16 Step Sequencer (+/-9V to +/-15V)

Article by Ray Wilson · Music From Outer Space · musicfromouterspace.com

This is an intermediate to advanced project and I do not recommend it as a first project if you are just getting started in synths or electronics. Only the circuit and some explanation are shown here. A lot of project building, troubleshooting and electronics experience is assumed. Additionally, electronic equipment ownership (scope, meters, etc.) is taken for granted. If you are interested in building this project please read the entire page before ordering PC boards to ensure that the information provided is thorough enough for you to complete the project successfully.

Digital board redesign eliminates need for previous version's kludges.

Previous Version for Reference (on Ray's original site)

Not Ray's words: this is the 2006 version of the sequencer, the one with the improved digital board, and every drawing below is rendered sharp from Ray's own PDFs rather than his small preview images. Each drawing opens full size when you click it, and the PDF link under it is the original file. The PDFs are drawn at actual size: the board outlines in his two parts layouts measure exactly the 6.30" x 3.30" and 5.50" x 2.60" printed on them. Print them at 100% (not "fit to page"), and check a print against a ruler before anyone drills a panel or a case.

Watch Thomas White's Excellent Sequencer Videos on YouTube

Thomas White used the MFOS sequencer boards to produce this incredible rotary sequencer. Visit his site to keep up with his latest awesome projects.

Thomas White's rotary sequencer, photographed at an angle under warm light. A tall black front panel is covered in knobs arranged in concentric circles around a central knob, with a column of switches and jacks down the right side and a row of jacks along the bottom. The words "music from outer space" run across the top of the photo.

MP3 Samples

(The recordings live on Ray's site.)

Features

Improved PC board (far less kludging)
Produces sequences of 4 to 16 steps in length
Modes include stop at count, reverse at count, reset at count and random 16 mode
Each step has coarse tune, fine tune, and switchable gate
Accepts external clock and external start pulse.
Simultaneous outputs with and without portamento.
Forward, Back, and Reset controls ease sequence set up.
Approximate current consumption: +12V (21.7 mA) -12V (10.5mA)

A finished MFOS 16 Step Sequencer in a wooden console case with a sloped front. The upper section holds two rows of eight steps, each step with a toggle switch, a small LED and two red knobs for coarse and fine. The lower angled panel, labeled MFOS Electronic Music, 16 Step Analog Sequencer, holds the jacks, the sequence rate and portamento knobs, the mode selector and four round pushbuttons.

Introduction

The main idea of a sequencer is to provide an automatic means of sequentially stepping through a series of adjustable voltages to drive a VCO (or any other voltage controlled device). Additionally, gate and trigger signals are generated at the moment the output of the circuit steps to a new voltage. Typically you use a sequencer to control the frequency of an oscillator (or several oscillators) to produce repeating tonal patterns, or arpeggios, which are further enhanced by filtering, modulation, addition of keyboard voltage etc. Sequencers are often used in electronic music production. This sequencer can produce a 4 to 16 note sequence. Additionally, this sequencer provides forward only, forward and back, and the unique ability for random sequencing. The gate/trigger can be included or not at each step (via a switch) and each step has coarse and fine voltage adjustment. Two circuit boards are required for this sequencer (unless you design your own) and I am offering both of them for sale. The digital board drives the sequencer and the analog board switches the control voltage from each set of coarse and fine pots to the output. You can start and stop the sequencer, reset it and step forward and/or backward to set up or manually walk through a sequence.

NEW! Adding More Analog Sequencer PCBs

16 Step Sequencer Schematic Page 1

Schematic titled 16 Step Analog Sequencer Digital Board Page 1 of 3, drawn by Ray Wilson, copyright August 2006: the clocking and counting section. Down the left, the Forward (S1) and Back (S2) pushbuttons each feed a debouncer built from a 10K resistor, a .01uF and a 0.02uF capacitor, 680K and 220K resistors and a CD40106 inverter (U1-A, U1-B), marked as giving a 4 to 5 mS pulse, through diodes D1 and D2. The Reset button S3 at right has the same kind of debouncer into U2-C. Flip-flop U3-B (CD4013) sets the count direction from the FWD, RST and REV points through D3, D11 and C5; inverters U1-F and U1-E with diodes D4 to D8 and 10K resistors R10 and R11 steer the clock to the UP or DN input of the CD40193 counter U4, whose DA to DD load inputs and QA to QD outputs run to labeled connection points at top right. Bottom left, the Stop/Run button S4 drives flip-flop U3-A, which starts and stops the clock oscillator U1-D through D9. The clock uses C10 1uF, R23 6.2K, R18 20K and the 1M Clock Rate Adjust pot R19, has an External Clock In at XCLK with a note that a CMOS level source with up to 1K on its output is OK, and buffers through U2-D to CKOUT via R41 1K and to the Clock Rate Indicator LED1 via R24 3K. XSTP and STP feed external start networks of 100K resistors and .01uF capacitors. A note reads: All diodes on all pages are 1N914 or 1N4148.

Schematic page 1 as PDF »

Page 1 shows the clocking and counting section of the circuit. This part of the circuit controls the manual and automatic stepping of the sequencer. U4 counts up when a positive going edge is applied to its UP input while its DN input is held high. Conversely it counts down when a positive going edge is applied to its DN input while the UP input is held high. If the LD input is brought low the outputs of U4 (QA through QD) follow the data on the load inputs (DA through DD). When the sequencer is not in Random mode the LD input is held high via R12 to +12V. A high level on the CL input of U4 causes the counter to reset to a count of zero.

S1 and associated components (R1, C2, C1, R2, R3, and U1-A) comprise a switch debouncer/low going pulser. When S1 is pressed a clean low going pulse of about 1 to 2 mS appears at the output of U1-A. In the same manner, S2 and its associated components and S4 and its associated components form switch debouncer/low going pulsers. S3 and its associated components work in the opposite fashion of S1, S2 and S4 in that when S3 is pressed a clean positive going pulse appears at U2-C pin 6. S3 is used soley to reset counter U4.

The clock (square wave oscillator) for the sequencer is made up of U1-D, C10, R23, R18, and R19 (clock rate adjust). It runs when U3-A's Q output is low thus reverse biasing D9. Due to U1-D being a schmidt trigger inverter it can be made to oscillate by applying its output back to its input via a resistor and connecting a capacitor to its input. When the output is high it charges C10 via R19, R18, and R23 in series until its high threshold is reached at which time its output snaps low and C10 discharges through the same path until U1-D's low threshold is reached when its output snaps high and begins the cycle anew. The purpose of the value changes needed for the clock input modification is to raise the impedance of the external clock input node so that external clocking from sources with output impedance up to 1K can reliably clock the sequencer. A clean rectangular clock source oscillating between ground and +V is assumed. If an external clock source with negative voltage excursions is used then a diode must be placed between the input jack and pin 9 of U1-D. The anode of the diode goes to the jack's hot and the cathode goes to pin 9 of U1-D.

If U3-A's Q output is high the clock is stopped (due to C10 being held fully charged via D9) and its output (U1-D pin 8) is forced low. Pressing S4 toggles the state of U3-A's Q output since U3-A is wired as a divide by two counter. Thus you can start or stop the clock by pressing S4.

The clock signal is fed to the inputs of U1-F and U1-E via 10K resistors R10 and R11 respectively. D4 and D5 are used (in conjunction with U3-B) to control which of these inverters propogate the clock signal.

U3-B is used to control the direction in which U4 counts. When the clock is running and U3-B's Q is high (and subsequently its NOT-Q is low) the clock pulses are allowed to propogate through U1-F but are stopped from passing through U1-E due to U1-E's pin 11 being pulled low via D8.

When the clock is running and U3-B's Q is low (and subsequently its NOT-Q is high) the clock pulses are allowed to propogate through U1-E but are stopped from passing through U1-F due to U1-F's pin 13 being pulled low via D4.

During operation U3-B's set and reset lines are pulsed appropriately to control the count direction.

Notice that the anodes of D5 and D1 are connected to U2-F's input (pin 13). If either U1-A pin 2 or U1-F pin 12 go low then U2-F pin 13 is pulled low (via D1 or D5 respectively). When both U1-A pin 2 and U1-F pin 12 are high, U2-F pin 13 is held high via R4 (47K to +12V). Thus a push of S1 or a low to high transition of U1-F pin 12 can cause U4 to count up. Also note that U2-E pin 10 follows the state of U2-F's input (pin 13).

Notice that the anodes of D2 and D6 are connected to U2-A's input (pin 1). If either U1-B pin 4 or U1-E pin 10 go low then U2-A pin 1 is pulled low (via D2 or D6 respectively). When both U1-B pin 4 or U1-E pin 10 are high, U2-A pin 1 is held high via R8 (47K to +12V). Thus a push of S2 or a low to high transition of U1-E pin 10 can cause U4 to count down. Also note that U2-B pin 4 follows the state of U2-A's input (pin 1).

Normally the UP and DN inputs of U4 are held high. Low to high transitions are used on either UP or DN (while the opposite input is held high) to cause clocking in either direction. When the sequencer is running (i.e. U3-A's Q is high and neither "Step Up" or "Step Down" are being pressed) and U3-B's Q output is high (counting up) U4's DN clock input (pin 4) is held high (as explained above). Thus the counter counts up. This continues until the count is reached that corresponds with the setting of S9 (SP12T selector switch).

Notice that U5 CD4514 (4-bit Latch/4-16 Line Decoder) is controlled by the counter (U4). The output that corresponds to the current counter's QA-QD outputs (one of S-0 through S-15) is high while all of the others are low. U5's outputs S-4 through S-15 are connected to the poles of S9 (S-4 to 1, S-5 to 2, S-6 to 3 through S-15 to 12). This is to allow the sequence to reset or reverse at the set step count. The common pole of S9 is controlled via switches S12, S15, and S16 to connect to:

Nothing (Random 16 or 16 Step Sequence is selected)
REV (Reverse count direction when selected step is reached)
CLR (Zero (or clear) count when selected step is reached)

Notice that any time the S-0 output of U5 goes high that U3-B is set (count up is set). This is so the counter starts to count up anytime the 0th count is reached.

Thus if the sequencer is in "Reverse At Count" mode the sequencer will count up to the step setting of S9 and then reverse direction and count down toward 0. This is because the high going level seen at the REV connection is used to flip U3-B into the state that causes the counter to count down (U3-B's Q is low and U3-B's NOT-Q is high). When 0 is reached the count direction is set to up again. This cycle continues as the sequencer counts up and down until the mode is changed or the clock is stopped.

If the sequencer is in "Reset At Count" mode the sequencer will count up to the step setting of S9 and then clear the counter to zero. The sequencer will continue to count from zero to count and reset until the mode is changed or the clock is stopped.

"16 Step Sequence" mode is provided to allow the sequencer to repeat all 16 steps until the mode is changed or the clock is stopped.

"Random 16" mode causes the counter to assume the count provided at the outputs of U8 CD4094 8 Channel Shift Register/Latch. The random counter is explained below.

16 Step Sequencer Schematic Page 2

Schematic titled 16 Step Analog Sequencer Digital Board Page 2 of 3: the step decoder, mode switches and gate outputs. In the center, the CD4514 decoder U5 takes QA to QD on its In-A to In-D pins and drives sixteen outputs S-0 to S-15. Two dashed boxes marked as panel mounted components hold, for each step, an LED (LED2 to LED17) with its cathode on the LED Cathode Bus CBUS, which goes to ground through R30 3K, and a gate switch (S5, S6, S7, S8, S10, S11, S13, S14, S17 to S24) with a diode (D10, D12, D14 to D27) feeding the Gate Bus GB, which has R25 4.7K to ground. A note reads: Use SPDT switches for all of the gate switches: S5, S7, S10, etc. Top left, a dashed panel box holds the SP12T Reset or Reverse Count Setting switch S9, its twelve positions wired to S-4 through S-15, its common through D13 (with C11 47pF to ground) to the Use Mode switch S12, which also selects Random 16 at RND; the SP4T Sequencer Mode Setting switch S25 picks REV (Reverse At Cnt), CLR (Reset At Cnt), STP (Stop At Cnt) or no connection for a 16 Step Sequence. Bottom left, the gate bus runs through R26 100K, with diodes D28 and D29 from the DN and UP points, into CD40106 inverters U6-C and U6-D to the GATE output via R27 1K and C12 .001uF, and through C13 .001uF and R28 100K into U6-E for the TRIG output via R29 1K and C14 .001uF.

Schematic page 2 as PDF »

As explained above U5's 16 outputs go high corresponding to the current count (0 thru 15) on the outputs of U4 (QA thru QD). They are used to power the LED corresponding to the current step number. This LED lets you know which set of Coarse/Fine pots is the active one. Additionally each output (S0 thru S15) is fed to a switch and the anode of a diode which is used to control at which steps gate/trigger outputs are produced. Essentially the outputs of U5 are anded with the clock signal if the switch for a particular step is closed. I recommend using SPDT switches (even though the schematic shows SPST) to facilitate the panel wiring as shown in the panel wiring diagram. Note that both D13 and C11 are included in the panel wiring and are not shown on the PC board. All of the LEDs, switches and the diodes connected to the outputs of U5 are also part of the panel wiring.

Gate Bus (GB) is not shown on the PC board. Details of where to connect GB are explained below in the PC parts layout section.

Not Ray's words: that sentence came across from the 2005 page, where the first board had no GB hole. On this 2006 board the drawing under 16 Step Sequencer Board to Panel Wiring shows a pad labeled GB beside D30. Ray's 2005 workaround (tying the wire onto R25's lead) is on his previous version page.

16 Step Sequencer Schematic Page 3

Schematic titled 16 Step Analog Sequencer Digital Board Page 3 of 3, Random Binary Number Generator. A 2N3904 transistor Q1, base-emitter junction reverse biased from -12V with R31 2M to +12V, is labeled: Select for best white noise. Cut off collector. Its noise passes through C15 0.01uF to TL082 op amp U7-A (R35 2M, R36 4.7M, R37 4.7K), then to comparator U7-B (R32 100K, R33 1M, C16 0.01uF), through diode D30 and R34 4.7K into CD40106 inverter U6-A and on to the DATA input of the CD4094 shift register U8. U6-B with R38 1M and C18 0.001uF forms the shift clock oscillator on the CLK pin; the main CLK point feeds U6-F, whose edge through C17 100pF and R39 10K pulses the STB pin. Outputs Q1 to Q4 of U8 go to DA, DB, DC and DD. Bottom right, supply bypass capacitors C24 and C19 0.1uF and C20 10uF on +12V, and C21 10uF on -12V.

Schematic page 3 as PDF »

This is the simplest way I could come up with to generate random binary numbers. These are truly random because they are based on white noise and not any repeating pattern. Feel free to use this circuit in your super computer. Essentially, white noise is generated by Q1 and amplified to digital levels by the op amps and U6-A. This noise data is presented to the input of the shift register who is constantly clocked by the oscillating output of U6-B. Thus random ones and zeroes are constantly flowing through the shift registers internal flip flop chain. A positive pulse that corresponds to the low going edge of the clock signal is applied to the strobe input of the CD4094 which causes whatever number is floating through the shift register to be latched and presented to its outputs (DA through DD). These outputs are connected to the data inputs of U4. When U4's pin 11 is held low (Random 16 mode selected) U4 propogates the random 4 bit count to U5 on each main clock cycle and thus the 16 steps are randomly selected. Tune the steps to the scale of your choice and select random mode to hear a never repeating random melody.

16 Step Sequencer Panel Wiring

Color wiring drawing, 16 Step Analog Sequencer (panel back view), for the control panel. A legend shows yellow tags as digital board connections and cyan tags as analog board connections. Along the panel: the 1M portamento pot R51 (tags R51-3 and R51-1&2); four v-out jacks in two pairs (CV1 to the upper pair, CV2 and CV3 to the lower two); the DPDT use mode switch S12 marked random 16 (RND); the action at step rotary switch S25 with lugs 2 REV, 3 CLR, 4 STP and 5 marked: No connection here for 16 step sequence position; the twelve-position action step rotary switch S9, positions 1 to 12 wired from S4 through S15, its common through diode D13 to S12 and through C11 47pF to ground; pushbuttons S1 forward, S2 back, S4 stop/run (each fed from +12V, out to STUP, STDN and STRN) and S3 reset (GND and RST); LED1 (RIN); the 1M sequence rate pot R19 (R19-1&2 and R19-3); and jacks for external start (XSTP), clock out (CKOUT), ext clk in (XCLK), trigger out (TRIG) and gate out (GATE). Notes read: Switch pin numbers are for relation to the schematic only and NOT meant to correspond with any numbers on the physical switch since they may vary from manufacturer to manufacturer. And under the +12V tag: +15V for +/-15V power supply.

Control panel wiring as PDF »

The control panel connections, read out as a list

tap to expand / collapse

Not Ray's words: the drawing above, read out tag by tag so a screen reader can reach it. The tag is the label on the board; the panel part is where that wire ends. Lug-level detail stays in the drawing.

Board tag	Board	Goes to on the panel
CV1	Analog	The upper pair of v-out jacks (the portamento outputs)
CV2	Analog	Lower left v-out jack
CV3	Analog	Lower right v-out jack
R51-3, R51-1&2	Analog	Portamento pot R51, 1M
+12V	Digital	Forward S1, back S2 and stop/run S4 pushbuttons (+15V on a +/-15V supply)
STUP	Digital	Forward pushbutton S1
STDN	Digital	Back pushbutton S2
STRN	Digital	Stop/run pushbutton S4
GND, RST	Digital	Reset pushbutton S3; GND also ties every jack sleeve together
RND	Digital	Use mode switch S12, the random 16 side
REV, CLR, STP	Digital	Action at step switch S25, lugs 2, 3 and 4; lug 5 has no connection (16 step); lug 1 goes to S12
S4 through S15	Digital	Action step switch S9, positions 1 through 12 in order; its common goes through D13 to S12 and through C11 47pF to ground
RIN	Digital	LED1, the clock rate indicator, other lead to ground
R19-1&2, R19-3	Digital	Sequence rate pot R19, 1M
XSTP	Digital	External start jack
CKOUT	Digital	Clock out jack
XCLK	Digital	Ext clk in jack
TRIG	Digital	Trigger out jack
GATE	Digital	Gate out jack

16 Step Sequencer Board to Panel Wiring

The digital board parts layout (silkscreen SEQ16DIGI20060828 REV 03, PCB size W-6.30 inches x H-3.30 inches) with yellow tags and blue lines showing where each panel wire lands: CKOUT, RST, RIN, CLR, RND, CBUS, TRIG, GATE, +12V and GND along the top; QA, QB, QC and QD in a dashed box marked To analog board; REV and XSTP at left; GB at right, pointing to a pad beside D30; R19-3 and R19-1&2, STUP, STDN, XCLK and STRN at the bottom left; and the sixteen step outputs S0 to S15 along the bottom right. S0 to S3 are marked: These go to the pot panel only. S4 to S15 are marked: These go to the control and pot panels. A dashed note at left reads: Solder STP wire to the lead of R46. No hole on PCB.

Digital board to panel wiring as PDF »

16 Step Sequencer Digital Board Parts List

Qty.	Description	Value	Designators
3	CD40106(s)	CD40106	U2, U1, U6
1	CD4013 Dual D Flip Flop B	CD4013-B	U3
1	CD40193 4 Counter	CD40193	U4
1	CD4094 8 Stage Shift/Store Reg	CD4094	U8
1	CD4514 4 Bit Latched 4 Dec.	CD4514	U5
1	TL082 Dual Op Amp	TL082	U7
17	LED(s)	General Purpose LED	LED1, LED5, LED3, LED9, LED7, LED13, LED11, LED17, LED15, LED4, LED2, LED8, LED6, LED12, LED10, LED16, LED14
31	1N914 Sw. Diode(s)	General purpose high speed switching diode	D2, D5, D6, D7, D1, D11, D3, D4, D8, D31, D9, D15, D12, D19, D17, D23, D21, D27, D25, D26, D24, D22, D20, D16, D18, D14, D10, D13, D28, D29, D30
1	2N3904	2N3904	Q1
1	Tantalum Capacitor	1uF	C10
4	Ceramic Capacitor(s)	.001uF	C14, C12, C13, C18
8	Ceramic Capacitor(s)	.01uF	C22, C23, C1, C3, C8, C7, C15, C16
5	Ceramic Capacitor	.022uF	C9, C2, C4, C5, C6
2	Ceramic Capacitor(s)	.1uF	C19, C24
1	Ceramic Capacitor	100pF	C17
1	Ceramic Capacitor	47pF	C11
2	Electrolytic Capacitor(s)	10uF	C20, C21
1	Linear Potentiometer	1M	R19
8	Resistor 1/4 Watt 5%(s)	100K	R47, R9, R46, R44, R45, R28, R26, R32
7	Resistor 1/4 Watt 5%(s)	10K	R1, R5, R10, R11, R17, R20, R39
4	Resistor 1/4 Watt 5%(s)	1K	R42, R41, R29, R27
4	Resistor 1/4 Watt 5%(s)	1M	R13, R14, R33, R38
1	Resistor 1/4 Watt 5%	20K	R18
4	Resistor 1/4 Watt 5%(s)	220K	R7, R3, R16, R21
2	Resistor 1/4 Watt 5%(s)	2M	R31, R35
1	Resistor 1/4 Watt 5%	3.9K	R43
2	Resistor 1/4 Watt 5%(s)	3K	R24, R30
3	Resistor 1/4 Watt 5%(s)	4.7K	R25, R37, R34
1	Resistor 1/4 Watt 5%	4.7M	R36
4	Resistor 1/4 Watt 5%(s)	47K	R40, R12, R8, R4
1	Resistor 1/4 Watt 5%	6.2K	R23
4	Resistor 1/4 Watt 5%(s)	680K	R2, R6, R15, R22
1	Single Pole 12 Throw Rotary Switch (non-shorting)	SP12T	S9
1	Single Pole 4 Throw Rotary Switch (non-shorting)	SP4T	S25
1	DPDT Switch	DPDT	S12
4	SPST PB Switch(s)	SPST	S1, S2, S3, S4
16	SPDT Switch (used to accomodate the gate diode and LED wiring)	SPDT	S5, S7, S10, S13, S17, S19, S21, S23, S6, S8, S11, S14, S18, S20, S22, S24

16 Step Sequencer Analog Board Information

16 Step Sequencer Analog Board Schematic

Either 2.5 Volt Reference chip will work.

Pinout, TO-92 package, Bottom View, LM336Z-2.5 or LM336BZ-2.5: three pins left to right, ADJ, plus and minus, with the zener reference symbol between plus and minus.

Pinout, TO-92 package, Bottom View, LM4040CIZ-2.5: three pins left to right, NC (no connection), plus and minus, with the reference symbol between plus and minus.

Circuit Description

The analog section is driven by U4 (CD40193 Synchronous 4-Bit Up/Down Binary Counter) from the digital board. The 4 control lines QA, QB, QC, and QD determine which of the 16 inputs of the CD4067 (CMOS Single 16 Channel Multiplexer/Demultiplexer) is turned on to allow the voltage from the wipers of the channel's coarse/fine pot combination to be fed to the summing node (pin 2 of U3-A) via the channels mixing resistors (100K and 2M). U3-A acts as an inverting summer the output of which is fed to inverting unity gain buffer U3-B. U3-B's output is fed to the non-inverting inputs of voltage followers U1-D and U1-B whose outputs feed two of the CV output jacks of the sequencer.

U3-B's output also connects to one side of the Portamento pot R51 which provides an adjustable means to cause the voltage to slew from one channel's level to the next. As the pot is advanced the time to slew from one level to another (the time needed to charge and discharge C4 .1uF cap) is increased and visa versa. The output of U1-C feeds the CV output jack to which portamento can be applied (via setting of R51). Caps C2 and C3 are power supply bypass caps.

U1-A in conjunction with VS1 (LM336-2.5V 2.5 volt precision voltage reference) create a 7.5 volt source to which one side of all of the pots are connected. The precision voltage source applies a very clean 2.5V to the non-inverting input of U1-A. Feedback resistor R25 (200K) and gain set resistor R26 (100K) set the gain around U1-A to 3 which is how we get 7.5V from the 2.5V reference.

In operation when a digital count between 0 and 16 is applied to the QA-QD - AND ALL FINE POTS ARE AT 0 LEVEL - you should see the voltage present at the wiper of the channel's corresponding coarse pot at the output of U3-B plus or minus the op amp's offset voltage which should be a few millivolts. To test this on an isolated analog board (i.e. not connected to the outputs of U4) you can apply power supply levels (+12V and ground) to the QA through QD inputs to simulate the counts. Inputs connected to +12V simulate logic one level and inputs connected to ground simulate logic zero level. All QA through QD inputs must be connected or the test will not work. Floating CMOS logic levels tend to toggle from the slightest EM field. For example to simulate channel 0 being on connect QA through QD to ground. To simulate channel 5 being on ground QB and QD and apply +12V to QA and QC. You apply the binary code for the channel you want to test.

The CV output level for any channel should range from 0 to about 7.5V (coarse control turned up). The fine control will add 1/20 of the 7.5V range (.375V) to the output when at full level since it is entering summing inverter U3-A via a 2M resistor. Use 100K or higher pots for the controls since the parallel combination of all of the pots is the load seen by U1-A. With 100K pots U1-A is seeing about 3.125K which it is capable of driving. Lower value pots will cause the parallel combination of all of the adjustment pots to be too low and strain the operation of U1-A.

Schematic titled 16 Step Analog Sequencer Analog Board Page 1 of 1. Top left, the LM336-2.5V reference VS1 (fed through R1 10K, R2 and R3 47K, C1 0.1uF) drives TL084 op amp U1-A with R26 100K and R25 200K, C6 470pF across R25, producing VSRC. In the middle, the CD4067 multiplexer U2 takes QA to QD on its A to D pins from the digital board, INH grounded. Its sixteen channel pins each connect to one step's pair of 100K front-panel pots, coarse through a 100K resistor and fine through a 2M resistor, all pots fed from VSRC and grounded at the other end; the pairs run R4 to R71. U2's common I/O pin feeds TL082 inverting summer U3-A (R73 100K with C5 470pF) and inverting buffer U3-B (R72 and R74 10K), then R75 22 ohms. That output drives voltage followers U1-D and U1-B to CV2 and CV3, and through the 1M Portamento Control pot R51 and C4 0.1uF into follower U1-C for CV1. C2 and C3 100uF bypass the +12V and -12V rails. Notes read: All of these pots are mounted on the front panel of the sequencer. You can use anything from 100K to 500K with little or no noticeable difference in operation. A higher value for R51 will permit longer maximum portamento times (glide between notes efffect). A lower value will cause shorter maximum portamento times.

Analog board schematic as PDF »

16 Step Sequencer Panel Wiring Diagram

It is a good idea to mount the analog board near the voltage adjust pots. Remember that only the four digital contol lines need to be connected to the analog board from the digital board so they don't have to be mounted close together. There are a lot of wires between the analog voltage processor board and the pots so the closer they are to one another the better.

Color wiring drawing for the pot panel, back view. Channels 15, 14, 13 and 12 are drawn left to right, then a dashed box reading Channels 11 through 1 continue this pattern, then Channel 0. Each channel has an LED (LED17, LED15, LED13, LED11 ... LED2) whose cathode joins a blue wire to CBUS, the cathode bus on the digi-board; an SPDT gate switch (S24, S22, S20, S18 ... S5) whose top terminal ties the LED anode, a diode (D27, D25, D23, D21 ... D10) and an orange wire from that step's digital output (S15, S14, S13, S12 ... S0); and the switch's bottom terminal on a pink wire to GB, the gate bus on the digi-board. Below each are two 100K pots, coarse above fine (for example R66 and R71 on channel 15, R63 and R69 on channel 0), with a green ground wire on one outer lug, a pink wire to VSRC on the analog board on the other, and the wipers running down as Coarse in (C) and Fine in (F) to the coarse and fine input resistors on the analog board, numbered 16, 15, 14, 13 ... 1. A note repeats: Use SPDT for all gate switches to facilitate the panel component mounting of the LEDs and Diodes.

Pot panel wiring as PDF »

16 Step Sequencer Gate Switch Wiring Detail

Back panel detail showing how each gate switch is wired. An SPDT toggle switch has three terminals. The top terminal is used as a solder tie point for the LED anode, the diode anode and the orange S(n) wire. The diode's cathode is soldered to the middle terminal. The pink Gate Buss is soldered to the bottom terminal. Above, the LED's cathode lead, marked by the flat on the LED body, is soldered to the blue Cathode Buss.

Gate switch wiring detail as PDF »

16 Step Sequencer Board to Panel Wiring Labels

The analog board parts layout (silkscreen RJWSOFT 16 STEP SEQUENCER ANALOG BOARD, SEQ16ANA20050130, PCB size W-5.50 inches x H-2.60 inches) with tags showing the wiring: QA, QB, QC and QD from the digital board at the top; R51-1&2 and R51-3 for the portamento pot; VSRC, CV1, CV2 and CV3 at right; and along the bottom edge sixteen pairs of pads marked C and F, numbered 1 to 16, To Coarse and Fine pots on front panel. A note reads: Solder C6 470pF cap in parallel with R25 (across it), with arrows to R25's two pads.

Analog board to panel wiring as PDF »

16 Step Sequencer Analog Board Analog Board Parts List

Qty.	Description	Value	Designators
1	CD4067 Analog Mux/DeMux	CD4067	U2
1	TL082 Dual Op Amp	TL082	U3
1	TL084 Quad Op Amp	TL084	U1
1	LM336 2.5V Ref.	LM336-2.5V	VS1
32	Linear Potentiometer(s) (don't forget to buy knobs)	100K (up to 500K will work fine.)	R11, R19, R32, R38, R46, R54, R63, R69, R4, R8, R18, R35, R44, R53, R62, R13, R22, R40, R34, R48, R57, R71, R66, R7, R15, R30, R24, R42, R50, R67, R59, R28
1	Linear Potentiometer	1M	R51
18	Resistor 1/4 Watt 1%(s)	100K	R10, R31, R45, R17, R36, R12, R33, R47, R65, R6, R41, R58, R5, R52, R23, R64, R26, R73
3	Resistor 1/4 Watt 1%(s)	10K	R74, R72, R1
1	Resistor 1/4 Watt 1%	200K	R25
1	Resistor 1/4 Watt 1%	22 ohms	R75
16	Resistor 1/4 Watt 1%(s)	2M	R27, R20, R37, R68, R21, R39, R70, R14, R29, R49, R9, R60, R55, R61, R56, R43
2	Resistor 1/4 Watt 1%(s)	47K	R3, R2
2	Ceramic Capacitor(s)	0.1uF	C4, C1
2	Ceramic Capacitor(s)	470pF	C6, C5
2	Electrolytic Capacitor(s)	100uF	C3, C2

Parts Layouts

Analog board parts layout, ghosted copper behind the silkscreen, PCB size W-5.50 inches x H-2.60 inches. The CD4067 U2 sits in the middle with TL082 U3 and electrolytics C2 and C3 to its left and TL084 U1, VS1, R1 to R3, R25, R26, C1 and C4 to its right. GND, -12V and +12V pads sit top left, QA to QD pads top center, CV1 to CV3 and VSRC right. Along the bottom, the thirty-two channel mixing resistors stand in a row from R64 and R68 to R65 and R70, above sixteen C and F pad pairs numbered 1 to 16.

Analog board parts layout as PDF »

Digital board parts layout, ghosted copper behind the silkscreen, marked SEQ16DIGI20060828 REV 03, PCB size W-6.30 inches x H-3.30 inches. Chips: U2 CD40106 and U4 CD40193 and U8 CD4094 across the top, U6 CD40106 top right, U3 CD4013 and U1 CD40106 at left, U5 CD4514 in the middle and U7 at right near Q1, C20 and C21. Resistors, ceramic capacitors and diodes D1 to D11 fill the left half; a GB pad stands beside D30. Pads along the edges: CKOUT, CLR, RST, RIN, RND, CBUS, TRIG, GATE, +12V, GND and -12V at the top and right; XSTP, REV and STP at left; STUP, STDN, XCLK and STRN along the bottom left; and outputs 0 to 15, S0 thru S15, along the bottom right.

Digital board parts layout as PDF »

Panel Overlays

Panel overlay 1, a long rounded rectangle between dashed cut lines, for steps 1 to 8. Each step has, top to bottom: the step number beside a hole for its LED, labeled on; a gate switch hole labeled gate, on above and off below; a coarse knob scale numbered 0 to 10; and a fine knob scale of tick marks running from minus to plus.

Overlay 1 as PDF »

Panel overlay 2, laid out the same way as overlay 1, for steps 9 to 16: LED, gate switch on and off, coarse scale 0 to 10 and fine scale minus to plus for each step.

Overlay 2 as PDF »

Panel overlay 3, the control panel, headed MFOS Electronic Music and 16 Step Analog Sequencer. Left column: jacks for external start, clock out and ext clk in. Next box: the sequence rate knob scale 0 to 10 with its indicator LED hole, and jacks for gate out and trigger out. Center box, sequence mode: the action step selector numbered 5 through 16; the action at step selector with positions reverse, reset, stop and none (16 step); and a use mode switch whose other position is random 16. Below that, four pushbuttons: reset, stop/run, back and forward, with arrow symbols. Right: the portamento knob scale 0 to 10 above two voltage out jacks, and a second pair of voltage out jacks below.

Overlay 3 as PDF »

Panel Overlay contributed by Jeff Johnson of Texas

This is a cool one piece template. I suggest you sketch a corresponding wiring diagram for it to avoid wiring errors during construction if you go with this template design.

Jeff Johnson's one-piece panel template, with registration crosses around the edge. Steps 1 to 8 fill the upper left and steps 9 to 16 the lower left, each with ON and GATE switch holes and COARSE and FINE knob scales. To the right: SEQ. MODE with the ACTION STEP selector numbered 5 to 16, ACTION AT STEP (NONE, STOP, RESET, REVERSE) and USE MODE / RANDOM 16; a column for STOP/RUN, RESET, FORWARD and BACK; SEQ. RATE and GLIDE knobs; and a jack field labeled GATE OUT, CV/GLIDE OUT, CV/GLIDE OUT, TRIG OUT, CV OUT, CV OUT, CLOCK OUT, EXT CLOCK IN and EXT START. Down the right edge in large type: MFOS ELECTRONIC MUSIC 16 STEP SEQUENCER.

Jeff Johnson's template as PDF »

Panel Overlay contributed by John Ibbotson of the United Kingdom

This is a cool one piece template. I suggest you sketch a corresponding wiring diagram for it to avoid wiring errors during construction if you go with this template design. This file is for use with Front Panel Designer.

A small preview of John Ibbotson's black one-piece panel: two rows of eight steps, each with white knob scales and red and green hole markers, a control section on the right with the mode selectors, buttons, rate and glide knobs and a jack field, and MFOS 16 STEP ANALOG SEQUENCER along the bottom.

John Ibbotson's panel as a Front Panel Designer file »

PCB Images X2 Artwork GIF files

By the time you've etched (double sided by the way) and drilled (587 holes) these boards yourself you'll wonder why you didn't buy the professionally manufactured, glass epoxy, plated through-hole, double sided, soldermasked, silk screened legend board from me. But have at it... These X2 images are provided for individual use and not for mass production or sale.

Download ZIP file »

Miscellaneous

1/16" to 1/10" Thick aluminum plates for mounting the pots and switches.
Wood or plastic to build a case with.
Assorted hardware 1" 6-32 nuts and bolts, 1/2" #8 wood screws, etc
Knobs for potentiometers, wire and solder.
Digital Volt Meter and a Signal Tracer or oscilloscope for testing.

Adding More Analog Sequencer PCBs

"Daisy Chaining" more Analog PCBs

You can drive more than one analog sequencer board from one digital board. This is accomplished by chaining the QA, QB, QC, and QD connections from the digital sequencer board to one or more additional analog sequencer boards. The illustration below shows this. Each additional analog PCB requires it's own set of coarse and fine pots and a new set of CV output jacks and portamento control. These are mounted on a panel and wired just like the original set of coarse/fine pots, CV out jacks and portamento pot.

The result is that you can now control separate modules with a synchronized 16 step sequence. You still only get 16 steps. Adding analog PCBs does not result in more steps. Adding more analog boards lets you do things like: have a 16 step sequence of chords (controlling separate VCOs) or control a VCF with one set of controls and some oscillators with the other set. You can imagine a ton of cool applications.

Drawing on a grey background: a section of the Digital Sequencer PCB at left with its QA, QB, QC and QD pads, wired by green, red, magenta and cyan lines to the QA to QD pads of two Analog Sequencer PCBs side by side, and on to the right, To additional MFOS analog sequencer PCBs. A note reads: Expander analog PCBs are wired to coarse and fine pots like the original. You can just wire the coarse pots if you like.

How should I drive additional channel indicator LEDs?

Although you can probably get away with another set of LEDs being driven in parallel with the original ones I recommend that you isolate the original driving circuit and add buffers of one kind or another to each set of new LEDs. Below I show three different ways to drive an expanded analog section's indicator LEDs. One way uses NPN transistors as buffers another way uses hex inverting Schmitt triggers (CD40106) and finally a single chip solution is to use a CD4514 (CMOS 4-Bit Latch/4-to-16 Line Decoder). Either will work fine and either can be built on a small daughter board. The choice of which to use may be as simple as what's in your parts cabinet currently, trannies, inverters or a spare CD4514.

Here, transistors are used to drive the LEDs. The original S0 through S15 circuit points can be accessed at the digital board by carefully tack soldering the new wires to the bottom of the board or at the panel where they connect to the gate switches and LEDs. A successfully tack soldered joint should look nice and shiny (like any other solder joint). If your tacked connection turns out clumpy then use some fluxed braid to remove the excess and try again.

Schematic, Driving LEDs for an expanded analog section (S0 thru S15 are from the sequencer's digital board). Sixteen identical stages in two rows of eight: each S point feeds a 100K resistor into the base of a 2N3904, emitter to ground, collector to the cathode of an LED. All the LED anodes share one rail fed from +12V through a 3K resistor, marked: Determines LED brightness. Lower value = brighter. I would not go below 1K.

Here I show you how to use inverting buffers to drive the LEDs. This method uses way less parts and is probably my favorite. Either of these methods should fit nicely on a small daughter board.

Schematic, Driving LEDs for an expanded analog section, using three CD40106B (or 74C14) hex Schmitt inverters, each powered from +12V on pin 14 and ground on pin 7. S0 to S5, S6 to S11 and S12 to S15 go into the inverter inputs; each inverter output pulls down the cathode of an LED, and all the LED anodes share a rail fed from +12V through a 3K brightness resistor (I would not go below 1K). The two unused inverters on the third chip have their inputs grounded.

Lastly this is the CD4514 method. It uses one chip and notice that the QA thru QD inputs are used to drive it. These come from the analog board and will most likely need to be tack soldered to the bottom the QA thru QD pads on the board.

Schematic, Driving LEDs for an expanded analog section (QA, QB, QC, and QD are from the sequencer's digital board). A CD4514 decoder U5 takes QA to QD on In-A to In-D (pins 2, 3, 21, 22), STB pin 1 to +12V, INH pin 23 to ground, +12V on pin 24 and ground on pin 12. Its sixteen outputs S-0 to S-15 each drive the anode of an LED; every LED cathode joins one bus that goes to ground through a 3K brightness resistor. A note reads: Follow the pinout closely. As you can see it is not in a very logical order.

All work © Ray Wilson / Music From Outer Space - musicfromouterspace.com. The 16 Step Sequencer, its circuit, text and drawings are Ray's. The rotary sequencer photo is Thomas White's, and the two one-piece panels are Jeff Johnson's and John Ibbotson's, as shared on Ray's page.

Mirrored and recoded by Mess O' Pedals to preserve Ray's work and keep it accessible. Only the HTML is mine - the design, the words, and the wit are all Ray Wilson's.