DIY SUB101A (diy SH-101 style sub-oscillator)

The SUB 101A (rev 1.5) is available as a KIT (PCB + parts + case + cables) or fully built (with case for desktop use + power cable).

If you want to add juicy bass to your Moog Mother 32, Behringer Crave or Neutron, this sub-oscillator will do the trick!

This little guy is inspired by the famous Roland SH-101 Sub Osc and works on a 9V battery or 12V power supply.

I put together a circuit that adds a square wave sub-oscillator to your semi-modular synth for some really beefy sounds

This sub-oscillator follows an oscillator signal from a VCO and generates a square wave -1 or -2 octaves below. Works best with sawtooth, triangle, sine, or simple square waves.

There is a pot that mixes between the 2 sub-octaves and if you set it to 50% it sounds like the famous Roland SH-101 pulse sub-oscillator.

For this to work, you need to route your synth's oscillator output to the sub-oscillator input. Then you get the sub-oscillator signal at the output. Mix it with the original through an audio input channel to take advantage of that juicy low end.

This circuit board is safe and RoHs compliant (lead-free).
Sub 101A (Rev1.5) BOM List for Eurorack

REF. | VALUE | DESCRIPTION | COMMENT

D1 red LED Ø 3mm (20mA)
D2 1N4002 Rectifier Check polarity before soldering
D3 1N4148 High Speed ​​Diode Check polarity before soldering
R2 27K 1/4W 5% or 10K Metal Film or Carbon
R1, R3, R4, R7 10K 1/4W 5% Metal Film or Carbon
R5, R8 120k 1/4W 5% Metal Film or Carbon
R6 1M 1/4W 5% Metal Film or Carbon
C1 100uF (16V) Electrolytic Check polarity before soldering
C2 100nF (50V) Ceramic
C3 10uF (16V) Optional Electrolytic: Not used for Eurorack
C4, C6 10uF (16V) Electrolytic Check polarity before soldering
C5 10nF (50V) Ceramic
Q1, Q2 2n3904 NPN BJT or BC547 / BC548
RV1 B10K Potentiometer Linear pot RK09 / PTV09A or similar
U1 CD4013 CMOS Dual D Flip Flop
J1, J2, J3 PJ301M-12 Audio jacks 3x female 3.5mm audio jacks
J4 2 x 5 pin Pin header To connect to a Eurorack power supply