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Basic Action about farmEG
(Based on "constracting farm921")

EG Using NE555

At first, you should better check this page for the basic operation of EG.


(it's one of MR. tanaka's pages. He write his all pages in Japanese . if you can't read them, you should better use this service(AltaVista - Babel Fish Translation))

the Most first module that I assembled
"1: Principle AR type EG " may be good reference for you.
Most important point is getting gether electricity through resistor onto the capacitor, and throwing away them through resistor.It can change the speed to do that. Big value of resistance is not easy to run through for electricity, or small value of them can discharge it easily. it may change their speed. the changeing voltage can be seen over the output buffer that has high input impedance.

NE555 have compalater and easy switch. they will make them easy to checking the moving voltage and switching and they will possible to form EG relatively simply.

As for the data seat of NE555
the 4th page of "1.Basic Operating Table" is the chart what we want to learn.

You may also need this schematics to verify
Second ADSR Schematic
Let's check the action of EG dividing in 4 period called attack, decay, Susteen and Release.

Attack period

  1. Making triger at the moment we get input gate, and put it into (2pin) of NE555.
  2. Making the voltage which does not depend on input level by transistor and put it in to reset of NE555 (4pin).
  3. Discharge of NE555 (7pin) will open. (in many cases, it's the same state as staring) there is no voltage difference at the both ends of the susteen volume, so there is no susteen voltage.
  4. Output (3pin) becomes on, setting of the attack time pot passes the voltage for attack and charges the capacitor.
  5. Attack period will ends by getting voltage threshold. it is 2/3 VCC. this value is set in the NE555.
Decay period
  1. When the Attack period ends, output (3pin) becomes off. there is no voltage to charge the capacitor
  2. Discharge (7pin) becomes on,(electricity flows to GND, voltage of the both ends of the susteen volume come back.
  3. At this point the voltage is higher than susteen level so it get start to discharge.and its speed is decided by the resistance of decay.
  4. Attack period will ends by getting voltage is same as susteen.
Susteen period
  1. The same state will continues untill input gate has been entered.
Release period
  1. When the input gate ends, discharge (7pin) becomes off this the signal which reverses reset (4pin) entering, and susteen voltage becomes off.
  2. Output (3pin) dose not chenge its state (it is off)
  3. Diode controlle the flows and release pot may change the speed to discharge. electricity in the capacitor may throw away into the emitter of the transistor inside of NE555.
making Susteen voltage is the core of this methods


EG may have big infruence for playng keyboard style. and I think that small mod is one of presure of DIY.

  • KUNII version
  • RadioJunkBox version
      Decay level going down to the susteen level. and its flows is controled by diode. so we can change the susteen level up word only. RadioJunkBox add the mod by only 1 FET to be able to change the susteen levels. http://homepage2.nifty.com/rjb/pdf/rjb_diy_synthe_501a_vca&eg_schem_revA.pdf
      his top page is here. You should better to check the page about moduler synth that have prohet5 like panels its so nice!

  • Return to the top page of HomeMadeSynth
    Returns to Takeda's home page

    This page is transrated from a part of my page that written in Japanese, named "constracting farm921".
    This page is just the report of experiments by amateur, And this page guarantees nothing else. I've been checking my page, but I can't still care about the trouble that may be coused by this page.
    In addition, the writer of the page that I had put by URLs to my page also has no responsibilities.

    Basic Action about farmEG" Copyright 2002 2004, Motohiko Takeda and Crow Hill Laboratory
    Motohiko Takeda Mail:takeda@aleph.co.jp