The OP277PA is an earlier version of the OPA277 precision opamp (Datasheet)
If you scroll down to the orderable information you will find this the orderable part number for the device in a plastic DIP package.
The final A refers to the die revision.
There are several aspects to consider:
If you increase the frequency, the time between two cycles goes down, so does the energy per cycle. This means you can use smaller capacitors and inductors when you target the same ripple (and really low ripple is important to make use of 24 bit ADC resolution).
If you increase the frequency, you increase capacitive ...
The OP277 was a part made by Burr-Brown. BB were bought by Texas Instruments and the original part was discontinued and replaced by the TI OPA277 (even though the datasheet only states "Replaces OP-07, OP-77, and OP-177")
All the letters after the numbers refer to package types and performance grades.
The answer is found in the OPA277 datasheet.
Op-amps, particularly older designs, often are available in different grades.
In the case of OPA277, the "A" grade device has slightly specifications:
There are additional relaxed specifications for input current, CMRR, etc.
So the basic chip here is the OPA277. The "P" suffix indicates the DIP package. And ...
It "sounds" like a ground loop or an impedance mismatch, but if everything is properly grounded, then a ground loop seems unlikely, but then again, if everything were perfectly grounded, then you touching anything should have no effect. In either case, a ground loop isolator should help significantly.
A ground loop isolator prevents interference in a ...
There are no catches (lol) Only Specs
The s-parameters start at 2GHz
! N-channel HJ-FET
! Vds = 2 V Id = 6 mA
# Hz S MA R 50
! f S11 S21 S12 S22
! Hz MAG ANG MAG ANG MAG ANG MAG ANG
2000000000 0.98035944 -29.159311 4.3293347 ...
First, JFETs usually have input voltage noise of ~nV and current noise of ~pA. In your case current noise will dominant.
Second, you are running the BF862 in ohmic region, which will degenerate it's noise performance. BF862 was designed to run near Idss.
Third, it looks like that the stability margin of your circuit was not enough. Which means it has more ...