Delayed modulation module failure

matinnin

All
Seeking any insight on building this module. 15volts. And made the recommended resistor changes.
This has been the worst month ever for building. I have never run into so many issues. This module is killing me. I built a second one to see if I would get a different result. Both are near complete failures due to not delivering the desired delayed modulation.
THEY Seem To Both have similar problems.

First the LFO speed is way too fast at lowest settings and speeds up too soon and ends up in an unusable speed for me. This is not the main issue. Correct me if I'm wrong but more resistance for R17 and/or R24 should fix that.

The main issue I have is that the envelope is not affecting the vca.
Modulation is always on. No adjustment of pots is doing any change
Thing is if I scope the AR output I see the adjustments and the envelope happening with a gate applied to input.
I also can probe all LFO outputs and see them.
So I can see each individual part and it seems to function. I can see each lfo shape , speed mod amount, shape switches all seem to operate ok.
High low works but seems to start exibiting issues. Probably because my issue appears to be in the connection to the vca.
I have changed out pots, switches, ics, transistors, wiring,but still no success. So I built another and it is not right either.
I'm beginning to suspect an error in the wiring diagram. I am at a loss right now and will just have to start pulling wires and removing parts of circuit pertaining to vca in order to isolate.
Has anyone built one of these that works either 12volt or 15 ?
Any ideas are welcome. I'm starting with wiring.
Thanks

sixbyseven · Joined: Jan 28, 2016 Posts: 26 Location: hamilton, Ontario

I just built this circuit as well. I have the exact same results. The EG does not effect it. I just turned it on for the first time Sunday, so I have not had enough time to play with it.

sixbyseven · Joined: Jan 28, 2016 Posts: 26 Location: hamilton, Ontario

This may be a dumb question, but are using this to modulate another VCO-VCA-EG patch? It works fine in that configuration. The LFO modulates the patch based on the modules EG setup.

matinnin · Posted: Mon Oct 16, 2017 8:08 pm Post subject: Circuit changes

Hi, i have been fighting this for several weeks, with my limited knowledge and understanding. i have been able to get one working.
in my pursuit of perfecting my MFOS Quad VCA (2boards) i think i discovered one of my issues. in that i seem to have damaged the LM13700 somehow, or maybe the circuit, because trying to get my VCA to bias out completely when no CV is applied. i seem to have slight remnant of biasing voltage that will not allow to completely 0 out. i changed the 2m resistor R46 and it toasted my OTA. not cool, i think i ended up 3 of them lost between these 4 boards im building.
any way i have made headway on the Delayed mod.
LFO speed i got to a manageable speed, could still be slower, changed R17 to 100R and R24 to 200k - much better

the other changes i made are in the AR U1 section. R12 i moved up to 100k and R14 to 10k

i still think theres other changes to improve some of the ability to adjust the A, and R times,
seems most of the suggested 15volt resistor changes did not work for me, so im having to work through them, hopefully not dorking out anymore LM13700 those are getting expensive

no, output straight into what i want to modulate, filter cv, VCO cv etc...

matinnin

Well, i got them both working now. made the changes i spoke of already on the resistors. there is still some work to do to get them where i want them, but at least i can get them working.
i read something somewhere, that has led me to think i really fouled up by using my temp extendo power cable off my cabinet over to my workbench, and was hot plugging these modules in and out, and the IC and JFET do not take kindly to having only 1 voltage present for any amount of time. so i ended up messing up some LM13700 and some JFET also some 3904/6 in my VCAs man, that's a lesson.

so to get it working more to my liking, LFO rate still doesnt afford enough adjustment, Modulation level on high is too high, on low its too low, and attack has to be all the way up to get any usable delay.
speed
R18 tried some values, didnt work, it wouldnt oscilate

for the Level i think i am going to try 200k on R15, (did this but it almost disappeared Low level, R26 may be the key)

my real challenge is extending the attack time out, im not sure what i should be looking at to change on this part of circuit to make that work for me, C2 larger?
R2 changed to 200k, i think it made a difference,
but what about R8,9,10 ? R1?

Bodo1967 · Joined: Aug 10, 2016 Posts: 15 Location: Germany

I got the module working today. Sometimes mistakes are so obvious you don't see them although (or because?) they are so simple. We call that "not seeing the forest for all the trees" in German.

Ray apparently forgot a connecting wire between the panel elements (jacks, pots and such) and the PCB in the panel wiring diagram. The GND connections are only intra-panel. I added that wire, and *bingo*.

I left all other components at their original values (except that I added another toggle switch so I have square, triangle and sine output for the LFO). In my case, it was really only that missing wire. Everything now behaves just as it should.

matinnin · Posted: Sat Sep 08, 2018 8:38 am Post subject: usable LFO Freq

well, i read your note and pulled mine to look , as i have repaneled these a few times - if it wasnt on his drawing i already caught that , as i have ground to panel -
the only issue i have is usable frequency range of the LFO - it should NOT run this fast - it should go from minutes to just below audible range - no more than 200 hz or so -
but as it is , it is only functional in about the first 5th or so of the frequency pot
ive just been using it as is for now as i have several other projects - but it works as it is

Bodo1967 · Joined: Aug 10, 2016 Posts: 15 Location: Germany

injektilo001 · Joined: Aug 21, 2020 Posts: 10 Location: Chile

Hello everyone, wish you all good electric vibes.
I've been fighting this module also, and i can confirm the LFO rate to be very sensitive in the first 1/5 turn , maybe a 100k log pot can help plus the changes Matinnin said.

MY PROBLEM is when i'm in GATE mode the modulation is always happening. This doesn't happen in trigger mode, it works as it should, I think.

I have measured the voltages at the AR output in both modes, without triggering.
In TRIGGER mode it reads something like -6,5V and in GATE mode reads something like 1,6V , maybe that's why the LM13700 is open? how can i solve this. I breadboarded just the EG, with the same results.

Help Friends.

JP

injektilo001 · Joined: Aug 21, 2020 Posts: 10 Location: Chile

Hello, i got it to work, i put another diode in series with the existing one in the Gate Input and now the modulation happens when I trigger.
The problem now is that in Gate Mode, the cycle doesn't stop right away when i release the button. It doesn't do all the cycle like in trigger mode, but still continues the cycle for a while, more noticeable with a long attack of course.
Somebody knows how to fix this, so the cycle stops in the moment I release the Gate Input? Sorry my bad english guys.
JP