Here is in-depth look at the upcoming Audio Alto Reference Anniversary 10 ANL Tube Preamplifier. Yes, this is not the "usual" tube pre-amplifier, but a result of painstaking in-depth quest for ultimate preamp, that was designed from ground up with utmost attention to the part selection, optimised/ signal paths and uncompromised sonic performance.
Enclosure
The main preamplifier and power supply unit are both in each dedicated enclosures. Chassis are made of high grade aluminum, copper and stainless steel sheets cover. Front, top and rear panels are from high grade high quality 5 mm thick CNC extruded anodized aluminum sheets. Both components have additional aluminum heat sinks fins, that's lowering internal temperature and prolong electronic parts lifetime. Both units are placed on the special and in-house developed anti vibration feet to minimize microphonics effect on vacuum tubes and capacitors
Main preamplifier unit highlights
- fully tube preamplifier
- no global negative feedback
- input and output section realized as module
- module base realized with 2 mm thick special treated copper sheet
- minimalistic no compromise design (cost no object)
- dual (per channel) Electro Harmonix 6922 low noise matched gold triode amplification for true balanced operation
- ceramic tube sockets with gold plated contacts
- truly balanced design
- dual mono completely separated signal channels
- mechanical symmetry design
- balanced and differential inputs (XLR and RCA)
- balanced and single ended outputs (RCA)
- WBT nextgen 0210 Cu RCA input and output connectors
- Neutric XLR input and output connectors
- pure silver Teflon sleeve coated signal wires (minimizing) the impact on reproduced sound
- inputs, that are not in use are completely detached from the preamplifier to minimize interference and noise impact
- source selection via special bistable signal relays with gold and silver contacts
- all active/switchable functions uses exclusively bistable relays
- bistable relays eliminates magnetic field when relay is active
- no electrolytic capacitor in audio path (including power supply circuits)
- only high grade polypropylene capacitors
- one or two high grade silver oil capacitors in audio path (only one capacitor with output transformer installed)
- Lundahl high grade output transformer for complete elimination of potential ground loops (transformer in as option)
- Lundahl transformer with Cardas high purity post annealed audiophile grade copper wire windings
- Kiwame audio high grade low noise high tension resistors
- Tackman audio high grade resistors
- Elma 48 positions shunt volume attenuator
- remotely controlled volume attenuator with stepped microprocessor controlled motor (remote volume control is optional)
- printed circuit boards use special board material that is thermaly more stable
- the absence of any solder mask layer on printed circuit boards. This minimize dielectric constant influence on reproduction
- copper gold-plated printed circuit boards connections
- mechanically damped printed circuit boards. This lowers vibration and stress for components and vacuum tubes
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Control unit
- CPU control unit designed to drive bistable signal relay and for minimalization of radiated noise
- separate enclosure for control circuitry for to minimimalizationof radiated noise
- galvanically isolated CPU control for the lower noise
- control and time delayed activation of different supply voltages
- remote control is activated with special radio frequency transmitter and receiver
- two +12V trigger outputs
Power supply
- power supply (PSU) in a separate enclosure
- completely separated power supply for left and right channel
- full symmetrical mechanical design
- module based power supply
- each module is made out of 2 mm thick special treated copper sheet
- symmetrical mains input filterfor each power supply unit - toroidal transformers protected from mains line DC voltage with special DC blocker
- four custom designed and wound 100VA toroidal transformers that five times exceed the required power to lower power supply distortion and unwanted harmonics generation
- separated transformers for high voltages
- separated transformers for tubes' heaters and low voltages
- toroidal transformer enclosed in iron pots to minimize the magnetic impact
- toroidal transformers with electrostatic shield between primary and secondary windings for elimination of the noise on power line
- tube heaters energy is supplied with current sources to maximally extend vacuum tube life
- high voltage for tubes is rectified by 6CA4 vacuum tube and smoothed with Lundahl symmetrical chokes
- tubes' heater rectifier is time delayed to extend tube life
- the high voltage power supply is designed in a innovative way to minimize the current spikes (drastically lowering PSU noise)
- use of special polypropylene filtering capacitor with »Kelvin« connection to extend the low impedance to 1 MHz
- all high and low voltages are regulated with shunt regulators
- shunt regulator are without negative feedback, stable and very fast
- dedicated digital counter that displays tube operating hours
Electric parameters (preliminary)
Frequency range
20 – 200.000 Hz -0,1 dB @ 100K ohm load (no output transformer)
10 – 120.000 Hz +/-0,5 dB @ 10K load (with output transformer)
Distortion
Less than 0,01 %
Gain
Main gain selection per channel: 12 dB, 15 dB, 18 dB
Additional gain selection per channel: -2 dB, 0 dB, +2 dB
Maximum output amplitude:
100K ohm load – 111V peak, 78,7V rms
600 ohm load – 29V peak, 20,5V rms (with output transformer), 8V peak, 5,67V rms (no output transformer),
Input and Output Connections
Sources
3x balanced or differential (selection)
2x differential
tape monitor loop
Output
2x balanced
2x single ended (RCA)