CDC preamp LV checkup

Following a tip-off from Lubomir that the LV reaching the preamp card might not be correct, I checked it at the board and found it to be 2.6V rather than 3V. This is due partly to voltage drop along the cable and partly to the preamp taking more current than the supply can put out. The original LV supply unit was a HPsomething. I switched it first for a Lambda LH121FM which could put out enough current (0.5A) at 3V but found this to have a wavering pedestal - +/-30 adc bins over the course of 24h, and then for a Global Specialties 1305 which is looking good after 3d. Both have more pedestal noise (pedestal s.d. ~15 bins) than the HP (~10 bins).

Things to check:

1. pedestal height - this was previously set to ch 100 - adjust offsets to bring this back to 100

With GS1305: ADC contents, one event (noise), first 3 are logic signals, rest are CDC prototype

1. pedestal noise and stability (did this before setting height)

Pedestal mean of samples 0-99, ch7, over 2.5days

Pedestal std dev, ch 7

Pedestal std dev has increased from ~11 to ~16 bins 4sigma for new setup is 64 ~ 6sigma old setup

1. tails from large pulses
2. gain

Max amplitude at 2100V, 45 degrees, old and new, hit thresholds matched at 6sigma and 4sigma respectively

Gain has increased also, Landau fit MPV from 260 to 400. This is a little scary. Try a lower HV and look at efficiency also.

Something unfortunate happened at 1.30am - LV dropped due to bad contact with -ve cable.

Pedestal mean of samples 0-99, ch7, over the following day

1. efficiency
2. resolution