LL1527 Lundahl Line Übertrager Input Audio transformer

Lundahl LL1527 general-purpose audio isolation transformer

The Lundahl LL1527 is a versatile transformer for microphone and line-level signals. It supports galvanic isolation, balanced-to-unbalanced conversion and the removal of ground-loop hum between audio devices.

Its four winding sections allow 1:1 isolation, 1:2 microphone step-up or signal splitting with one direct and one transformer-isolated output.

Suitable applications

• Galvanic isolation between DACs, preamps, mixers and power amplifiers
• XLR-to-RCA and RCA-to-XLR signal conversion
• Microphone input with a 1:1 or 1:2 ratio
• One direct and one isolated signal output

Technical specifications

Transformer type

General-purpose microphone, line and isolation transformer, one channel per component

Winding arrangement

1 + 1 : 1 + 1

Connection ratios

1:1 with series or parallel windings and 1:2 with parallel-primary/series-secondary wiring

Core and enclosure

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

Shielding

Electrostatic shield between primary and secondary windings

Frequency response

10 Hz to 150 kHz within ±0.2 dB using an 800 Ω source and 4 kΩ load

Level and distortion at 50 Hz

0.1% at +6 dBu or below 1% at +16 dBu

Insertion loss

Approximately 0.4 dB under the documented test conditions

Self-resonance

Above 200 kHz

Insulation

4 kV between windings and 2 kV between windings and shield

Dimensions and weight

Approximately 38 × 24 × 17 mm and 48 g

Mounting

PCB mounting with 5.08 mm pin spacing and recommended 1.5 mm holes

Connection and selection notes

1:1 line isolation

Primary and secondary sections are connected in series

Low-loss 1:1 isolation

Both winding sides may be paralleled for low-impedance sources

1:2 microphone step-up

Primary windings are connected in parallel and secondaries in series

Signal splitting

Suitable for one direct and one isolated output; a dedicated splitter is preferable for two isolated outputs

For complete galvanic isolation, an RCA connector and its signal return should be insulated from the local chassis and signal ground. Wiring should follow the relevant Lundahl connection diagram.

Questions about choosing an audio transformer

Which transformer helps remove hum between a DAC, preamp and power amplifier?

The Lundahl LL1527 is a proven 1:1 isolation transformer for this purpose. It interrupts the galvanic signal path and can eliminate a ground loop carried through the audio connections. Input and output grounds must not be reconnected directly elsewhere in the system.

Which Lundahl transformer converts a balanced XLR signal to unbalanced RCA?

The LL1527 can provide 1:1 conversion while galvanically isolating the connected devices. The RCA connector should be insulated from the chassis so that the source return is not unintentionally bonded to the local signal ground.

Can the LL1527 passively step up a low-impedance microphone signal?

Yes, its parallel-primary and series-secondary connection provides a 1:2 turns ratio and approximately 6 dB of passive voltage gain. Source impedance, preamp input impedance and maximum signal level must suit the chosen arrangement.

Is the LL1527 suitable for signal splitting?

Yes, it can provide one direct and one galvanically isolated output. For one direct plus two isolated outputs, Lundahl recommends a transformer designed specifically for multiple isolated feeds.