New CODD Pick-up Amplifier

PCB and schematic modifications

• General

  • Increase the depth of the cut-out for BNC connector by 0.5mm, so I won't have to cut back the insulation on the central conductor.
  • The X channel input should be displaced 2mm outward, to avoid interference between the mounting holes of the N-connector and a cover screw hole.
  • There are too many bypass capacitors in the relay driver stages. Suppress C61, C122, C183
  • Mount input connector flanges on the inside of the box. Shorten PCB to fit.
  • More copper on the top layer between the inputs and the screening boxes.

• Pre-amplifiers

  • Add impedance correction networks at amplifier inputs. See input impedance.
  • Rearrange the filter coils for better accessibility.
  • Use fatter traces and more GND vias in the attenuators.
  • Correct the the attenuator control. The bits are exchanged.
  • Component changes: L8=0, L24=0, L40=0, R31=0, R95=0, R195=0, L10=0, L26=0, L42=0, R38=inf, R102=inf, R166=inf, R33=2k2, R97=2k2, R161=2k2, R32=inf, R96=inf, R160=inf, L7=inf, L23=inf, L39=inf, C46=0, C107=0, C168=0.

• Main amplifiers

  • Remove solder mask lacquer from cooling pad under THS3061 output amplifiers.
  • Add bias current resistor at AD811 positive inputs
  • AC coupling capacitors C26, C87, C148: 22nF instead of 1uF. (Between AD811 and AD603.)
  • Capacitors C39, C100, C161: 100nF instead of 470nF. (Before AD811.)
  • Invert signals: Remove C12, C73 and C134, change R8, R72 and R136 from 220 to 51 Ohm, ground them. Connect R7, R71 and R135 to the AD603 outputs through new 100nF capacitors. Update frequency compensation: R4, R68, R132: 3k9 instead of 5k1. C7, C68, C129: 36p instead of 27p (2x18pF //).
  • Change series termination at outputs to 51 Ω (R2,R66, R130).