Bill and Will's Synth
MOTM 800 Construction
(includes Tellun 800 Daughter Board)
"Envelope Generator"

March 2007 - 

The MOTM 800 Envelope Generator Module is rated a difficulty of "1" (on his difficulty scale of 1 to 5) by Paul Schreiber, but we decided to add Scott Juskiw's daughter board (Tellun DB800) and LEDs to our 800s and we knew this would make the project more of a challenge.  We're planning to have 5 800s in our synth.

We built four of our 800s from an old-style Synthesis Technology kit. In August, 2009, we finally got to building our fifth 800 - it's from a "2.0" For those of you who are building this as of "MOTM 2.0," you can download a Bill of Materials (BOM) we made for 2.0 users by clicking here. We didn't include parts for the Tellun Daughterboard in the BOM yet.

We figured the first step is to build the DBs then the 800s.

Using the instructions from the 800 as a template, we applied the steps to the DB800 - just the basic stuff - first the resistors, then the capacitors, etc.

For those who are constructing an 800, Larry Hendry didn't include the 800 in his excellent set of construction photos - so, unfortunately, there isn't our usual cross-reference here.

For those who are constructing a DB800, however, please check out Scott Juskiw's DB800 construction photos by way of cross-reference.

the 800 package laid out

Table of Contents

This page has become really long, so here's a table of contents that we hope will make it easier to traverse:

Background - presents an explanation and Paul Schrieber's initial description of the module.

Exact Behavior - illustrates the exact behavior of the module.

Modifications - presents details of Scott Juskiw's Modification and Daughterboard

Parts - presents a Bill of Materials and notes about it

Panel - presents the MOTM format panel

Construction Phase 1 - Resistors, Capacitors, IC Sockets, Power Plugs, MTA headers

Construction Phase 2 - Trimmers, Panel connections

Set up / Testing

Background

As general background, we found this great piece at Wikipedia as part of their Sound Synthesis article:

"One of the major characteristics of a sound is how its overall amplitude varies over time. Sound synthesis techniques often employ a transfer function called an amplitude envelope which describes the amplitude at any point in its duration. Most often, this amplitude profile is realized with an "ADSR" (Attack Decay Sustain Release) envelope model, which is applied to a overall amplitude control. Apart from Sustain, each of these stages is modeled by a change in volume (typically exponential). Although the oscillations in real instruments also change frequency, most instruments can be modeled well without this refinement.

"Attack time is the time taken for initial run-up of the sound level from nil to its peak amplitude. Decay time is the time taken for the subsequent run down from the attack level to the designated sustain level. Sustain level is the amplitude of the sound during the main sequence of its duration. Release time is the time taken for the sound to decay from the sustain level to zero."

But specifically, about the MOTM-800, Paul Writes:

"The MOTM-800 provides the standard ADSR (Attack, Decay, Sustain, and Release) envelope for controlling VCAs, filters, and other CV inputs. Both positive-going (0V to +5V) and negative-going (0V to -5V) envelopes are simultaneously available.

"Attack, Decay, and Release times can be set from 1ms to over 14 seconds using the smooth feel, conductive-plastic Bourns log pots.

"The MOTM-800 actually can be operated in one of 3 modes:

• GATE & TRIGGER: a full ADSR (Attack-Decay-Sustain-Release) cycle, with re-triggerable AD portion with GATE on and a new TRIGGER.
• GATE only: A-D-S-R using Roland "drop GATE" synths (SH-101, etc). MOTM-800s generate full ADSR cycles with GATE only.
• TRIGGER only: A-D cycle, useful for "stretching" drum pad envelopes.

Exact Behavior

The following diagrams illustrate the exact behavior of the EG based on our own observations and careful measurements: (click on the images to see larger ones) The measurements were taken by patching the SQR-A Output of a MOTM-390 LFO to the GATE input of the MOTM-800.  The cotrolling waveform from the LFO was very slow.  The duration of the sustain is determined by the GATE thus created (apx 15 seconds).  If the gate had been created by a keyboard controller it could have been much longer <g> - as long as the key was depressed.

Theoretically, Sustain Time = Gate Time - (Attack Time + Decay Time).  Our measurements don't actually bear this out (who knows why), but they come close.

Modifications - Add DB-800 Daughterboard

Scott Juskiw writes:

"The DB-800 is a daughterboard for the MOTM-800 EG. The DB-800 adds a comparator to the GATE input and a clipper to the output of the MOTM-800 EG. The MOTM-800 requires a relatively fast rising signal at the GATE input to generate an envelope. Slow rising signals, like the SINE output from an LFO, will not normally trigger the MOTM-800. The comparator squares up any signal at the GATE input so that any voltage rising above +1.4 volts will trigger the EG. Two optional LED drivers are also provided, one for the GATE input and another for the EG output."

photos from Scott Juskiw

Parts

If you're building this as a Two Dot Oh kit, please check out the 2.0 Page here.

But click here for the BOM we put together for the 2.0 project. The parts are correct.

Panel

Because we're including the Tellun 800-DB, we need to modify the Synth Tech panel to include two LEDs - one green - one yellow - which will serve as indicators for the action of the clipper and the progress of the envelope.

we took a close look at the MOTM-390 because it's a 1 Unit wide module that has LEDs on the left side of its face.


It's a little hard to see from this photo, but the 390 LED holes are 3/32" from the left side and the holes are 5/16" in diameter.

We had worked out an elaborate scheme of measurement and for building a jig for the task of drilling the LED holes, but we've opted for a simpler method; a paper template we designed with Powerpoint that we'll attach to the panel to show us where the holes should be.

The Panel has little studs on its back that the bracket attaches to.  Our drill press has slots in its table right where those studs are - so the panel lies flat on its back and we can drill from the front.  We've found that the advantage of drilling from the front is that the little burrs from drilling wind up on the back where you can easily file them off or ignore them.

When printed on our printer, the template design prints out on an 8" x 11" piece of paper such that the distances between Pot holes and the width of the panel work out perfectly.  And so by cutting out the template and taping it to the panel, the center lines for the LED holes wind up in the exact right spot.

Click here to download the Powerpoint file which has both front and rear templates.

Template oriented for drilling from the front.

cutting the template

fitting the template on the panel

the templates taped up

the "center punch"

! (bang <g>)

a nice little dent

Now - we got so involved in drilling, that we didn't take pictures of the process.  But here's what we did:

1. we took the templates off the panels.
2. we drilled 1/8in holes
3. we taped the front of the panels to protect them during drilling
4. we used our step-drill to drill the holes out to 5/16in

all done - looks just fine

The print on one of the panels came off with the tape. In all other panels we've drilled, we've never had this happen before. We'll have to replace it.

Construction 800 Phase 1

All the stuff in Phase 1 gets soldered using "Organic" Solder.  At every break in the action, we wash the board off to get rid of the flux.

First thing we wanted to do was consider how we'd connect the DB800 to the 800. Per Scott Juskiw's DB800 User Guide, under the "Construction Tips" section, there are two methods for connecting the Clipper to the 800 PCB.

The first method involves cutting two traces on the underside of the 800 PCB. The second method, for us (given we're buiding the 800s and not retrofitting the DB800 into an already built 800), involves bending pin 3 of the 8-pin TL072 Op Amp so it no longer connects to the PCB. Even though our 800s aren't already built, we felt more confident cutting the trace rather than messing with the Op Amp pin.

We also considered mounting an 8 pin DIP socket (Mouser has one with part number: 575-393308) onto the board and bending the #3 pin on that—idea being, we'd just plug the Op Amp into the modified plug. But, in the end, we still favored the idea of cutting the traces instead.

It bears noting that our concern about bending that pin was unfounded. Later in the construction of the 800s, as we were soldering the Op Amps in, we realized how easy it would have been to bend the pin.  Too late, of course - nonetheless, in the end, our decision to cut the traces worked out just fine anyway.

I used a Dremmel Tool to gently grind away the PCB and traces.

soldering resistors

As usual with us, whereas we are vigilant about orienting all the resistors, caps, etc. consistently so their values can be read easily (in case we need to trouble-shoot them later), we oriented the resistors with the "Tolerance" stripe on the left (relative to the text on the pcb).  Why did we do it this way?  'Cause the gold stripe is so pretty and easy to see (of course)... and so we put it on the left - well - just because.  You might want to do it the opposite way.  (For the table of resistor value markings click here.)

in go the caps

the plugs and ferrite beads are in

ready for the ICs

ICs are in

OK - so for the sake of being complete, here is pin #3 on the Op Amp.  You can see how easy it would be to bend the pin straight out rather than soldering it into the board.  I think it also illustrates how using heat shrink tubing here as Scott advises is a good idea - it's kind-of close quarters.

And another idea would be to use a IC socket here. That would have given the Op Amp a little more altitude and made the connections to the bent pin even easier. If we were to do it over, we'd definately do it this way.

the transistors and diodes are in
after washing, it's snack time!

MOTM 800 Construction Phase 2

PCB Mods

First, we had to account for the modifications needed for the 800 to connect to the DB800.  We made a jumper to bridge the cut traces on the underside of the 800 PCB, and connect the various leads that will go to the DB.

we decided to jump all the way from the underside of R to the underside of R, so we needed a 1-5/8" jumper.  This is not how Scott does it.  He neatly jumps only between where the traces are cut - click here.  But we weren't confident we can get a good joint there (we're idoits - relative newbees, remember).

stripping the ends

tinning the jumpers

here's how we've soldered in the jumper

and now the clipper connection

in go the Pots and wires

it's time to put the little jacks on the clipper connection

we're not sure whether to call this connector thing a jack or not because the jack is customarily the obviously male piece whereas this is kinda female even though it's the part that plugs into the stationary part on the board.  <sigh>  So maybe it's a Jill.  Nonetheless, it's time to put the Jills on the clipper wires.  We're using a special AMP tool.

Click here for details.

so then we dealt with the comparator connection - fist separating the white wire from the wires coming from V

and then putting another connector into the line like this along with an extra piece of wire - 8" long.

Mounting Bracket

ready, set - - go

So - the spacer that comes with the MOTM kit is 1/8" (on the left) - but now we've got stuff soldered onto the bottom of the PCB!  We're going to substitute a 1/4" spacer and longer (5/8") screw (on the right).  As it turns out, the tolerances of the Synth Tech bracket will just barely tolerate this 1/8" difference.

 here we go

 screwed onto the bracket

and with the stand-offs

panels at the ready

ready to mount

mounted
for more detail of a classic mounting implementation, click here

Daughter Board Mounting

so here we are... we reversed the left most mounting screws and put little stand-off s in there for the daughterboard

the daughter board mounted

Panel Mounted Components

jacks

from the back

ready to wire them up

wired

LEDs

here they are

the LEDs inserted... the yellow for the gate on top - the green for the envelope on the bottom.

the LEDs inserted

wired up

the heat-shrink

tied up

Knobs

here they are

done!

Set up / Testing

Use Notes