Sunday, 29 December 2019

Synthesizer Build part-14: AD/AR Envelope Generator.

This Envelope Generator is a fantastic little extra to put in your synthesizer. It's always handy to have a few extra envelope generators in your synth to trigger filter responses or other parameters. I build a 'proper' ADSR a few pages back and this simple version is just perfect to have as extra. I found this on the LookMumNoComputer website and Sam has also done a video about this on YouTube which you can watch here:


Because the LFO from the last blog post didn't have a synchronization input I needed something that could trigger a filter response when I pressed a key on the keyboard so I decided to build this. I had just enough room left on the panel for the LFO to include this and it only needs a small bit of stripboard to build it up on.

Here is the layout that I made, which is just a copy of the one on the LMNC website but with a few changes (see text below. All potmeters viewed from the front.):



AD stands for Attack and Decay, this is when the switch S2 is in the Trigger position. That means there is no sound after you let go of the key. AR stands for Attack and Release and this is when S2 is in the Gate position and now the tone will fade out after you let go of the key.
It's fun to build it like Sam does in the video with a big arcade button with an internal LED light.
It's pretty straight forward build. In fact, it's so simple that I didn't even test it before building it in and luckily it worked straight away. It didn't work perfectly though. It needed pretty high voltage Gate signals and Triggering didn't work at all. There was a discussion about this on the LMNC Circuit Discussion Group Page on FaceBook and it turned out that Sam had advised to lower 3 of the 100K resistors to 10K and an other suggestion was to remove the diode from the input to the switch and make it a normal wire connection. I implemented these changes in the stripboard layout but I left the diode in place. I also advise to put in a bigger capacitor than mentioned on the original layout.  I was lucky enough to have kept some bi-polar capacitors that I took out of some circuitboards years ago because they came in very handy in this build. On top of the 1µF cap I put an extra 2,2µF bi-polar cap to get 3,2µF in total. (put in 5µF if you can) That gives a bit more time for the release to fade out. With just the 1µF it fades in just a few seconds.
Because I mounted this on the same panel as the LFO I was able to just connect the power leads to those of the LFO stripboard because they both use + and - 12 volt. So no need for an extra power cord and connector. This circuit can also be powered by +/- 15V.

Now, if you want something that is just as small but works a lot better then I can refer you to my 'Synthesizer Extra's No:01 SIMPLE AD/AR using the 7555'

This article is about the Thomas Henry designed AD/AR from 2014. He used the 7555 and his design works very well.

Okay, that's all for this one. If you have any questions about this or other builds on this website then please put them in the comments and I'll answer them asap. And while you're here, leave me a comment anyway!
Until the next one!

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