Music Easel Adaptation – Envelope Generator

Music Easel Adaptation – Envelope Generator

Version 0

Original
circuit by
Don Buchla
(used with his kind permission);
adapted by Aaron Lanterman

This is based on the envelope generator circuit of
Board 3 of the Music Easel.
You should spend some time studying the
original
schematics.

Demo

Schematic & layouts

Schematic
Complete PCB layout
PCB, silkscreen
PCB, top copper layer
PCB, bottom copper layer

Errors

Surprisingly, and fortunately,
there are no errors on this board that require changing
connections or adding missing parts!

  • R10 should be 68K, not 0u22 as labeled (obviously)
  • I set some of the silkscreen text to the wrong laywer in Eagle, so it
    didn’t appear. Missing text includes “D1 is 1N457,” “D5 through D7 are
    1N457A,” “R112 may optionally be 1K.” The 8 pin chips are RC4558s, and
    in the right column, from top to bottom, the chips are MC14016 (close
    to the 2N1711 transistor), MC14025, and MC14001 (close to the power header).

Notes

  • I am convinced that the 50K sliders marked on the original schematics
    (and this version of the board) should actually be 10K linear.     The 120K
    input and shaping resistors (R117 through R128)
    are off-board in the original Easel,
    but included on-board in this adaptation.

 

  • The circuit has been tested with RC4558s, which was deemed to be
    electrically similar to the original RC4136s used in the Easel.
    Other op amps will probably
    work (many will probably work better!), but they have not been tried.

 

  • Buchla went to the effort to specify 1N457 in one instance and
    1N457A in another instance, so I’d be nervious about changing what dioes are
    used. I’d be curious if to know if other diodes, such as 1N4148s or 1N914s,
    will work.
  • I have a tradition
    of specifying 2.2 ohm resistors (should probably be 1/2 watt)
    at the power inputs
    to perform power supply filtering along with 10 microfarad
    electrolytics. I picked 2.2 ohms since this choice shows up on some Buchla
    schematics; I did not pick it through any particularly scientific means. Any
    low resistance should work here.
    I actually use “ferrite beads,” as suggested by Ken Stone, and not resistors
    in these spots.
  • Dan independently developed his own board for the Music Easel
    Envelope Generator, and made some modifications to the circuit. I only
    tested it in transient mode; I didn’t test it in sustain mode, and much
    of Dan’s work addresses the sustain mode.

    Here is a snippet
    from an e-mail describing his work.     I’m curious to see if other people
    come across similar issues.
  • Bjorn wrote: “I am not sure whether a solution to get the transient function of the envelope generator with a regular gate signal has been proposed yet. Anyways, I have been able to get this functionality by replacing R101 with a 10nf cap.”

    Connections

    Front panel connections usually have a square and round pad together in a
    white box. The round pad is the signal, and the square pad provides a
    convenient ground.

    ATIN, DURIN, DECIN – attack, duration, and decay CV inputs; influence is
    controlled by ATCV, DURCV, and DECCV settings, respectively

    PIN – pulse input

    B3P6 – corresponds to original Easel Board 3, Pin 6

    TRAN, SUS – connect TRANS and SUS to the extremes of a single-pole
    on-none-on switch, and connect B3P6 to the common terminal of this switch.
    This lets the user switch been “transient” and “sustained” modes. (Note
    I only tested the transient functionality.)

    POUT – pulse output

    ENVOUT – envelope output

    LED – on the Easel schematics, this is actually called “LAMP” and is
    shown going through a lamp-looking symbol to a +12 V supply. I haven’t
    tried doing anything with this, since it’s a low priority for me, but if
    someone can get something to light up I’d love to hear about it.

    +13.5 V – a supply created using a buffer op amp (most users will not need
    this)

    Potentiometers

    The Easel schematics and this version of the PCB say these should be 50K,
    but I recommend 10K linear.

    ATOS, DUROS, DECOS – attack, duration, and decay offsets

    ATCV, DURCV, DECCV – attack, duration, and decay CV controls; control
    influence of ATIN, DURIN, and DECIN inputs, respectively

    Disclaimer

    These should be considered advanced projects, and should only be attempted
    by people with extensive knowledge and experience in electronics,
    particularly
    in terms of practical construction and debugging techniques. The boards
    are
    dense and the documentation is sparse.
    If you are just
    getting started with Synth DIY, we recommend starting with kits
    by Blacet Research or
    PAiA, or boards by
    Music
    from Outer Space    . (There are numerous other kit and
    PCB manufacturers, but those are relatively newbie-friendly.)

    If you try to build one of these projects, you must assume that you will be
    on your own, and be confident enough to tackle the project under those
    circumstances. I am interested in learning about people’s experiences
    in building the boards, and will try to answer questions over e-mail,
    but I don’t have time to do any hand holding.

    Any PCBs made available to the public are provided as-is, with no
    guarantees or warranties whatsoever. Similarly, no guarantees or warranties
    are made about the correctness or usefulness of the information on these
    webpages.

    Any electronic project may present a risk of injury or
    death, particularly when
    dealing with mains voltages. It is important to follow appropriate safety
    practices. The author of these
    pages, Aaron Lanterman,
    disclaims any liability for injury, death, or other damage caused in
    using the PCBs or any of the information contained on these webpages.