Music Easel Adaptation – Envelope Generator

Revision 1

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


Schematic & layouts

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


  • The holes and traces on the Revision 1 PCBs are the same as on
    Version 0. The only changes I made were to the silkscreen.

  • I am convinced that the 50K sliders marked on the original schematics
    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.

  • 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.”


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


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


These should be considered advanced projects, and should only be attempted
by people with extensive knowledge and experience in electronics,
in terms of practical construction and debugging techniques. The boards
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
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

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.