LMNC Bandpass Filter

Oh, I don’t think it’s wrong, it’s just that you moved the Res 2 leg to that strip itself. Leaving it in place just means that wire connects Knob 1-1 to pin 14 of the IC. I would suggest moving leg 2 back and implementing Sam’s fix, then connect 1-1 to pin 14, but either way works. Alternatively, get rid of the wire to pin 5 of the IC and just put Res 2 directly on it.

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I might be wrong but when I checked the schematics that wire needed to be on the same line as the 1k and 6k8 resistor.

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This just made me realize that I definitely need to wait to build this module until after you guys have perfected everything! :grin:

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True, though I still enjoyed this one before all the troubleshooting. I have 3. The original layout works, just not quite right. Haven’t tried the newest ideas yet. Maybe later today.

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Is your circuit working well if so I will modify mine to yours

Yeah it works perfectly.

I have videos on my instagram Instagram.com/jonny3snares

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it works pretty well with your changes

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Glad to hear it! I’m a complete noob with electronics so that’s music to my ears

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Hey @ChristianBloch and @jonathanhipgrave …can you answer a question about this please? Sam suggested that you could swap the two diodes with LED’s and panel mount them to signal when the resonance is high. Jonathan, I saw you ran your wiper on the res pot off of the line with the diodes. If you swapped out the diodes for LED’s do you know how it would that affect the modifications you did? Or is there a way to keep the diodes but still have the LED’s? Having LED’s for reference helps me so I’d like to add them if at all possible?

LEDs are diodes so swapping is really, more or less, the same circuit

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Thanks. I didn’t realize that. :slight_smile:

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They have different forward voltages so the resonance won’t behave in exactly the same way, but there’s no reason not to try it.

1N4148 to the left, a random red LED to the right:

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Resonance is all about feedback where the amplification of a circuit nears or exceeds -1. At -1 the system starts to oscillate and it does not need an input signal anymore. If you dampen that, you get the resonance used a lot in electronic music. The forward voltage on LEDs is much higher than that of a 1n4148, so you may need to experiment with different coloured LEDs, because different colours have different forward voltages and maybe change the series resistor. I’d also suggest to try 2 different LEDs. Possibly this makes for a different tonal quality in the resonance because the waveform might get asymmetric. If this is interesting I can imagine adding a switch which will allow to choose a LED combination because of its tonal quality. Can anybody try this?

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I haven’t tried the switch thing. Cool idea. I have experimented with many different coloured leds in different filters they apply to. I’ve settled on blue for the most of em.

What are these diodes there for anyway / what is their function? Given there are 2 in opposite directions it can not be because they rectify the signal. Does this have to do with their capacitive value ( like in diode based Moog-kinda filter topologies )? Or is it the forward voltage that creates some sort of offset?

I don’t know if this will help to answer your question about the diodes or not but here’s the schematic this band pass was based on. I know it was posted earlier in this thread but I’m posting it here for ease of reference. Does reading this answer your question about the diodes function?

FB165C0C-35C4-42AB-A4F0-85274347C69C

No, thx for reposting it, but I saw the diagram and wondered what they are there for. I’m asking myself what would be different if they were replaced by a simple wire. Then the 0.6 Volts forward voltage would not be there, but what effect would that have? Maybe someone who has one of these could try that. There is no risk of blowing anything since we are talking small signal levels and currents here. As as I mentioned in my earlier post, could it be they are used as a voltage dependent capacitor ( like in the MOOG ladder filters ) ?

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The resonance feedback loop has two paths – either via the 22k/50k/4.7k variable divider, or the fixed 6.8k/15k divider and the diodes. As the diodes start conducting, the fixed path will add to the positive feedback, introducing non-linearities.

(I don’t think capacitance is involved, but then I’m not sure what Moog ladder you’re referring to – doesn’t the traditional Moog filter use a symmetric transistor ladder, with capacitors in between? Time for some reading, I guess :slight_smile: )

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The traditional Moog ladder had transistors the diodes in which are used as capacitors. There are also capacitors between the transistors, but the capacitance value of the transistors diodes themselves can be controlled via a DC voltage and they play an important role in the filtering effect. This makes the filter’s cutoff frequency voltage controlled. This is as far as I have understood how it works. The values of the fixed capacitors can not be voltage controlled. Seeing the diodes in this diagram I started wondering whether they had a similar function.