can’t wait to build these! they ruleee 
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Today I built the k25 Envelope Generator. I had to drill a hole for the switch in the front panel, because I didn’t notice the gerber files on github were not updated yet. But drilling the hole was easily done 
. And I still think the front panel looks very nice 
It is working now, but I have a small problem with it: it always gives a small voltage on the CV output. I didn’t measure how much, but when I use it as a CV input for my VCA, I always hear a sound and the output led is always glowing faintly.
I thought it was because I substituted R6 with 20K, because I didn’t have a 18K te resistor. To troubleshoot if this was the problem, I replaced the 20K with some resistors in series to get a value of 18K, but that didn’t solve thee problem. I also noticed the Jack for TRIG input is not connected to GRND (you can even see it in the schematic), but I don’t know if this is a real problem.
I reflowed all the solder points to make sure there were no cold joints, but that didn’t solve the problem either.
Is there anything else I can do to check what I have done wrong?
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That trig not being connected is definitely an error. Luckily the panel holes are grounded so that’s probably making it ok. Try wiring up the trig ground to one of the other ground points
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The 358 is supposed to swing to ground? I’m going to check my build, I didn’t notice it on mine but I could have missed it I suppose.
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So…my LED is ever so slightly lit even when no trigger applied. However the output is only outputting 0.07v in positive mode and -0.06v in negative, which is not enough to open up any of my VCAs, even with the volume cranked on studio monitors.
So, now I’m wondering what’s up with your build @MacMannes let me know if you figure anything out. That missing ground is problematic for sure and I appreciate you catching it, but I don’t think it’s related to your issue
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I’d persuaded myself the circuit design in fact didn’t allow the capacitor to fully discharge, giving a low output voltage that would never go away, but that was just my very inadequate grasp of how diodes work. I did a simulation in which you can see indeed the capacitor voltage does drop to zero, though it takes a while.
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I soldered a wire between the two ground points of the jacks, but that didn’t make any difference.
I also took some measurements and my outputs are 76.6 mV and in positive mode and 64.5 mV (don’t know how to change the scale of my multimeter), so I guess my build is the same as yours, but my bipolar LED is clear, so I think it’s easier to notice when it is slightly lit up.
As for the VCA: the only one I have at the moment, is the one that’s on the Funky Filter and I used the bottom VCACV input, which is apparently not affected by the LVL knob and I always hear the sound of the oscillator. When I use the top VCACV input, I can dial te LVL knob down to make the sound of the oscillator go away.
When searching the internet for a possible solution, I stumbled upon this envelope circuit, which is almost the same as yours, but the resistor values of R5, R6 and R7 differ. I’m fairly new at electronic circuits (I think R5 and R6 are voltage dividers), but I don’t know what the effect this has on te LM358 or if this may cause the very small voltage on the output, so I think I can’t find a solution for this on my own.
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You’re correct that R5 and R6 (in Corey’s diagram) are a voltage divider. Its purpose is to set the threshold for detecting a gate. Since the one you found runs on 9 V and Corey’s uses 12 V it makes sense that the resistors would be changed to make a similar threshold, although really that threshold isn’t critical. It wouldn’t affect the sustained output level.
R7 sets the minimum rise or fall time in conjunction with the 1 µF capacitor. Corey uses a slightly smaller one. That shouldn’t affect the behavior you see either.
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Something you could try if you’re up for a bit of kludging is to add a diode and resistor immediately after U1B (before R11):
In my simulation, without the diode the voltage does tend to 0 V but very slowly; after 5 seconds (with both pots in the middle) it’s still about 100 mV. With the diode it’s about 2 mV.
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Gave it a shot, no change. ~70mV on the outputs
I see what you were thinking tho. I wonder if a smaller resistor would work…
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Built my attenuvert the other night and finally got around to testing it last night. Not sure if I’m misunderstanding how it should work or if I should be checking my work because it doesn’t seem to do what I would expect it to.
I just patched a VCO straight to it and then out to my mixer. With the slider in the middle it seems normal. But as I move the slider in either direction the signal gets louder for a division or two, then suddenly falls off to nothing, then starts to creep back up a bit.
I was expecting more of a linear response where it just got quieter as I got further from the center. Am I misunderstanding something or do I need to check my construction?
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It’s for CV signals not audio.
Try with an LFO or envelope
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I figured it’s really meant for CV. Just figured using audio would be easy for a quick test so I could hear it more obviously. Will test it with CV tonight
Audio signals hang out on both sides of 0v, inverting the positives and negatives isn’t going to do what you expect. Once all the positive or negative part of the audio signal gets inverted it’s no longer oscillating
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Now I’m curious though, like the trick with the LMNC OBA sam posted about the other day.
Yeah, once you pointed out it’s not meant for audio and I stopped to think about it that was what I realized.
I’ve been a little sleep deprived lately with the new dog and his opinions about my face making a nice pillow at 2AM the past week I think he’s starting to get the the message that it’s not. Now he’s just doing an impersonation of an extra heavy weighted blanket 
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Hahaha I feel you. I haven’t been able to work on any modules in awhile working 50 hrs a week for the time being. when I get home my brain won’t do stuff.
One of the awesome parts about this hobby tho i can just make some noise when I’m tired. Or zone out on soldering. Save the big brain stuff for the weekend 
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If you have the OBA, try plugging your Vco into it and messing with the offset, barely fiddle with it and it cuts the sound but just a smidge and it’s like a Lo-fi distortion. I’m gonna take a listen to the same with the attenuverters
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I do have the OBA…but…it’s still on my todo list.
Tested the attenuvert on a CV and works as expected. So all seems good. Thats 2 k25’s down. Think I’ll build the LFO next since I’m still not happy with either of my two existing LFO’s my own quick and dirty just doesn’t go slow enough…and the 1145 is just too fancy for a lot of things I want a LFO for…I love it…but sometimes simpler is better!
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This little k25 LFO is nice cause the bipolar led will show you exactly what’s happening and you can get pretty slow frequency. But of course, you only have two waveforms.
The electric Druid chip is really cool, i looked at it on the scope—the wave forms are absolutely wild. And it has the sample and hold, and sync. it’s super powerful.
That being said it’s hard to control and hard to select which wave u want if you are just jamming out and you just need a wobble lfo or something simple.
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