Re: Differential voltage probes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 18:28 27/06/03 -0600, you wrote:
>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>Hi All,
>
>Finn and I have been thinking about differential voltage probes that would 
>be useful for solid state Tesla coil work.  Rather than spend $$$$ on 
>commercial ones, say from Tek, we were wondering about just making our own.

Hi Terry, I like your design (tres simple) and I would add a couple of 
suggestions:

*Clamp diodes from the op-amp inputs to the rails

*A trimpot on one of the 1K resistors for CMRR trim (maybe T-network type 
thing)

*A variable capacitor somewhere for HF CMRR trim (maybe put a small 10pF 
fixed capacitor across one 1K resistor and a 2-20pF trimmer capacitor 
across the other)

*Metal film resistors because carbon ones have a voltage coefficient of 
resistance

I have all the parts lying around and I'll give it a try

Steve C.