John Roberts,
thank you for the answer, i wasn't sure about the statement you made (and because the That line driver can be configured for dc servo operation -not sure for 1646 but for 1606 i am). Now it's clear.
Abbey Road d'enfer,
Thank you too. Most of you explained i wasn't aware of or hadn't think about it enough but it make perfect sense (tolerance, audibility/deterioration of sonic of cap related to voltage thru them).
About 105°c range, i had to recap some AMS/Neve VR and SSL in the past and each time the studio owner made the choice of 85°c (for cost) they regrets it afterward.
AMS did made the choice to use 105°c (probably military speced and 125°c but i'm not 100% sure about that- the one in metal can looking like el caps you sometime find on high quality PC motherboards) for the stock VX which is the last iteration of the V range and for the 2 desk i've seen and used in France they never had to change one of those caps ( and there is high ambient temp into this chassis).
Ian,
there is a lot of debat in the monitor/loudspeaker field about the audibility of phase (for the low end especially). I'll try to find the last serious study i have (or refrence) and point them to you but it could take some time as i have them burried in one of my HDD and i'm short of time at the moment.
I agree with Abbey road in that even FIR in the low end can be audible as i witnessed when seting my monitoring system (Filtered using a mix of IIR and FIR with a Lake processor). But i must confess that it could have been something else that the processor by itself as many variable take place and i havent made it scientific when comparing (no abx, quick and dirty analysis with barely tolerable analysis gear -mic and preamp especially).
Personnaly i will stick to the definition of a sound i've learned: a sound is a relationship of frequency, amplitude and phase.
Modify one of the parameter and you introduce distortion.
And now i've got historical and engineering answer for the how and why, i'am less dumb about this now, applying 'recipes' i don't know why.
Thank you for that.