Music Easel Adaptation – Pulser & Inverter
(used with his kind permission);
adapted by Aaron Lanterman
This is based on the pulser & inverter circuits on Board
of the Music Easel
You should spend some time studying the
(Note this video is of Version 0, so pay no attention to any mention I make
of errors on the PCB; those comments are not relevant to Revision 1.)
Schematic & layouts
are some errors in the schematic and the silkscreen. Fortunately these
only involve incorrect names and values; addressing these issues does not
require any trace cutting or jumpering. First note that the “R11” and “R22”
on the PCB are accidentally swapped; the parts themselves are in the
correct place. The resistor closer
to the 2N1711 transistor should be labled “R22”
and the one closer to the MC14016s should be labeled “R11.” Thanks to Dave
Brown for catching this error.
schematic around the 2N1711,
you’ll see R21, R22, and R28 are 6K8.
This is a copy-and-paste error
in the resistor values,
since only one of them should be 6K8.
R21 should be 6.8K, but R22 should be 2.2K
(I think – it’s hard to tell on the original
Buchla schematic, it looks like it
might be 22K?), and R28 should be 100R. Thanks to Dave Brown for catching
these error; I never tried hooking an LED or light bulb up, so I never
noticed this error before. Dave also noted that the 100R values for R28
may be specific to using an incandescent bulb.
- I am convinced that the 50K sliders marked on the original schematics
should actually be 10K linear. The 120K
input and shaping resistors (R105, R106, R107, and R108) are off-board in
the original Easel, but included on-board in this adaptation.
- The original Easel has a 13.5 V supply, created using an op amp and a
transistor. If you have such a supply, you may hook it to the +13.5 pin
and omit R103 and R104.
Otherwise, leave the +13.5 pins unconnected and use R103
and R104, which create a “soft” +13.5 V supply.
I found it important to lower
R103 to something like 3.3K to counteract loading, so I marked R103 as
3.3K on the PCB. You may want to experiment with other values.
- 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.
- D3-D6 are 1N457s.
I suspect a 1N4148s or a 1N914 will work, but I have not tested them.
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
PIC, PIO, FB – Pulse Input Common, Pulse Input One-Shot, and Feedback. You
want to try to find a single-pole on-off-(on) switch, where the (on) indicates
momentary operation. Hook PIC to the common switch terminal, hook PIO to
the (on) terminal, and hook FB to the regular on terminal. This will let you
do just one “pulse,” or if you switch to the feedback mode quickly after
doing one pulse, the
pulser will drive itself and you will get repeated pulses. The middle position
turns off the pulsing. If need be, you could just use a regular on-off-on
PCVA, PCVB – Pulser CV outputs A and B. A is active when AEN is set high; B
is active when BEN is set high.
PPA, PPB – Pulser pulse outputs A and B. A is active when AEN is set high; B
is active when BEN is set high.
Y1, Y2 – terminal of an electronic switch; connection made when BEN
is set high (untested).
Z1, Z2 – terminals of an electronic switch; connection made when BEN is
set high (untested).
ANOT, BNOT – logical “not” of AEN and BEN
AEN, BEN – A and B enables; see other connection instructions for details of
what they enable. I plan to connect these to a switch that will let be switch
between automatically-on (connect to +15 V) and connect to an external input.
Most users will probably just want to tie AEN to +15 so the A outputs are
always enabled. Some users may want to just ignore the B outputs entirely.
Some might want to only use the “B” part of the circuit to control the
Z1,Z2 and Y1,Y2 electronic switches, and ignore the pulser B outputs. Do
whatever makes you happy.
INVI, INVO – inverter input and output; takes 0-10 V CV and outputs 10-0 V
CV. The inverter is independent of the rest of the pulser, so you can invert
whatever CV signals you want.
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.
LOS – Level (pulser rate) Offset
LCV – Level (pulser rate) CV; controls amount of influence of the LIN
TRIM – Trims the pulser rate – set to personal taste
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.