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RE: Water probe: improvements

Original poster: "Denicolai, Marco" <Marco.Denicolai@xxxxxxxxxxx>

Hi Bob,

I'll try removing the diodes to see if they are responsible for the
noise, but only after I get rid of the bump.

Thanks very much for your help.

Best Regards

> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: 4. tammikuuta 2005 02:18
> To: tesla@xxxxxxxxxx
> Subject: Re: Water probe: improvements
> Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>
> Hi Marco,
>   More thoughts. Perhaps with that 100pf input C and output
> impedance are your first corner frequency as a low pass.
> You may have higher corner frequencies effects too but lets
> assume their above your bandwidth requirements or we will
> deal with them later.
> First reduce the C, with lower C diodes or connect the other
> side of the diodes to a unity gain version of the input
> voltage note this can cause instability.
> Best of all dump them if you think you can.  Calculate the
> corner frequency of what you have left and add that as a lead
> term to the amp.
> The next corner frequency probably a lead will now be much
> closer.  If its within range of your bandwidth requirement
> just add the hf lag at the same frequency. You may need the
> hf lag to ensure stability of the opamp anyway. It levels off
> the gain to give you flat hf boost and can be selected
> experimentally as described in one of my other posts.
> Again it assumes quadratic terms caused by L are well out
> side your bandwidth and or have a very low Q because of the
> high R. I am guessing but they are probably very high
> frequency wave resonances of the tube probably too damped to
> have much effect.
> I hope this makes sense to you.
> Bob