Walter P. Gruber’s satire Aus dem Leben Hödlmosers really helped me understanding how ridiculous heroism and nationalism can be. I’m not sure why this novel sprang to mind when I scored a second hand TD-3-MO-SR. Well, MO-SR is already four letters deep into Moser…
While I don’t like every option the TD-3-MO offers, I it can serve as a good template for implementing mods other than the ones Behringer readily took from the Whittle/xoxbox-continuum. Part of my feelings here is that you cannot treat a DIY community like an infinite resource, but also that the Devilfish is not the alpha-omega 3D fish liver oil cure for all acidic ailments. I guess I want fun and creativity, so first of all, apologies for not documenting every nook and cranny of the MOSER (and it’s incredibly roundabout subosc) but rather keep stuff at a level of – this was fun to toy with. Moreover, if you want more, just do more. Happy to link your findings here!
Deactivate those LEDs: twiddle that blinkenbox while sipping on your neon-green energy drink? If that’s not your style, you can unscrew the bottom lid and use gaffer. Or take out the 330ohm resistors and NPN transistors near each led section.
PSU MOD: like the non-murdered TD, this synth derives its 5.333V and +12V supplies from an op-amp setup. Like on the XOX, the TD3 and other clones, the power supply of that same op-amp can be throttled by increasing a single resistor. On the MOSER this is R109 (10ohm) near the tune knob. Replace this with another SMD resistor (or through hole on the back of the PCB, as shown below) – I dunno what’s best for you as I changed the op-amp to another type on my unit and ended with some 22ohm. You might find anything up to 100ohm useful on yours. Simply test what’s what. Stuff can get a bit wonkier on this one than on the normal TD3.
SQUARE ADJUST: The Moser-square is better adjusted an the one on the simple TD-3. Still, I found that I could hollow mine out even a bit more by wiring a 220k resistor between +12V (tapped from C86). and the anode of the cap marked below. Maybe that’s a homeopathic exercise, dunno, listen to A/B…
THE PSU adjustment can easiest be done by soldering to the anode of the cap marked here: middle cap left hand of the wave form switch. This cap stabilizes the power supply for the transistor generating the square, and if we change the supply voltage a bit (either by adding some from +12V or by pulling down to ground), we change the pulse width. NB that the square of the 303 is a weird one that changes pulse width along with frequency.
Rubber Mod: funny mod that was laughed at full tilt first but seems to have persevered. The normal TD3 sound quite stiff and sometimes staccato. As the VCA envelope was a bit changed around the “soft attack” mod, and variable VCA decay mod, this seems to be a bit different here. While the “classic” rubber mod results in clicks here, I found a 560nf-1uf cap between ground and TP4 works well for rounding stuff a bit off. While you’re at it, try some 220nf between ground and the middle pin of the VCA decay knob (simply called DECAY on the MO) as well – this shifts the pot action a bit.
Manual Slide: Just insert a momentary ON switch/pushbutton between ground and this point marked here:
Change the dual NPN ladder filter transistors (difficult!): Like the normal TD3, the Moser sports dual NPN transistors where the original 303 has single NPN pairs. Now, if you are in the camp of people finding the TD3 resonance on the shriller side, this is your reason. Since the dual NPN package in SMD form are very well matched (in addition to reasonably well matched capacitors), the spread of transfer functions across your three lowpass stages (the first of the four is a tad different) is closer than with less well matched transistors.
Changing caps may make this somewhat diffuser but will not be as effective (despite some very verbose claims by our usual suspects) as using single NPNs (I used BC550B in my example below). 303-redesigners who know their stuff (xoxheart, for instance) go that route, the TT303 MK1 is like that (MK2 has matched pairs)… You see, while I renounce the church of capacitor, I subscribe to the temple of transistors…
Stock TD3 ladder:
BC550B for T34, T35, T36:
Unfortunately, this is not an easy mod since you need to pull 3x sot23-6 package transistor pairs and fit 6 new single transistors. The filter ladder being placed very close to the vco waveform switch doesn‘t help either…
FFM from filter out: cut the trace from the VCA output buffer cap (C129) leading to R249 and the FFM pot. Then rewire PIN3 of the FFM pot to the cathode of the VCF out cap (C72). You get mellower FFM action this way.
in normal and later on in high pass mode:
Rubberduck (filter slew): wire 4.7uf cap cathode to ground and anode to on/off switch. The other lug of the switch goes to the middle pin of ENVELOPE (amount) potentiometer.
HIGH PASS/PHASEY FILTER: This is fun, though a bit more complicated to set up. Basically, you route the direct VCO out signal to the VCA input (at C65) via a pot. When the VCF out signal and your new “direct VCO out” signal are at the same volume level, the phase relationship between the two signals turns your lowpass into a high pass. Sounds like this:
In terms of setting this up, I decided I do not want the pre-vcf overdrive, so I pulled out the CATHODE of C101 and wired my VCO select switch via 220k and my variable sub out via 330k directly to VCF in. I then also wired the wiper of the “Overdrive” knob via 1k (if memory serves) to that VCF input node. When pulling up the former “OD” knob, high pass now fades in.
VCA overdrive: replace R114 (220k) with a 250k pot and 6.8k resistor in series. this makes the CV-to-VCA-amount variable and (on highest setting) much higher than usual. With the muffler mod on, you get nice crunchy sounds. NB this potentially increases the noise floor a bit… here are two examples:
More soon…