I would appreciate some practical advice on a problem I'm having with a project I'm working on. I have implemented a simple voltage adding circuit using an op-amp. (see http://homepages.which.net/~paul.hills/Circuits/Adder/Adder.html for the generic circuit) Using one amp of a LM348 op-amp, the circuit performs as expected. The application for this is to add the output from an array of detectors into one signal...and that works just fine at low frequencies. As I increase the frequency of the signal, the magnitude of the op-amp output drops. I think it is due to the slew rate of the LM348 being about 0.6V/uS. Which at 40kHz does not leave a lot of "breathing room" to get a 5V p-p signal ramped up. So I head out and look for a new "better" op-amp with improved slew and GBW parameters. I'm trying the TI OPA4228 (see http://focus.ti.com/docs/prod/folders/print/opa4228.html ) I drop it in the circuit (having been forwarding-looking enough to use a socket instead of soldering the Op-Amp right to the board)...and I get no output. (well.more accurately I get a DC output at some level) I try a couple of the op-amps all with the same behavior. What in the world could cause such a dramatic difference in the behavior between the op-amps? What can I do to trouble shoot the problem? Or what can I do to understand if a given model op-amp will work in my circuit before I just write Digi-key and tell them to send me one of everything they've got . Thanks for your help.