Re: First look at GlueX Preamp response with FDC

[Gerard Visser <gvisser@indiana.edu>]

Hi Simon,
	Looks great! It would, as Mitch points out, be useful to see what 
happens when you turn down the chamber gain. Though I fully expect the 
receiver/shaper board does need some gain change to work well with the 
new ASIC as opposed to the CLAS preamp that it was previously set up 
for. I'm working towards this...
	About the absence of signals on the upper 8 channels of the 
receiver/shaper, that is channels 8-15, that is no mystery. The 
16-channel ASIC preamp board as built uses channels 0-7 and 16-23 on the 
cable (pairs 1-8 and 17-25; pair 0 is the test pulser connection). So in 
order to use this with the receiver-shaper board the cable needs a 
special breakout in attaching the connector at one end (I suggest the 
receiver/shaper end), to move pairs 17-25 at the preamp board to pairs 
9-16 at the receiver/shaper board end. (Similarly, if two 24-channel 
ASIC preamp boards are to be used with 3 receiver-shapers the 2 cables 
need a special breakout connection to 3 connectors at the 
receiver/shaper board end. _That_ we always knew about, but the need for 
a special breakout in the 16-channel case was something of a surprise to 
me when I saw the preamp board - but it is really not a big deal, I hope 
Joe or Fernando can fix you up with this. Meanwhile you'll have to use 
only 8 channels.)

	- Gerard

Simon Taylor wrote:
> Hello, everyone.
> 
> Fernando and I looked at real signals from the FDC prototype using the
> GlueX preamp boards this afternoon.  The pulses were generally quite large
> to the point of possibly saturating the output of the shaper board I am
> using to look at the signals.  The noise level was low.
> I have put some photographs of scope traces on the web in the FDC logbook
> at
> http://www.jlab.org/htbin/PHYSICS/halld/enote112.pl?nb=notebook&action=view&page=348
> 
> Simon