As promised, attached to this post you’ll find the schematics in PDF and the eagle files for the umodular. Released as open source hardware, so hack away and please provide feedback! The eagle designs are not editable using the free version because of the size of the PCB, sorry. Check the list below; one of the outstanding wishes is to divide the large board into smaller, attachable boards – all below the 100mm x 80mm constraint.
Following is a list of todo’s, build notes and other observations I did while building the prototype. Future versions will include features and fixes from this list.
TODO’s and WISHES
vco: own design, open source and open source hardware
vco: replace CA3046 with modern matched transistors BCM847DS
vco: pulse should also work, even without controlling it through PWM width with a voltage
vco: triangle out
vco: sine out
vco: trimpot for base frequency
vco: option to follow osc 1 pitch
vcf: for now working with MFOS “Simple State-Variable VCF” design, open for non-commercial use but (c) Ray Wilson
vcf: replace ray’s filter with own variant
vcf: voltage controlled resonance in LP filter
vcf: more filter options (BP, HP, LP)
vcf: dual filter?
adsr: Working with a design by Rene Schmitz, permission for use granted.
adsr: vc for d and s?
vca: cost effective to develop version without THAT 2180?
mix: Update mixer volume control. Sounds like highpass filter now
pcb: all TL274 -> TL074
pcb: fix potentiometer orientation. All pots are inverted! full left is now +5 should be -5
pcb: check log pot instead of lin pots
pcb: footprint 78xx != footprint 79xx! Replace footprint of 7909 with actual footprint!
pcb: a nice manual routing, reducing the amount of via’s. Busses for power.
pcb: general layout
pcb: add small capacitors for decoupling
pcb: integrate Arduino more
pcb: split pcb in two for better shipping etc? multiple parts, max 100*80 to also enable eagle free software
pcb: add designators for capacitors! value, type and placement. For all components!
power: work on a DC adapter solution
power: replace the 6 3300’s with 6×1000’s because 2×3300 seems to be enough power
functional: Have “standard” switchable (flip switch) connections between vCO’s VCF VCA and mix out
functional: Dual/triple VCO mixer
functional: all individual modules with dedicated cv and audio paths? Save in shipping, saves in prototyping costs.
functional: have a module connector with +9v, GND, -9v and 4 audio and 4 cv paths. Modules can grab audio or cv from one of the paths and return audio or cv on the paths.
functional: 4 oscillators with LFO switch
func: digital LFO using Arduino
vcf: 560nF -> 560pF
adsr: replace 10uf with 10nf or 1nf
adsr: R72 -> 1k
adsr: R86 -> 1k
vca: 1n34a -> 1n60 (1n4454)
vca: QUAD_OPADMPP TL274-6A should be non-inverting
vca: add 100ohm to GND and 1000uF to GND inbetween TL274-6C out and THAT2180A pin 2.