I’d put the switch on a breadboard and poke around it with batteries and LEDs if I were you. Once you know how it works, then you’re ready to use it in a circuit.
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Did a bit more studying of the schematic and probing of the switch over lunch. Pretty sure it’s correct. At least I’m 99% sure that in LP mode it’s connecting the right things together so for now that’s enough to test the rest of the circuit.
Also fired up the scope and started tracing things out. Was having a hell of a time until I noticed I had bumped the X1-X10 switch on my probe…I should know to check that by now!
Once I got the probe settled and started tracing things it seems to look good up to R6 where it drops to almost nothing. But the value of the resistor looks correct so that’s probably what should be happening - I need to look at the actual range on the scope and not just eyeball the waveform to see how much it’s dropping. But I still have a discernable waveform after. Looks good through the switch and up to C5…but then on the other side of C5…I’m seeing basically nothing. C5 is 2.2uf as called for and the polarity is correct (both based on the assembly diagram and the schematic)
But it may not be C5 it may just be what’s happening on the other side of C5 (the actual filter itself) is where something is going off the rails. Will have to do more research tonight.
So far nothing obvious like I found on my 808 kick though 
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Hey @juggle I found this 808 snare circuit which has a super high resolution layout for your board printing setup: http://sound-force.nl/?page_id=1980
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I am looking for a nice snare. Like the sound of the Tom/Snare that @Dud shared in the verified stripboard layouts thread. But I can’t find a schematic for it (the original video it came from has a comment from the designer saying “Sorry you’ll have to reverse engineer it yourself I didn’t make a schematic”) and the stripboad layout that’s shared just kind of bugs me the way it’s done 
This look like an interesting option. The silk layout doesn’t really help me much…but he does share a schematic so doing a board of it wouldn’t be too hard - just have to redraw the schematic and lay it out.
And an 808 snare to go with my 808 kick would be kind of nice.
Though - I really want another oscillator or two before I do more drums. So for now this is going in my bookmark list. Thanks for sharing!
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One other thing I noticed…and I’ve seen this on a few circuits. He’s using two TL072’s for four op-amps instead of just using on TL074. Which…seems kind of silly to me unless you happen to have a bunch of 072’s on hand (which I actually do right now.) It may be to help with board layout I assume…having 2 on one end of the board and 2 on the other may make it easier to route some signals on a little eurorack board.
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Using 72’s can sometimes mean a more efficient layout than with just one 74. Sometimes with through hole you have to compromise.
Oh yeah, it’s the screen for the top of the pcb, not for etching your own! Duh. Still, something to keep in the pocket. I’ve also been looking at the hex inverter mutant clap panel.
Man, I swear I’m not usually this dumb, but I’ve been making brainmistakes like this all week. Is it just me? I think this is going to be a very long winter.
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I built this one. SoundForce is good stuff.
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Ah, the fun of a mistake revealing the problem.
Spent 30 minutes tracing the circuit with the scope and getting totally different results than I did at lunch. The signal never disappeared. It was looking much better overall. Though…the signal did keep getting smaller which seemed odd…it should have been boosted back up by the opamp. Oh well I plugged it into the speaker - and nothing. What, I saw signal why don’t I hear anything?
Then I realized…I never connected the power.
But wait…why were things looking better with no power. I can understand not getting any output without power…but adding power didn’t help…and the signal disappeared sooner with power.
Then it hit me. The TL074 I had put in was one that I had pulled out of something else because I suspected it may have been damaged. I had never swapped it back in anything else to confirm it was bad. So…let’s just swap in another TL074…
It’s alive!
Which makes sense in retrospect because right at the start of tracing it things “just didn’t look right” at the input pin of the buffer. The output looked “ok” so I just figured I was making a mistake with my probing. But the opamp being bad all along now makes a lot of sense.
No sound sample yet though … the resonance is a bit out of control on this thing. I saw notes from a few other people who built it from Yusynths schematic warning that they had to experiment with different values for R18 to get the resonance responding decently. Sure enough it kind of goes from nothing to out of control squealing all but instantly. (I even splurged and got an actual reverse audio taper pot for the resonance since I had order a few other things anyway.)
And I still need to adjust the trimmers anyway. And it’s a bit late to be making much noise in here and I won’t feel like putting on headphones right now. So…project for tomorrow! And I get to wire up the ARP 4072 as well.
Then I can finally dig in on some more oscillators later this weekend
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Sounds familiar. Sometimes I manage to put a label on the part or put it in a box I keep for suspected dud components. Sometimes I end up wondering what this electronics thingie is doing in my shirt pocket, and it gets used in another project.
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So…started working on an oscillator last night. Starting from Sam’s 3340 stripboard with square out and PWM CV…as I reverse engineered a schematic out of it and cross referenced the 1222 schematic and the various 3340 schematics on this great post: https://electricdruid.net/cem3340-vco-voltage-controlled-oscillator-designs/ I noticed a few things:
First…these two resistors appear to be a bit of a mistake:
if you trace it out they’re in parallel so it’s the same as just having 1 - 5k resistor. But both the 1222 and the reference schematic call for a 10k pulldown here.
This capacitor also threw me off:
It’s marked as .1nf but the reference schematic and 1222 both use a 1nf there which appears to be the correct value.
Searching the forum I’ve found a few scattered references to these being known issues but apparently the main page has never been updated and it’s easy to miss the info if you’re just building from the stripboard layout and not thinking about the underlaying circuit.
I did get a board drawn up:
But I’m not very happy with the layout on it.
It will probably work, and even with re-organizing I doubt I’ll be able to eliminate many more jumpers. I made a few final attempts to eliminate some last night but every time I did I wound up generating 2 or 3 more jumpers in place of the one I eliminated. So…figured it was time to get some sleep and take a fresh look at it today.
Need to do some yard work, and hit the hardware store for a few things - will pick this back up this afternoon and if I’m feeling better about it will try and etch a board since I’ve got all the components on hand.
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The dots are pins, not decimals. The correct value is 1 nF.
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Ha! I didn’t see the other dot at all so it never occurred to me that it might be a pin indicator.
Though - this is why I generally like to redraw stripboards before building them - or drawing out schematics and boards before building them. Just building from an image like that I would have interpreted that as .1nf and while it would have seemed an odd way to note a value I would have probably just gone with it.
But if I had redrawn the stripboard myself I’d have realized it was the pin indicator.
And reversing the schematic and doing my own PCB layout has given me even deeper understanding of what’s going on in this circuit (like noticing the two 10k’s are in parallel - not very obvious looking at the stripboard briefly - but jumps out at you when you look at a schematic.)
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And with a bit more work I managed to get a cleaner layout with only 4 jumpers:
I’m not big on RV3 being rotated 180 out from it’s neighbors…but…I can live with it. (note - I have all of those headers away from the edge of the board on purpose to make sure I have room for any pots/jacks sticking up from the panel.)
And I’d still like to get J2 (my outputs) over near the other headers on the other side of the TL074. But…the effort it would take doesn’t seem worth it. I could probably pull it off…but…it won’t eliminate any more jumpers and may require adding more.
This would be a lot easier with dual layers and/or less restrictive design rules with tighter clearances so I could sneak more things between pins in some places. But…I want to make sure it’s easy to etch, and while my process is getting better and more accurate…I’m still playing it save with 0.5mm traces and 0.4mm minimal clearances.
Don’t think I can get this much better. So going to go ahead and etch it.
Part of me wants to add the voltage reference and a sine output…but…I have a few more 3340’s still so I think I’m just going to build this one up to do it, the PCB material is cheap so I can always build up more fancier ones later 
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Very nice. Can I make an old school suggestion; get the capacitor as close to the 3340 as possible.
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Yes, i have been tripped up with this very same observance.
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Yes … @fredrik has contributed to my knowledge of timer caps on this very circuit.
I want to be like @fredrik
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It is, same with the decoupling caps on the TL074. At least as close as I can get with a 2.54mm grid and a socket on the IC’s.
I might be able to get them closer…but it would be a VERY snug fit physically.
Or I could cheat and use a different grid spacing to locate them. But for this I’m ok with how it is.
Trying to photograph all the steps of making the PCB so I can do a thread on how to DIY PCB’s as well…just screwed up and damaged the UV film for the first time since the first day I worked with it though. So need to clean the board and start over.
And realized I forgot some stuff from the store for a different project so need to make one more trip before I can get back to PCB stuff.
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They won’t fit on the other side?
When decoupling at least, I often wonder why people don’t just piggyback the capacitor across the power pins of the op amp. There’s no rule that says every component has to be connected through the circuit board.
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