LDR recommendations with large decay time

[liddokun]

Hi folks!

Scoured the forums but couldn't find quite the answer for this;

Building up a few OTC-201 compressors soon.  These are dual vactrol designs, the circuit employs the VTL5C4, which as many of y'all know, is discontinued and increasingly pricey for whatever stock is left. 

Even with drop-in replacements coming in around $5USD, and with the sucky Canadian dollar increasing costs, thought I'd try to roll my own. 

However the VTL5C4 has a really long down time of 1.5 seconds, in comparison to most of the 30-40ms I've seen for most LDRs I could find.

Does anyone have a recommendation for an LDR that I could use in this case? 

[PRR]

Like we all have all details of a "OTC-201" at fingertips.

https://aionelectronics.com/blog/tracing-journal-dinosaural-otc-201-opticompressor/
https://aionelectronics.com/wp-content/uploads/2019/08/otc201_schematic.pdf

IMHO, for *this* design, a "fast" opto is not a real problem. Increase C8 and C10 to taste.

[liddokun]

Hi Paul,

I'm trying to wrap my head around the different parts of the circuit.  If I were to use a faster opto, say 30-50ms release vs 1.5 seconds, how does increasing C8 and C10 impact the circuit?

[r080]

C8 and C10 charge and discharge at a rate proportional to the capacitance and resistance of the circuit (RC time constant). Assuming the resistance doesn't change, increasing the capacitance increases the time for the charge and discharge.

It looks like that 1.5 second value for the VTLC4 is a maximum, and typical is more like 500ms. Assuming everything else stays the same, if your opto release time is 50ms, increasing C8 and C10 to 100uF could make the release time close enough.