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Re: New Preamp Tests



Hall D Electronics:

Hi Fernando, Simon,
	Great to hear of the successful tests so far for the FDC! I wasn't 
expecting to hear good news so quickly, I guess I am too pessimistic, I 
thought it would take days of work at least... I look forward to seeing 
the pictures (FDC online logbook?)
	Of course the CDC prototype is _much_ bigger and more open in its 
construction than the FDC prototype, issues of grounding and shielding 
are probably more troublesome by the nature of the CDC. I do still 
intend to travel to CMU to work with them on it.
	I'm not so sure I agree with your dismissal of the long and winding 
ground path of the preamp to CDC endplate as a potential source of 
trouble (pickup / oscillations). Perhaps. But I still list it among my 
prime suspects. A diagram from Yves showing all the connections will be 
helpful, of course. But as you say I am also not very hopeful of making 
a remote diagnosis and cure.

	Gerard

Fernando J. Barbosa wrote:
> Hi Yves,
> 
>     I looked at your most recent tests and the pictures really helped.
> It seems to me that all point to a ground problem - not easy to diagnose
> remotely. In particular, connecting the shield to GND or the bypassed HV
> causes oscillations is suggestive of noise being coupled from GND to the
> preamp input. I also noticed that there may be a long path from the
> end-plate (straw tube ground) to the preamp GND, although this is
> something to consider later and not the cause of the oscillations at
> this time.
> 
>     I have a bit of great news from here. Simon and I got the new
> preamps installed and running on the FDC prototype and the system is
> very quite (~20 mV p-p noise floor) and with huge pulses (some >1.3V).
> We looked at both anodes and cathodes with 18 m cables connected to
> Gerard's shaper cards (these should not be a factor in the oscillations
> you get, I think). Aside from a few things to check with Gerard
> (polarity and gain), the system looks good.
> 
>     Simon will send an email tomorrow to a link where all the pictures
> and notes will be placed. I suggest looking at the overall ground
> connections - a simple diagram illustrating every connection (shields,
> cables, braids, power supplies) would be very helpful. Per your
> suggestion, it would be great if Gerard could visit with you after the
> collaboration meeting. If you are here for the collaboration, we could
> also discuss this issue and go over the FDC set-up as a reference.
> 
> Best regards,
> Fernando