Just mind wandering.
Some of my shots bring me great satisfaction, not always because they are so good but because they show me something new.
As Jim Schulmann so properly described, the Strega is ideal for clear roasts, bringing out delicate flavors and tastes, impossible for other espresso machines, and it's not specially meant for dark and strong roasts.
I believe the reason is that the Strega is a taste amplifier, aromas and taste are amplified, but also taste defects, including slight bitter tastes, from darker roasts, that getting also amplified are a little too much for me.
I've got another pump machine, it's a Graef ES90, it's an inexpensive home machine but with many, quite advanced, features that, amazingly, work quite well. It has no high quality components and must be handled with silk gloves, but has two aspects that I really appreciate: it consistently pulls very good shots, and the taste profile is very near from my friend's LM FB80. Not with all the intensity, clearness, body and mouthfeel from the LM, but near enough as to get the same overall sensation.
When I get a bean that, after a few tries, doesn't satisfies me on the Strega I try it in the Graef, and normally it will hide the defect (bitterness, "in your face", an unbalanced aroma or taste, etc) and it will at least make an OK shot.
As Jim already stated, the distinctive taste profile of the Strega might come from it's high Punch, resulting from it's unique pressure an PI handling, that may be tweaked by "levering", dosing and by using different filters, and should be capable to emulate almost any other taste profile (Cremina, LM, La Pavoni, Elektra Mcal, etc.).
All this introduction was to say that I'm trying to find a "forgiving" pull, not in the extraction and flow sense, but on the unwanted taste aspects, and that could be used with these defective or more problematic beans, and even with dark roasts.
While using bigger baskets and also with "shorter" pulls, I managed to do it (eventually), at least with some of them, but not in a consistent and repeatable manner.

I'd suggest doing the Dimmer switch mod if you want a more versatile Strega. I can fill the boiler at any pressure from 2 bar to 11 bar. Filling the group at 2-3 bar mimics a plumbed in traditional lever machine & you can use any roast level you'd like. When I have a single origin bean that benefits from the higher P/I pressure I just turn the knob to that setting & proceed.

Thank you for your hints John !
I'm still giving YOU some more time, to try out the dimer through-fully, and see your final veredict, with everything tested and with the suitable "operating instructions"
I'm not a good tinkerer, and have only a handful of tools, I'm specially ignorant with electricity and electronics, just the basics ...
Anyhow, I would appreciate if you could indicate some information sources, where I could begin getting familiar with the idea and the required proceedings.

It is all pretty basic unless you decide to add a gauge. I'm already sold on it but haven't had the time to make a stand for my gauge. Once I get the entire set up done I'll post some photos in a separate thread. If you just want to add the dimmer you only need to make up or buy a 3 wire harness a few feet long & the dimmer. Is your machine 120v or 240V?

It's an Italian Unit: 220- 230 volt, 6.6 A, 50/60 cycles, 1,45Kw , at least that's what's written on it.
Here in Brasília we've got around 220 volts (depends on the hour of the day) and 60 cycles.

The Ulka pump is just 55 watts or so, so a dimmer for the pump alone does not to be expensive. Doing the lower pressure preinfusion "by ear" is somewhat hit or miss. The alternative is to cut the dose without changing the grind, so the espresso starts flowing at lower pressure. Once you see flow, lift the lever slighty (or move it to the right) to cut the pump and finish the preinfusion by holding it there for a few seconds

This is more precise, since you can determine dial in the best tasting pressure drop by lowering the dose weight a fixed amount; but it also changes the characteristics of the shot once the spring takes over, and you will need to do more retarding. However, my informal observation is that darker roasts, with spice and dark caramel flavors, do better at higher flow rates anyway, in order to build a foamier crema. If you find this to the case, the reduced dose will not spoil the shot.

Trank you Jim, I'll give it a try.

But .... If I decrease the dose, let's say from 17 to 14gr, with the same grind, the flow might get too fast ...
Only if I would use a single basket, however I believe that 14gr would be quite an overdose.

Or should I grind the 17gr as fine as possible, just at the limit of over extraction, and then getting down to the 14gr with retarding ?

another_jim wrote:The Ulka pump is just 55 watts or so, so a dimmer for the pump alone does not to be expensive. Doing the lower pressure preinfusion "by ear" is somewhat hit or miss.

True but with a p/f pressure rig you can quickly determine where to make the various pressure setting marks on the switch plate. Once you've done that then it's no different then filling the group at 9-11 bar. Simply let the pump run until it gets quiet & the group is filled whether you are pumping at 2 bar or 11 bar. The only noticeable difference is that the pump is much more pleasant to listen to at the lower pressure/voltage settings.

bmb wrote:Trank you Jim, I'll give it a try.

But .... If I decrease the dose, let's say from 17 to 14gr, with the same grind, the flow might get too fast ...
Only if I would use a single basket, however I believe that 14gr would be quite an overdose.

Or should I grind the 17gr as fine as possible, just at the limit of over extraction, and then getting down to the 14gr with retarding ?

Same grind, same basket. If the espresso flows at 10 bar at the normal dose, then 2 grams less, it will flow at 2 to 4 bar. Then you will need to hold back the lever a it rises to keep the flow to where you want it.

This is true whether you use a dimmer or do it by ear

another_jim wrote:The Ulka pump is just 55 watts or so, so a dimmer for the pump alone does not to be expensive. Doing the lower pressure preinfusion "by ear" is somewhat hit or miss. The alternative is to cut the dose without changing the grind, so the espresso starts flowing at lower pressure. Once you see flow, lift the lever slighty (or move it to the right) to cut the pump and finish the preinfusion by holding it there for a few seconds

I cut the pump once I see coffee coming out from the basket. Even I hold the lever there, the flow has started nonetheless. So the preinfusion I have, if I can call it a preinfusion, is one with the shot already started.