Need Guru to look at 5534 scope shot,something is wrong.

[Brian Deese]

Does your design call for maybe a 3pf (or more) feedback capacitance across the 5534 i/o, or maybe 3pF (or more) across pins 5~8?

You've thrown us a bone, what about showing us the whole front end?

Ok, here it is.

[porkluvr]

Does your design call for maybe a 3pf (or more) feedback capacitance across the 5534 i/o, or maybe 3pF (or more) across pins 5~8?

You've thrown us a bone, what about showing us the whole front end?

[Brian Deese]

Most likely the coil is very slightly underdamped, not enough to see it on the scope but enough to make the preamp flip. Slightly reduce the damping R by adding a resistor in parallel (perhaps 10k) and see if it goes away.

Ok I put 10k resistor across the existing 330r resistor(in parallel) and the results are-the negative going pulse in question gets slightly wider about 1uS and the curve gets a little longer,very slight but if you touch the 10k intermittently you can see it change.The schematic calls for 390r and I am using 330r because I didnt have 390r.

[Carl-NC]

Most likely the coil is very slightly underdamped, not enough to see it on the scope but enough to make the preamp flip. Slightly reduce the damping R by adding a resistor in parallel (perhaps 10k) and see if it goes away.

[bklein]

How about you just try putting a trimpot for the feedback resistor and you may get a better understanding of what is happening.

[Brian Deese]

Yeah, thats much better,I resized the pictures.sorry for the medium quality,I use a good camera next time.What the hell is up with this amp?

[Brian Deese]

I was having a look at an old pi machine I have that doesnt work very good,using my new scope I saw what looks like ringing on the preamp output.This machine has 330 ohm damping resistor so I didnt think it was ringing.I check the coil signal before the limiting diodes and it looks good,no ringing.I check at the peamp input and it looks good smooth tx pulse,flyback,and tailout to zero volts.But the output of the preamp shows tx pulse,flyback,cross zero opposite polarity,then tailout to zero.Let me post a picture for you.The yellow is the input,the red is the output,second pic yellow is coil signal before diodes,no ringing.