LL1935 Lundahl Übertrager 1:10 DI transformer - Guitar to Mic

Lundahl LL1935 passive DI and microphone-input transformer

The Lundahl LL1935 was developed for passive DI applications using guitar or bass. It steps a high-impedance pickup signal down to a lower level and output impedance suitable for a microphone preamplifier.

When used in reverse, it operates as a 1:10 microphone-input transformer and matches a low-impedance microphone to a high-impedance solid-state or valve preamp input.

Suitable applications

• Passive DI box for guitar, bass and high-impedance pickups
• Galvanically isolated instrument connection to a mic preamp
• 1:10 microphone step-up for tube or studio preamplifiers
• High-quality DI and microphone-preamp DIY

Technical specifications

Transformer type

Passive DI and microphone-input transformer, one channel per component

Winding arrangement

1 + 1 : 5 + 5

DI ratios

5:1 or 10:1 from the high-impedance instrument side to the mic input

Microphone step-up

Up to 1:10 when used in reverse

Core and enclosure

High-permeability mu-metal core in a mu-metal can

Winding construction

Dual coils, electrostatic shield and low-capacitance high-impedance winding

Frequency response as 10:1 DI

10 Hz to 45 kHz within +0/−2 dB using a 100 kΩ source and 1 kΩ load

Frequency response as 1:10 microphone input

10 Hz to 80 kHz within ±1 dB using a 200 Ω source and open secondary

Level and distortion

Below 0.1% at −5 dBu input, +14 dBu output and 50 Hz in the documented 1:10 test

Insulation

4 kV between windings and 2 kV between windings and shield

Dimensions and weight

Approximately 38 × 23 × 16 mm and 46 g

Passive-pickup notes

The impedance presented to the instrument depends on the turns ratio and microphone-preamp input impedance. At 10:1, the mic-input impedance is reflected to the pickup side by a factor of 100.

A 2 kΩ microphone input therefore appears as approximately 200 kΩ to the pickup. The resulting tonal balance should be checked with particularly resonance-sensitive passive pickups.

Questions about choosing a DI or microphone transformer

Which transformer suits a passive guitar or bass DI box?

The Lundahl LL1935 was developed specifically for this application. At 10:1 it reduces instrument level, presents a higher reflected input impedance to the pickup and delivers a galvanically isolated signal to a microphone preamp.

Which input transformer suits a high-impedance tube microphone preamp?

The LL1935 can operate in reverse at 1:10. A low-impedance 150 or 200 Ω microphone then receives passive voltage step-up and is matched to the high-impedance input of a valve or transistor stage.

Can the LL1935 operate as either a 5:1 or 10:1 DI transformer?

Yes, both ratios are available through different secondary connections. A 10:1 ratio provides greater attenuation and a higher reflected input impedance, while 5:1 gives a higher output level but loads a passive instrument more heavily.

Is the LL1935 suitable for galvanic isolation in a DI connection?

Yes, its separate windings interrupt the direct ground path between the instrument and microphone preamp. The enclosure, shield and connectors must be wired so that this isolation is not unintentionally bypassed.