ACMS: Analog Circuits for Music Synthesis

Final Project – Spring 2016

For the project, you will construct an analog synthesizer
module to expand our existing modular
system. You will be allowed to
use existing schematics you find from the web and elsewhere.
I will allow you to work in groups of up to two people; although there
will be benefit to splitting up the work such as having one person build
the circuit on the breadboard while another starts inputting the schematic
into Eagle,
please try to have everyone involved at least a little bit with every aspect
of the process.
Projects with two people should be slightly larger in scope than
projects with one person. (I will often use the word “team” to refer
to “teams” of just one person as well as two people,
so don’t let that confuse you.)
I will help you
scope your project accordingly.
If two people independently come up with similar
project ideas, I may suggest that they join forces.

You could “modularize” part of a complete synthesizer circuit (i.e. build
a module based on the VCO, VCF, or whatever of a subcircuit
of a complete synthesizer).
This may
involve adding/modifying input and output circuitry so that the resulting
module matches the specifications given below, and also may involve “updating”
the circuit to use modern parts. It would be nice if this was relatively
“original,” in that a modularized version doesn’t already obviously
exist on the web.

You can do something more original. If you’re doing a project that is based
less on existing proven designs, I will put priority on helping you out during
the design process. (The more original a design is, the less strict I will
be about how “polished” the final result is.)

You must be sure to give credit to
the original inspirations of your designs wherever
possible. If you
eventually consider marketing your design (say, starting a business
to sell boards), karma demands that you consider discussing
sharing a portion of your
with the original sources of your design, if possible.
(As mentioned in class, schematics
can be
but circuits can’t, so if a circuit isn’t patented, you can legally
use it
and sell it however you like – but what’s morally the right thing to do
may be a different story.)

You aren’t constrained to use any existing designs if you don’t want to.
If you are feeling adventurous and want to
try making something
up out of thin air, or some combination of thin air and existing
designs, that’s
OK. I’m allowing you to make such extensive use of
existing designs since (a) most of the synth
I know of actually got their start from tinkering around and modifying older
designs, and (b) even getting a circuit from a published schematic working
can be challenging.

Your module must either make audio (i.e. an oscillator), or process audio
(i.e. a filter or nonlinear waveshaper), or sometimes both (i.e. a filter that
self-resonates when the Q is turned up really high).
Since this will be a component of a synthesizer, in general,
some aspect of your module
should be controllable via a control voltage; for instance, a filter
whose cutoff is solely controlled by a pot won’t do.

Here is an extensive
list of
project ideas
You shouldn’t by any means feel restricted to pick something on
that list (which I’ll keep adding to as random ideas strike me);
you can use the list to
get an idea of the sort of things I’m looking for.

Collaboration policy: Teams are
are strongly encouraged to help other teams
out, both with bantering around design ideas and
particularly with debugging.
Often, the
mere act of trying to explain what’s on the breadboard to someone else
will cause
you to discover the source of a bug.
You can draft people from outside the
class to help you design and debug too. Feel free
solicit advice on online forums (the
SDIY list that I’m going to make you join will be particularly helpful.)
only caveat on all this is that you must
thank the people who aided you
and describe
how they aided you in your report. (Also, don’t be dishonest about it,
i.e. don’t try to con someone online into designing an entire circuit for

Timeline: How about the following tentative timeline:

  • By Thursday, March 31, send me an e-mail about what you want to do
    for your project.
    (If you have absolutely no clue, I’ll try to suggest something, but I’d prefer
    if people picked something they’re enthusiastic about).
    I want to have a diversity
    of projects, so if someone tells me they want to do a project someone has
    already picked, I’ll probably suggest they try
    something else (or suggest some additional twist).
    First come, first serve, more or less. Put “ACMS project idea” in your e-mail
    so I can easily sort through them. The sooner you get this to me, the
    better; I have an encyclopedic knowledge of obscure synthesizer related
    tidbits (you may have noticed), and I can probably suggest some ideas to
    to give you a head-start. I will get together with you and give you whatever
    parts you need.

  • Depending on your project, it would be a good idea for you to get me
    a draft schematic as soon as possible – you can scan it and e-mail it to me.
    I may put it on a website and post it to the SDIY mailing list to get
    comments and suggestions. If you’re modularizing or modifying an existing
    design, you can print out the schematic and kind of sketch out the changes
    you are planning to make, or just send me a URL to the schematic and describe
    the changes you plan to make in an e-mail.

  • By Thursday, April 7,
    have your circuit assembled on the breadboard.

  • By Thursday, April 14, let’s have a fully debugged and refined design
    on the breadboard.
    Debugging circuits is tricky; it
    requires a detective’s mind! There may be a problem in the hookup on the
    breadboard, or there may be a problem with the underlying design in the
    schematic, and you never know which is the case at first.

  • By Tuesday, April 19, have a PCB layout of your circuit design
    ready for fabrication.
    I will help you with the PCB layout. Do the
    schematic capture in Eagle (you can download the free-to-use version), and
    I will basically do most of the PCB
    layout while you watch me do it. (I’m trying
    that as a new approach this year based on my experiences from last year.
    Basically, your first several PCB layouts are guaranteed to be pretty bad.
    So, I will explaining to you what I’m doing while I’m doing it so you
    can pick up tips and tricks on the things I sort of do subconsciously.)

  • Sometime during the weekend of April 29-May 1 —
    show me a working, soldered module. (You’ll probably discover errors on your
    PCB; you may “hack” these however you need to get them going.)
    That weekend, all the senior design students will have largely cleared out
    and we will have the labs to ourselves.

In addition to the project, I want a brief user’s manual (in electronic
form, e-mailed to me) explaining
what your module is,
what the
controls do, etc., and a few basic notes about how you came up with the
design, any calculations you made (for instance, to get something
to match the MOTM standards), etc. Please include photos of your final
built circuit board. (Including a photo of the breadboarded version would
be nice, but is optional.) Basically, your report should be sufficiently
detailed for someone else to reproduce your work.
This should be reasonably slick, i.e. the
text should not be
handwritten. I’d like to
emphasize the word “brief.” I am more interested in PRODUCT
than I am in PROSE.
Do not write something lengthy, since
I will not have time to read it anyway. Please get this to me sometime
during the week of April 2 to April 6. finals week.

Due dates, sort of:
The above timeline is just a guideline to help you gauge your progress;
I won’t be carrying a specific checkoff list.
(However, if you start falling behind these guidelines, you should redouble
your efforts to catch up.)

Specifications: Your module should satisfy the MOTM standards
(taken from the MOTM website):

  • 1/4″ jacks for connections (I will get a bunch of 1/4″ jacks)
  • In general, a 1 volt-per-octave
    response for VCOs and filters (you may want to include
    an additional linear input, if appropriate). Some filter designs won’t have
    a clear exponential control mechanism; don’t feel obligated to try to add one.

  • When running wires to the jacks,
    use black for ground (this will make debugging easier).

  • Positive-going GATE voltages (+1.5 V threshold)
  • Positive-going triggers
  • Audio levels of 10 V peak-to-peak (i.e., -5 V to +5 V)
  • VCAs respond from 0 to +5 volts
  • Use the standard
    MOTM power connectors. There’s two kinds,
    depending on what you
    need. If the long tab
    is to the
    “right,” then reading from top to bottom, the MOTM power supply gives -15 V DC,
    two ground pins, and +15 V DC. (The MOTM website says these are “standard
    AMP MTA-156 4 position” connectors.)
    If you are using some digital logic (TTL, CMOS, whatever),
    you can use the six-pin connector. The bottom four pins are the same as the
    for the four-pin connector, and the topmost pin gives +5 V DC
    and a “digital ground”
    (so you can try to keep digital switching noise away from
    the “analog” part of your circuit.) The ECE lab staff stocks these; ask in
    the stockroom.


for a partial list
list of specialized synth-related parts I may have personally stockpiled.
If you want something to
experiment with or put in
your final design, just ask. A lot of more standard
parts, including pots and
TL08x type op amps (which are a good workhorse audio
op amp) are
available form the ECE lab stockroom.
If you need some other part that I don’t currently
have, let me know and I’ll see if I can get it.

Tips on jacks:
The jacks we are using allow connections to be “normalled,” which may come
in handy in your design. If you look at the jacks, you will see that ground
is ground, but the signal connection can go to one or two points. When you
plug in a cord, the signal part of the plug will connect to the “signal”
part of the jack. But if you don’t plug anything in, the signal part of
the plug will snap to a “default” connection.

In lab, you can use the various signal generators to provide audio, and you
can use the many speakers hooked to the computers in the lab to listen to
the audio. It is often convenient to clip allegator clips directly to the
jacks themselves to emulate plugging something in.

Grading: Your project grade
will be based on how impressed I am.

I consider
the project to be the most important thing in the class; hence, your course
grade will max out at whatever your project grade is, e.g., if you do B work
in the exams and homeworks but turn in an A project, you might get an A
for the class,
or you might get a B; but if you do A work on everything else but turn in
B level project, your grade won’t be an A.

My general procedure in this class is to push each student until I see what
I consider “A” level work.