Amplifiers
Overview
Lenard Valve Towers are a perfect addition to any Lenard Opal or Custom Opal system, for those wanting a sweeter, warmer experience.
Each amplifier cabinet consists of five 100 Watt Ultra-linear valve amplifiers. The amplifiers are mounted vertically. There is a separate amplifier for each speaker. The two lower amplifiers drive the bass speakers and top amplifiers drive the higher frequency speakers; the order is logical to follow.
The amplifiers for the cone speakers (bass and lower voice) are in class AB which enables 100 Watts of power to be achieved. However the amplifiers for the upper voice 2in compression driver and tweeter are in class A which limits power to 40 Watts.
The efficiency of the compression driver and tweeter is approx 100 times greater than the lower frequency cone speakers and only requires 1/100 the power to achieve the same level.
The high frequency drivers are very sensitive to detail and it is essential for the amplifiers to be as close to class A as possible to achieve the lowest distortion figurers.
The 4 four way active crossover is at the top of the cabinet and the controls easily accessible. The crossover frequencies are calibrated to achieve the best performance from the speakers.
The level controls of the crossover are calibrated for free field which means zero room reverberation. The controls can be easily re-adjusted to give the best performance to suit the room environment and music. The crossover is Linkwitz-Riley 4th order time aligned.
Valve Towers are available for AUD16,000 each. Sales enquiries please email us.
Amplifiers
Valves
Each 100 Watt amplifier is a separate module and can be changed easily if required. Each valve bias (temperature) can be easily externally adjusted New valves take approx 2 two weeks to stabilise.
The 2 two red LEDs (light emitting diodes) in front of each valve in this pic are a comparator. When both LEDs are at the same light level the valve bias is correct.The amp modules are vertically aligned in the cabinet and therefore the LEDs are in the vertical position as in the pic on the right.
The middle LEDs in-between the valves indicate by flashing if a valve has failed and needs to be replaced. Replacement valves are readily available and each system is provided with spare valves.
The driver circuitry is solid-state which is absolutely silent and non-microphonic. This is essential for very efficient active speaker systems that use compression drivers. The microphonic and thermolic noise (hiss) generated by small driver valves would be audible and intolerable. The unique sound quality of valve amplifiers is created by the output stage (power valves and output transformer). This unique quality is not created by using small pre amp valves
Amplifiers
Power Supply
The power supply is mounted on the right side of the chassis.
The small top toroid power transformer (+-20V and +-100V) is for the electronic crossover and driver circuits of KT88 output valves.
The two medium toroid for the 12.6V DC valve heater supply of 8 Amperes. The DC heater polarity + - is reversed each time the amplifier is turned on. This insures valve filaments and cables are free from electrolytic deterioration.
The large toroid transformer creates the 600V HT supply. The HT supply is constructed from 3 X 200V supplies in series. This enables a 400V supply for the 2 high frequency amplifiers in class A push pull.
The power turn on management system is at the bottom of the chassis. All power transformers are toroid, to insure zero magnetic interference, and are also electrostatic shielded.
Amplifiers
Output Transformers
The output transformers and Electronic crossover are mounted on the left side of the chassis. All output transformers are toroid and are of greater frequency range than required for each defined bandwidth. All output transformers are also frequency specified flat at 200W full power.
Amplifiers
Amplifier Class
Questions are often asked about valve amplifier class Push pull Single ended A AB B
Single ended refers to the 1 single output valve in small cheap radios and radiograms that were made before 1960. A single output valve is only capable of small power and produces a non-synchronous second harmonic distortion. Some audiophiles claim this distortion has spiritual qualities similar to magical crystals and crop circles.
Class A single ended refers to the 1 output valve needing to be at maximum quiescent temperature to obtain the small power available. This is similar to a one legged person riding a one pedal push bike. As it is not possible to pull up and push down on the pedal with identical energy, the output is non-synchronous.
Push pull refers to 2 two output valves, similar to a 2 cylinder auto engine, or a push bike with 2 pedals. Push Pull produces 4 times the power than single ended and has minimal distortion, due to being fully synchronous balanced. The correct way to make valve amplifiers, and push bikes.
Push Pull 2 two output valves is naturally efficient with minimum distortion. There is no scientific evidence that push pull achieves lower distortion by running the output valves at the maximum allowable temperature. However greater academic linearity is achieved by running the valves, with lower voltage and higher current, resulting in less power, insuring zero distortion. Sometimes referred to as class A push pull.
Class AB refers to push pull for audio application. The valves are run at medium temperature insuring there is an overlap where one valve takes over from the other for each half of the wave form. Increasing the temperature increases the overlap, referred to as Class AB1 and AB2. The latter has the least overlap.
Class B refers to push pull but not for audio application. In radio transmitters the valves are run at the minimum quiescent temperature (zero overlap) to obtain maximum power . If class B were used for audio there would be a gap between the top and bottom half of the music signal, which would be clearly audible as 3rd harmonic distortion.
Many of todays audiophile valve amplifiers are constructed similarly to the original designs that were made in the 1950s and 1960s. This is done for romantic nostalgia similar to grandfather clocks. However advances in modern technology and transformer design (toroid) has since enabled valve amplifiers to be vastly improved as in the Lenard designs.
Tower Options
Finish
This finish is fabricated in Stainless steel and is made to last a lifetime!
and capacitors.
