[IN STOCK] Eurorack: Discrete State-Variable VCF v1.4

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[IN STOCK] Eurorack: Discrete State-Variable VCF v1.4

Post by negativspace »

There is a long and helpful thread on the filter itself HERE. I'll re-post the critical stuff:

This filter started life as the SVF design (based on the J. Haible discrete 2040 gain cell) which Scott Stites posted over at electro-music in April. I'd been wanting to work with another filter for a while and this one looked interesting, so I started playing with it. I lopped off the audio input section and grafted on the CP3 mixer (moar transistors!) Eventually I made a few other changes - I got it self-oscillating, added a 1v/oct CV input with scale trim, and did some work in the resonance circuit - and the end result of all of that is the filter heard here:


Ignore the photo in the Soundcloud clip, that's a different project using the same circuit. The panel for this one is 14hp, and depth is in the ~40mm range with the two PCBs stacked parallel to the panel. I'll get better photos of the panel and update this post ASAP.


Scott has given his blessing on both a DIY run and a retail release of this filter - so with my deepest thanks to him for the lion's share of this circuit I declare game on.
Last edited by negativspace on Tue May 26, 2015 11:01 pm, edited 13 times in total.
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Post by negativspace »

Eurorack Panel + Bare PCB set: $45/ea
Bare Filter PCB: $20/ea
Shipping: $3/USA, $10/Canada, $15/Overseas
The Paypal address for payment is jcoates42@gmail.com

[1] 1M R45
[1] 390k R13* (* = change to alter signal level from mixer to filter section. Suggested range is ~270-470k.)
[1] 240k R33
[2] 200k R36,R41
[1] 180k R19
[1] 110k R47
[5] 100k R15,R17,R38,R39,R40
[1] 62k R42
[1] 47k R10
[1] 39k R16
[4] 22k R1,R2,R3,R35
[3] 15k R5,R7,R43
[7] 10k R18,R27,R28,R29,R30,R31,R32
[3] 6.8k R8,R14,R46
[3] 1k R21,R22,R44
[2] 560R R9,R11
[3] 470R R20,R34,R37
[1] 240R R48
[4] 220R R23,R24,R25,R26
[1] 200R R6
[2] 100R R4,R12

[1] 3.3nF Film, C5
[1] 2.7nF Film, C13
[2] 1nF Polystyrene/Polypropylene *main timing caps in VCF
[2] 10-100uF Electrolytic *power decoupling caps, value noncritical
[3] 220pF MLCC, C7,C11,C12
[1] 150pF MLCC, C6
[5] 10uF Electrolytic, Q8,Q9,Q10 = audio path. The other two are for decoupling the +5 and -6V rails.
[2] 0.1uF MLCC

[11] 2N3904/Other NPN [PN100A] Q1,Q4,Q5,Q8,Q9,Q10,Q11,Q14,Q15,Q16,Q19
[2] 2N3904 Q17,Q18
[6] 2N3906/Other PNP [PN5138] Q2,Q3,Q6,Q7,Q12,Q13
[2] 1N4001

[3] TL072 *or other standard pinout dual opamp.
[1] LM337LZ, TO-92
[1] LM78L05 *silkscreen on v1.2 PCB is reversed; TO-92
[3] 8P DIP socket (optional)

[1] 20k Trimpot (v/oct)
[1] 2k Trimpot (-6V)
[1] 100r Trimpot (null)
[2] Ferrite Bead
[1] 16P Header (power)
[2] 12P Header + socket (board to board interconnections)
[4] 7/16" Nylon standoff + 3/4" #4-40 screw + hex nut set. (Use 12mm standoff if metric)

Panel Controls
[3] A20-25k Pots (lugs) - audio inputs
[4] B100k Pots (pins) - CV inputs, cutoff frequency
[1] B10k pot (pins) - notch balance
[1] B10k Dual-ganged Pot (pins/lugs - BYOC, Banzai, or Small Bear) - resonance
[12] 3.5mm Jack (Erthenvar-style preferred, 16PJ138 in a pinch)
[6] 1900H or clone
[1] Davies 1913BW
[1] Davies 1910CS

Surface Mount Parts:
[2] 0.1uF 0805 ceramic, install on back of main PCB
[2] 0.1uF 0805 ceramic, control board
[2] 22pF 0805 ceramic, control board
[4] 47k resistor, 0805, control board
[2] 330R resistor, 0805, control board
[1] TL072, SOIC, control board

Instructions for trimming
the -6V and null trimpots:
No cables in the module. No inputs, no outputs. Use the test points on the board.

1) The grounded test pad is over by the lower screw hole on the left-hand side of the PCB.

2) Adjust -6V trimpot until the test point "-6V" reads -6.00V. This test point is down by the LM337. Once you set this, for fuck's sake leave that trimpot alone!

3) Measure the test point labelled "-". This incorrectly corresponds to the jack labelled 'mix +' on the front panel. It should read somewhere between 55 and 110mV, give or take. The null trimpot won't effect this measurement, so just note the voltage. It may bounce around a bit. Just... ballpark it.

4) Measure the test point labelled "+". The null trimpot will effect this voltage so you now have two choices:
4a) Recall the voltage from Step 6 and adjust the null trim until the voltage at TP "+" reads the inverse.
4b) Forget Step 6 and adjust the null trim until the voltage at TP "+" is ~0.00V.

5) You're done with the mixer.

PCB v1.2
- note reversed power regulators & resistor lead jumper in bottom left corner. Not necessary on v1.4 PCBs:
Image Image

Method for connecting the audio input pots - use the same technique for dual-ganged pots with lugs if you're going that route:


Here is a photo guide for the surface-mount section on v1.4 boards:


Here is the pinout diagram for the headers, if you're wiring them up the old-fashioned way:

Last edited by negativspace on Mon Apr 11, 2016 4:20 pm, edited 17 times in total.
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Post by negativspace »

Schematic, sans SMT section:

Last edited by negativspace on Fri Oct 23, 2015 5:13 pm, edited 141 times in total.
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Post by sammy123 »

Full set with panel please.
Last edited by sammy123 on Thu Apr 17, 2014 7:53 am, edited 1 time in total.
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Post by lintfresh »

In for one set! Been waiting eagerly for this one.
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Post by spneca »

One full set, please.
Last edited by spneca on Thu Apr 17, 2014 5:36 pm, edited 1 time in total.
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Post by qp »

Add me for 1 set + Panel!
Last edited by qp on Thu Apr 17, 2014 7:04 am, edited 1 time in total.
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Post by dropmotif »

One PCB set for me. No panel.
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Post by rosch »

1 full set pcb+panel for me please!
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Post by 3M-10 »

Please put me down for 2 full sets of PCB's + Panels.

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Post by sduck »

negativspace wrote:BOM

[0] 100k
Now this is my kind of BOM!
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Post by skyshaver »

I am interested in a pcb and panel set.
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Post by lodsb »

I am interested as well, 2x (pcbs + panel) please!
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Post by thetwlo »

2 sets: PCBs + Panel, please.

Beautiful work! Thanks!!!!
Last edited by thetwlo on Fri Apr 18, 2014 2:49 pm, edited 2 times in total.
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Post by Barcode »

One PCB set for me. No panel needed. I've been waiting for this one for a while now. :tu:
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Post by mikecameron »

I'm in for one.
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Post by mDang »

Sound great ! And it can do stereo :)
One full set for me please !
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Post by Rigo »

One full set for me please ... makes my backlog happy :hihi:
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Post by regenbot »

one set for me :tu:
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Post by qfactor »

Me too, negativspace!
I set (pcb/panel) for me!
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Post by mcop »

I'm in for a pcb & panel set
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Post by apophis93 »

Take my money already! :hyper:

one set.

- Daniel
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Post by mxmxmx »

1 x pcbs + panel, please.
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Post by negativspace »

mxmxmx wrote:1 x pcbs + panel, please.
Finally I can ship your CP3. It's still sitting here with a note "Wait for SVVCF" :hihi: :deadbanana:
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Post by Thonk Support »

1 PCB + panel please
Thonk - CLICK HERE - Modular Synth DIY + Eurorack Accessories Store

AS of October 2020 this account which used to go by the name of Monobass is now manned by various staff at Thonk.
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