Our power supply chokes are designed to work at 100/120Hz and with voltages around 100V. Most induction meters work at a few volts or less, at around 1kHz. This is not the correct operating point for a power supply choke, and the reading on the induction meter is usually around half the specified value of the choke. Best way to measure the inductance in a power supply choke is to connect the choke to something like 100V, 50/60Hz, measure voltage and current and calculate inductance. I use a variable autotransformer connected to my mains outlet for this measurement. Be careful however how you connect the autotransformer to the mains, so you do not touch 220V when you think your terminal is at 0V.

EAGLE CAD Lundahl library (created by Bob Starr of RTZ Audio): https://cadsoft.io/resources/libraries/?query=lundahl CADSoft EAGLE PCB Design Software is a CAD software available for a number of different platforms. A limited function version is available free of charge for personal use. Please see http://www.cadsoft.io for downloads.

An audio line is a cable transferring an audio signal from the output of one device to the input of another. Normally the input impedance is fairly high, >1k for mic preamps and >10k for line inputs. If the impedances in both ends of an audio line are high, any noise current picked up by the cable will be easily audible, as the current will generate a significant voltage across the input resistor. But if one side is low impedance, the noise current will be short circuited and no voltage will be generated. Even if the impedance of your output amplifier is fairly low, the use of an LL1540 will add almost 3k to the output impedance, which in most situations is far too much. In addition to the noise problem above, you will also get a certain signal loss across the LL1540, in particular if the input impedance of the next device is less than 10k. A better choice is one of our general purpose transformers (LL1527, LL1588) or a dedicated line output transformer such as LL1517 or LL1585.

I guess you are right. It _IS_ confusing. If we assume a certain DC current, there are two ways to reach a desired core operating point: 1. With a given coil, adjust the core air-gap or 2. With a given core air-gap, adjust the number of turns on the coil The type number LL1660S/18mA is designed such that at 18mA DC current and ALL PRIMARY WINDINGS CONNECTED IN SERIES, the core operating point is 0.9T But if you connect the windings in a different way (such as suggested in ”Alt B”), the number of magnetizing turns will be different, and the core will have a different operating point unless you change the DC current. So for LL1660S/10mA, used in connection ”Alt B”, the necessary DC current required to reach the operating point 0.9T is 18mA I hope this is an answer to your question.

The internal structures of the LL1581XL and LL1570XL are quite different. The LL1581XL is a splitting transformer with very high immunity to external noise and noise crosstalk. When used as a splitting transformer, the LL1570XL may pick up electromagnetic hum (from e.g. motrs or power supplies).

It appears that one should obtain a 50% tap in this manner. Yes, you can use the LL1620 in UL mode if you connect the screens as you describe.