DI & Reamp Guide — GP Tools

Recording a DI'd signal and reamping it later are two ends of the same chain. Get both right.

Passive vs Active — choose the right type

Passive DI — use when:

• Source has a strong, low-impedance output (active bass, line-level keyboard, guitar with active pickups)
• You need transformer isolation for ground loop elimination
• No phantom power available (passive needs none)
• Running directly off a DI split at line level (FOH and monitor splits)

Best for: Active basses, keyboards, high-output sources, live splitting. Jensen-transformer passives (Radial J48 passive, Whirlwind IMP-2) are the gold standard.

Active DI — use when:

• Source is high-impedance and low-output (passive guitar, vintage passive bass, piezo pickup)
• Long cable runs before the DI where you need buffering
• The passive DI is loading the source and causing tone loss
• Phantom power (48V) is available from your preamp or console

Best for: Passive guitar/bass direct recording, piezo acoustic, long stage runs. Radial J48 (active), Rupert Neve RNDI.

Impedance reference

Source	Output impedance	DI input needs
Passive guitar pickup (humbucker)	~7–15 kΩ	≥1 MΩ input (active DI recommended)
Passive bass pickup	~5–20 kΩ	≥500 kΩ input (active DI)
Active bass / EMG pickup	~100–1000 Ω	10–50 kΩ is fine (passive DI works)
Keyboard / synth line out	~100–600 Ω	10–50 kΩ (passive DI works well)
Amp speaker out (re-amp send)	~4–16 Ω (speaker)	Use a load box — don't DI a speaker output directly
Piezo pickup (acoustic guitar)	1–10 MΩ	10 MΩ+ input needed — specialized piezo preamp or Fishman-style buffer

Ground loop fix

Ground loops cause 60 Hz (US) or 50 Hz (EU) hum. They happen when the same signal travels through two different ground paths at slightly different potentials.
The transformer in a passive DI breaks the ground loop — the transformer magnetically couples the signal without connecting the grounds electrically.
If you're still getting hum after using a DI: check the ground lift switch on the DI (lifts pin 1 of the XLR output). Try it both ways. One will hum, one won't.
Don't use ground lifts as a default. They're a fix for a specific problem. A ground lift in the wrong place creates a shock hazard by floating the chassis ground.

Common use cases

Passive guitar → recording interface

Use the interface's instrument input directly (it has high-Z built in) OR an active DI box. Don't use a passive DI — it will load the pickups and kill your high-end.

Bass → FOH + monitor split

Passive DI with Jensen transformer. One XLR to FOH, instrument thru to amp, second XLR to monitor world. The transformer handles splitting without level loss or ground issues.

Keyboard → two console inputs

Passive DI or Y-cable. Passive DI provides isolation and prevents ground loop if keyboards are on a different power circuit from the console.

Amp speaker out → interface

Never connect a speaker output to an interface input. Use a proper load box (Two Notes Torpedo, Rivera RockCrusher) with a DI out, or mic the cabinet instead.

Why a plain interface output sounds wrong

Interface line out is ~24 dB too loud and wrong impedance — tone goes dull, compressed, no attack.

Guitar pickup~-20 dBu · high-Z

Interface line out+4 dBu · low-Z (~100 Ω)

Reamp box output~-20 dBu · ~10–50 kΩ

The fix — reamp box (passive DI in reverse)

A reamp box (or passive DI used in reverse) uses a Jensen-style transformer to:
• Step the impedance up from ~100Ω → ~200kΩ (closer to what pickups expect)
• Attenuate the signal from line level (~+4 dBu) down to instrument level (~-20 dBu)
• Provide electrical isolation to break ground loops

✓ Dedicated reamp box

Radial ProRMP, Radial X-Amp, Lehle Reamper, Rupert Neve RNDI (reverse). Passive Jensen transformer, correct impedance and level. The right tool. ~$100–300.

✓ Passive DI in reverse

Any Jensen-transformer passive DI (Radial J48 passive, Whirlwind IMP-2) used backwards: XLR input → 1/4" output. Hacky but works — the transformer provides the impedance match. Results vary by DI quality.

△ Interface → amp direct

Works in a pinch. Lower the output level on the interface as far as it'll go. Expect some tone difference vs the live performance. Fine for rough reamping, not ideal for final takes.

△ Re-inject plugin (UA, etc.)

Some interfaces have dedicated reamp outputs (UA Apollo, SSL 2+). These handle the level conversion in hardware. Still won't replicate the transformer's impedance behavior but better than bare line out.

Signal levels reference

Guitar pickup output (passive humbucker)~-30 to -20 dBu

Guitar pickup output (active EMG)~-10 to -5 dBu

Interface line output (balanced)+4 dBu

Interface line output (unbalanced consumer)-10 dBV (~-7.8 dBu)

Reamp box output (line in → instrument out)~-20 to -15 dBu

Amp instrument input impedance~500 kΩ – 1 MΩ

Interface output impedance~50 – 200 Ω

Reamp box output impedance~10 – 50 kΩ

Recording the DI for reamping

Raw signal, dry, peaking at -12 dBFS. Everything else causes problems when you reamp.

Pre-FX only

Instrument input on the interface, before pedals. Raw pickup signal — nothing printed on it.

Level

Peak ~-12 dBFS Too hot = clipping. Too quiet = noise floor when you crank the reamp send.

No time FX

Delay/reverb on the DI gets reamped and doubled. Record dry, add FX in the mix.

Phase

Tracked DI + mic together? Align phases before the reamp session. Saves headaches.