On Wed, Mar 31, 2010 at 3:19 PM, ivp wrote: >> You are exceeding the common-mode range of the opamp by having >> 10v/2 going into each input. > > Bob, do I have an issue with this circuit, bearing in mind that the meter > now zeroes and the output (from subsequent stages) is a linear 4V / 1000rpm, > with no baseline offset ? No, you are still exceeding the common-mode voltage range of the TLC271. At 10V supply, the common-mode range is 0.2 to 9V minimum. This is measured from the negative supply, so max CM voltage in circuit is -5+9, or 4 V. Regards, Mark markrages@gmail -- Midwest Telecine LLC markrages@midwesttelecine.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist