LL1930 Lundahl Line Übertrager Input Output Audio transformer

Lundahl LL1930 parafeed line-output transformer for tube preamps

The Lundahl LL1930 is a line-output transformer for DC-free parafeed valve stages. It steps down the relatively high voltage and impedance of a tube preamplifier to provide a robust balanced line signal.

Ratios of 5.8:1 and 11.6:1 support different output levels and impedance requirements. The LL1930 is suitable for tube preamplifiers, phono stages and valve-equipped DAC output stages.

Suitable applications

• Parafeed line output from a tube preamplifier
• Transformer-coupled output from a tube phono stage
• Balanced output from a valve DAC stage
• Output stages using 6SN7, ECC99, 5687, 12BH7 or 6N6P valves

Technical specifications

Transformer type

Parafeed tube-preamp line-output transformer, one channel per component

Winding arrangement

5.8 + 5.8 : 1 + 1

Available ratios

5.8:1 or 11.6:1 depending on the secondary connection

Core material

High-permeability mu-metal core

Shielding

No internal Faraday shield and no magnetic shielding enclosure

Frequency response

20 Hz to 30 kHz within less than ±0.1 dB using a 10 kΩ load

Level and distortion

Below 0.1% at 50 Hz and below 1% at 25 Hz with a +30 dBu primary signal

Documented source impedance

4.5 kΩ in the data-sheet test

Documented secondary load

10 kΩ

Insulation

4 kV between windings and 2 kV between windings and core

Dimensions and weight

Approximately 47 × 28 × 23 mm and 105 g

Mounting

PCB mounting with 5.08 mm pin spacing

Parafeed-circuit notes

The LL1930 must not carry anode DC in its intended application. An anode choke or active current source supplies the valve, while a suitably rated parafeed capacitor couples only the audio signal into the transformer.

Because the transformer has no magnetic shielding enclosure, it should be placed at a substantial distance from mains transformers and chokes and may benefit from 90-degree orientation. An additional external mu-metal shield can be useful in interference-sensitive equipment.

Questions about choosing a tube line-output transformer

Which Lundahl transformer suits the line output of a 6SN7, ECC99 or 5687 tube preamplifier?

The LL1930 is intended for DC-free parafeed outputs using these types of valve stages. Operating points with a source or output impedance of a few kilohms are particularly relevant. The 5.8:1 or 11.6:1 ratio is selected according to the required output level and line load.

Which output transformer suits a tube phono stage or valve DAC?

The LL1930 is an attractive solution when the final valve stage is coupled through a parafeed capacitor and requires a lower-impedance balanced line output. The data sheet documents exceptionally flat response into a 10 kΩ load.

Can the LL1930 drive a balanced 10 kΩ line input?

Yes, this is the secondary load used in the Lundahl data sheet. The valve, anode load or current source must nevertheless be designed so that source impedance and available voltage swing suit the selected turns ratio.

Is the LL1930 suitable for a completely DC-free parafeed output stage?

Yes, this is its intended application. The parafeed capacitor must block anode DC reliably and be rated for the circuit voltage. The unshielded transformer should be positioned away from mains transformers, chokes and other magnetic-field sources.