Matching VTLs for the P100

[Govmnt_Lacky]

So I am thinking about building the P100 from JDs site. I have sourced the VTLs (optocoupler/vactrols) and have 3 ready to go however, I am wondering if these optocouplers need to be matched like the FETs in a Phase 90.

Can anyone answer this for me? If they do, is there a circuit I can build like the FET matcher from goefx?

[Mark Hammer]

No, they generally do not.  The issue with FET matching is that they reach a point where they will not change drain-source resistance any more, and it becomes like a canoe where some, but not all, of the occupants are rowing.  The sweep becomes clumsy. 

In the case of LDRs, it is much less likely that the light source will either reach a maximum brightness, where the LDR simply cannot drop any lower in resistance, or reach a degree of darkness where the LDR can not achieve a greater resistance.  I don't know about you, but I have a hard time getting LDRs to reach maximum resistance when they are covered in black heat shrink, covered by my cupped hands, and held under a table away from light.

The phase shift introduced is always summed across stages.  So, even if the actual specific resistances of the JFETs, or LDRs, is not identical, as long as they are all changing at once, the cumulative phase shift is incrementing or decrementing, and that is pretty much what you are interested in.  Again, JFET matching is to find a set that will all be moving together, whatever their individual d-s resistances might be at any given point in the cycle.  Whether you're walking in front of me, or beside me, or exactly 6 feet behind me, as long as you are moving along at the same speed and start time, I know we will all reach the end, and return to the beginning, as a group.

[Govmnt_Lacky]

Thanks Mark! You pretty much answred my question (That would be a NO for the matching I think) Also, cudos on the info you have given on mods to the P100. I was just in the archives reading some of your brilliance!!!

[Mark Hammer]

Well as a government lacky myself, it would be rather uncooperative of me to not help out a fellow lacky.