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What is this Synth Mod Checker?
MI Module Tester, with a few very minor changes, see over on Eurorack Synth Noodle Toaster v2 - #44 by analogoutput.
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If you use and install the heatsink that @analogoutput mentioned just know that you will need to modify the height of the MI case file because the board wonât fit in otherwise. Also, solder all of your electrolyticâs down towards the PCB. (forgot if I mentioned that already and Iâm too lazy to check my previous message.) 
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For avoidance of doubt, this is the heat sink that Iâve got.
Yes, youâve mentioned this before. However, either Iâve got wildly different electrolytics, or deeper issues, as theyâre shorter than the trimmer POTs on the front, and way smaller than the MIDI socket on the bottom.
Iâm guessing Iâll need to modify the case file anyway, as my power socket isnât in the right place any more, and the MIDI socket isnât the same as was on the original BOM. Might have to chop up some cardboard and make a prototypeâŚ
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Yesterday evening, I was playing around in DIY Layout Creator. This is three of the @lookmumnocomputer Super Simple Oscillators, going into the Super Simple Mixer:
And hereâs the same thing on an actual breadboard:
The addition of the TL074 (I donât have any TL072) for the mixer means that I get noise throughout the full range of the POTs. This may be helped by using +12V rather than +9V, as I was before, Iâm not sure.
I wouldâve posted a quick video of it buzzing, but itâs so flipping quiet, you can barely hear it. I naively assumed that plonking those op amps wouldâve allowed it to buzz with more oomph. So Iâm assuming I need to fiddle with the resistors to boost the signal from 1:1 to something else, like 1:4 or something.
Either way, this is progress!
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You donât really need to put the signal through two op amps. The first inverts it and the second re-inverts it, but for an audio signal that isnât really necessary (unless youâre mixing the result with some un-inverted variant of the original). You can just leave the second one out.
If you do want to use the second op amp, though, you can lower its input and feedback resistors from 100k to 10k, and that should help on the noise front.
But even as is, I donât see anything here that should introduce serious amounts of noise.
That seems strange. The amplitude of the oscillator output should be a few volts [Edit: few hundred millivolts] peak to peak. It shouldnât be quiet. The only thing I can think of would be if you were sending the output into something with a low input impedance.
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Presumably if I had the DSO Shell oscilloscope Iâve ordered, Iâd be able to tell⌠
It was all plugged into a Creative MUVO mini, no idea what the input impedance is on that. The other options, are to plug it into my Audio Pro C10, or take it into the house and plug it into the Cambridge Audio receiver under the telly box.
I might change the input resistor on the reinverting op amp from 100k, and try various values to see what happens. I have 10k, 33k, 47k, 56k, 62k and 82k to hand, at least one of those should result in an increase in volume. 
Thereâs a mistake in your layout, isnât there? The output resistor should connect to the transistor emitter (and + capacitor leg), not the collector (and - capacitor leg).
But (with that corrected) my âseveral voltsâ was overstating it, I get about 200 mV peak to peak. Which should still give you good volume.
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One of these images is wrong then� Both the 2N3904 and the SS9018 have the same EBC TO-92 package arrangement. I also know that there is variation in where the transistor, capacitor and LED join together in the various images too.
Maybe this is one of those, it doesnât matter things? Or maybe the difference in the images is important, i.e. if the transistor doesnât match the capacitor +/- legs, then you should take the output from the collector, otherwise if they do, take it from the emitterâŚ?
I should try it just to be sure, easy enough to move a few wires and see what happensâŚ
Both images are from the project pageâŚ
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Huh, never noticed that. In that one the capacitor is from emitter to ground rather than emitter to collector, which is how Kerry Wong did it. And, yes, the outputâs connected to the collector.
I had your version on a breadboard and wasnât seeing anything, and then looked at the emitter and saw oscillations, so I figured that was it. But you should get oscillatory voltage on the collector, otherwise the LED wouldnât blink. [Edit: Oh duh, current, not voltage. The voltage on the collector is just the LED forward voltage, of course it doesnât oscillate.] So I dunno. I already pulled the breadboard circuit apart but maybe Iâll put it together again.
Anyway, yeah, the two diagrams are quite different. And yours has the capacitor like one diagram but the output like the otherâŚ
Later:
Huh, interesting. This circuit
looks like this
where yellow (top) is emitter, blue (bottom) is collector. This:
looks like this:
Wait, I just said the collector voltage doesnât oscillate because itâs just the LED forward voltage, and here itâs oscillating. Man. I get so confused by transistors and diodes.
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Time for a bit of experimentation⌠
So I tweaked my breadboard to take the output from the emitter, rather than the collector, but the sound was even worse! Barely audible in amongst a sea of random noise, so not sure if Iâve got an issue somewhere else with that layout or not.
So I switched to this layout:
Iâd say itâs working nicely now. 
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Hell yeah dude thassa drone!
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Finished up rebuild of my ribbon controller interface
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I LOVE THESE! Very nice colors!
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How linear is this response? Would be cool to have 6 of these to use as a guitar fretboard, like a lapsteel.
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With 6 you must work your taping guitar style
good idea but too expensive
I made myself a diy ribbon but if it wasnât so expensive I would like 1 like this one, maybe one dayâŚ
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Yeah, that SoftPot sells for about $25 each. 
But itâs as linear as your software makes it. Itâs wired up as a voltage divider with a fixed upper resistance and variable lower, so the voltage it produces isnât linear in the position, but itâs easy enough to apply the transformation to linearize it in the Arduino code.
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