My first DIY modules - starting a Kosmo format build

I’m actually thinking about doing both. I need a VCA anyway. I have the board for Sam’s quad VCA/mixer coming (Got a response from his store that they are resending my order that arrived empty) but I don’t want to wait and “you can never have too many VCA’s” and I have the parts to build a simple dual VCA so might as well do it.

But also figured it might be nice to add the attenuator on the input as well since it’s fairly simple to add. And I want to do a little rework on the filter anyway to fix the two +/-12v wires to the cutoff pot which aren’t on a connector. And need to reprint the plate to fix the label and beef up the board supports. So while I’m at it may as well add in a little attenuator circuit :smiley:

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So adding a 100k pot on the input definitely helped. I can still get it to lock up with some extremes but it’s much less frequent and it recovers when I back off now. Also reversed the wiring on the resonance pot because it felt “backwards”.

It still seems a bit off. Like the response when adjusting the cutoff or the resonance isn’t smooth at all…So may still experiment with some different pot values on there. (I think I’m running a b100k on the cutoff and a100k on the resonance right now)

Just playing around but kind of liked how this was coming out - the little bass hit at the end of the swoop caught me by surprise. And I loved the way it fell apart when I pulled the power and let the caps in the power supply slowly drain :smiley:

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Is the forward voltage of the LEDs really that noticeable in this circuit? I also have blue LEDs and think my filter is doing really well. Has anyone already tested the difference and can say something about it?

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I’ve seen a few comments in other threads that it can have an effect - but I’m not at all convinced it’s why mine seems unpredictable and jumpy. I need to get a video of it while I twiddle the knobs to share to see if it’s just my perception or if it really is a bit wonky (and if it is I’m guessing it’s the pot values I’m using just letting me get out of the “Sweet spot” on some things.)

In other news - the mailman just stopped by and it looks like I’ll get to take a night or two off from strip boards to build a few PCB’s:

This package thankfully arrived 100% intact :smiley:
And yeah…I don’t need a delay and really don’t need a mega drone in here right now…but…the mega drone will help fill some space and bit a bit of fun…and the delay was actually the first module I ordered the PCB and parts for because I’ve been looking for a delay for my cigar box guitar for awhile and figured I may wind up routing it through there at some point (and with one of AO’s Mikrokosmos’s on it’s way as well I should have a nice way to bring the signal from the CBG up to where I can have a bit of fun with it.)

I also just had to get a megadrone since after not thinking about modular for a few months the video of it suddenly popped up in front of me somewhere and led to me deciding it was time to finally dig in on building some modules. So…I felt I kind of hand to get one just in honor of it spurring me on.

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I’ve been pluralizing it as “Mikrokosmi” but then I was already probably going to Hell anyway.

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Speaking of which…I just looking at the BOM and making sure I have all the parts on hand for when the boards arrive.

And I’m curious.

Why is the TL072 labeled as U2 when there’s no U1 in the circuit?

Oh, and have you seen the interactive BOM generator for Kicad? https://github.com/openscopeproject/InteractiveHtmlBom

I forget where I first ran across it but found it pretty impressive.

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<Tooth grinding noises>

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For “cosmos” in the sense of “universe”, Merriam-Webster provides no plural, presumably on the grounds that none is needed (apparently there being no Everett-Graham-Wheeler enthusiasts at MW). But in the botanical sense:

plural cosmos\ ˈkäz-​məs , -​məz \ also cosmoses\ ˈkäz-​mə-​səz \

In Greek the plural of κόσμος (kósmos) is κόσμοι (kósmoi).

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<Contented sigh>

I’m not a classicist, but I know enough Latin and Greek to feel icky when plurals are faked.

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So first I had a 100k pot for the cutoff where I think 4.7k belonged. When I swapped it, I found it much better. And it does not start self-oscillation until much later, about half a to three-quarters of a turn. I have a feeling that it can be done better.

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Added my Mikrokosmos and since I have a cigar box guitar with a piezo pickup I had to try patching it though. Not enough modules to do too much yet…and i’m really bad at playing with a slide…(but with a horribly bowed neck and misisng frets that’s the only real option on this thing) but was starting to get some interesting sounds out of it:

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That sounds way better than it has any right to :astonished:

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Thanks. I should have compared it just running the piezo in the CBG straight to an amp. It’s actually much better behaved through the mikro and doesn’t go into feedback as easily. Which…surprises me since the extra gain the miko gives it I would expect to make that more likely.

I also tried the other CBG that’s juts sticking to the frame on the right size in front of the strat, it has half of a precision bass pickup and sounds a lot cleaner straight to an amp. But also worked well through the Mikro and filter - though not as gritty.

Either way they’d both sound a lot better with someone who’s got some talent with stringed instruments :laughing: I’ve been trying to learn guitar off and on for almost 40 years - admittedly mostly off until the last 10 years when I’ve tried to get more serious about it.

I really need to try building a MIDI wind controller one of these days, Something like a yamaha EZ-TP or a Morrison digital trumpet. I mean I’d love to just buy one but there’s no way I can justify the expense. But trumpet is the one instrument I’ve ever been good at. Keyboards and guitars - I understand the theory of how to play them…it’s just that my muscles don’t seem to want to learn to move the way my brain tries to tell them to :wink:

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I haven’t put the circuit together yet…but printed up a panel for a simple single PT2399 delay last night…I thought @Bitnik may appreciate the solution I came up with to fit “Feedback” on there given his suggestion about how to label the reverse avalanche :wink:

The circuit will basically just be Sam’s simple version from the triple splashback (which I have built except for the 100k pots I’m waiting on - gave in and ordered from small bear, just had to order more than I was planning on to get a price break that puts them where I was willing to pay :smiley: ) I made a few minor tweaks to the stripboard layout to add an eurorack power connector and bring all the connections to 6 adjacent pins so I can use a JST-XH connector to attach the panel:

There’s some wasted space vertically…I could eliminate 7 rows of stripboard very easily. But that would have caused some issues with positioning the board supports on the panel and them interfering with the jacks or pots. And some extra space means I have room to experiment if want to try squeezing anything else in there down the road.

Hope to have it soldered up tonight.

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Ok, didn’t get to melting ANY solder last night :frowning:

Instead I decided to work on solving a knob problem. Going back to my first 2nd post and my quest to 3d print aesthetically pleasing custom knobs. Printing knobs that fit knurled or D-shaft shafts is easy…I have no problems with either of those. The problem has been coming up with something that works on smooth shafts since adding a set-screw doesn’t really work well as they tend to just strip out.

I had mentioned the possiblity of pursuing a 2 part solution. And that’s what I finally decided to try last night. An inner soft housing printed in Siraya tenacious flexible resin, with a hard outer knob printed in standard resin.

And it seems like it may work.

First I tried just printing my original design in 100% tenacious. (I also tried dying the finished print with analine dyes to see how that would work…it…didn’t work great.)

This wasn’t very successful. The thin inner part that grips the shaft was TOO flexible. So the parts with the cutouts did nothing and the solid part deeper in wasn’t quite tight enough.

So - dual material it would be. My first attempt was similar to the commercial knobs I’ve been using that came with some cheap amazon pot’s - just an innner circle slightly smaller than 6mm (5.9 to be precise) with 4 “arms” coming off to the outer shell. I printed a few up and tried them. And at first they seemed to have promise - but after about 30-40 seconds they loosened up and didn’t grip the shafts well enough anymore.

So back to the drawing board. I made the center a bit smaller (5.7mm) and added twice as many arms. Also tweaked the depth of the arms a bit to make the fully supported top a bit deeper:

insert_bottom

insert

I printed a few of those…

And hey this has promise! They were a snug fit, and stayed snug. Even this morning they were still tight enough to turn the knobs - if I really torque them at the ends of their movement they can rotate on the shaft - but they still grip well enough to move my smooth shaft pots and these are fairly stiff pots so I’m happy.

Next time to model up a hard shell to go over the inserts:

My idea is that the shell should compress the soft inner part a bit to give an even tighter grip. So I left no clearance between them. (the top of the insert is chamfered partly to make it easier to put the cap on but also partly to compensate for “elephants foot” from printing.) I just drew up a quick and dirty design very similar to the commercial knobs. Then printed a few of them off in basic grey resin (since I have lots of it…I’m almost out of my nice black resin.) I printed half of them with the top on the build plate, and half with the bottom on the build plate. Both had issues…but work.

The ones printed with the top against the build plate had pretty bad elephants foot and the indicator mark was lost. The ones printed with the bottom against the build plate the mark was visible…but the bottom had bad elephants foot - and on one of them part of the bottom blew out due to resin getting caught inside while printing. Printing these angled is probably the best bet…but will cause it’s own issues. Further experimentation required.

But they have the nice tight fit I was hoping for:

The hard shell also seems to make them fit snugger like I was hoping - with the shells on these are really hard to pull off and it takes even more torque to get them to slip even on the smooth shafts.

They’re not what I want aesthetically yet…but they’re functional and a step forward:

You can see that top knob has no indicator and gnarly elephants foot. And on the two printed the other way they both have a small dimple in them which again is due to the forces of the resin while printing. So i’m going to have to try another batch printed at an angle with supports to see how that goes.

As for cost/time…

The inserts I can print 15 at once it looks like. Due to how resin printing works printing 15 or 1 takes the same amount of time which is just under an hour and a half. The tenacious resin is pretty expensive $65 for a kg (or about 1l) even so 15 of them only use about $0.88 worth of resin according to my slicer which works out to just under $0.06 per insert.

The caps I’m still experimenting with the best way to print. Without support they take about 1:15 minutes to print up to 10. But as my first test shows that gives less than optimal results.

With supports I can only fit about 6 at once and they time goes up to an hour and 45 minutes…cost is negligible. The standard resin I use is $30 per kg (which is also about 1l) and my slicer is reporting that it’s about $0.17 worth of resin to print 4 with supports. Or about 4.25 cents per cap.

So while details on the caps is still pending it looks like about $0.10 per knob with this method and about 5 hours time on the printers to make 15 knobs. Since I have two printers I can do inserts and caps at the same time so my time is closer to 3:30 to do 15 running the printers in parallel. The caps are the slow part though and since I’m still experimenting with them that could change. If I could get them printing well without supports it would really speed things up…but I can’t think of a way to do that without adding a hole at the base somewhere.

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Heck yeah, function first, then pretty it up! Looks like you got a winner!

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Just thinking about cheap knobs, has anybody tried just supergluing a pop bottle cap to the end of the shaft?

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Or a wine bottle cork with a hole drilled in it.

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For the record…I bought my neutron before Behringer took that idea to a very ugly place :disappointed:

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And the simple/single delay earns it’s knobs.

Speaking of which…here’s a closeup of my latest knob attempt:

That little hole in the skirt seems to be key to getting them to print well without any blowouts. It gives just enough room for uncured resin to escape while printing. I’m not huge on leaving a hole like that…but…it beats the broken skirts I get without it. I may have to order some more black resin now and start working on knobs I’m happy with aesthetically rather than just functionally.

This is based on LMNK’s single delay from his 2399 Splashback, I just added a 10 pin power header and moved all the I/O to 6 adjacent pads so I could use a JST-XH connector to attach the panel:

Note - there are a few minor changes to the layout compared to what I posted earlier. A few minor corrections and a few optimizations based on how the build went.

Since I wound up mounting it along the left edge I really should have shifted things a bit to clean up the wasted vertical space. It would not be hard at all to save 10 strips…which is enough to build some other circuits on so probably worth doing. Live and learn.

The wiring isn’t the cleanest…but with it all coming to one connector it is at least easy to remove the circuit from the panel:

And for you solder fetishists…

Thankfully I took the time to do a no chip power test before trying it. The power readings I was seeing didn’t make any sense at all and I started to smell the distinct smell of overheating electronics…hmmm. The LM7805 was on the verge of going incandescent. Then it suddenly made sense. I had managed to install the 10 pin header backwards. Whoops. Apparently LM7805’s don’t like being fed -12v! But despite heating it enough that the metal tab started to discolor it apparently still functions when fed positive voltage. With that out of the way I popped in the chips and gave it a go.

No video to confirm it’s functionality…since I don’t have a VCA and envelope generator in the rack yet I don’t really have a way to generate tones that would echo properly. I did test it with the Mikro both with my CBG plugged in and just scraping/tapping on the piezo and it does work. Just…the sounds used to test at this point weren’t worth sharing :smiley:

Also - I started organizing all my notes and files in a git if anyone is interested: https://github.com/jhitesma/Modular-Synth-Build

I realized that I really prefer having the original DIYLC file to work from instead of just a PDF or PNG of the layout since then you can use their net inspector tools to trace things out easier and make sure you’re building correctly. Plus…it’s easier to change something that already exists than start from scratch when making minor layout changes. So I wanted a good way to share my original DIYLC files for the layouts I’m using, and at that point figured may as well just start putting everything together in one place. I also have exports of the F360 projects for the panels in there as well as links in the README.md’s for each module to the live F360 projects in case I forget to update things in the repo.

I see I have an unexpected delivery coming today from Fedex. Fingers crossed it’s my new LMNK boards to replace the ones that were meant to be included in the empty cardboard sleeve I received a week or so back. If not…then I’ll probably dig in on a VCA (probably LMNK’s 1181) tonight.

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