Oldschool BPF by Electronics For Music , as found on waybackmachine , notes from MAXX Modular :

Maxx BPF-1A

---

The BPF-1A is based on a design I found in a magazine somewhere. Thats about as close as I can get on this one. Maybe someone can help? The BPF is a bandpass filter or wah-wah curcuit. There are lots of wah designs out there but the only ones that seem to work are the ones with noisy hard to find inductors in them. This is a little different. It's like a piece of a state variable.. anyway it works very well. With modulation at times it sounds a lot like a phasor but more often sounding like a Leslie or Univibe type thing.

Moog Source VC-LFO , schematics and PCB Layout  in 300dpi

Korg MS20 VCF as in Electronics or Music Clone schematics available here , this is single VCF version , IC's are LM13700  , PCB layout is 300dpi 

Serge ' 73 VCF , suitable for eurorack format , PCB is tested and working with single cv input , so simply don't install the bottom IC and you got a working '73VCF as it was meant with single input , low freq option is added


 

Aries AR-314 VCF , schematics here  , PCB layout is still untested

Befaco VC Slew Limiter , schematics is here ,opamp is TL074,  PCB untested is 300dpi  (edit - this is a tested working layout , bit much slew on 15V PSU , potentiometers are 100K )

Envelope Follower and preamp from the book Nouva Generation de Musicales Istrumentos electronikos , PCB layout is 300dpi not tested

EM&M Harmony Generator redrawn layout , print is in 300dpi 

Dome Filter designed by Osamu Hoshuyama , i assume there can be a pot to get a 3rd phase , PNP layout is 300dpi not tested 

Fixed Filter Bank Based on design by Juan Bermudez's Nueva generación de instrumentos musicales electrónicos , i added 4 more bands following the capacitor table , high q settings on the resistors , individual outs , PCB is 160x100 mm 300dpi

Xfade Dual Crossfader based on Buchla circuit , PNP layout is in 300dpi  , more about the circuit here : http://electro-music.com/forum/topic-17019.html matched transistors are BCM847 (edit: this is a working circuit ,however you need to add 68K or similar at the audio inputs to fix the gain problem)

Roland System 700 Analog Switch, here is schematics  , without the manual push button ,only 3 inputs i needed for my synth, pcb is still untested the single op-amp is TL071  , it's 300dpi ready for PNP

Save File II : Serge VCO (Retro) , Serge R-Series Envelope ,Buchla 291 BPF , Yamaha GX VCF ,Xfade x 2 , Clock Divider , Experimental Hardware Neurons G.R. ,Dome Filter O.H. , EMS Ring Modulators , Monotron Drums ,Hip Bass Drum C.A. ,DC and Audio Mixer ,18 Band Fixed Filter Bank J.B. ,Noise Gate J.H. ,Roland Analog Switch

R Series Serge - Envelope Generator ,before it cycles

Serge VCS in Eurorack

Buchla 192 Dual VCF / DC Mixer-Processor / CV Twister - Eurorack format 

   Buchla VCO's Eurorack panel

Demo : https://soundcloud.com/r25990127/buchla-258-x-2

Buchla 258 VCO PCB 

Serge VCFQ and Waveshapers eurorack panel

Multi Phase Waveform Animator circuit from http://electronotes.netfirms.com/ #87, by Bernie Hutchins , original layout by Scott Bernardi ,i just draw over it , there was mistake in original layout with power lines as it's described here http://www.bernacomp.com/elec/og2/og2_waveanim.html , there are four jumpers on the print png instead , print image should be 300 dpi , you might need to rescale it 

my 'save file' . loading with pcb's .

https://archive.org/details/SketchbookIi-SynthacksModular

Synthesizer patch using Serge VCS , Serge Negative Slew , Analog Neuron , Jerk Chaos , MFOS VCO , NLC VCA , Polivoks VCF , Clock Divider , Buchla @08 Random ,NLC Difference Rectifier ,Morphlag , E4M Xmix

Dual VCO and dual Waveshaper Combo - Eurorack

Serge '73 VCF in Eurorack format  ,demo here :
https://soundcloud.com/r25990127/serge-73-vcf-demo

Serge '73 VCF demo 

https://soundcloud.com/r25990127/4-5-modular-synthesizer

synthesizers . re-new synthacks mini-modular
- MFOS VCO
- Moog Parametric Eq
- Polivoks VCF
- Serge Negative Slew
- Serge VCS
- Buchla Music Easel Random
- Yusynth Quadrature VC-LFO
- VCA
- CGS Grinder
- NLC Analog Neuron
- Clock Divider
- H. Bissel Morphlag
- E4M Xmix
- NLC Difference Rectifier
- NLC Single Jerk Chaos
- Yusynth Noise

redrawn layout for Electronotes 87 ,Waveform Modulator by Bernie Hutchins ,original layout by Scott Bernardi ,this one is tested and working   http://www.bernacomp.com/elec/og2/og2_waveanim.html ,