ADSR V1 Attack Time

[Sebo]

Hi Yves:
I recently start to tweak and modify some modules.
I was feeling that there was something wrong with my ADSRs, so I measured the minimum times for Attack, Decay and Realease in my four ADSR V1.
In all four the decay times where about 1.5ms and the release times where about 1.3ms. That is good as I don't need shorter times.
But the attack times where a different story, two envelopes have an attack of 2.3ms and other two have an attack of 4.5ms. They where too long for my taste.
I started lowering R11 from 100 ohms to 20 ohms (that was what I have at hand) in one of the longer attack envelopes. That didn't have much effect, the attack gets reduced only 0.2ms (to 4.3ms). I then shortened R11 with no change at all in the attack time.
Then I compared why two envelopes behave better that the other two, and I discovered that the ones with the shorter attack have Intersil and Harris 7555s, while the ones with the longer attack have another brand (with the ICM prefix). So I changed the two 7555s for some Intersil ones, and the attack time lowered to 2.4ms in one envelope, and to 1.9ms in the one that have R11=20 ohms. Then I changed all R11s to 20 ohms and now all attack times are 1.9ms. That's much better.
I think that the 7555 limits the current that charges the timing cap, and that's why I can't get shorter times. Also different brands of 7555 limits the current more than others, and may be there are a brand that works better than Intersil or Harris.
Also is it possible that changing the 7555 for a 555 will be less current limiting? I know about the extra current compsumption and noise spikes, but just want to know if it will have shorter times.
I'm happy with the envelopes at the moment, but I'm going to build two ADSRs V2 with the short settings to see if I get shorter times.
Hope this help somebody.