Isolator

Happy Nerding 4HP
I/O UTILITY MIXER

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4 HP stereo output interface: transformer galvanic isolation to 1/4-inch TRS balanced outs plus headphone jack (v2 panel). Level drives the mains, Phones the cans. L input mono-normals to R when R is unpatched.

Patch Ideas · 5

★ Final stereo out to a mixer
Route the stereo master from a eurorack mixer through Isolator into a studio desk or interface with no ground hum.
Walkthrough
  1. Patch your main stereo mixer (L) -> Isolator (L In) with a 3.5mm TS cable.
  2. Patch your main stereo mixer (R) -> Isolator (R In).
  3. Run a 1/4-inch TRS cable from Isolator (Out L) to the mixer/interface Left line input.
  4. Run a second 1/4-inch TRS cable from Isolator (Out R) to the Right line input.
  5. Start with Isolator Level fully CCW, un-mute the destination, then raise Level until the destination meters read around -12 dBFS on the loudest part.
  6. If hum still appears, try a TS (unbalanced) cable on the destination end, or lift the destination's own ground at its end — v2 has no front-panel ground-lift switches.
Signal out Out L and Out R — transformer-isolated balanced line level to the destination's TRS inputs.
Listen for The full eurorack stereo mix arriving clean at the destination. Compared to a plain 3.5mm-to-1/4-inch cable, the noise floor drops and any 50/60 Hz buzz disappears. The transformer adds a subtle warmth on transients.
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 4 connections. Modules: Isolator, Eurorack Mixer, Audio Interface. Signals: 4 audio.IsolatorEurorack MixerAudio InterfaceLevel: set to taste (start CCW)L InaudioR InaudioOut LaudioOut RaudioOut LaudioOut RaudioIn LaudioIn Raudio11. 1/4 TRS balancedaudio
★ Mono jam to stereo PA
Send a single mono bus to both sides of the PA using the L-to-R normalled routing.
Walkthrough
  1. Patch your mono output (drum bus, single VCA, etc.) -> Isolator (L In).
  2. Leave Isolator (R In) empty — this is the key step; the L signal normals to R internally.
  3. Run 1/4-inch TRS from Isolator (Out L) -> PA Left; from (Out R) -> PA Right.
  4. Set Level fully CCW, bring up the PA, then raise Level to reach the PA's target input level.
  5. If one side still hums at the venue, swap cables or try a DI-style lift at the PA end — transformer isolation usually kills the loop on its own.
Signal out Out L and Out R — identical mono signal fed through two transformers to both PA sides.
Listen for Centered mono image across the PA with hum-free isolation. If the performance is mono but you only have a stereo snake, this saves a splitter cable and guarantees both sides match in level.
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 3 connections. Modules: Isolator, Mono Bus, PA. Signals: 3 audio.IsolatorMono BusPAR In: empty (mono normalling active)Level: to PA targetL InaudioOut LaudioOut RaudioOutaudioLeftaudioRightaudio11. normalled copy of Laudio
★ Silent headphone pre-check
Audition the rack on headphones with the balanced outs muted before unmuting the house.
Walkthrough
  1. Patch stereo mix -> Isolator (L In) and (R In) as usual.
  2. Turn Isolator Level fully CCW so the 1/4-inch outs are silent — the PA stays dark.
  3. Plug headphones into Isolator (Phones).
  4. Bring up the Phones knob until monitoring is comfortable — the balanced outs remain muted because Phones is independent of Level.
  5. When the patch is performance-ready, raise the Level knob to feed the PA.
  6. Keep Phones steady or lower it once the room is loud, to protect your ears.
Signal out Phones jack only — headphone-level stereo. Out L / Out R stay silent while Level is CCW.
Listen for Full stereo mix in your headphones while the house speakers stay quiet. Perfect for tuning a new patch or sound-checking a sequence without disturbing the room.
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 3 connections. Modules: Isolator, Eurorack Mixer, Headphones. Signals: 3 audio.IsolatorEurorack MixerHeadphonesLevel: full CCW (balanced outs muted)Phones: to tasteL InaudioR InaudioPhonesaudioOut LaudioOut RaudioInaudio11. balanced outs silentaudio
Laptop-free recording chain
Record the rack straight into a USB interface on battery power using Isolator to kill the laptop ground loop.
Walkthrough
  1. Run a 3.5mm stereo (or two TS) from the eurorack output mixer into Isolator (L In) and (R In).
  2. Connect Isolator (Out L) and (Out R) to two line inputs on the USB interface with 1/4-inch TRS cables.
  3. Unplug the laptop charger so the laptop runs on battery — this is the scenario where ground hum is worst without isolation.
  4. Arm record on the DAW. Start Isolator Level CCW and raise it until the DAW peaks around -6 dBFS.
  5. If a 50/60 Hz buzz persists even on battery, check whether the interface is also on its own ground — the Isolator already breaks the rack side.
  6. Plug headphones into Isolator (Phones) for latency-free monitoring while you record.
Signal out Out L / Out R -> interface line ins. Phones -> direct monitoring without DAW round-trip latency.
Listen for A clean stereo recording free of the charger-whine and laptop-buzz that plagues direct 1/8-inch-to-1/4-inch captures. Latency-free direct monitoring in the cans while the DAW does its thing.
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 5 connections. Modules: Isolator, Eurorack Mixer, USB Interface, Headphones. Signals: 5 audio.IsolatorEurorack MixerUSB InterfaceHeadphonesLevel: DAW peaks ~ -6 dBFSPhones: comfortableL InaudioR InaudioOut LaudioOut RaudioPhonesaudioOut LaudioOut RaudioLine 1audioLine 2audioInaudio11. zero-latency monitoraudio
Two destinations, one isolator
Feed a pedal chain from the balanced outs while the performer monitors on headphones at a different level.
Walkthrough
  1. Patch stereo mix -> Isolator (L In) and (R In).
  2. Patch Isolator (Out L) and (Out R) via 1/4-inch TRS into a stereo pedal's L/R inputs — the isolation kills the notorious stompbox-power ground loop.
  3. Plug headphones into Isolator (Phones).
  4. Set Phones knob for comfortable listening, independent of the Level feeding the pedals.
  5. Adjust Level so the pedal input LED sits below clip — most pedals expect lower-than-line level so back off if the pedal overdrives unintentionally.
  6. If pedal-power hum returns despite isolation, try a different wall outlet for the pedal PSU or a dedicated isolated pedal-power brick.
Signal out Out L/R -> pedal chain at line/instrument level. Phones -> independent monitor at performer-comfortable level.
Listen for Pedal reverb/delay tails on the main mix with no ground buzz, while the player hears a separate balance on headphones. Great for stage or home-studio hybrid setups.
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 5 connections. Modules: Isolator, Eurorack Mixer, Stereo Pedal, Headphones. Signals: 5 audio.IsolatorEurorack MixerStereo PedalHeadphonesLevel: below pedal clipPhones: performer comfortL InaudioR InaudioOut LaudioOut RaudioPhonesaudioOut LaudioOut RaudioIn LaudioIn RaudioInaudioaudio

Behaviors

Transformer galvanic isolation always on (passive signal path)

Both 1/4-inch outs pass through audio transformers. No DC path exists between the eurorack ground and the destination ground — this kills hum caused by connecting a laptop/mixer on a different outlet. Expect a very slight low-end roll-off and subtle harmonic coloration characteristic of small audio transformers.

Mono-to-stereo normalling R In jack empty

With nothing in R In, the L In signal is internally routed to the right channel of both the balanced outs and the headphone amp. Plug only a mono source into L and get identical stereo output — no mult or splitter needed.

Independent headphone monitoring patch anything into L/R

The Phones knob is separate from Level, so you can crank headphone monitoring while the balanced outs stay at performance level (or vice versa). Handy for check-listening before unmuting on a PA.

Headphone gain trim via jumpers open the module, rear PCB (v2)

Default jumpers set the headphone amp for max gain so even 250-ohm studio cans drive loud. If low-impedance IEMs or 32-ohm cans distort or are harsh, power down and pull both jumpers to drop the gain stage.

v1 vs v2 panel hardware revision

v1 (original, discontinued): one Level knob, two 3.5mm inputs, two 1/4-inch balanced outs, plus a ground-lift switch per channel on the front panel — no headphone output. v2 (current): adds a Phones knob and front-panel headphone jack and drops the ground-lift switches; internal jumpers set headphone gain. This sheet reflects v2 — the version sold today.

Controls

Main L+R Level Master attenuator feeding the isolated 1/4-inch TRS outputs. Controls both channels together — no per-channel trim.
stereo-linked attenuator · CCW: silent · CW: unity / line level
Headphone out (v2) Phones Independent level for the front-panel headphone jack. Moves separately from the balanced Level knob, so you can monitor loud while the mains stay muted.
dedicated headphone attenuator · independent of Level
Internal (rear PCB, v2) Headphone gain jumpers Two removable jumpers behind the panel set the headphone amp gain. Installed from factory for max gain; pull both if the amp is too loud/harsh with low-impedance cans.
both in: max gain (default) · both out: reduced gain

I/O

IN · 2

  • L In (3.5mm) eurorack line level (±5V typical) AUDIO
    Left channel audio input on a 3.5mm mini jack at eurorack line level. Normalled to the right channel so a mono signal plugged here alone reaches both balanced outs and both headphone sides.
    NORM → R channel when R In is unpatched (mono sum to stereo)
  • R In (3.5mm) eurorack line level (±5V typical) AUDIO
    Right channel audio input on a 3.5mm mini jack at eurorack line level. Breaks the mono normalization once patched — L and R then stay discrete.

OUT · 3

  • Out L (1/4" TRS) balanced line level · transformer-isolated AUDIO
    Left balanced line-level output through a transformer. Send to mixer/interface TRS input. DC blocked and galvanically isolated from the eurorack bus — no shared ground path to the destination.
  • Out R (1/4" TRS) balanced line level · transformer-isolated AUDIO
    Right balanced line-level output through its own transformer. Matches Out L. If R In is unpatched, carries the L In signal (mono-to-stereo).
  • Phones headphone amp · gain set by internal jumpers
    Stereo headphone output driven by the on-board amp. Taken post-transformer so it benefits from the same isolation. Level set by Phones knob, not by Level.