Praga

Xaoc Devices 20HP
fw 1967/1.2
MIXER VCA UTILITY

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Four-channel stereo VCA mixer with per-channel unipolar/bipolar CV modes, clickless mutes, two post-fader aux sends with stereo returns, direct VCA outs, and chainable sub-mix bus. Hrad expander adds master level and gate mutes.

Patch Ideas · 9

★ Four-voice performance mixer with gated mutes
Four voices into INPUT 1–4 · each channel in unipolar (green) with envelope → VOL CV · manual mutes for live arrangement · sum via STEREO SUM to main out
▸ Show diagram
Patch diagramPatch diagram with 8 modules and 8 connections. Signals: 6 audio, 2 cv.PragaVoice1Env1Voice2Env2Voice3Voice4OutputCh1 Mode: UNIPOLARCh2 Mode: UNIPOLARCh3 Mode: UNIPOLARCh4 Mode: UNIPOLARINPUT 1audioVOL CV 1cvINPUT 2audioVOL CV 2cvINPUT 3audioINPUT 4audioSTEREO SUM LaudioSTEREO SUM RaudioOutaudioOutcvOutaudioOutcvOutaudioOutaudioLaudioRaudioaudiocv
Tremolo on one channel via bipolar LFO
Switch Ch1 to bipolar (red) · LFO ±5V into VOL CV 1 · VOL knob sets tremolo depth (open = full depth, ~half = subtle) · other channels stay in unipolar
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 4 connections. Modules: Praga, Pad, LFO, Output. Signals: 3 audio, 1 cv.PragaPadLFOOutputCh1 Mode: BIPOLARCh1 VOL: 7 (depth)INPUT 1audioVOL CV 1cvSTEREO SUM LaudioSTEREO SUM RaudioOutaudioSinecvLaudioRaudioaudiocv
Auto-panning pad
Pad into Ch2 · slow LFO ±5V → PAN CV 2 · PAN knob at noon for symmetric sweep · channel in unipolar, envelope shapes amplitude
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 5 connections. Modules: Praga, Pad, AD Env, Slow LFO, Output. Signals: 3 audio, 2 cv.PragaPadAD EnvSlow LFOOutputCh2 Mode: UNIPOLARCh2 PAN: noonINPUT 2audioVOL CV 2cvPAN CV 2cvSTEREO SUM LaudioSTEREO SUM RaudioOutaudioOutcvTricvLaudioRaudioaudiocv
★ Reverb send with pre-delay
Vocal/lead into Ch1 · AUX full CW to send B · AUX SEND B → reverb in · reverb L/R → AUX RETURN B pair · pre-delay via delay in the send path
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 7 connections. Modules: Praga, Voice, Delay, Reverb, Output. Signals: 7 audio.PragaVoiceDelayReverbOutputCh1 AUX: full CW (send B)INPUT 1audioAUX RETURN B LaudioAUX RETURN B RaudioAUX SEND BaudioSTEREO SUM LaudioSTEREO SUM RaudioOutaudioInaudioOutaudioInaudioOutLaudioOutRaudioLaudioRaudioaudio
Parallel compression via dual aux loop
Drum bus into Ch3 · AUX full CW (B) → external compressor → AUX RETURN B · AUX full CCW (A) unused or to saturator · blend dry Ch3 with smashed parallel return
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 6 connections. Modules: Praga, Drums, Compressor, Output. Signals: 6 audio.PragaDrumsCompressorOutputCh3 Mode: UNIPOLARCh3 AUX: full CWINPUT 3audioAUX RETURN B LaudioAUX RETURN B RaudioAUX SEND BaudioSTEREO SUM LaudioSTEREO SUM RaudioOutaudioInaudioOutLaudioOutRaudioLaudioRaudioaudio
Multitrack via VCA OUTs
Four voices in · record each VCA OUT to a separate DAW track (still VCA-shaped, no pan) · use STEREO SUM for headphone monitor mix with pan and aux fx
▸ Show diagram
Patch diagramPatch diagram with 7 modules and 10 connections. Signals: 10 audio.PragaVoice1Voice2Voice3Voice4InterfaceOutputCh1-4 Mode: UNIPOLARINPUT 1audioINPUT 2audioINPUT 3audioINPUT 4audioVCA OUT 1audioVCA OUT 2audioVCA OUT 3audioVCA OUT 4audioSTEREO SUM LaudioSTEREO SUM RaudioOutaudioOutaudioOutaudioOutaudioCh1audioCh2audioCh3audioCh4audioLaudioRaudioaudio
CV mixer for modulation summing
Use DC-coupled path to mix multiple CVs. Envelopes into INPUT 1–3 in unipolar mode, faders set weights · VCA OUT 1 (or STEREO SUM L) drives a filter cutoff
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 4 connections. Modules: Praga, EnvA, EnvB, LFO, Filter. Signals: 4 cv.PragaEnvAEnvBLFOFilterCh1 Mode: UNIPOLARCh2 Mode: UNIPOLARCh3 Mode: UNIPOLARINPUT 1cvINPUT 2cvINPUT 3cvSTEREO SUM LcvOutcvOutcvOutcvCutoffcvcv
Cascaded 8-channel mixer (two Pragas)
Praga#1 channels 1–4, Praga#2 channels 5–8. 6-pin ribbon from Praga#1 OUT header → Praga#2 IN header. Praga#2 STEREO SUM carries all eight.
▸ Show diagram
Patch diagramPatch diagram with 11 modules and 10 connections. Signals: 10 audio.Praga#1Praga#2Voice1Voice2Voice3Voice4Voice5Voice6Voice7Voice8Outputall channels: UNIPOLARall channels: UNIPOLARINPUT 1audioINPUT 2audioINPUT 3audioINPUT 4audioINPUT 1audioINPUT 2audioINPUT 3audioINPUT 4audioSTEREO SUM LaudioSTEREO SUM RaudioOutaudioOutaudioOutaudioOutaudioOutaudioOutaudioOutaudioOutaudioLaudioRaudioaudio
★ Sidechain duck via bipolar mode
Bass on Ch1 unipolar · kick-triggered envelope inverted → VOL CV 1 in bipolar mode · knob sets duck floor · kick punches a hole in the bass
▸ Show diagram
Patch diagramPatch diagram with 5 modules and 5 connections. Modules: Praga, Bass, Kick, Env, Output. Signals: 3 audio, 1 cv, 1 trigger.PragaBassKickEnvOutputCh1 Mode: BIPOLARCh1 VOL: 8INPUT 1audioVOL CV 1cvSTEREO SUM LaudioSTEREO SUM RaudioOutaudioTrigtrigTrigtrigInvcvLaudioRaudioaudiocvtrigger

Behaviors

Unipolar volume mode (envelope VCA) long-press ACTIVE|MODE · button lit green

VOL knob biases the CV input. Full knob + 8V CV opens channel to 0dB, closed knob silences the channel to ~-85dB. Dynamic response to CV is preserved regardless of knob position — behaves like a CV-offset VCA. Above 0dB gain is soft-compressed (+3dB ceiling), giving a compressor-like taming rather than clipping.

Bipolar volume mode (LFO amp mod) long-press ACTIVE|MODE · button lit red

VOL knob scales the bipolar CV together with an internal offset. Depth of AM (in dB) shrinks as the knob closes — modulation is maximal only when the fader is up. Optimized for ±5V LFOs; +5V fully open = 0dB, fully closed ≈ -56dB steady. No clipping above 0dB; response compresses instead.

Clickless mute / unmute short-press ACTIVE|MODE

Fades the channel to -90dB over a few milliseconds instead of hard-cutting. LED extinguishes while muted. Pressing again fades back in. Safe for performance muting under audio.

Knob-as-offset with CV patched cable in VOL CV or PAN CV

Knobs become offsets rather than primary controls when CV is patched. In unipolar mode, VOL still sets the floor of attenuation; in bipolar mode, it still scales depth. PAN knob biases the center point of CV-driven panning.

Post-fader aux sends AUX knob off noon

Sends tap the per-channel VCA output, so envelope/LFO amplitude modulation carries into the send effect. Channel mute also silences the send. AUX is bipolar with A on the CCW half and B on the CW half — noon is no send.

Stereo aux returns route to main bus cable into AUX RETURN A or B

Returns are stereo pairs summed directly into the main bus, not back through any channel. Aux A return shares its input jacks with the left pair, aux B with the right pair (see panel labels).

Soft-clipped sum bus sum > 16Vpp

The stereo bus gently saturates when multiple hot sources sum. Prevents harsh hard-clipping. Manual recommends keeping faders 50–80% for clean headroom with typical modular levels.

Chainable sub-mix via rear headers 6-pin ribbon between OUT → IN headers

Multiple Pragas (or compatible mixers) cascade: each upstream unit injects its mix bus 1:1 into the next unit's bus, so the final Praga's STEREO SUM carries everything. IN of the first unit and OUT of the last remain open.

Hrad expander integration Hrad connected via expander header

Adds line-level outputs, master LEVEL with meter, headphones, cue input, gate inputs for automated muting, CV over the aux amounts, and channel insert points between VCA and aux selector.

DC-coupled signal path any patch

All channels pass DC, so Praga doubles as a VCA/mixer for CV as well as audio — useful for summing envelopes, crossfading CV, or muting modulation sources.

Controls

per channel (1–4) VOL Channel attenuator. Function depends on active volume mode — offset in unipolar, bipolar scaler in bipolar.
0–10 · unipolar: fully open = 0dB at 8V CV · bipolar: fully CCW = -56dB, no modulation
per channel (1–4) ACTIVE|MODE Illuminated button. Short press toggles clickless mute · long press switches volume control mode.
green = unipolar · red = bipolar · unlit = muted · mode-switch works while muted
per channel (1–4) PAN Stereo panorama offset. Sums with PAN CV. 3dB equal-loudness pan law, compressed near 0dB to prevent loudness rise.
bipolar · CCW = L · noon = center · CW = R · CV expects ±5V
per channel (1–4) AUX Bipolar send to aux A (CCW) or aux B (CW). Post-fader, derived from channel VCA output.
noon = no send · CCW = send A · CW = send B · post-fader only
per channel (1–4) Post-fader LED meter Five-bar peak indicator referenced to 10Vpp. Thresholds -32 · -20 · -12 · -6 · 0dB.
top LED = clip warning · reads post-VOL, pre-pan/aux split

I/O

IN · 5

  • INPUT ±10V (DC-coupled) CV
    Channel audio input. DC-coupled signal path accepts modular-level audio or CV.
  • PAN CV -5V to +5V CV
    Pan-position CV, summed with the PAN knob as offset.
  • VOL CV unipolar 0–8V · bipolar -5V to +5V CV
    Volume CV. Response differs per mode — unipolar for envelopes, bipolar for LFOs. Higher amplitudes tolerated but compressed above 0dB gain.
  • AUX RETURN A (L/R) ±10V audio AUDIO
    Stereo return pair for the aux A send. Summed directly into the main stereo bus.
  • AUX RETURN B (L/R) ±10V audio AUDIO
    Stereo return pair for the aux B send. Summed directly into the main stereo bus.

OUT · 5

  • VCA OUT ±10V audio AUDIO
    Per-channel direct post-VCA tap, unaffected by PAN. Uses a separate VCA chip for a clean copy — intended for multitracking or insert-style routing via Hrad.
  • STEREO SUM L
    Main mix bus, left. Soft-clipped above ~16Vpp to tame sum overs.
  • STEREO SUM R
    Main mix bus, right. Soft-clipped above ~16Vpp to tame sum overs.
  • AUX SEND A
    Mono post-fader send for bus A.
  • AUX SEND B
    Mono post-fader send for bus B.