Sagan Delay and Modulation

[Timko]

I'm slowly going through some pedals I've built over the past couple of years and resolving some percieved issues that I've found.  One of them is the addition of a modulation board to my Sagan Delay.  I used a Grind Customs pLFO board, and rolled my first vactrol, but I've noticed sever motorboating when I have the delay speed on delay #1 anywhere past 10:00.  It doesn't matter where I set the controls on the LFO.  Below 10:00 I get a cool chorus effect, but I've found myself not using the modulation unless the delay is set short.

For people who've built a Sagan delay, do you find similar things?  If not, perhaps my vactrol isn't very good?

[flanagan0718]

I haven't built my Sagan yet but I have rolled a bunch of vactrols. I've noticed a few things. Red, yellow, and green diffused give the best results. Yellow is less pronounced than green. Red is pretty standard sounding to me. I typically stick with green for mine. I also don't prefer super deep modulation. I also use the LDR from Tayda. That's just what I've noticed.


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[Boba7]

Might just be the ldr you use. ldr's vary a lot, and you might want to modify the lfo circuit depending on the ldr you use. Do you have another ldr you could use?

[Timko]

I think I built mine with Tayda LDRs and red diffused LEDs.  According to the build doc, that's what is suggested.
http://stompage.juansolo.co.uk/GCFX-Docs/PLFO.pdf

I'll try to post some videos later tonight, showing you what I'm talking about.

[Timko]

I made a couple of videos of the issue last night, but it took Google Photos all morning to sync.

The first video has a simple loop playing the delay with no modulation, then has the modulation on a slow speed for the first delay.  I then start slowing it down, and eventually turn the signal off all together.  You'll hear the sound that I'm talking about.  I go through the other delays to make sure that they don't have the same issue.
https://photos.app.goo.gl/fg8OLHyuRXQfUdyG2

The second video starts off with no guitar signal.  I cycle through the controls to show what else is happening.  Aside from getting some weird stuff when changing the sync control, I'm not sure what's going on. 
https://photos.app.goo.gl/Pln7ukjC77Qh13vA3

I went through half a dozen or so PT2399s when I originally built this in the summer of '16.  But it's possible there's a problem there.

[BrianS]

Your build was my inspiration to put the GC LFO in mind but I haven't got all the kinks worked out yet. 

Just an after thought but where is the 2399 from?  I know I've read somewhere that the ones from Tayda have a tendency to motorboat and make a lot of noise when turned up.  If it's from there and you have a chip from another place I would give that a go, if you haven't already.

[Timko]

I have some from Smallbear and some from Tayda.  None of which made a difference.  Also, it's only turning on the modulation that causes the issue.  If I turn it off, and dime both the volume and delay time I don't get those weird sounds.

[blearyeyes]

Where is the Modulation resistance attached to the PT circuit? Did you attach it to the speed pot? I had a similar issue with Modulation going to the PT chip in a Moodring. I lowered the depth pot value on the Modulation board and put the output of the mod board to a pin on the depth pot instead of straight into pin 6 of the PT chip... don’t know if that will help but thought I would throw that out there...

[Timko]

The Sagan actually has a pad to attach the modulation to.  As far as I'm aware that's the only pad you have to connect to.  When I get home tonight I'll double check the connection and post a picture of the inside with the connections traced out.

[diablochris6]

My own build uses a GrindCustoms PLFO board with a hand-rolled Vactrol. I used a Tayda LDR and a diffused yellow LED. The most pronounced effect I would get is within the last third of the depth and rate controls. My modulation circuit is actually in a separate 1590A enclosure and connects to the delay via 1/4" jack; the LFO signal goes to the MOD pad.

On the delay control, I would start getting the lo-fi, PT2399 chatter that is inherent with long delay times, especially when all three delay chips are synchronized. It seems to be a compromise in order to get reasonable delay times when the chips aren't synchronized. I am currently tweaking the design of the Sagan.  I am removing the sync/unsync feature and have the PT2399s tied to each other all the time, so I can choose a smaller delay time pot value and avoid some of that noise in the more unusable delay times of the PT2399.

This might not help with all your issues with the pedal, but hopefully it gets you in the right direction.