Analog simulation of analog tape recording experiments part 4, overloading magnetic materials

An Advance electron tube sinewave generator of generous max output, somewhat less than 40dB.


A 40dB 600Ω pad before the headphones to protect ears and headphones. A greater attenuation would have given more protection and less headache.


Signal path, setup:


Advance Electronics J2C - transformer or coil - 40dB 600Ω pad - Sennheiser HD580


The mostly usedfrequency was around 50Hz. Similar effects happened at high excitation frequencies but as expected the voltage had to be greater (in order to keep the current constant).


Inductors (Pleiades filters) and transformers of various core materials were tested.


Magnetec Nanoperm cores gave very bright distortion suggesting high order harmonics.


The Canford impedance matching transformers used as transformers or just inductors (connecting only the primary) gave less bright harmonics.


A core that came as spare from Coles for a Coles 4038 microphone (is it mumetal?) wound with wirewrap wire (1 layer) gave less harmonics too than the Nanoperm.


By far the least high order distortion came from the German inline transformer described in an earlier post. It is called GSM 1. It was used both as a Pleiades filter with just one winding in parallel to the signal path or as a 600Ω to 500Ω with its switch at the appropriate position.


At about 50Hz it started overloading at about 0dBm. Then as the signal from the generator was increased to up to 30dBm the sound was still with not to many harmonics. And it was clear to the ear that first the 2nd harmonic came (octave), then 3rd (octave and a fifth), then 4th etc.


A VTVM was connected to measure voltage across headphones while this was happening. It was surprising that the needle did no move much indicating great limiting action with no high order harmonics.


This transformer should be great for tape simulation experiments?


A Philips cassette head was also connected. As signal input was increased it could not cut as much the low frequencies (possibly due to its high series resistance). Harmonics were high at overload and for some strange reason the pitch was somewhat shifting with input level.