Post
by J3RK » Sun Dec 11, 2016 6:12 pm
Hey!
Sorry I missed your post.
I haven't tested 5C3s in this new version of the circuit. However, there are a few things that will impact the response.
First thing is that the 5C1 has wider dynamic range than the 5C3 (around an octave more). It also has a faster response time in general.
The CV section of my version of the LPG is a simple emitter follower configuration. The values were chosen to keep the response mostly within the linear range of the transistor. I'd have to dig up the exact target current values. I keep the range going through the vactrol LED between 0 and around 6mA. This is a lot lower than the full range of most VTLs, but it's the specs of the 5C1 that complement this well.
The 5C3's range doesn't extend as far, so that's likely why it takes it so long to close (and then probably not all the way.)
We'd need to figure out a good balance of the 5C3's range, response time, and the emitter follower values to make it work more like a 5C1. IMO it's worth it to track down the 5C1s. I know that they'll be carried by a few of the DIY shops at some point, CabinTech has them, and maybe a few other places at this point. I have a little original stock left, so I haven't looked for a little bit. The XVive 5C1s should be fine too.
As far as the resonance goes, that's kind of the way it typically works on these. My resonance circuit is nearly identical to the versions of the 292C that have resonance (like the TW292 etc.) You can try swapping out the op amp for a different type, you could try a film cap, but it's still going to be fairly harsh at higher settings, it won't have the smooth range of control that most filters would have for resonance.
Some of the variation is due to the vactrols, but in my experience they don't vary as widely (at least within the Excelitas era) I've often heard from others. (maybe that's also down to the 5C1s vs 5C3s... Not sure.) I've also had different CA3140 op amps behave differently in the resonance loop funny enough, so maybe try something like an LF351, TL071, etc.
Film caps IMO do make an audible difference in filters, and possibly in the resonance loop here (though I haven't tried one there.) It's worth a try, though I don't believe it has a huge impact on the sound being as small a value as it already is. You could try increasing it a bit too. Maybe 47pF. MLCCs are ceramic, so that won't give you much of a change either.
My suggestion would be to grab 5C1s if you can. Next item, (if you socketed, or can desolder the resonance op amp cleanly, try another type there. You could try a log pot instead of linear there to get the range to smooth out a bit too. I'd start with these. I will also try to grab those resistor/current values for the CV circuit as well, and post them here. I've got them somewhere.
These circuits do vary a bit from one build to the next, but we should be able to get this to behave the way you want it to.
I would still try some of the items from above first, but if you want to try to tweak the CV section for 5C3s this might help a little. If I have a couple of 5C3s on hand, I could build up a board and try as well. I'm not sure if I have two of them or not though. (have only been buying 5C1s in recent years) 
