Gregor, You wrote: <------------------------------------------------------------------> It may be that this is a trivial question: What is the effect of combining log and lin amplification, e.g. for FITC and 7-AAD, on hardware compensation on instruments using analog log amplifiers? My guess is that the setup probably only has been designed and validated for log to log compensation. Probably someone can comment on where the compensation is actually performed on such instruments (before or after log amplification)? <------------------------------------------------------------------> I don't think this is a trivial question at all - so here goes: PMT -> preamp -> dual differantial amps -> lin/log amp -> acquisition Compensation is performed before log compression, while things are still linear. So, you *can* setup using the log amp, then swith back to linear to acquire the data as long as you don't change the HV (PMT sensitivity) or make any further adjustments to the compensation. You may also then adjust the linear amp gain once compensation is set. Keep in mind that 10V on the linear is 10V on the log, but that 10% of the linear scale (1V) is 10^3 on the 4 decade log scale. So if you use log:log to compensate, you should setup the DNA G0/G1 peak somewhere between 1V -> 3V so it doesn't drop down off scale when you switch back to linear after performing compensation. Obviously, this can be tricky. Everything depends on how you setup the sensitivities among the detectors as to wheather or not accurate compensation may be done with reasonable values. FITC (log) and 7-AAD (lin) are very straight forward in this regard as long as you're sober about it. Joe
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