Help with damping resistor please

[plumabob]

Hi all,

It's been awhile since I messed around with PI mono coils and I'm a bit rusty. Can somebody show me a diagram and or explanation of exactly how to hook up a damping resistor to a PI mono coil. Is it better to do this inside the coil housing or at the point where it attaches to the circuit board. I was lucky with my first mono as it samples in the 8-9us range, but my second attempt is causing lots of frustration...

Thanks

Bob

[Carl-NC]

The damping R connects across the coil. Most times it's placed in the instrument.

[plumabob]

Thanks Carl,

I tried what you said and it worked out well. I think part of the problem is that my scope is not working correctly, so I got a bit confused.

Bob

[mikebg]

I think part of the problem is that my scope is not working correctly, so I got a bit confused.

Bob, I think your scope is working correctly, but you connect it incorrect. Note that input of scope has relative large capacitance. That's why at critical adjusted damping, without scope the network appears overdamped. You should connect the scope inductively in order to reduce imported by it capacitance.

[porkluvr]

If you have your preamp working correctly you should be able to monitor the results of damping resistor adjustments by probing at the output of your preamp.

[plumabob]

Thanks for the tips guys, but I'm really bad at this. I can build coils and boards but don't have a clue what is going on. I have no problem scoping my DD coils for alignment, but that is the extent of my knowledge. On the surf PI there are 2 test pins that don't show me much as far as I can tell. If anyone could show me exactly where to probe I would appreciate it. A diagram would even be better. I'm a good looker but a bad reader...LOL

Thanks all!