the Filter sounds very good - one of the best Filter i heard (MOTM440, MOTM480 too)
Building guide: 2612_BuildDoc.pdf
i go forward to use a 2n3958 like the original instead of 2x2n5459, in building guide " there are markings for usage of 2n3958"
Parts/BOM (listed only non standard parts)
pcb (control and main pcb from steffcorp
1x tempco 1k87 (i used a 3500ppm KRL, check thonk.co.uk and synthcube.com )
1x LM301AN or LM301AH
4x 3k32 (3k3 works fine too)
1x 23k2 (Tip: check cermet 22k for tolerances
2x 250R trimpot multiturn or 500R trimmer
1x 10k trimpot multiturn
1x 100k trimpot multiturn
Panel 4072 panel from Bridechamber.com, you can add the finetune on the pcb /the 4072 bridechamber panel dont have a finetune pot
2x 100k lin bourns pot (frequenncy, resonance) - prefered due to handling
2x 100k log Bourns pot (input1, input2) usage of alpha/alps are fine too
2x 100k pot for CV
all 2N3904/2N3906 was matched by me within 1mV
a pair 2N5459 was matched too
resistors, caps, sockets, transistors was stuffed by me, pcb washed, all trimmer and ics added later,
for MOTM conversion: make sure you connect both pcb in correct way !!
wiring of jacks: make sure you connect for CV1-CV2-v/oct the jackswitch to the pcb.
i used shielded cables (RG174) for input/output jack
calibration: see build document and double check it , in my case was the gain and offset related to the initfrequency at beginning.
V/oct calibration result was not perfect but better as some other filters i have build in last years.
copy from https://steffcorp.se/product/2612/
This is a clone of the 4012 VCF used in the ARP 2600.
Other than some substituted parts and a “sandwich-layout” mainly adjusted for the eurorack standard, I have tried to keep all the original quirks as close to the original as possible.
The “sandwich-layout” simply means the VCF is split in 2x PCB’s mounted in parallel on top of each other.
The Core-PCB contains the main circuit, while the Control-PCB contains the controlling elements as well as the buffers.
See the Build-Document for more detailed info/options regarding the build.
Frequency & Fine-tune
Attenuators for Audio and FM inputs
Buffered inputs & output
Depth about 35mm, depending on choice of components