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Today I tried something that I was thinking about. I put a 5 ohm resistor between the 550 ohm damping resistor and ground.I have a 200v flyback pulse and the voltage divider calculator says thats 1.8v measured between the two resistors.So I probed it with the scope and it looks very similar to what you are used to seeing on a coil just smaller.So I fed that to the input of the preamp.I left the 1k resistor in circuit, but I removed the diodes.It didnt blow up the preamp,it even worked.However the sensitivity was poor and could detect iron pliers at 6" or so. The integrator really liked this mod,and had the lowest mv output I have seen from it, sampling right up to the curve at about 17uS. I dont know if I remove the 1k input resistor if the preamp will smoke,maybe Ill try it. On another note,I had my 7660 running at its internal frequency and man that is a bad idea.The preamp output looked like a rip saw. I synced it with the tx like it was supposed to be and its quiet as a mouse. I even verified that by probing the pin 4 on the 7660 and the preamp output on another channel and it was perfect.Switches the cap during tx and stays at that level for the entire period,then switches the alternate direction for the sequential period.
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The resistor divider network causes a reduction in signal amplitude of 99.1%, and hence the poor sensitivity.Originally posted by Brian Deese View Post
Your experiment heavily attenuates the whole of the input signal, whereas the original clipping diode setup only removes the high voltage content, leaving the target response intact.
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