aion Straylight ramping

[Itchy Scratcherson]

It's imo among the best-sounding diy univibes. Two notes re: the build doc, though:
(1) Although the schematic shows a 250K there, and the doc describes why a 250k Offset Trimmer is best, the BOM still lists the Offset trimmer as 100k. (No matter, I still got mine sounding fine.)
(2) Should the description about 2 separate speed pots really state "two preset speeds with ramp-up/ramp-down effect between the settings"? Pretty sure the ramping is only a function of the responsiveness of the lamp itself... which means when the Speed stomp clicks any speed change is pretty much instantaneous. I could easily be wrong but I can't find R.G.Keen's ramp/LFO doc schematic elements in the Straylight.
Again, great sounding project, and I love the lightbox.
~Christopher

[Itchy Scratcherson]

schematic:

[ElectricDruid]

(1) Although the schematic shows a 250K there, and the doc describes why a 250k Offset Trimmer is best, the BOM still lists the Offset trimmer as 100k. (No matter, I still got mine sounding fine.)

Given the various options, it can't be that critical. Aion's advice if you leave the trimmer out is 47K+100K, so about 150K total, and wiper at 1/3rd. With a 100K trimmer in you've got 47K+100K+47K = 200K total roughly. With a 250K trimmer, you've got more like 350K total, and a bit more adjustment range. So it really can't possibly be something that's absolutely critical, or it simply wouldn't work with all those options.

(2) Should the description about 2 separate speed pots really state "two preset speeds with ramp-up/ramp-down effect between the settings"? Pretty sure the ramping is only a function of the responsiveness of the lamp itself... which means when the Speed stomp clicks any speed change is pretty much instantaneous.

Well, the lamp warming up isn't going to make any "instantaneous" changes, and neither are the LDRs, so I wouldn't expect that but equally, like you, I don't see anything that's going to ramp between Slow and Fast settings over a second or more like a real Leslie cabinet would. But honestly, I haven't analysed that LFO in any depth and I don't understand it without digging into ti, so I'm probably just missing something. It needs someone more versed in Univibe LFOs to tell us more!

[Itchy Scratcherson]

Thank You for the input. I'm combing through Big Monk's «The Monk Vibe: A Modernized Univibe» and his «ElectroVibe Modifications Thread» (etcetera!), too.

https://forum.pedalpcb.com/threads/the-monk-vibe-a-modernized-univibe.18431/
https://forum.pedalpcb.com/threads/electrovibe-modifications-thread.8703/
~Christopher

[aion]

(1) Although the schematic shows a 250K there, and the doc describes why a 250k Offset Trimmer is best, the BOM still lists the Offset trimmer as 100k. (No matter, I still got mine sounding fine.)

That's a mistake in the build doc, I'll get it updated. It should be 250k in the BOM. It was a last minute change right before project launch, it originally made more sense to me to use 100k but I eventually settled on 250k. But yes, as ElectricDruid says, it really doesn't matter either way and any of the methods from the build notes will work.

(2) Should the description about 2 separate speed pots really state "two preset speeds with ramp-up/ramp-down effect between the settings"? Pretty sure the ramping is only a function of the responsiveness of the lamp itself... which means when the Speed stomp clicks any speed change is pretty much instantaneous. I could easily be wrong but I can't find R.G.Keen's ramp/LFO doc schematic elements in the Straylight.
Again, great sounding project, and I love the lightbox.
~Christopher

Yes, there is no added ramping feature or mod in this implementation - it's strictly based on the nature of the Univibe LFO which ramps naturally as the speed pot resistance changes.

I haven't run the math or anything, but my assumption is that it's a combination of the lamp's thermal time constant and the series of 1uF capacitors in the feedback path which store a charge. (Other LFOs like in the Small Stone or Jet Phaser do the same thing.)

Either way, though, it does smoothly transition between speed settings when the resistance is instantaneously switched, as opposed to some types of LFOs that will just click over to a new speed in a fairly obvious way when the speed resistance is switched. But, there is not a way to control the ramping speed directly.