Analog simulation of tape recording part 7 Overloading badly with a modified Jensen Transformer

Around 2008? a Jensen mic input transformer was opened with a thin saw.


The primary turns were reduced to only 69? if memory is correct.


Most laminations were removed to further reduce the primary inductance.


It was in an attempt to create a Sleeping Satelite - Tasmine Archer bright vocal sound with an MD421 black type.


The inductance after the operation is 3.5 - 4mH only giving a very high frequency low cut (Pleiades filter) turnover point.


Then the secondary was connecte through a capacitor to the gate of a K117 JFET in source follower configuration.


Everything in one box with a 2 AA battery holder. This is the Pleiades T1.


Today it was revisited again. Gain was not as high as expected (sometimes the gate is statically charged). Nevertheless the line output of the Sony CD Walkman was connected to the XLR input and a test sinewave tone CD played.


When the female announcer was stating the frequency it was real distortion, but interesting one reminding of cassette overdriven badly.


Interesting sound.


It was of course extremely bright as the frequency rising 6dB per octave slope was not de emphasized by a corresponding high cut filter.


The Jensen transformer as modified is now a very high turn ratio transformer 1:70?. This means it also has a high cut roll off. This may be interesting as it may also simulate the high frequency reduction due the tape loss head gap wavelength - speed effects.


It is uncertain though were was the clipping taking place. The transformer?, the JFET? Or the following preamp? This experiment may be repeated much more slowly with an oscilloscope or signal tracer with adequate headphone pad for ear protection.


Setup, signal path:


Sony CD Walkman line out, Z=370Ω - (Pleiades T1 ie modified Jensen transformer - K117) - Realistic disco mixer at line in input - Sennheiser HD580


Other experiments may include 2 or 3 E laminations from a Canford bought BBC transformer inserted in a small bobbin wound for somewhat greater inductance. It is hoped that a few laminations would simulate the saturation of tape at a small H field or magnetic excitation level.