After some more thorough testing, I determined that the volume of the 3320 VCF was a little on the quiet side, noticeably lower than my other modules. Putting this down to the use of 100k resistors rather than the 91k specified on the circuit board, I decided to replace them and am happy to report this did the trick!
Resonance seems to self-oscillate nicely from about 50% onwards and seems pretty easy to tune. There are also optional solder points on the PCB for a 1v/Oct input, so I’ve no doubt it could be quite a capable oscillator too.
All in all, a great addition to my modular synth and looking forward to trying out some other Guru Gara Synth modules in the future!
Finally got the new 3320 VCF module working after tearing my hair out a little. With the lockdown, I’ve had to source the components in dribs and drabs and can’t always get the exact components stated on the circuit board.
About a week ago, I finally took delivery of the last capacitors I needed then excitedly plugged it in and heard… nothing.
A bit of headscratching later, I chanced upon the idea of sending a voltage through the CV input which initially did nothing, until I swept the filter knob, which revealed a comb filter type noise, but only when the knob was pointing straight up. Resonance did nothing to the sound, and I had silence at either end of the filter range.
Where do I start?
My first thought was that perhaps the 100k B potentiometers were faulty, or that I had bought the wrong ones and got my Linear vs Exponentials in a twist. So, I checked stock at http://www.thonk.com and fortunately they had some.
Then, this morning, I had the joy of desoldering the old pots and installing the (arguably superior) new ones. Unfortunately, it didn’t fix the issue.
I checked my soldering again – all looked sound to me – so as a last resort double checked that I’d used the correct resistors. And low and behold, the 91k resistors I had been sent (and which were in a bag labelled 91k) were actually 910k! In fairness, the difference between the two is just a red stripe rather than an orange one, and even my wife wasn’t sure what colour they were when I asked her to check. So I desoldered all four of them, and replaced with 100k resistors (the closest I could find) and I’m pleased to say the module sprung into life.
I still didn’t have any resonance though, but tracked this down to some damage I’d inadvertently caused on the board around one of the resonance knob pins. I could just about work out where the pin was meant to be going though, so added a jumper wire to link to the appropriate resistor, and I have resonance too!
Whether the 100k vs 91k resistors makes a difference to the sound, I’m not really sure, but it sounds good to me and I’m currently enjoying feeding some sample and hold through the CV input.
This was the first time I’d built a module just from a PCB and Panel, rather than a full kit, and it definitely makes me appreciate the convenience a full kit gives you, even if I did save a bit of money along the way.
Not sure what the plural of Mantis is, but I now have three of the Tip Top Audio cases of the same name, laid out end-to-end on my desk like a mini mission control.
Mission control
Analog Synth Mantis
To the left is the Analog Synth Mantis which is probably the more ‘vanilla’ of the three cases. Built around three different oscillators (OSC303, Tip Top Z3000 and the Doepfer A-110), each with a separate, dedicated filter (VCF303, Intellijel uVCF and Doepfer A-105 respectively), as well as the usual array of VCA’s, ADSR’s and LFO’s (Mainly Doepfer or Erica synths modules).
Dinsync’s excellent Modseq module allows me to do some repeatable Sample and Hold style manipulation of the filter cut-offs, or paired with the Ladik Easy Quantizer module, makes a mean bassline sequencer for the OSC303.
Other modules of note include the FoH Choices joystick, which is paired with the clever little Ladik Joystick Math module which makes it a lot more flexible, and a small selection of Make Noise modules including the Moddemix and LXD which are both great for teasing out plucky, percussive sounds.
Digital & Sequencing Mantis
The middle, Digital & Sequencing Mantis has something of a split personality. The top row provides the master clock for the whole system, which I have distributed between the three cases using a combination of different powered multiples to create a semi-permanent clock backbone.
It also provides additional sequencing and quantizing capabilities, courtesy of a Turing Machine with the Pulses and Voltages expanders and the GMSN Pure Sequencer, both paired with Doepfer A156 Dual Quantizer. These are great when I want something a little more unpredictable than the ES-40 / Ableton Live combination or my Beatstep Pro. Alternatively, the sequencers work great as modulation sources for my percussion modules.
The lower row houses my ‘Digital’ modules, including the obligatory Mutable Instruments trilogy of Braids, Rings and Clouds, as well as Erica synths Black Hole DSP which has some lovely Shimmer effects. A Mutable Music Things ‘Ears’ module rounds things off, used primarily to trigger the strum input of Rings.
Gates & Percussion Mantis
Moving to the right we have the Gates & Percussion Mantis which has a wide variety of drum and percussion modules as well as gate triggers, clock dividers and logic modules which are great for coming up with abstract drum patterns.
The sound sources themselves include the ALM Taiko modules (Still on the lookout for the limited Haswell’s Taiko if one ever comes up on eBay or Muffwiggler), multiple kick drum synths (With the Hexinverter Mutant Bassdrum being a current favourite) and a selection of Tip Top Audio 808 modules.
It’s worth remembering that percussion modules don’t have to be limited to providing drum sounds though, as many have pitch CV inputs which allow you to use them for basslines and tuned percussion alike. They also often have built in VCA’s and envelopes, further increasing their effectiveness for a relatively low cost.
Also in this case are some additional effects courtesy of the Sara VCF filter from DinSync, ALM’s EQ and Music Thing’s Spring reverb module. There’s also a passive ring modulator I made with some germanium diodes which is pretty unique sounding.
And last but not least, we have the Audiodamage ADM09 USB audio interface which is normally linked to an iPad 3 running the stunning Borderlands 2, granular synthesis app. You can coax some amazing sounds out of Borderlands, particularly when feeding it a diet of modular synth noises from the ADM09.
One day, I might even learn what it all does 🙂 Seriously though, I’ve just signed up to the Learning Modular Patreon page which gives regular hints and tips on how to get the most out of your modular synth, as well as free access to a course of your choice on the main Learning Modular site. Can’t be bad!
I’d hope I’m comfortable with the basics, so went with the ‘Level 2 Eurorack expansion’ which is very comprehensive and appears to be regularly updated to keep it current. Chris Meyer who created and presents the course has a great knack of making complex concepts sound easy and I’m learning so much already. Here’s an excerpt from the course…
Well, this house building business takes a lot more time than I had expected, and whilst I’ve become something of a dab hand at building airing cupboards and fitting out utility rooms, I’m finally coming out of the other side and getting a bit of time to work on my music.
I’ve recently taken delivery of a third Mantis case (someone should have told me this Eurorack hobby would turn into an obsession!) and am working out what modules to put into the gaps.
DIY time
As you can never have enough filters, I decided to go DIY and search for something interesting for the last 8HP of the ‘Analogue Synth’ Mantis case.
This led me to a PCB and Panel kit by Guru Gara Synth, based around the 4-pole 24dB CEM 3320 filter. The filter was used in lots of classic 80’s music technology including most notably the Prophet 5 synth (Rev. 3), the Fairlight II, PPG Wave 2 and the Oberheim OB-SX – none of which I would ever expect to be able to own! (Unless Behringer feels like cloning them of course).
The kit doesn’t come with any build instructions, but the PCB is very clearly laid out, so that’s no biggie. As the CEM3320 has been out of production for some time now, I went for the AS3320 from soundtronics.co.uk which is a modern equivalent and very reasonably priced. From the YouTube videos, it does sound rather nice!
More info on the 3 Mantis cases themselves and how I’ve configured them in a future post.
This outputs three channels of drum triggers (or gates) through the CV Pal module, all perfectly synced to Ableton Live. So I wanted to do something creative with the unused fourth CV Pal output.
Max For Live Patch
I came up with a simple Max For Live patch which outputs a MIDI note at regular intervals ranging from half-notes through to 32nd notes. By using this in-line with the Grids emulation and CVPal controller, it acts as a clock source for the Pico Trigger module giving me lots of trigger options for my drum modules.
Have decided I needed a few more HP’s for drum synth modules, both to expand my sound palette and add extra modulation sources. So, I purchased a Make Noise 104HP Skiff and have just finished filling it up – isn’t she pretty!
I still want to revisit using Arcade buttons as triggers in the future, but for now this is providing a lot of random percussion fun! This is thanks in large part, to the three Erica Synths Pico modules which give a nice mix of controlled and uncontrolled triggers, lfo’s, sample and hold and noise. And all in bite-sized 3HP chunks!
More tea vicar?
The Bastl Instruments Tea Kick is another of the new modules and it sounds lovely and clear with a real weight behind it, but still very musical too. It’s inspired by the Twin-T Resonant Structure as employed in the Roland TR808 Kick, but capable of a much wider range of sounds. It also has a CV input for tuning along with a separate square wave output, so can even be used as a rudamentary bassline oscillator. This is in the new, aluminium styling, rather than the quirky wooden front panels Bastl normally use but it looks amazing.
Along with the Synthrotek DSM, and a bargain priced Tip Top Audio RS808 rimshot module (Which is more flexible than it sounds), I can now get a much wider range of sounds that really compliment my two Taiko modules.
But, that also means I need a more flexible mixer with extra inputs, so the Tip Top Audio Mix Z fits the bill.
Integration with Ableton Live
As much as I love the self-contained nature of the drum skiff, you can never have enough trigger sources and that’s where the Mutable instruments CV Pal comes in. CV Pal is being used with Max For Live to emulate the Mutable Instruments Grids, meaning I can keep the patterns locked in tempo with my Ableton Live sessions, and a great job it does at that! Dead simple to set up too, so will put together a post on that perhaps. You can get the CV Pal in a kit at Thonk for under ÂŁ30 (plus VAT) , and it’s well worth looking into.
Well, I’m making rapid progress. Have already built the frame for the Eurorack Drum Machine, based around a repurposed Pittsburgh Modular Cell 48 case, and installed three of the modules.
The Pico Trigger is amazing and really easy to program with the browser based pattern editor which works great from my iPad. 8 patterns can be stored in the module at any one time, even after powering off.
I particularly like the way that each of the 4 tracks has an independent length parameter (1 to 16 steps), great for programming polyrhythmic patterns that change over time.
The arcade buttons aren’t yet functional, but there is a DIY section on the Doepfer website which helpfully explains how to build a manual gate so I’ll start there; just waiting for some veroboard and a 6HP blank panel to be delivered first.
Also contemplating squeezing in a Synthrotek 555 LFO too to add some modulation.
Nearly finished with my rebuild of the modular synth. The Tiptop Mantis Case is full and I’ve also built a second suitcase synth based around modules from Mutable Instruments, Including the ‘Ears’ module which Santa got for me 🙂
So now I’ve turned my attention to building a portable, Eurorack based Drum Machine. Here’s a mock-up of what it could look like…
The core pattern sequencing will be handled through the Erica Synth Pico Trigg module, with the 5 arcade buttons at the bottom allowing me to manually trigger Accent and Choke on the two ALM Taiko modules as well as the Trig input on the ALM Pip Slope.
An ALM PE-1 rounds things off, doubling as a handy 2:1 mixer in addition to EQ duties.
The new rack is starting to take shape, but I have hit a bit of a snag! The case (made by Tip Top Audio) isn’t deep enough to house my Mark 1 Z3000 oscillator (also made by Tip Top Audio)! So it’s a good job I bought the Mark 2 version.
More selling on ebay methinks!
Also looking to get a Mutable Instruments Ears module soon to trigger my Rings module, as ably demonstrated in this video…
