DDRK Omega Sampler

DDRK Omega Sampler is the low-level member of the DDRK Omega pack. Where the Unified KSampler does the whole job - model, conditioning, latent in, image latent out - this node only hands you a SAMPLER object for the stock SamplerCustom node to consume. If you just want images, use the Unified node and move on. Reach for this one when you're building a custom sampling graph where you control the SIGMAS yourself, doing img2img with a hand-picked schedule, or experimenting with the HC2 integrator in isolation.

What it is under the hood

Same engine as its big sibling: the sampler auto-detects whether your model is flow matching or EDM by reading the sigma schedule, routes sampling through three phases, and can use the HC2 exponential integrator - second order at one model call per step, a multistep method in the DPM-Solver++/UniPC line. The node itself takes no model input at all; it's a pure sampler configuration. Your wiring job is to pair it with a scheduler node that produces SIGMAS (the pack's DDRK Omega Scheduler works, so does any stock one) and feed both into SamplerCustom.

The inputs you'll actually set

• integrator - auto, hc2, rk4, heun, euler. This is the main event. hc2 is the pack's second-order-at-one-call integrator; auto picks per phase and step.
• sde_strength - ancestral stochastic noise, FM only (silently ignored on EDM, which uses s_churn instead). 0 = deterministic.
• sharpness - final-step perceptual sharpen, FM only by design. Set it on SDXL and nothing happens.
• saber_fusion - spatial stabilization weight; 0 disables the module entirely. If you're doing text or graphics, that's usually the number to zero out.
• dyn_thresh_percentile - a percentile latent limiter, 1.0 = off. Despite the name this is not Imagen-style dynamic thresholding; the README is upfront that the renormalization step is deliberately missing.
• latent_rescale - attenuates values beyond ~2 std from the per-image mean. The tooltip hammers this home: it is not classical CFG-rescale, because ComfyUI combines conditional and unconditional predictions before the sampler runs, so the two tensors that method needs aren't available here. It was renamed from cfg_rescale to stop implying otherwise.

Then the specialized clusters: limiter_kappa and hc2_max_order control HC2's slope limiter and order; hc2_corrector and sigma_adapt are marked experimental and default off (no measurable effect in the author's testing); s_churn/s_tmin/s_tmax/s_noise are Karras Alg 2 churn for EDM; sde_seed set to -1 derives the noise seed from the workflow seed so runs repeat from the seed widget.

Installing and wiring it

Same pack, same install, no extras - the README lists no dependencies beyond what ComfyUI already requires.

cd ComfyUI/custom_nodes/
git clone https://github.com/HVOSTOVSKY/DDRK-Omega-Sampler.git

Restart, then: DDRK Omega Scheduler → SIGMAS and this node → SAMPLER, both into SamplerCustom.

Gotchas

• At ≤6 steps the integrator is forced to euler unless you picked hc2; the console prints the override.
• Remember the model-call arithmetic: HC2 and Euler cost one call per step, Heun two, RK4 four. On EDM, HC2's advantage evaporates - the author's measurements put it at +1.2% dynamic range while using 10% more calls. auto or heun is the EDM call.
• sde_strength doing nothing on EDM and sharpness doing nothing on EDM are features, not bugs - they're gated per family.
• Something weird in your latent? debug_mode writes a per-step JSON+CSV+summary to the ComfyUI output folder, which is honestly the fastest way to see which enhancers actually fired.