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Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

offset voltage, common mode distortion 627 vs. 637, output load

193.98.189.3

doubt that top grade, i.e. lowest offset voltage and/or military tempareature will do any good in audio applications

any FET input op amp will have problems when used in non-inverting mode due to common-mode-input-voltage-dependend input transistor capacity causing distortion

the 6x7 may be less prone due to alleviating action of cascode circuit

the 627 and 637 are the same except for minimum noise gain - in applications above noise gain of 5, the 637 will offer higher bandwidth which helps to reduce hf and intermodulation distortion

look at D. Self web site - he tested op amp performance with an audio precision one unit - not the most meaningful test, but still, it is interesting to observe discrepancies to manufacuturers' data sheets! the OP-275 turns out to be pretty poor btw!

i have had good experience unsing a 627 in inverting mode and with a diamond transistor output buffer that keeps thermal influence from output load outside of the chip - minimizing thermal coupling and hence LF distortion

for non-inverting mode I recomment a fully complementary discrete op-amp

greetings,

Eric


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