15 '13 at 20:16

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