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Re: News on the preAmp + CDC



Hi Curtis,

It is always great to hear good news!

We are in the process of specifying the power supplies and power distribution in the hall and that includes the FDC and CDC. HP supplies usually have very good specs as linear bench supplies. Linear supplies generally have good noise specs of the order of 2 mVrms. Some switching supplies we use in crates for high power, but with very well filtered outputs, approach that spec at 2 to 5 mVrms. They are all expensive but worth every penny. I will let you know what supply we decide to try.

As for the drift time, terminating the far side would not account for the time structure you observe but perhaps there is some pick-up or this may be related to the ground problems you observed. I recall I didn't observe this behavior with the straw-tubes at BNL on E850 but we had charge division readout.

Regards,
Fernando

Curtis A. Meyer wrote:
Yes, it was a very productive day. There were a number of issues
with the grounds on cables that we learned about today, and even
the DC power supply that I had (that was not cheap) was noisy.
This leads me to wonder if we should try to "spec out" a reasonable
low-noise DC suppy that can be used in the experiment. Gerard
liked HP's, but Fernando's input would also be useful. I would like
to try and purchase one so we are closer to the final configuration.

   I would also note that to date we have not used Gerard's shaper.
He was putting a connector on for it this afternoon, but I believe that
all of the pulses are without it.

   cheers - curtis
On Mon January 21 2008, Fernando J. Barbosa wrote:
  
Hall D Electronics:

Hi Yves,

It looks like you and Gerard are making quite a lot of progress with the 
FDC. The pulses look reasonable but there is still some work left in 
trying to understand the source of the oscillations you observed before.

I also looked at the drift time spectra at different sampling rates that 
you obtained. The time structure of the main pulse is similar and of the 
order of 200 ns. There shouldn't be any aliasing as the pulse structure 
out of the preamp is already over 10 ns. However, there seems to be some 
reflection or after pulsing, as the 200 MSPS picture clearly shows. If 
you are using the shaper, check if this is not an artifact from the 
shaper. Gerard may have chosen the shaping constants based on the CLAS 
preamp. I and Simon observed a similar characteristic with the anode 
shaper on the FDC.

Regards,
Fernando



Yves Van Haarlem wrote:
    
Hi Fernando,

Gerard is now looking at the CDC setup with the new preAmp. First 
findings can be found on the CDC wiki (it looks much better now):

http://www.jlab.org/Hall-D/software/wiki/index.php/CDC_23_01_2008

("news on the preAmp" part)

Cheers,
    Yves


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