Oh, Thank you ! I am glad you like it! Sometimes simple but almost alive patches bring me to stop patching and just listen for a good while…
I tried adding a few things too but nothing worked…
Also I love the way the filter introduces some unquantized sound when it self resonates, and how this makes the FM go out of tune. Like a dialog between order and chaos, nature and culture…
Just so you all know, there’s a much easier way to get such a wide frequency range without having to use multiply Pony VCOs, it also has less alaising. I was able to go from the top of the audio spectrum all the way down to a near-stopped oscillation using a Palm Loop VCO and a +/- 10V attenuverter fed into both the V/Oct and the Linear FM inputs. This creates a nice knob response that can reach both extremes while still having a large sweet spot in for “moderate” speeds as oppsoed to the exponential sweep of a traditional source fed to V/Oct. It also leaves the additional exponential FM input open for patching the modulator mix to.
Yes, there is a lot to be said for the Palm Loop VCO. Interesting idea to patch both the V/Oct input and the exponential FM. (You wrote linear FM, but I am pretty sure you wrote that reversed. The linear FM does not slow down as you go negative, but rather inverts the wave form and begins speeding up again as you go more and more negative. That is a critical feature of through 0 true FM).
I experimented with Palm Loop extensively (along with some other VCOs) when I was exploring 0 Hz carrier through 0 linear FM - It works very well for that. Palm Loop was the most CPU efficient and yet had the least amount of aliasing when modulating at high frequencies. The anti-aliasing technique used is unlike most of the other VCOs. I like Palm Loop a lot, and I think it has never gotten the attention it deserves.
The thing I find unfortunate about the Palm Loop is the saw wave is an octave higher than the triangle and square. Both octaves are available for the sine. I tried to program a derivative module that provided the same octave for all wave forms, but the anti-aliasing technique broke down in my hands when I did that.
Both the Blippoo Box and the Benjolin only require triangle and square, so I think you may be on to something. Palm Loop probably is a good choice to try.
I can’t wait to go to the studio this afternoon and hook it up to a controller 
It’s a lot of fun!
Have been refining it still in the meantime and will share an updated version soon.
@officialdjglitch Thanks for the tip! I will look into the oscillator 
Blippoo Box by the late and great Rob Hordijk,
Small world. I recently came across his name when researching and fiddling with VOSIM (but that’s a whole other world of synthesis).
The Blippoo Box is yet another machine to emulate and yet more concepts to experiment with.
About the most mysterious component of the Blippo Box, the Rungler (as invented by Rob Hordijk). I noticed that Michael Hetrick of HetrickCV actually implemented a (free) Rungler for use in VCV Rack.
I have not downloaded and tried any Blippo Box / Benjolin patches yet, but in I didn’t see the HetrickCV Rangler in the thread text or the demo patch videos. Maybe I missed it, maybe there’s another reason…
Anyway…
Rungler
The Rungler is related to the Analog Shift Register. It is based on a modified ASR circuit by the late, great Rob Hordijk. It is used in a number of his classic designs, including the Blippoo Box and the Benjolin.
The Rungler is an eight-bit shift register, with a stepped, analog output signal generated by the state of the last three bits in the register. A Clock input advances the register. A Data input assigns the On/Off value to the first bit (On when the Data input is above the value set by the Compare knob). The stepped output’s amplitude is modified by the Scale knob.
The XOR/Direct toggle on the bottom changes a key behavior of the Rungler. In Direct mode, the module emulates the behavior of earlier Runglers where the Data input directly sets the value of the first bit. XOR mode emulates the Rungler behavior present in the Benjolin and other designs. In XOR mode, the state of the first bit is determined by the logical XOR of the Data input and the state of the last bit. This is a lot less predictable!
The Write/Loop toggle determines a different feedback parameter. In Write mode, the module acts as described. In Loop mode, the Data input is ignored and the first bit is set only by the state of the last bit.
We were aware of the module, but thanks for the tip! After its update -so you could use linear feedback on the shift registers with XOR logic, it resembles the Rungler circuit found in the Benjolin much better.
The Rungler circuit by itself is not that complicated, when you start to understand what it is made of:
A shift register (4 or 8 bit)
A R2R DAC connected to the 3 last bits of the shift register.
In the Benjolin there is only one rungler, with a (XOR) feedback path as well on the shift register. In the Blippoo Box there are two (where the two oscillators are swapped) but there is no feedback path on the shift registers.
By patching it together instead of using a programmed module, at least I learned its inner workings much better
So true.
In systems analysis and design a system is basically a collection of components that interact (work together) to achieve some goal. Just like in modular synthesis…
Breaking stuff down into their smallest functional components and figuring out how these components interact to achieve some goal helps you to understand how and why stuff works. And this can subsequently spark new ideas and enable the actual realization/implementation of ideas.
Also…can give you a healthy respect for the pioneers who came up with ideas and/or implemtations first.
@officialdjglitch - I tested the Palm Loop VCO in my Benjolin patch and it worked great. There was no need to use both V/Oct and FM inputs. Just as with the Pony VCO, I have the +/-10V main freq knob + attenuated CV + attenuated rungler all going to a mixer that attenuates the mix to 92% so as not to be 1V/Oct. That mix then goes to the Palm Loop V/Oct input. With the Octave set to 1, Course to -1.5 steps, and the Fine to -0.12012, I am able to get the same frequency range I was getting with the Pony. (I don’t remember the numbers, but it is close to the original Benjolin spec)
I also checked it and it works wonderful, Thanks for the tip! It makes the patch a bit more transparant on the oscillator part. Agree with @DaveVenom that you don’t need the double exp fm for the range, but you can make it really slow now which is also very nice and useful. Thanks again.
I will share my updated patch probably this weekend when I make some time for it
That Blippoo Box emulation is a gem. Sounds great and is fun to play with. I also tried various other filters, but non match the Vult Unstabile (Free). Deep round low end and crisp high end.
I might try some more filters including the suggested Squinky Stairway.
Here’s Hainbach talking about and demonstrating the Ciat Lonbarde Benjolin/Peterlin. Also talking about Rob Hordijk (whom he knew and met) and the Benjolin/Blippoo Box. Also some talk and demo by Richard Scott of some specific versions of the Benjolin built by Rob Hordijk himself.
Thanks! I have been pretty thrilled with the results of both the Benjolin and Blippoo Box emulations. And yes, that Unstabile filter is a beast in these patches.
Generally I get more excited over the Benjolin sounds than than the Blippoo Box. I feel I work a little harder to get self generated movement on the Benjolin, but I am more satisfied and intrigued with the results. Then again, I have spent much more time on the Benjolin emulation than the Blippoo Box.
I did have an opportunity to compare my Benjolin with a real After Later Audio hardware Benjolin, and the emulation held up amazingly well. We were able to dial in very similar sounds across both.
Seriously…Blippoo…Very fun name…cartoon
Yes. I guess I’m gonna use the Vult Unstabile more often as a sort of Resonator.
One of the more unique things with Unstabile is that when fed an audio signal there’s a slight slew in pitch before it gets to a stabile state. This slew follows the overall amplitude of the incoming signal and definitely adds to its character. Especially in feedback loops and/or when output is used for modulation.
In the Vult Unstabile product documentation it states:
With Unstabile remade the model (…) introduced nonlinearities that can occur when the circuit is fed with low voltage.
BTW
When fiddling with possible alternative filters at high resonance, approaching self resonance, I also tried the Instruo I-047 (emulating the ARP2500 1047 filter).
The Instruo I-047 has an 18 dB/Oct slope and has a nice ‘ring’ to it, without going into self resonance. I used two in series (it has no BPF, so I use LPF and HPF in series). I added Instruo Tanh to introduce/control some amplitude dependent non-linearity. Also an envelope follower connected to inverted cutoff modulation, emulation the Unstabile cutoff slew (prominent at high resonance). That configuration can sound somewhat similar to Vult Unstabile.
Amazing how something as unique and quirky as the Benjolin and Blippoo box can actually be emulated in VCV Rack…
I am using the cytomic CF100 filter now in my emulations. Not free, but amazing sounds and very, very pingable.
Yes - I have been experimenting with the CF 100 filter in other patches with great success, and was wondering how it would sound in the Blippoo Box and Benjolin. Now after your recommendation I will definitely check it out. Thanks.
It has a very controllable resonance (if you stay under 7.5 it has a large range of almost oscillation) I use the lp4 out for the emulations and feeding back the lp2 into the exp fm, creates the right harmonic distortion as described by Rob Hordijk.
But agree with you and @kwurqx that the Vult filters are awesome too. I am curious what will come with the updated code of the Vult filters!
This module also recently got added to the library.
I did not try it yet, but it sure looks like a Benjolin inspired module
You are right! Reading the manual it appears to be heavily influenced by Rob Hordijk’s Benjolin. I played with it very briefly. It seems pretty cool. But I am disappointed the manual does not at least acknowledge Rob Hordijk or his Benjolin and Rungler designs.