The Dominion 1 by MFB is quite a beast in terms of its sonic power and synthesis capabilities. Yet, as well as it is constructed, a couple of things offer themselves to alteration and can indeed be tweaked easily. In my unit I did a couple of relatively straightforward mods that increase the synth’s already wide sonic palette and amend a few minor shortcomings. These are:
- Fixing the click on the 3,5mm envelope outputs
- Filtering the white noise to have it sound a tad duller
- Installing pre-filter overdrive to have more leeway for gain staging
- Installing Filter FM from the VCA output (for some acid vibes)
Free sample pack (WAVs and MPC ONE/LIVE/X programs)
Here are some samples of my modded Dominion 1 and a preview mp3 is here:
While the VCO, VCF and VCA sections are fully analogue, its envelopes and LFOs are generated by a CPU. All sound parameters are digitally controlled and most of them stored in a sound preset.
On the right side of the synth/CPU board we find three voltage controlled oscillators, which are modelled after the second revision of the Moog Model D OSC. Board.
The core of the three VCOs comprises a LM393 comparator and six op-amps each. One half of each LM393 makes the SAW core of the VCO and the second half is used for the Saw to Square shaper. Further to the right there are three LM3046M transistor array ICs, used for expo conversion. On the very right, just over the white LED, you see a MC1496 and a TL062C, which make the analogue ring modulator circuit. Just over the leftmost rotary switch you see a quadruple X-OR-gate IC (HC86) used for digital ring modulation duties (VCOs 2 &3). Finally, there are six quadruple digital potentiometers (MCP433), which, I assume, are used for waveform selection, wave shape control, VCO FM, Sync input regulation, and VCO mixer level (needs verification). If MFB were into PR, they might have advertised all this as extended “Memory-Mini.” VCOs.
The Dom’s filter is a discrete 4pole VCF with some quite nifty features. The LM3047M transistor array is for expo conversion, and the four identical quadrants of transistors on the left make the four poles. While parts of the two quad-opamps (TL064C) are used for inversion duties, the LM13700M serves as resonance feedback VCA and output buffer. The HEF4053BT switch is used for switching/mixing filter modes. The setup of four identical blocks on the left suggest that the chosen design is very close to Jürgen Haible’s discrete version of the SSM 2040, a VCF originally used in low-pass configuration in such iconic synthesizers as the SCI Prophet 5 and the SRM Cat. Just as with OTA based filters, however, flipping and mixing your filter poles gives you different multimode applications, as for instance in the Digisound 80 Multimode filter or this cool Eurorack project. (Still a bit of speculation in all this/need to have a look again for verification of some parts.)
If you intend to work on the Ribbons, the VCF PCB and/or the 3,5mm jack sockets only, disassembly is easy since all of these do not require you to take the pot knob off.
First, take off the wooden side cheeks by taking out the screws with some hex key.
After that, take off the marked screws on the top chassis back.
You can now (carefully) lift up the entire upper part of the Dom 1 – keybed, the MIDI PCB and the PSU are fastened to the bottom chassis. The ribbon cables inside are long enough for you to work comfortably.
There are a couple of ribbons, none of which are labelled, so if you intend to take them off (a teaspoon can help you lifting them gently, btw), label them and the corresponding connector pins beforehand.
If you need to take out the ribbon PCB, unscre the four nuts and pull off the blue stripes. BTW, your ribbons can easily be replaced with 10k potentiometers.
Except for the PCB around the LCD and the patch storage buttons, most other PCBS are merely for control to and from the CPU, i.e. they are not a primary component of the sound circuits.
The VCF is installed on a little piggyback PCB on the backside of the synth/CPU PCB. Unscrew and lift – there are a couple of pin connectors, so be firm but gentle.
The VCO control section is already comprehensive, and I do not intend to cut traces on the PCBs. As long as I have not dabbled yet with controlling those quadruple digi-pots and/or undergone more sleuthing for points to tap the VCOs directly, my suggestions will be limited. Potentially, there could be individual waveform output per VCO, wave shaping CV inputs including PWM CV inputs, CV for VCO FM, CV for ring mod level, CV for VCO2 and 3 Sync on/off.
Make your white noise a bit duller
I find the white noise on the Dominion 1 *as is* a tad too bright, so I made it a bit duller with the aid of a 3.3uf capacitor. The process is easy and similar to the ENV OUT click fix pictured above. Since the noise is normalled to the EXT IN jack socket (plugging in a cable replaces the white noise signal with an external input signal), you can just wire a capacitor (higher values = duller sound) between the normal pin and ground of EXT IN.
While you’re at it, and don’t mind having more jack sockets in your Dom1, you can also tap this point for a dedicated white noise output.
Proper External Filter Input
Someone asked me about a fix for the external input problem they had with their Dominion 1 (thanks, Janis!), and after noticing that several users had reported clipped audio when feeding signals in, I followed this up and can confirm this behaviour. Apart from being a tad quiet, the external input signal is rectified, i.e. the negative phase of the signal appears to be somewhat clipped. This is not so much noticeable with saw waves, but definitely audible with sine waves and other material. Here’s what it looks like:
As you can hear, the sine wave is quite a bit warped when fed into the extisting “Ext In”. I need to analyze the filter board still a bit more to state what causes this specifically, yet ATM I assume this is on account of buffering (probably through one of the LM13700 buffer stages). Be it as it may, while the internal VCOs sound fine to me, EXT IN signals go meh…
If you want to use an additional EXT IN which does not warp your input signal, wire a jack socket to a 100k resistor, which goes to a 100k potentiometer. The middle pin of your potentiometer goes to a 10uf capacitor (anode), and the remaining pin to ground. The cathode of your 10uf capacitor goes to the “output” terminal of what is labelled R1 on the following picture. You can ditch the potentiometer and use a jack socket via a 100k resistor directly.
This mod also has the benefit that you can keep the noise/ext in level control in the mixer for noise exclusively.
The filter input is attenuated by a 68k resistor (the one with the two cables attached on the picture below). By lowering the value of this resistor, you can gain a very sweet sounding pre-filter drive. Depending on the selected filter type and amount of reduction, this gives you ample saturation or can be used more subtly to liven up your sound. In some cases, I tend the VCO sound of the Dom 1 to be a tad static, yet playing with the gain staging changes this impression.
For implementing this mod, you can use an on/off switch that engages a 20k resistor in parallel to the existing 68k resistor. I personally, do without a switch by taking the signal from the input terminal of the 68k (white cable on the picture above) and feeding it through a 47uf capacitor, the cathode of which goes to a 100k potentiometer. The middle pin of the potentiometer goes through a 20k resistor, which, in turn, is wired to the output terminal of the 68k resistor (red cable on the pic), and the remaining terminal of the potentiometer goes to ground. This setup retains the filter input attenuation at 68k when the pot is fully closed and reduces it to about 15k when fully open. This is more volume than wanted in most applications but just the right thing in some 🙂
FFM from VCA output
The Dom 1 has ample FM and FFM options. One of my favourites, however, is missing – FFM from the VCA output, as popularized in Robin Whittle’s Devilfish mods for the TB303. I prefer this over FFM from VCO or VCF output since the amplitude is not constant but follows the overall amplitude of the sound, which sounds more dynamic.
The very easiest way to obtain FFM from VCA is to use an attenuator and two Eurorack cables, connecting your main out socket and the FFM in socket. As I wanted to keep these free, however, and like the mod enough to have it permanently installed, I tapped the 3,5mm main out signal, fed it through 47uf capacitor, followed by a 100k potentiometer. The middle pin of that goes to a 56k resistor, which goes to the FCV pin of the filter board (see pic in the VCF description and white cable with black heatshrink on the pic above). The remaining pin of your potentiometer goes to ground.
Envelope outputs click fix
Several Eurorack users have noticed the three envelope output sockets of the Dom1 having an audible digital-ish click on their onset and end, which makes them hard to use with a couple of modules. The click is more noticeable on short attack/release settings and thankfully not so audible in the Dom’s internal sound engine. My Vermona quad VCA, however, does not play well at all with them, so I went for a quick and easy fix by “softening the blow” of these envs by means of some slew.
On the back of the Jack PCB you see the pins of all your 3.5mm jack sockets. The tips of many of these are normalled to ground, as you can see from the PCB trace connecting to the six uppermost pins on the top left pictured above. By adding a 1uf capacitor between each tip lug (centre left) of the ENV OUT jacks and ground (top pin), you still have snappy envs spit out by the Dom, yet the spikes on note onset and end are greatly reduced.