LA5 transformer line pre-amplifer

Transformers sound best!

Well made audio transformers can provide perfect coupling in a hi fi system. Free from the “mechanical” sound of solid state and the deficiencies of output capacitors, they can make reproduction more vibrant and focussed.

The heart of the LA5tx are two very special line level output transformers, developed “in house” over several years to give what we think is the best sound balance.

Something for nothing?

If you use only a transformer for “gain” the results will vary depending upon the “power” (or source impedance) of the previous stage. If it is not “strong” the signal will start to distort, giving unstable results. In electronics you cannot get something for nothing! The LA5tx single 6SN7 valve “buffers” the input source, this way the LA5tx always presents a constant high impedance load, so the “strength” of the previous stage is irrelevant. The “strong” output of the 6SN7 then drives our transformer to give either a perfect “balanced” output as well as a phono RCA.

The very low 250Ω output impedance of the LA5tx is then strong enough to drive virtually any length or type of interconnect cable without loss or damage to the precious signal.

So we feel that this is a better solution than just using a transformer alone.

The LA5tx is designed for the very best transistor and valve power amplifiers where purity is required rather than starkness.

The audio valve we use is the 6SN7 double triode. This 1940 vintage valve has all the best characteristics for the job, and its larger size means long life and good stability. Also the sound is more musical as we feel these have a more fluid sound. You can experiment with both vintage and modern types.

A high end pre amplifier must have the best power supply. The LA5tx has two chokes in double Pi configuration for well conditioned power giving superb smoothing for velvety inky black silence.

The rectifier valve, which makes a surprising difference, is the excellent 274B. This outstanding Western Electric design is one of the finest sounding power valves.

Specifications and Features

• Icon Audio custom output transformers
• All hand wired point to point
• ALPs Blue motorised volume pot.
• Stepped attenuator option
• All Triode simple design
• 2x 6SN7 valves
• 274B Valve rectifier (also use GZ34/5AR4/5U4)
• Double Choke HT supply
• DC heater supply
• Signal to noise level -90db#
• Freq response 20Hz-15kHz +0 -0.5db
• Freq response 13Hz-20kHz +0 -1db
• Freq response 7Hz-28kHz +0 -3db
• THD typically less than 0.18% (0.5v output)
• Gain 2.3x, 7db
• Max output level 20v for 8.75v input
• Low output impedance of 250Ω
• Suitable for power amps 100mv-2v sensitivity
• High quality 2w metal film, & wire-wound resistors
• Solen/SCR audio capacitors (Jensen option)
• Silver TEFLON audio cable
• Gold plated Input terminals
• Four line inputs
• Record loop
• 220/240volts 75watts#
• Comprehensive manual supplied
• C E compliant
• 345W, 310D, 195H (with 274B), or 170H with GZ34 18kg with packing
(Specifications subject to change, errors & omissions excepted 04/10/12)

Various valve and capacitor upgrades are available, contact us for more information.

A simple low gain pre-amplifier that buffers the input and provides the transformer with optimum drive to achieve the full potential from the special output transformers.

LA5tx Line Pre-amplifier Leaflet