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Post by tarcreeper on Dec 16, 2020 13:50:04 GMT
This is my first DIY module so forgive me if the schematic isn’t formatted properly. It’s a low pass gate based on the design of this youtube video. i.imgur.com/7zWhGxk.jpgi.imgur.com/1PMXms8.jpgI changed some resistor values and added a buffer to power a visual LED. As mentioned in the video, It can be completely passive if you’re looking for a good beginner (I am one) project and can live without the LED. That would look like this. i.imgur.com/iiqG8QC.jpgi.imgur.com/eLht49D.jpgThe power is coming directly from the CV source so that’s what’s plugged into the “+”. |
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Post by keurslagerkurt on Dec 16, 2020 14:04:39 GMT
This is my first DIY module so forgive me if the schematic isn’t formatted properly. It’s a low pass gate based on the design of this youtube video. i.imgur.com/7zWhGxk.jpgi.imgur.com/1PMXms8.jpgI changed some resistor values and added a buffer to power a visual LED. As mentioned in the video, It can be completely passive if you’re looking for a good beginner (I am one) project and can live without the LED. That would look like this. i.imgur.com/iiqG8QC.jpgi.imgur.com/eLht49D.jpgThe power is coming directly from the CV source so that’s what’s plugged into the “+”. Thanks for sharing!! Seems like an ideal first module to build for me  I hope my MCP opamps get delivered before the weekend! |
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Post by Morn Valley on Dec 16, 2020 15:11:22 GMT
I was thinking about this too, I’d definitely get a breadboard out and try different resistor values running some gate triggers, envelopes and lfos through it and try different values.
In the commercial Vactrols I’ve read that red LEDs are used if that helps.
I’ll be trying this too so I’ll post my results to this thread.
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Post by keurslagerkurt on Dec 16, 2020 16:05:50 GMT
I'm a beginner, so I try to understand the circuit, so I have a few questions: - So if I'm not mistaking, the 2K resistor before the LED would just be to prevent it from burning out right? And then any CV above 0.6 volt should start lighting the LED and triggering the LDR? - The LDR + capacitor make the low pass filter, would adding a potentiometer in series with the LDR make the cutoff frequency controllable? Thanks for helping a noob out in advance! |
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Post by tarcreeper on Dec 16, 2020 16:20:24 GMT
I'm a beginner, so I try to understand the circuit, so I have a few questions: - So if I'm not mistaking, the 2K resistor before the LED would just be to prevent it from burning out right? And then any CV above 0.6 volt should start lighting the LED and triggering the LDR? - The LDR + capacitor make the low pass filter, would adding a potentiometer in series with the LDR make the cutoff frequency controllable? Thanks for helping a noob out in advance! Yes the 2K resistor is just for preventing LED burnout. It does effect the intensity of the light so changing that value gives you a different sound. I tried several different values but 2K worked the best with the LEDs I used. I did try a potentiometer there but it changes the level as well as the filtering and didn’t seem very useful. Sorry I can’t give you a ton of information on it because I am a noob as well. |
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Post by tarcreeper on Dec 16, 2020 16:23:56 GMT
I just realized I changed the capacitor too. 100nF gave me much better results.
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Post by Morn Valley on Dec 16, 2020 19:29:55 GMT
 Here’s a passive version I had in my notebook. It’s an RC circuit so the capacitor should affect the filter character. Using a pot on a test board in place of an LDR and trying out different caps from 3n3 to 100nf is useful. I built a load that all had different caps and LEDs and they were all unique and quick to make. |
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Post by keurslagerkurt on Dec 16, 2020 23:46:57 GMT
So the downside of the passive version would be that it 'loads' the CV input, possibly making it unstable? Or would it never really be a problem in the AE case?
Hope you don't mind me asking so much questions! 😅
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Post by robertlanger on Dec 17, 2020 9:14:16 GMT
So the downside of the passive version would be that it 'loads' the CV input, possibly making it unstable? Or would it never really be a problem in the AE case? Hope you don't mind me asking so much questions! 😅 You can always put an opamp voltage follower before the LED to avoid the load for the CV signal. The most basic usage for opamps... www.learningaboutelectronics.com/Articles/Voltage-follower |
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Post by robertlanger on Dec 17, 2020 9:15:54 GMT
BTW: I will make my own mini-vactrols available in the shop very soon, together with some other DIY components :-)
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Post by keurslagerkurt on Dec 17, 2020 9:21:45 GMT
BTW: I will make my own mini-vactrols available in the shop very soon, together with some other DIY components :-) Yay, very cool!! 😁 |
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Post by tarcreeper on Dec 17, 2020 9:57:47 GMT
View AttachmentHere’s a passive version I had in my notebook. It’s an RC circuit so the capacitor should affect the filter character. Using a pot on a test board in place of an LDR and trying out different caps from 3n3 to 100nf is useful. I built a load that all had different caps and LEDs and they were all unique and quick to make. I only happened to have 3 different cap values on hand so I didn’t tweak it very much but I have more on the way so I’m excited to try out different ones. One question about that schematic though. I attempted basically the same thing in my initial tinkering but found that I couldn’t get both LEDs to work without buffering the signal. Any thoughts on why that might be? Being able to eliminate the op amp from the circuit would make things a lot simpler. |
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Post by keurslagerkurt on Dec 17, 2020 22:18:40 GMT
View AttachmentHere’s a passive version I had in my notebook. It’s an RC circuit so the capacitor should affect the filter character. Using a pot on a test board in place of an LDR and trying out different caps from 3n3 to 100nf is useful. I built a load that all had different caps and LEDs and they were all unique and quick to make. I only happened to have 3 different cap values on hand so I didn’t tweak it very much but I have more on the way so I’m excited to try out different ones. One question about that schematic though. I attempted basically the same thing in my initial tinkering but found that I couldn’t get both LEDs to work without buffering the signal. Any thoughts on why that might be? Being able to eliminate the op amp from the circuit would make things a lot simpler. Well, LEDs actually react to current, not only voltage (thats why they need a current limiting resistor). If I'm correct, usually in modules/fx/audio your input should be 'high impedance', which means that your module should not draw a lot of current from the input (eg. CV here), or in other words, it should have a high resistance (=impedance) at its input. If you draw to much current at the input, the Voltage of the input will drop (because you actually create a voltage divider). As an example: lets say for example that you get CV from another module, and in that other module, there is a 1k resistor between the voltage source (could be an op amp in that module) and the output where you draw CV from. If you now take that CV as the input for your circuit and you place a LED with a 2k resistor to ground at the start of the circuit. You now actually created a voltage divider over the two modules with the 1k from the one module and the 2k from the other. This would mean that if your original CV voltage is 5V, your voltage at the LED would actually be 2/3 * 5V. So it would drop. If you place two LEDs in parallel, the resistance to ground gets even lower, and the voltage drops further, probably to a point where its not high enough to light the LEDs. I think the only thing worth trying without an op amp is bigger resistors and more sensitive LEDs. I hope this helps you in some way! And if I'm saying nonsense, I hope someone corrects me!  |
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Post by tarcreeper on Dec 18, 2020 6:23:33 GMT
I only happened to have 3 different cap values on hand so I didn’t tweak it very much but I have more on the way so I’m excited to try out different ones. One question about that schematic though. I attempted basically the same thing in my initial tinkering but found that I couldn’t get both LEDs to work without buffering the signal. Any thoughts on why that might be? Being able to eliminate the op amp from the circuit would make things a lot simpler. Well, LEDs actually react to current, not only voltage (thats why they need a current limiting resistor). If I'm correct, usually in modules/fx/audio your input should be 'high impedance', which means that your module should not draw a lot of current from the input (eg. CV here), or in other words, it should have a high resistance (=impedance) at its input. If you draw to much current at the input, the Voltage of the input will drop (because you actually create a voltage divider). As an example: lets say for example that you get CV from another module, and in that other module, there is a 1k resistor between the voltage source (could be an op amp in that module) and the output where you draw CV from. If you now take that CV as the input for your circuit and you place a LED with a 2k resistor to ground at the start of the circuit. You now actually created a voltage divider over the two modules with the 1k from the one module and the 2k from the other. This would mean that if your original CV voltage is 5V, your voltage at the LED would actually be 2/3 * 5V. So it would drop. If you place two LEDs in parallel, the resistance to ground gets even lower, and the voltage drops further, probably to a point where its not high enough to light the LEDs. I think the only thing worth trying without an op amp is bigger resistors and more sensitive LEDs. I hope this helps you in some way! And if I'm saying nonsense, I hope someone corrects me! That is very helpful. I’ll have to mess around with it some more. |
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Post by rodney on Dec 28, 2020 10:15:25 GMT
Has anyone tried this using optocoupler chips?
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Post by Morn Valley on Jan 2, 2021 20:29:22 GMT
Just breadboarded a basic voltage follower using MCP6002 and it works perfect with 2 leds from a single output and a 1k resistor for each LED. Reckon this is the way forward for me in AE format, due to low voltage and current. Passive always worked fine for me in Eurorack but I’ll be using a voltage follower for my AE stuff from now on.
Quite easy to add an attenuator at the input too. 50k seems to give me a good range of brightness atm. Will mess with this more and post my circuit.
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