Other Parts Discussed in Thread: OPA827,
Tool/software:
I'm using the OPA828 as a preamp for a reproduce head in an analog magnetic tape recorder. This is the first time I've tried using a FET-input opamp for this job, because opamps prior to the OPA827 & OPA828 had too much LF noise.
Power supply is +/- 12 volts. The head is directly connected to the + input of the OPA828. When testing my prototype, I found that the head had become slightly magnetized, which is not good. Subsequent bench testing of the OPA828 shows that + input current peaks at about 40 microamps as power supplies transition from 0.6 to 3.0 volts even if the + and - supplies remain perfectly matched. If they are not perfectly matched peak current can be as high as 100 microamps.
My solution in the prototype was to add a power supply monitor and a relay which shorted the head when power supplies were below 90% of nominal. This works, but it increases the cost.
Does the OPA827 have the same problem? Do other FET opamps? I can test an OPA827 but I haven't done that yet.
Any suggestions?