Neutron-sound.com

Synthesizer projects

DuoFonik is a dual version of the Fonik SSM2044 board (with some added spice)

Here is a nice Write up on a build by Richard Brewster on his excellent modular pages.

The main differences are that both filters can be controlled together, inverting inputs are available, and the mix output.

Used in combination, this allows the output to be not only low pass, but high pass and band pass like as well.

There is also a "divergence" control voltage input which will modulate the filters in opposite directions.

The board is 4.2 x 2.1 inches so it can be mounted flat with standoffs in most formats of modular panel.

prototype pictures.

Media:
Soundcloud examples.

REV1.0 ERRATA

1:The rev1 board has a small error. please place a jumper instead of "c9" this is a stability capacitor, which is usually not needed, but if your op amp oscillates, then you can solder the capacitor between pins 13 and 14 of U2

2: the output A and B are mixed up, B goes to A output jack, and A goes to B output jack

Schematic

External connections are just a suggestion, as used on my panel. of course you are free to use multiple pots instead of pots+switches, or set it up as a simple dual filter with no master controls, or even use 2 of them with shared master controls, as a 4 channel filter for polyphony.

Wiring diagram for building with a setup like this panel.

Connector labels and their meanings.

A Res CV	CV	Filter A resonance control voltage
	A+B	Filter A and filter B resonance control voltage
A Q POT	A	Filter A resonance potentiometer anticlockwise
	W	" wiper
	C	" Clockwise
A + B Q Pot	A	Filter A + filter B resonance potentiometer anticlockwise
	W	"wiper
	C	"clockwise
A Cut POT	A	Filter A and filter A+ B cutoff frequency pot anticlockwise
	W	Filter A and cutoff frequency pot wiper
	A+B W	filter A+ B cutoff frequency pot wiper
	C	Filter A and filter A+ B cutoff frequency pot iclockwise
A cut CV	1	Filter A cutoff frequency CV 1
	2	Filter A cutoff frequency CV 2
	A+B	Filter A and Filter B cutoff frequency CV
A IN	+	Filter A input noninverting
	-	Filter A input inverting
A Res CV	GND	Ground connection for jacks and pots.
	CV	filter B resonance control voltage
B Q POT	A	Filter B resonance potentiometer anticlockwise
	W	" wiper
	C	" Clockwise
B Cut POT	A	Filter B cutoff frequency anticlockwise
	W	" wiper
	C	" Clockwise
B cut CV	1	Filter B cutoff frequency CV 1
	2	Filter B cutoff frequency CV 2
	div	Divergence. filters are modulated in opposite directions.
B in	+	Filter B input noninverting
	-	filter A input inverting
OUTS	GND	Ground
	A	Filter A out [see rev1.0 errata]
	B	Filter B out [see rev1.0 errata]
	MIX	Mix output.

components.

Click on image to download front panel express file.

note the countersunk head holes. these are for countersunk Allen head M3 DIN74B screws which will fit in standoffs. they are perfectly aligned for the board.

if you create a euro, MU or other version please let me know on muffwiggler forums and I will add it here.

paypal is set up to prevent over ordering of items i do not have in stock, You will need the first item to build the duophonic no matter what, the second is for pairs of tested and matched SSM2044s

SSM2044 pairs are tested to work on a baseline version of the board with the low frequency set to 30 hz (on my test reference chip), frequencies at the maximum and minimum cutoff knob setting, and onset of resonance (some resonate more easily than others). you would get the closest matched pair from the latest batch. so far i have not found any "strange but working" SSM2044s they work or they dont with about a 15% range of frequency, and about 25% difference in self resonance voltage.

2012 J.Matheson [DeFex,Neutron7]