Picotest J2120A Line Injector for PSRR Measurments

[sixtimesseven]

I'm looking into measuring to PSRR of different switching / linear regulator / filter combinations (about 1-2A for 5-15V).

There is this nice injector from Picotest, J2120A (5A at 50VDC max). However, here it is about 620 Euros with tax which is a bit much for a fun project and more than I paid for my 3577A 

I found surprisingly little regarding psrr measurment so far. Most usefull was: http://www.ti.com/lit/an/slaa414a/slaa414a.pdf
The active summing amplifier based on the THS3120 is good voltage wise but only does 490mA max.

So my question is how does Picotest manage this? I don't assume they use the passive summing since their inductor becomes to big and their performance at 10MHz would not be great. However, 500mA seems to be the limit for the fast opamps in that range. So maybe an opamp and a bjt / mosfet in a series configuration?
Maybe a owner had a look inside one already? 

[exe]

The active summing amplifier based on the THS3120 is good voltage wise but only does 490mA max.

Put two in parallel? May be a small resistor will be needed for better current sharing... unless ferrite bead is already enough.

[sixtimesseven]

The active summing amplifier based on the THS3120 is good voltage wise but only does 490mA max.

Put two in parallel? May be a small resistor will be needed for better current sharing... unless ferrite bead is already enough.

Well if they put 10 of them in parallel in there then at least the BOM / price ratio of the picotest box gets better