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RE: Preamp tests

Hall D Electronics:

Hi Yves,
  Well I can't say what you have on the other boards, but the one you sent me is 33pF. If you have 330pF on the others, great. (But for real board I still maintain that an NP0 type is preferred, I doubt you are using it - because I've never seen a leaded ceramic disc capacitor of that size in such a capacitance and voltage and be NP0. However, this is _not_ related to any oscillation or pickup issue, don't be concerned about it right now.)
  What is the value of the bypass caps? If these are also 330pF I think it may be too small. As mentioned you can certainly get 3.3nF in a reasonable size. These caps _may_ influence the oscillation issue, especially the one that bypasses the chamber signal cable shields to ground, of course only when this shield connection is actually used.
  I suggest to first beef up the ground connection between the chamber and the HV board / preamp board assembly, and again strongly suggest to route the chamber signal wires well away from the preamp output cable. [I am going to fix up the board you sent me to do this, and can bring it then when I come to CMU.]
  Can you post some pictures showing the ground connection details if you make changes there, and showing the new preamp board and signal cable positioning? Thanks,

  Gerard

________________________________________
From: owner-halld-electronics@jlab.org [owner-halld-electronics@jlab.org] On Behalf Of Yves Van Haarlem [yvhaarle@ernest.phys.cmu.edu]
Sent: Thursday, December 13, 2007 7:48 PM
To: Fernando J. Barbosa
Cc: halld-electronics@jlab.org
Subject: Re: Preamp tests

Hall D Electronics:

Hi Fernando,

First of all, we rechecked the capacitors we are using and it turned out
that the ones we use now are 330 pF NOT 33 pF. When we brought the HV
board outside we used a new one which is stuffed with 330 pF capacitors.
The one we sent to Gerard is the old one which probably has the 33pF ones
one it. Gerard, is this true? I updated the wiki page containing these
values and apologize for the confusion.


I soldered the cable shield to the HV board but unfortunately it did not
change a thing. More details can be found on:

http://www.jlab.org/Hall-D/software/wiki/index.php/CDC_19_12_2007

(You have to scroll down a while to find the added part, maybe I have to
rethink how to report these things in the future)


I made a small summary of proposals I could filter out of the emails:

        - Change R50 resistor to 10 kOhm
        - Change ground connection to end plate using braid and make it
          as short as possible.


Cheers,
        Yves