Great results there, Axel. We'll be running off coin cells soon 😁 I've used the Recom DC-DC converters in my QCX kits and also dropped the LCD backlight brightness way down which has brought current consumption down to just over 70 mA or so. Your IC replacement sounds worthwhile so I might give that a bash.
BTW. The LT1366 is a bit expensive but there are other opamps that are much cheaper and approach the same success. You just have to consider that IC10 has to bring around 20mA-30mA ... but with IC6-IC9 you can use e.g. TL072 which also only 2.8mA Quiescent Current. Possible other replacement types have already been discussed in the forum. Also for the LM7805 replacement there are cheaper versions of Recom which noise should also be good and only cost half of it :)
The R48 change (from 270 to 1k5) saves 15 mA. Each opamp (IC6 to IC10) requires 10 mA ... the LT1366 requires 0.7 mA (I didn't change IC5 because low noise is important). So let's say this saves another 45 mA The rest is due to the change of the LM7805.
I have been quite satisfied with the DC-DC converters I have used in the past from a noise standpoint. Do you have data as to what the effect was of each change. I was going to make the backlight intensity a small potentiometer on the front panel.
