Source: SCM-140-ADSR on Github
The following modifications were made by me:
- Converted schematics and board to Kicad
- Added component values to silk screen
- Added a PCB faceplate in Kicad
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Main board silkscreen is missing values, transistor types, and IC types
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IO board silkscreen is missing values
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Main board is meant to be mounted upside down (note the +12V/GND on JP5). More clear on that.
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R43 and R13 from 47k to 137k (otherwise the attack phase doesn't hit high enough until decay. Still, maximum is 9.3V now)
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Consider reducing the main cap lower than 3.3uF, envelope is too long. Changed to 0.47 uF
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See if we can add something to toggle (allow turn off) auto-retrigger
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Note: Electrolytic polarity, also for the main state caps!
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Note: NPN transistors are EU-style (BCxxx), PNP transistors are US style (2Nyyyy)! <-- check the BOM as well.
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Note: TL072 seems to have less output noise than LM4558, but that may just be a part issue.
A CircuitJS simulation is available.