Well, the four Electrosmith VCAs aren't a bad idea...for modulation and CVs. These are linear, DC-coupled VCAs, which are better used for those purposes. For audio, you want exponential VCAs with AC-coupling, which is why you often see VCAs such as Veils, Intellijel's Dual VCA, etc used so often; since these have a control per VCA that can shift the VCA's response between full linear and full exponential.
Why this is important is because we perceive "apparent loudness" on an exponential curve...with a unit called the decibel. Decibel readings are confusing at first, but as long as you keep in mind that adding 10 dB of amplification to a signal, you're only increasing the apparent loudness in doubles.
Gonna mess with this, starting with a bigger and portable cab off the bat. I'm designing this around a Case From Lake 3 x 126 device, which is here: https://www.casefromlake.com/product-page/9u-eurorack-case-powered-120-or-126-hp-patched-resealable-modular-synthesizer And it runs only EUR 495, compared to EUR 379 (@ Schneidersladen) for the Doepfer. But the CFL one has a lid, strap, MUCH more amperage capacity, and if you want any tweaks to the basic design, they can do that too. Anyway...
Banged on this A LOT. Instead of having a bunch of Mutable modules, I opted for the ultimate tweak-head ones: Buchla. Or rather, the Tiptop reissues of the original Buchla 200 modules. Then I built around that.
TOP: This is the "audio" row. Starts off with the very useful Konstant Labs PWRchekr to keep an eye on your DC rails' health. Then a 1 hp blank, followed by a more comprehensive input module, the Doepfer A-119...sort of the OG of Eurorack input modules. It gives you a comparator for creating gates out of audio levels, plus a CV from the amplitude of the input signal...AND it has a proper 1/4" jack, not a 3.5mm. Then, a pair of Buchla 258t for s paired with a Dannysound Timbre...a waveshaper derived from the circuit in the Buchla 259, so I suppose the result here are "258 1/2s"? Anyway, Veils, then another curveball: Uli's clone of the ARP 2500 VCF. There IS a 200 series VCF...but it's not been reissued (yet), so why not drop in another famous early modular VCF? But after that, you get the Buchla take on that, with their 292t quad LPG...so you can have either a straight audio feed from the VCF to the row's stereo mixer, or you can have four of those vaunted Buchla lowpass gates...or both, why not? Anyway, the end mixer is right after the LPGs, a manual stereo mixer with four pannable inputs to help stereoize the signal before it hits the Beads, or you could just run the LPGs down to the performance mixer individually, or or or...tons of potential, and I've not even got into the next row yet! I put the Disting last in this row, as it'll be easier to get at both patch-wise AND finger-wise for the various purposes it's got.
MIDDLE: Modulation-ish. The famous Buchla "Source of Uncertainty" kicks the row off, then your Maths is after that. I put together a little array of the Electrosmith dual VCAs and a Buchla 257t for mixing and/or mangling modulation signals. Then there's a pair of Buchla 281ts with a Doepfer diode OR combiner for triggers and gates. It's worth noting that the individual envelope gens in the 281ts can be clocked way on up into the audio range, at which point they become something like CVable variable waveform generators. And there's a lot more of that sort of "hidden trickery" in here, since it's a weird hybrid of West and East Coast principles all functioning in Eurorack; back in the day, most of this would be in systems that couldn't necessarily be cross-patched due to CV and/or trig/gate differences that we, for the most part, don't have now across the Eurorack module gamut.
BOTTOM: Pam's, then a Doepfer dual quantizer for pitch constraint and a Eurorack Essentials 2 x 2 sequential switch. More about that in a bit. Then a second switch, this time from Doepfer and with a 4 x 1 circuit. After that is the first of two Buchla 245t sequencers, and then the second is separated by another Doepfer 4 x 1 switch. And why are those switches important? OK...sequential switches shift between two or more incoming CV signals when they receive (in this case) a trigger pulse. So the switches form a timed network to step through all sequencer rows, then send these over to the quantizer for discrete pitch tunings. Or you could just as easily use one sequencer as your "line" and the other as "transpose". Need divided timing for any of that? The Pam's deals handily with this need. After the sequencer section, you've got a Qu-bit Mixology. That performance mixer gives you CV control over your amplitude level, panning, and FX send per channel, plus a manual per-channel solo and mute. This also has a parallel FX processing bus, so your sends go out via the mono send and come back in through the stereo return. With that, I opted for a more straightforward FX processor, namely Freq Central's Stasis Leak, which gives you mono-to-stereo tap delay, chorus, and reverb. Note, also, that you can also opt to use the Beads post-mixer, hence one reason why they're close vertically. And all the way at the end is your balanced outputs, a second stereo return (useful if you split off the send to the Beads, then you can send the Beads output to the second return), a headphone preamp, and main level controls.
Yeah, OK...it's bigger. But unlike the Doepfer LC, this is designed to be portable, as the CFL cab comes with a lid (and yes, you have room to keep things patched beneath it) and a carry-strap. It's about the size of a large briefcase, which is a good form factor, especially for fitting it into an overhead bin on a plane. And the current limits are...well, if you go with the Meanwells that CFL offers, you'll never have to worry about exceeding current limits in this build. Ever. And while it definitely costs more than the initial plan, you probably won't need to add anything to this for years to come. You WON'T exhaust this build's possibilities!