I've a DSO-X 3000 that I use for day to day work which has the advantage of an active probing interface, which Agilent called AutoProbe. While great for current clamps and the Agilent active probes they lack a low noise differential probe in their catalogue which is where the Tektronix ADA400A comes in. Having used one before I was happy with the performance but had not realised how cheap they have become since the TekProbe interface is getting rather historic and not directly supported by any recent scopes. The great news is the bottom of the connector case is a surprisingly accurate match for the alignment of the Agilent Autoprobe lands on the front of their current model scopes, which leads to this mod.
Around the cable and connector are a clamshell 2 piece case that is held in the classical way with moulded plastic clips, in a tough and resilient plastic so no fears of snapping any of this when disassembling. The TekProbe pogo pins are held in place by friction only and can be slid out without drama to leave the ring clear of connections. A small scrap of double sided PCB was shaped to snugly fit the AutoProbe aperture and the old pogo pins reused to make the new connections, +/- 12V and +5V were wired through the original cable by terminating into the pads that the pogo pins sat on originally. Pinouts for the interfaces can be found in US patents 6385550 and 5939875.
The DSO-X 3000 powers the Autoprobe interface without any handshake, and will shut down automatically if there is an overload, helpfully asking you to remove excess probes to continue.
Performance, 1.2MHz -3dB point at full bandwidth (slew limited) with less than 8uV RMS of noise. Adding in the 100Hz low pass filter, less than 3uV RMS.
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